NAT + STUN Probes...

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

.github/workflows/codeql.yml

@@ -0,0 +1,45 @@
+name: "CodeQL Advanced"
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+  schedule:
+    - cron: '0 0 * * 0'
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ${{ (matrix.language == 'swift' && 'macos-latest') || 'ubuntu-latest' }}
+
+    permissions:
+      security-events: write
+      packages: read
+      actions: read
+      contents: read
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: actions
+            build-mode: none
+          - language: rust
+            build-mode: none
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v4
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: ${{ matrix.build-mode }}
+          config-file: .github/codeql/codeql-config.yml
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v4
+        with:
+          category: "/language:${{ matrix.language }}"

.github/workflows/queries/common/ProductionOnly.qll

@@ -0,0 +1,20 @@
+import rust
+
+predicate isTestOnly(Item i) {
+  exists(ConditionalCompilation cc |
+    cc.getItem() = i and
+    cc.getCfg().toString() = "test"
+  )
+}
+
+predicate hasTestAttribute(Item i) {
+  exists(Attribute a |
+    a.getItem() = i and
+    a.getName() = "test"
+  )
+}
+
+predicate isProductionCode(Item i) {
+  not isTestOnly(i) and
+  not hasTestAttribute(i)
+}

.github/workflows/queries/qlpack.yml

@@ -0,0 +1,4 @@
+name: rust-production-only
+version: 0.0.1
+dependencies:
+  codeql/rust-all: "*"

README.md

@@ -188,6 +188,7 @@ tls_domain = "petrovich.ru"
 mask = true
 mask_port = 443
 # mask_host = "petrovich.ru" # Defaults to tls_domain if not set
+# mask_unix_sock = "/var/run/nginx.sock" # Unix socket (mutually exclusive with mask_host)
 fake_cert_len = 2048
 
 # === Access Control & Users ===

config.toml

@@ -44,10 +44,11 @@ client_ack = 300
 
 # === Anti-Censorship & Masking ===
 [censorship]
-tls_domain = "google.ru"
+tls_domain = "petrovich.ru"
 mask = true
 mask_port = 443
 # mask_host = "petrovich.ru" # Defaults to tls_domain if not set
+# mask_unix_sock = "/var/run/nginx.sock" # Unix socket (mutually exclusive with mask_host)
 fake_cert_len = 2048
 
 # === Access Control & Users ===
@@ -74,6 +75,6 @@ weight = 10
 
 # [[upstreams]]
 # type = "socks5"
-# address = "127.0.0.1:9050"
+# address = "127.0.0.1:1080"
 # enabled = false
 # weight = 1

src/config/mod.rs

@@ -1,32 +1,55 @@
 //! Configuration
 
+use crate::error::{ProxyError, Result};
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::net::{IpAddr, SocketAddr};
 use std::path::Path;
-use chrono::{DateTime, Utc};
-use serde::{Deserialize, Serialize};
-use crate::error::{ProxyError, Result};
 
 // ============= Helper Defaults =============
 
-fn default_true() -> bool { true }
+fn default_true() -> bool {
-fn default_port() -> u16 { 443 }
+    true
-fn default_tls_domain() -> String { "www.google.com".to_string() }
+}
-fn default_mask_port() -> u16 { 443 }
+fn default_port() -> u16 {
-fn default_replay_check_len() -> usize { 65536 }
+    443
-fn default_replay_window_secs() -> u64 { 1800 }
+}
-fn default_handshake_timeout() -> u64 { 15 }
+fn default_tls_domain() -> String {
-fn default_connect_timeout() -> u64 { 10 }
+    "www.google.com".to_string()
-fn default_keepalive() -> u64 { 60 }
+}
-fn default_ack_timeout() -> u64 { 300 }
+fn default_mask_port() -> u16 {
-fn default_listen_addr() -> String { "0.0.0.0".to_string() }
+    443
-fn default_fake_cert_len() -> usize { 2048 }
+}
-fn default_weight() -> u16 { 1 }
+fn default_replay_check_len() -> usize {
+    65536
+}
+fn default_replay_window_secs() -> u64 {
+    1800
+}
+fn default_handshake_timeout() -> u64 {
+    15
+}
+fn default_connect_timeout() -> u64 {
+    10
+}
+fn default_keepalive() -> u64 {
+    60
+}
+fn default_ack_timeout() -> u64 {
+    300
+}
+fn default_listen_addr() -> String {
+    "0.0.0.0".to_string()
+}
+fn default_fake_cert_len() -> usize {
+    2048
+}
+fn default_weight() -> u16 {
+    1
+}
 fn default_metrics_whitelist() -> Vec<IpAddr> {
-    vec![
+    vec!["127.0.0.1".parse().unwrap(), "::1".parse().unwrap()]
-        "127.0.0.1".parse().unwrap(),
-        "::1".parse().unwrap(),
-    ]
 }
 
 // ============= Log Level =============
@@ -96,7 +119,11 @@ pub struct ProxyModes {
 
 impl Default for ProxyModes {
     fn default() -> Self {
-        Self { classic: true, secure: true, tls: true }
+        Self {
+            classic: true,
+            secure: true,
+            tls: true,
+        }
     }
 }
 
@@ -117,6 +144,24 @@ pub struct GeneralConfig {
     #[serde(default)]
     pub ad_tag: Option<String>,
 
+    /// Path to proxy-secret binary file (auto-downloaded if absent).
+    /// Infrastructure secret from https://core.telegram.org/getProxySecret
+    #[serde(default)]
+    pub proxy_secret_path: Option<String>,
+
+    /// Public IP override for middle-proxy NAT environments.
+    /// When set, this IP is used in ME key derivation and RPC_PROXY_REQ "our_addr".
+    #[serde(default)]
+    pub middle_proxy_nat_ip: Option<IpAddr>,
+
+    /// Enable STUN-based NAT probing to discover public IP:port for ME KDF.
+    #[serde(default)]
+    pub middle_proxy_nat_probe: bool,
+
+    /// Optional STUN server address (host:port) for NAT probing.
+    #[serde(default)]
+    pub middle_proxy_nat_stun: Option<String>,
+
     #[serde(default)]
     pub log_level: LogLevel,
 }
@@ -129,6 +174,10 @@ impl Default for GeneralConfig {
             fast_mode: true,
             use_middle_proxy: false,
             ad_tag: None,
+            proxy_secret_path: None,
+            middle_proxy_nat_ip: None,
+            middle_proxy_nat_probe: false,
+            middle_proxy_nat_stun: None,
             log_level: LogLevel::Normal,
         }
     }
@@ -212,6 +261,9 @@ pub struct AntiCensorshipConfig {
     #[serde(default = "default_mask_port")]
     pub mask_port: u16,
 
+    #[serde(default)]
+    pub mask_unix_sock: Option<String>,
+
     #[serde(default = "default_fake_cert_len")]
     pub fake_cert_len: usize,
 }
@@ -223,6 +275,7 @@ impl Default for AntiCensorshipConfig {
             mask: true,
             mask_host: None,
             mask_port: default_mask_port(),
+            mask_unix_sock: None,
             fake_cert_len: default_fake_cert_len(),
         }
     }
@@ -255,7 +308,10 @@ pub struct AccessConfig {
 impl Default for AccessConfig {
     fn default() -> Self {
         let mut users = HashMap::new();
-        users.insert("default".to_string(), "00000000000000000000000000000000".to_string());
+        users.insert(
+            "default".to_string(),
+            "00000000000000000000000000000000".to_string(),
+        );
         Self {
             users,
             user_max_tcp_conns: HashMap::new(),
@@ -355,11 +411,11 @@ pub struct ProxyConfig {
 
 impl ProxyConfig {
     pub fn load<P: AsRef<Path>>(path: P) -> Result<Self> {
-        let content = std::fs::read_to_string(path)
+        let content =
-            .map_err(|e| ProxyError::Config(e.to_string()))?;
+            std::fs::read_to_string(path).map_err(|e| ProxyError::Config(e.to_string()))?;
 
-        let mut config: ProxyConfig = toml::from_str(&content)
+        let mut config: ProxyConfig =
-            .map_err(|e| ProxyError::Config(e.to_string()))?;
+            toml::from_str(&content).map_err(|e| ProxyError::Config(e.to_string()))?;
 
         // Validate secrets
         for (user, secret) in &config.access.users {
@@ -376,8 +432,34 @@ impl ProxyConfig {
             return Err(ProxyError::Config("tls_domain cannot be empty".to_string()));
         }
 
-        // Default mask_host to tls_domain if not set
+        // Validate mask_unix_sock
-        if config.censorship.mask_host.is_none() {
+        if let Some(ref sock_path) = config.censorship.mask_unix_sock {
+            if sock_path.is_empty() {
+                return Err(ProxyError::Config(
+                    "mask_unix_sock cannot be empty".to_string(),
+                ));
+            }
+            #[cfg(unix)]
+            if sock_path.len() > 107 {
+                return Err(ProxyError::Config(format!(
+                    "mask_unix_sock path too long: {} bytes (max 107)",
+                    sock_path.len()
+                )));
+            }
+            #[cfg(not(unix))]
+            return Err(ProxyError::Config(
+                "mask_unix_sock is only supported on Unix platforms".to_string(),
+            ));
+
+            if config.censorship.mask_host.is_some() {
+                return Err(ProxyError::Config(
+                    "mask_unix_sock and mask_host are mutually exclusive".to_string(),
+                ));
+            }
+        }
+
+        // Default mask_host to tls_domain if not set and no unix socket configured
+        if config.censorship.mask_host.is_none() && config.censorship.mask_unix_sock.is_none() {
             config.censorship.mask_host = Some(config.censorship.tls_domain.clone());
         }
 
@@ -394,7 +476,7 @@ impl ProxyConfig {
                 });
             }
             if let Some(ipv6_str) = &config.server.listen_addr_ipv6 {
-                 if let Ok(ipv6) = ipv6_str.parse::<IpAddr>() {
+                if let Ok(ipv6) = ipv6_str.parse::<IpAddr>() {
                     config.server.listeners.push(ListenerConfig {
                         ip: ipv6,
                         announce_ip: None,
@@ -405,7 +487,7 @@ impl ProxyConfig {
 
         // Migration: Populate upstreams if empty (Default Direct)
         if config.upstreams.is_empty() {
-             config.upstreams.push(UpstreamConfig {
+            config.upstreams.push(UpstreamConfig {
                 upstream_type: UpstreamType::Direct { interface: None },
                 weight: 1,
                 enabled: true,
@@ -425,9 +507,10 @@ impl ProxyConfig {
         }
 
         if self.censorship.tls_domain.contains(' ') || self.censorship.tls_domain.contains('/') {
-            return Err(ProxyError::Config(
+            return Err(ProxyError::Config(format!(
-                format!("Invalid tls_domain: '{}'. Must be a valid domain name", self.censorship.tls_domain)
+                "Invalid tls_domain: '{}'. Must be a valid domain name",
-            ));
+                self.censorship.tls_domain
+            )));
         }
 
         Ok(())

src/crypto/hash.rs

@@ -55,12 +55,11 @@ pub fn crc32(data: &[u8]) -> u32 {
     crc32fast::hash(data)
 }
 
-/// Middle Proxy key derivation
+/// Build the exact prekey buffer used by Telegram Middle Proxy KDF.
 ///
-/// Uses MD5 + SHA-1 as mandated by the Telegram Middle Proxy protocol.
+/// Returned buffer layout (IPv4):
-/// These algorithms are NOT replaceable here — changing them would break
+/// nonce_srv | nonce_clt | clt_ts | srv_ip | clt_port | purpose | clt_ip | srv_port | secret | nonce_srv | [clt_v6 | srv_v6] | nonce_clt
-/// interoperability with Telegram's middle proxy infrastructure.
+pub fn build_middleproxy_prekey(
-pub fn derive_middleproxy_keys(
     nonce_srv: &[u8; 16],
     nonce_clt: &[u8; 16],
     clt_ts: &[u8; 4],
@@ -72,7 +71,7 @@ pub fn derive_middleproxy_keys(
     secret: &[u8],
     clt_ipv6: Option<&[u8; 16]>,
     srv_ipv6: Option<&[u8; 16]>,
-) -> ([u8; 32], [u8; 16]) {
+) -> Vec<u8> {
     const EMPTY_IP: [u8; 4] = [0, 0, 0, 0];
 
     let srv_ip = srv_ip.unwrap_or(&EMPTY_IP);
@@ -96,6 +95,40 @@ pub fn derive_middleproxy_keys(
     }
 
     s.extend_from_slice(nonce_clt);
+    s
+}
+
+/// Middle Proxy key derivation
+///
+/// Uses MD5 + SHA-1 as mandated by the Telegram Middle Proxy protocol.
+/// These algorithms are NOT replaceable here — changing them would break
+/// interoperability with Telegram's middle proxy infrastructure.
+pub fn derive_middleproxy_keys(
+    nonce_srv: &[u8; 16],
+    nonce_clt: &[u8; 16],
+    clt_ts: &[u8; 4],
+    srv_ip: Option<&[u8]>,
+    clt_port: &[u8; 2],
+    purpose: &[u8],
+    clt_ip: Option<&[u8]>,
+    srv_port: &[u8; 2],
+    secret: &[u8],
+    clt_ipv6: Option<&[u8; 16]>,
+    srv_ipv6: Option<&[u8; 16]>,
+) -> ([u8; 32], [u8; 16]) {
+    let s = build_middleproxy_prekey(
+        nonce_srv,
+        nonce_clt,
+        clt_ts,
+        srv_ip,
+        clt_port,
+        purpose,
+        clt_ip,
+        srv_port,
+        secret,
+        clt_ipv6,
+        srv_ipv6,
+    );
 
     let md5_1 = md5(&s[1..]);
     let sha1_sum = sha1(&s);
@@ -107,3 +140,39 @@ pub fn derive_middleproxy_keys(
     
     (key, md5_2)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn middleproxy_prekey_sha_is_stable() {
+        let nonce_srv = [0x11u8; 16];
+        let nonce_clt = [0x22u8; 16];
+        let clt_ts = 0x44332211u32.to_le_bytes();
+        let srv_ip = Some([149u8, 154, 175, 50].as_ref());
+        let clt_ip = Some([10u8, 0, 0, 1].as_ref());
+        let clt_port = 0x1f90u16.to_le_bytes(); // 8080
+        let srv_port = 0x22b8u16.to_le_bytes(); // 8888
+        let secret = vec![0x55u8; 128];
+
+        let prekey = build_middleproxy_prekey(
+            &nonce_srv,
+            &nonce_clt,
+            &clt_ts,
+            srv_ip,
+            &clt_port,
+            b"CLIENT",
+            clt_ip,
+            &srv_port,
+            &secret,
+            None,
+            None,
+        );
+        let digest = sha256(&prekey);
+        assert_eq!(
+            hex::encode(digest),
+            "a4595b75f1f610f2575ace802ddc65c91b5acef3b0e0d18189e0c7c9f787d15c"
+        );
+    }
+}

src/crypto/mod.rs

@@ -5,5 +5,5 @@ pub mod hash;
 pub mod random;
 
 pub use aes::{AesCtr, AesCbc};
-pub use hash::{sha256, sha256_hmac, sha1, md5, crc32};
+pub use hash::{sha256, sha256_hmac, sha1, md5, crc32, derive_middleproxy_keys, build_middleproxy_prekey};
 pub use random::SecureRandom;

src/main.rs

@@ -1,4 +1,4 @@
-//! Telemt - MTProxy on Rust
+//! telemt — Telegram MTProto Proxy
 
 use std::net::SocketAddr;
 use std::sync::Arc;
@@ -6,8 +6,8 @@ use std::time::Duration;
 use tokio::net::TcpListener;
 use tokio::signal;
 use tokio::sync::Semaphore;
-use tracing::{info, error, warn, debug};
+use tracing::{debug, error, info, warn};
-use tracing_subscriber::{fmt, EnvFilter, reload, prelude::*};
+use tracing_subscriber::{EnvFilter, fmt, prelude::*, reload};
 
 mod cli;
 mod config;
@@ -20,13 +20,14 @@ mod stream;
 mod transport;
 mod util;
 
-use crate::config::{ProxyConfig, LogLevel};
+use crate::config::{LogLevel, ProxyConfig};
-use crate::proxy::ClientHandler;
-use crate::stats::{Stats, ReplayChecker};
 use crate::crypto::SecureRandom;
-use crate::transport::{create_listener, ListenOptions, UpstreamManager};
+use crate::proxy::ClientHandler;
-use crate::util::ip::detect_ip;
+use crate::stats::{ReplayChecker, Stats};
 use crate::stream::BufferPool;
+use crate::transport::middle_proxy::MePool;
+use crate::transport::{ListenOptions, UpstreamManager, create_listener};
+use crate::util::ip::detect_ip;
 
 fn parse_cli() -> (String, bool, Option<String>) {
     let mut config_path = "config.toml".to_string();
@@ -47,10 +48,14 @@ fn parse_cli() -> (String, bool, Option<String>) {
     let mut i = 0;
     while i < args.len() {
         match args[i].as_str() {
-            "--silent" | "-s" => { silent = true; }
+            "--silent" | "-s" => {
+                silent = true;
+            }
             "--log-level" => {
                 i += 1;
-                if i < args.len() { log_level = Some(args[i].clone()); }
+                if i < args.len() {
+                    log_level = Some(args[i].clone());
+                }
             }
             s if s.starts_with("--log-level=") => {
                 log_level = Some(s.trim_start_matches("--log-level=").to_string());
@@ -64,17 +69,27 @@ fn parse_cli() -> (String, bool, Option<String>) {
                 eprintln!("  --help, -h              Show this help");
                 eprintln!();
                 eprintln!("Setup (fire-and-forget):");
-                eprintln!("  --init                  Generate config, install systemd service, start");
+                eprintln!(
+                    "  --init                  Generate config, install systemd service, start"
+                );
                 eprintln!("    --port <PORT>          Listen port (default: 443)");
-                eprintln!("    --domain <DOMAIN>      TLS domain for masking (default: www.google.com)");
+                eprintln!(
-                eprintln!("    --secret <HEX>         32-char hex secret (auto-generated if omitted)");
+                    "    --domain <DOMAIN>      TLS domain for masking (default: www.google.com)"
+                );
+                eprintln!(
+                    "    --secret <HEX>         32-char hex secret (auto-generated if omitted)"
+                );
                 eprintln!("    --user <NAME>          Username (default: user)");
                 eprintln!("    --config-dir <DIR>     Config directory (default: /etc/telemt)");
                 eprintln!("    --no-start             Don't start the service after install");
                 std::process::exit(0);
             }
-            s if !s.starts_with('-') => { config_path = s.to_string(); }
+            s if !s.starts_with('-') => {
-            other => { eprintln!("Unknown option: {}", other); }
+                config_path = s.to_string();
+            }
+            other => {
+                eprintln!("Unknown option: {}", other);
+            }
         }
         i += 1;
     }
@@ -83,7 +98,7 @@ fn parse_cli() -> (String, bool, Option<String>) {
 }
 
 #[tokio::main]
-async fn main() -> Result<(), Box<dyn std::error::Error>> {
+async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
     let (config_path, cli_silent, cli_log_level) = parse_cli();
 
     let config = match ProxyConfig::load(&config_path) {
@@ -115,8 +130,6 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         config.general.log_level.clone()
     };
 
-    // Start with INFO so startup messages are always visible,
-    // then switch to user-configured level after startup
     let (filter_layer, filter_handle) = reload::Layer::new(EnvFilter::new("info"));
     tracing_subscriber::registry()
         .with(filter_layer)
@@ -125,21 +138,38 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     info!("Telemt MTProxy v{}", env!("CARGO_PKG_VERSION"));
     info!("Log level: {}", effective_log_level);
-    info!("Modes: classic={} secure={} tls={}",
+    info!(
-        config.general.modes.classic,
+        "Modes: classic={} secure={} tls={}",
-        config.general.modes.secure,
+        config.general.modes.classic, config.general.modes.secure, config.general.modes.tls
-        config.general.modes.tls);
+    );
     info!("TLS domain: {}", config.censorship.tls_domain);
-    info!("Mask: {} -> {}:{}",
+    if let Some(ref sock) = config.censorship.mask_unix_sock {
-        config.censorship.mask,
+        info!("Mask: {} -> unix:{}", config.censorship.mask, sock);
-        config.censorship.mask_host.as_deref().unwrap_or(&config.censorship.tls_domain),
+        if !std::path::Path::new(sock).exists() {
-        config.censorship.mask_port);
+            warn!(
+                "Unix socket '{}' does not exist yet. Masking will fail until it appears.",
+                sock
+            );
+        }
+    } else {
+        info!(
+            "Mask: {} -> {}:{}",
+            config.censorship.mask,
+            config
+                .censorship
+                .mask_host
+                .as_deref()
+                .unwrap_or(&config.censorship.tls_domain),
+            config.censorship.mask_port
+        );
+    }
 
     if config.censorship.tls_domain == "www.google.com" {
         warn!("Using default tls_domain. Consider setting a custom domain.");
     }
 
     let prefer_ipv6 = config.general.prefer_ipv6;
+    let use_middle_proxy = config.general.use_middle_proxy;
     let config = Arc::new(config);
     let stats = Arc::new(Stats::new());
     let rng = Arc::new(SecureRandom::new());
@@ -152,41 +182,193 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let upstream_manager = Arc::new(UpstreamManager::new(config.upstreams.clone()));
     let buffer_pool = Arc::new(BufferPool::with_config(16 * 1024, 4096));
 
-        // Connection concurrency limit — prevents OOM under SYN flood / connection storm.
+    // Connection concurrency limit
-        // 10000 is generous; each connection uses ~64KB (2x 16KB relay buffers + overhead).
+    let _max_connections = Arc::new(Semaphore::new(10_000));
-        // 10000 connections ≈ 640MB peak memory.
-        let max_connections = Arc::new(Semaphore::new(10_000));
 
-    // Startup DC ping
+    // =====================================================================
-    info!("=== Telegram DC Connectivity ===");
+    // Middle Proxy initialization (if enabled)
-    let ping_results = upstream_manager.ping_all_dcs(prefer_ipv6).await;
+    // =====================================================================
-    for upstream_result in &ping_results {
+    let me_pool: Option<Arc<MePool>> = if use_middle_proxy {
-        info!("  via {}", upstream_result.upstream_name);
+        info!("=== Middle Proxy Mode ===");
-        for dc in &upstream_result.results {
+
-            match (&dc.rtt_ms, &dc.error) {
+        // ad_tag (proxy_tag) for advertising
-                (Some(rtt), _) => {
+        let proxy_tag = config.general.ad_tag.as_ref().map(|tag| {
-                    info!("    DC{} ({:>21}):  {:.0}ms", dc.dc_idx, dc.dc_addr, rtt);
+            hex::decode(tag).unwrap_or_else(|_| {
-                }
+                warn!("Invalid ad_tag hex, middle proxy ad_tag will be empty");
-                (None, Some(err)) => {
+                Vec::new()
-                    info!("    DC{} ({:>21}):  FAIL ({})", dc.dc_idx, dc.dc_addr, err);
+            })
-                }
+        });
-                _ => {
+
-                    info!("    DC{} ({:>21}):  FAIL", dc.dc_idx, dc.dc_addr);
+        // =============================================================
+        // CRITICAL: Download Telegram proxy-secret (NOT user secret!)
+        //
+        // C MTProxy uses TWO separate secrets:
+        //   -S flag    = 16-byte user secret for client obfuscation
+        //   --aes-pwd  = 32-512 byte binary file for ME RPC auth
+        //
+        // proxy-secret is from: https://core.telegram.org/getProxySecret
+        // =============================================================
+        let proxy_secret_path = config.general.proxy_secret_path.as_deref();
+        match crate::transport::middle_proxy::fetch_proxy_secret(proxy_secret_path).await {
+            Ok(proxy_secret) => {
+                info!(
+                    secret_len = proxy_secret.len(),
+                    key_sig = format_args!(
+                        "0x{:08x}",
+                        if proxy_secret.len() >= 4 {
+                            u32::from_le_bytes([
+                                proxy_secret[0],
+                                proxy_secret[1],
+                                proxy_secret[2],
+                                proxy_secret[3],
+                            ])
+                        } else {
+                            0
+                        }
+                    ),
+                    "Proxy-secret loaded"
+                );
+
+                let pool = MePool::new(
+                    proxy_tag,
+                    proxy_secret,
+                    config.general.middle_proxy_nat_ip,
+                    config.general.middle_proxy_nat_probe,
+                    config.general.middle_proxy_nat_stun.clone(),
+                );
+
+                match pool.init(2, &rng).await {
+                    Ok(()) => {
+                        info!("Middle-End pool initialized successfully");
+
+                        // Phase 4: Start health monitor
+                        let pool_clone = pool.clone();
+                        let rng_clone = rng.clone();
+                        tokio::spawn(async move {
+                            crate::transport::middle_proxy::me_health_monitor(
+                                pool_clone, rng_clone, 2,
+                            )
+                            .await;
+                        });
+
+                        Some(pool)
+                    }
+                    Err(e) => {
+                        error!(error = %e, "Failed to initialize ME pool. Falling back to direct mode.");
+                        None
+                    }
                 }
             }
+            Err(e) => {
+                error!(error = %e, "Failed to fetch proxy-secret. Falling back to direct mode.");
+                None
+            }
+        }
+    } else {
+        None
+    };
+
+    if me_pool.is_some() {
+        info!("Transport: Middle Proxy (supports all DCs including CDN)");
+    } else {
+        info!("Transport: Direct TCP (standard DCs only)");
+    }
+
+    // Startup DC ping (only meaningful in direct mode)
+    if me_pool.is_none() {
+        info!("================= Telegram DC Connectivity =================");
+
+        let ping_results = upstream_manager.ping_all_dcs(prefer_ipv6).await;
+
+        for upstream_result in &ping_results {
+            // Show which IP version is in use and which is fallback
+            if upstream_result.both_available {
+                if prefer_ipv6 {
+                    info!("  IPv6 in use and IPv4 is fallback");
+                } else {
+                    info!("  IPv4 in use and IPv6 is fallback");
+                }
+            } else {
+                let v6_works = upstream_result
+                    .v6_results
+                    .iter()
+                    .any(|r| r.rtt_ms.is_some());
+                let v4_works = upstream_result
+                    .v4_results
+                    .iter()
+                    .any(|r| r.rtt_ms.is_some());
+                if v6_works && !v4_works {
+                    info!("  IPv6 only (IPv4 unavailable)");
+                } else if v4_works && !v6_works {
+                    info!("  IPv4 only (IPv6 unavailable)");
+                } else if !v6_works && !v4_works {
+                    info!("  No connectivity!");
+                }
+            }
+
+            info!("  via {}", upstream_result.upstream_name);
+            info!("============================================================");
+
+            // Print IPv6 results first
+            for dc in &upstream_result.v6_results {
+                let addr_str = format!("{}:{}", dc.dc_addr.ip(), dc.dc_addr.port());
+                match &dc.rtt_ms {
+                    Some(rtt) => {
+                        // Align: IPv6 addresses are longer, use fewer tabs
+                        // [2001:b28:f23d:f001::a]:443 = ~28 chars
+                        info!("    DC{} [IPv6] {}:\t\t{:.0} ms", dc.dc_idx, addr_str, rtt);
+                    }
+                    None => {
+                        let err = dc.error.as_deref().unwrap_or("fail");
+                        info!("    DC{} [IPv6] {}:\t\tFAIL ({})", dc.dc_idx, addr_str, err);
+                    }
+                }
+            }
+
+            info!("============================================================");
+
+            // Print IPv4 results
+            for dc in &upstream_result.v4_results {
+                let addr_str = format!("{}:{}", dc.dc_addr.ip(), dc.dc_addr.port());
+                match &dc.rtt_ms {
+                    Some(rtt) => {
+                        // Align: IPv4 addresses are shorter, use more tabs
+                        // 149.154.175.50:443 = ~18 chars
+                        info!(
+                            "    DC{} [IPv4] {}:\t\t\t\t{:.0} ms",
+                            dc.dc_idx, addr_str, rtt
+                        );
+                    }
+                    None => {
+                        let err = dc.error.as_deref().unwrap_or("fail");
+                        info!(
+                            "    DC{} [IPv4] {}:\t\t\t\tFAIL ({})",
+                            dc.dc_idx, addr_str, err
+                        );
+                    }
+                }
+            }
+
+            info!("============================================================");
         }
     }
-    info!("================================");
 
     // Background tasks
     let um_clone = upstream_manager.clone();
-    tokio::spawn(async move { um_clone.run_health_checks(prefer_ipv6).await; });
+    tokio::spawn(async move {
+        um_clone.run_health_checks(prefer_ipv6).await;
+    });
 
     let rc_clone = replay_checker.clone();
-    tokio::spawn(async move { rc_clone.run_periodic_cleanup().await; });
+    tokio::spawn(async move {
+        rc_clone.run_periodic_cleanup().await;
+    });
 
     let detected_ip = detect_ip().await;
-    debug!("Detected IPs: v4={:?} v6={:?}", detected_ip.ipv4, detected_ip.ipv6);
+    debug!(
+        "Detected IPs: v4={:?} v6={:?}",
+        detected_ip.ipv4, detected_ip.ipv6
+    );
 
     let mut listeners = Vec::new();
 
@@ -220,17 +402,23 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                         if let Some(secret) = config.access.users.get(user_name) {
                             info!("User: {}", user_name);
                             if config.general.modes.classic {
-                                info!("  Classic: tg://proxy?server={}&port={}&secret={}",
+                                info!(
-                                    public_ip, config.server.port, secret);
+                                    "  Classic: tg://proxy?server={}&port={}&secret={}",
+                                    public_ip, config.server.port, secret
+                                );
                             }
                             if config.general.modes.secure {
-                                info!("  DD:      tg://proxy?server={}&port={}&secret=dd{}",
+                                info!(
-                                    public_ip, config.server.port, secret);
+                                    "  DD:      tg://proxy?server={}&port={}&secret=dd{}",
+                                    public_ip, config.server.port, secret
+                                );
                             }
                             if config.general.modes.tls {
                                 let domain_hex = hex::encode(&config.censorship.tls_domain);
-                                info!("  EE-TLS:  tg://proxy?server={}&port={}&secret=ee{}{}",
+                                info!(
-                                    public_ip, config.server.port, secret, domain_hex);
+                                    "  EE-TLS:  tg://proxy?server={}&port={}&secret=ee{}{}",
+                                    public_ip, config.server.port, secret, domain_hex
+                                );
                             }
                         } else {
                             warn!("User '{}' in show_link not found", user_name);
@@ -240,7 +428,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                 }
 
                 listeners.push(listener);
-            },
+            }
             Err(e) => {
                 error!("Failed to bind to {}: {}", addr, e);
             }
@@ -258,7 +446,9 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     } else {
         EnvFilter::new(effective_log_level.to_filter_str())
     };
-    filter_handle.reload(runtime_filter).expect("Failed to switch log filter");
+    filter_handle
+        .reload(runtime_filter)
+        .expect("Failed to switch log filter");
 
     for listener in listeners {
         let config = config.clone();
@@ -267,6 +457,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         let replay_checker = replay_checker.clone();
         let buffer_pool = buffer_pool.clone();
         let rng = rng.clone();
+        let me_pool = me_pool.clone();
 
         tokio::spawn(async move {
             loop {
@@ -278,12 +469,23 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                         let replay_checker = replay_checker.clone();
                         let buffer_pool = buffer_pool.clone();
                         let rng = rng.clone();
+                        let me_pool = me_pool.clone();
 
                         tokio::spawn(async move {
                             if let Err(e) = ClientHandler::new(
-                                stream, peer_addr, config, stats,
+                                stream,
-                                upstream_manager, replay_checker, buffer_pool, rng
+                                peer_addr,
-                            ).run().await {
+                                config,
+                                stats,
+                                upstream_manager,
+                                replay_checker,
+                                buffer_pool,
+                                rng,
+                                me_pool,
+                            )
+                            .run()
+                            .await
+                            {
                                 debug!(peer = %peer_addr, error = %e, "Connection error");
                             }
                         });

src/protocol/constants.rs

@@ -202,6 +202,17 @@ pub static RESERVED_NONCE_CONTINUES: &[[u8; 4]] = &[
 // ============= RPC Constants (for Middle Proxy) =============
 
 /// RPC Proxy Request
+
+/// RPC Flags (from Erlang mtp_rpc.erl)
+pub const RPC_FLAG_NOT_ENCRYPTED: u32 = 0x2;
+pub const RPC_FLAG_HAS_AD_TAG: u32    = 0x8;
+pub const RPC_FLAG_MAGIC: u32          = 0x1000;
+pub const RPC_FLAG_EXTMODE2: u32       = 0x20000;
+pub const RPC_FLAG_PAD: u32            = 0x8000000;
+pub const RPC_FLAG_INTERMEDIATE: u32   = 0x20000000;
+pub const RPC_FLAG_ABRIDGED: u32       = 0x40000000;
+pub const RPC_FLAG_QUICKACK: u32       = 0x80000000;
+
 pub const RPC_PROXY_REQ: [u8; 4] = [0xee, 0xf1, 0xce, 0x36];
 /// RPC Proxy Answer
 pub const RPC_PROXY_ANS: [u8; 4] = [0x0d, 0xda, 0x03, 0x44];
@@ -228,7 +239,56 @@ pub mod rpc_flags {
     pub const FLAG_QUICKACK: u32 = 0x80000000;
 }
 
-#[cfg(test)]
+
+    // ============= Middle-End Proxy Servers =============
+    pub const ME_PROXY_PORT: u16 = 8888;
+    
+    pub static TG_MIDDLE_PROXIES_FLAT_V4: LazyLock<Vec<(IpAddr, u16)>> = LazyLock::new(|| {
+        vec![
+            (IpAddr::V4(Ipv4Addr::new(149, 154, 175, 50)), 8888),
+            (IpAddr::V4(Ipv4Addr::new(149, 154, 161, 144)), 8888),
+            (IpAddr::V4(Ipv4Addr::new(149, 154, 175, 100)), 8888),
+            (IpAddr::V4(Ipv4Addr::new(91, 108, 4, 136)), 8888),
+            (IpAddr::V4(Ipv4Addr::new(91, 108, 56, 183)), 8888),
+        ]
+    });
+    
+    // ============= RPC Constants (u32 native endian) =============
+    // From mtproto-common.h + net-tcp-rpc-common.h + mtproto-proxy.c
+    
+    pub const RPC_NONCE_U32: u32           = 0x7acb87aa;
+    pub const RPC_HANDSHAKE_U32: u32       = 0x7682eef5;
+    pub const RPC_HANDSHAKE_ERROR_U32: u32 = 0x6a27beda;
+    pub const TL_PROXY_TAG_U32: u32        = 0xdb1e26ae;  // mtproto-proxy.c:121
+    
+    // mtproto-common.h
+    pub const RPC_PROXY_REQ_U32: u32       = 0x36cef1ee;
+    pub const RPC_PROXY_ANS_U32: u32       = 0x4403da0d;
+    pub const RPC_CLOSE_CONN_U32: u32      = 0x1fcf425d;
+    pub const RPC_CLOSE_EXT_U32: u32       = 0x5eb634a2;
+    pub const RPC_SIMPLE_ACK_U32: u32      = 0x3bac409b;
+    pub const RPC_PING_U32: u32            = 0x5730a2df;
+    pub const RPC_PONG_U32: u32            = 0x8430eaa7;
+    
+    pub const RPC_CRYPTO_NONE_U32: u32 = 0;
+    pub const RPC_CRYPTO_AES_U32: u32  = 1;
+    
+    pub mod proxy_flags {
+        pub const FLAG_HAS_AD_TAG: u32    = 1;
+        pub const FLAG_NOT_ENCRYPTED: u32 = 0x2;
+        pub const FLAG_HAS_AD_TAG2: u32   = 0x8;
+        pub const FLAG_MAGIC: u32         = 0x1000;
+        pub const FLAG_EXTMODE2: u32      = 0x20000;
+        pub const FLAG_PAD: u32           = 0x8000000;
+        pub const FLAG_INTERMEDIATE: u32  = 0x20000000;
+        pub const FLAG_ABRIDGED: u32      = 0x40000000;
+        pub const FLAG_QUICKACK: u32      = 0x80000000;
+    }
+    
+    pub const ME_CONNECT_TIMEOUT_SECS: u64 = 5;
+    pub const ME_HANDSHAKE_TIMEOUT_SECS: u64 = 10;
+    
+    #[cfg(test)]
 mod tests {
     use super::*;
     

src/proxy/client.rs

@@ -3,26 +3,25 @@
 use std::net::SocketAddr;
 use std::sync::Arc;
 use std::time::Duration;
+use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite};
 use tokio::net::TcpStream;
-use tokio::io::{AsyncRead, AsyncWrite, AsyncReadExt, AsyncWriteExt};
 use tokio::time::timeout;
-use tracing::{debug, info, warn, error, trace};
+use tracing::{debug, warn};
 
 use crate::config::ProxyConfig;
-use crate::error::{ProxyError, Result, HandshakeResult};
+use crate::crypto::SecureRandom;
+use crate::error::{HandshakeResult, ProxyError, Result};
 use crate::protocol::constants::*;
 use crate::protocol::tls;
-use crate::stats::{Stats, ReplayChecker};
+use crate::stats::{ReplayChecker, Stats};
-use crate::transport::{configure_client_socket, UpstreamManager};
+use crate::stream::{BufferPool, CryptoReader, CryptoWriter};
-use crate::stream::{CryptoReader, CryptoWriter, FakeTlsReader, FakeTlsWriter, BufferPool};
+use crate::transport::middle_proxy::MePool;
-use crate::crypto::{AesCtr, SecureRandom};
+use crate::transport::{UpstreamManager, configure_client_socket};
 
-use crate::proxy::handshake::{
+use crate::proxy::direct_relay::handle_via_direct;
-    handle_tls_handshake, handle_mtproto_handshake, 
+use crate::proxy::handshake::{HandshakeSuccess, handle_mtproto_handshake, handle_tls_handshake};
-    HandshakeSuccess, generate_tg_nonce, encrypt_tg_nonce,
-};
-use crate::proxy::relay::relay_bidirectional;
 use crate::proxy::masking::handle_bad_client;
+use crate::proxy::middle_relay::handle_via_middle_proxy;
 
 pub struct ClientHandler;
 
@@ -35,6 +34,7 @@ pub struct RunningClientHandler {
     upstream_manager: Arc<UpstreamManager>,
     buffer_pool: Arc<BufferPool>,
     rng: Arc<SecureRandom>,
+    me_pool: Option<Arc<MePool>>,
 }
 
 impl ClientHandler {
@@ -47,10 +47,18 @@ impl ClientHandler {
         replay_checker: Arc<ReplayChecker>,
         buffer_pool: Arc<BufferPool>,
         rng: Arc<SecureRandom>,
+        me_pool: Option<Arc<MePool>>,
     ) -> RunningClientHandler {
         RunningClientHandler {
-            stream, peer, config, stats, replay_checker,
+            stream,
-            upstream_manager, buffer_pool, rng,
+            peer,
+            config,
+            stats,
+            replay_checker,
+            upstream_manager,
+            buffer_pool,
+            rng,
+            me_pool,
         }
     }
 }
@@ -132,12 +140,20 @@ impl RunningClientHandler {
         let stats = self.stats.clone();
         let buffer_pool = self.buffer_pool.clone();
 
+        let local_addr = self.stream.local_addr().map_err(ProxyError::Io)?;
         let (read_half, write_half) = self.stream.into_split();
 
         let (mut tls_reader, tls_writer, _tls_user) = match handle_tls_handshake(
-            &handshake, read_half, write_half, peer,
+            &handshake,
-            &config, &replay_checker, &self.rng,
+            read_half,
-        ).await {
+            write_half,
+            peer,
+            &config,
+            &replay_checker,
+            &self.rng,
+        )
+        .await
+        {
             HandshakeResult::Success(result) => result,
             HandshakeResult::BadClient { reader, writer } => {
                 stats.increment_connects_bad();
@@ -149,15 +165,26 @@ impl RunningClientHandler {
 
         debug!(peer = %peer, "Reading MTProto handshake through TLS");
         let mtproto_data = tls_reader.read_exact(HANDSHAKE_LEN).await?;
-        let mtproto_handshake: [u8; HANDSHAKE_LEN] = mtproto_data[..].try_into()
+        let mtproto_handshake: [u8; HANDSHAKE_LEN] = mtproto_data[..]
+            .try_into()
             .map_err(|_| ProxyError::InvalidHandshake("Short MTProto handshake".into()))?;
 
         let (crypto_reader, crypto_writer, success) = match handle_mtproto_handshake(
-            &mtproto_handshake, tls_reader, tls_writer, peer,
+            &mtproto_handshake,
-            &config, &replay_checker, true,
+            tls_reader,
-        ).await {
+            tls_writer,
+            peer,
+            &config,
+            &replay_checker,
+            true,
+        )
+        .await
+        {
             HandshakeResult::Success(result) => result,
-            HandshakeResult::BadClient { reader: _, writer: _ } => {
+            HandshakeResult::BadClient {
+                reader: _,
+                writer: _,
+            } => {
                 stats.increment_connects_bad();
                 debug!(peer = %peer, "Valid TLS but invalid MTProto handshake");
                 return Ok(());
@@ -166,10 +193,18 @@ impl RunningClientHandler {
         };
 
         Self::handle_authenticated_static(
-            crypto_reader, crypto_writer, success,
+            crypto_reader,
-            self.upstream_manager, self.stats, self.config,
+            crypto_writer,
-            buffer_pool, self.rng,
+            success,
-        ).await
+            self.upstream_manager,
+            self.stats,
+            self.config,
+            buffer_pool,
+            self.rng,
+            self.me_pool,
+            local_addr,
+        )
+        .await
     }
 
     async fn handle_direct_client(mut self, first_bytes: [u8; 5]) -> Result<()> {
@@ -192,12 +227,20 @@ impl RunningClientHandler {
         let stats = self.stats.clone();
         let buffer_pool = self.buffer_pool.clone();
 
+        let local_addr = self.stream.local_addr().map_err(ProxyError::Io)?;
         let (read_half, write_half) = self.stream.into_split();
 
         let (crypto_reader, crypto_writer, success) = match handle_mtproto_handshake(
-            &handshake, read_half, write_half, peer,
+            &handshake,
-            &config, &replay_checker, false,
+            read_half,
-        ).await {
+            write_half,
+            peer,
+            &config,
+            &replay_checker,
+            false,
+        )
+        .await
+        {
             HandshakeResult::Success(result) => result,
             HandshakeResult::BadClient { reader, writer } => {
                 stats.increment_connects_bad();
@@ -208,12 +251,24 @@ impl RunningClientHandler {
         };
 
         Self::handle_authenticated_static(
-            crypto_reader, crypto_writer, success,
+            crypto_reader,
-            self.upstream_manager, self.stats, self.config,
+            crypto_writer,
-            buffer_pool, self.rng,
+            success,
-        ).await
+            self.upstream_manager,
+            self.stats,
+            self.config,
+            buffer_pool,
+            self.rng,
+            self.me_pool,
+            local_addr,
+        )
+        .await
     }
 
+    /// Main dispatch after successful handshake.
+    /// Two modes:
+    ///   - Direct: TCP relay to TG DC (existing behavior)  
+    ///   - Middle Proxy: RPC multiplex through ME pool (new — supports CDN DCs)
     async fn handle_authenticated_static<R, W>(
         client_reader: CryptoReader<R>,
         client_writer: CryptoWriter<W>,
@@ -223,6 +278,8 @@ impl RunningClientHandler {
         config: Arc<ProxyConfig>,
         buffer_pool: Arc<BufferPool>,
         rng: Arc<SecureRandom>,
+        me_pool: Option<Arc<MePool>>,
+        local_addr: SocketAddr,
     ) -> Result<()>
     where
         R: AsyncRead + Unpin + Send + 'static,
@@ -235,168 +292,63 @@ impl RunningClientHandler {
             return Err(e);
         }
 
-        let dc_addr = Self::get_dc_addr_static(success.dc_idx, &config)?;
+        // Decide: middle proxy or direct
-        
+        if config.general.use_middle_proxy {
-        info!(
+            if let Some(ref pool) = me_pool {
-            user = %user,
+                return handle_via_middle_proxy(
-            peer = %success.peer,
+                    client_reader,
-            dc = success.dc_idx,
+                    client_writer,
-            dc_addr = %dc_addr,
+                    success,
-            proto = ?success.proto_tag,
+                    pool.clone(),
-            "Connecting to Telegram"
+                    stats,
-        );
+                    config,
-        
+                    buffer_pool,
-        // Pass dc_idx for latency-based upstream selection
+                    local_addr,
-        let tg_stream = upstream_manager.connect(dc_addr, Some(success.dc_idx)).await?;
+                )
-        
+                .await;
-        debug!(peer = %success.peer, dc_addr = %dc_addr, "Connected, performing TG handshake");
+            }
-        
+            warn!("use_middle_proxy=true but MePool not initialized, falling back to direct");
-        let (tg_reader, tg_writer) = Self::do_tg_handshake_static(
-            tg_stream, &success, &config, rng.as_ref(),
-        ).await?;
-        
-        debug!(peer = %success.peer, "TG handshake complete, starting relay");
-        
-        stats.increment_user_connects(user);
-        stats.increment_user_curr_connects(user);
-        
-        let relay_result = relay_bidirectional(
-            client_reader, client_writer,
-            tg_reader, tg_writer,
-            user, Arc::clone(&stats), buffer_pool,
-        ).await;
-        
-        stats.decrement_user_curr_connects(user);
-        
-        match &relay_result {
-            Ok(()) => debug!(user = %user, "Relay completed"),
-            Err(e) => debug!(user = %user, error = %e, "Relay ended with error"),
         }
 
-        relay_result
+        // Direct mode (original behavior)
+        handle_via_direct(
+            client_reader,
+            client_writer,
+            success,
+            upstream_manager,
+            stats,
+            config,
+            buffer_pool,
+            rng,
+        )
+        .await
     }
 
     fn check_user_limits_static(user: &str, config: &ProxyConfig, stats: &Stats) -> Result<()> {
         if let Some(expiration) = config.access.user_expirations.get(user) {
             if chrono::Utc::now() > *expiration {
-                return Err(ProxyError::UserExpired { user: user.to_string() });
+                return Err(ProxyError::UserExpired {
+                    user: user.to_string(),
+                });
             }
         }
 
         if let Some(limit) = config.access.user_max_tcp_conns.get(user) {
             if stats.get_user_curr_connects(user) >= *limit as u64 {
-                return Err(ProxyError::ConnectionLimitExceeded { user: user.to_string() });
+                return Err(ProxyError::ConnectionLimitExceeded {
+                    user: user.to_string(),
+                });
             }
         }
 
         if let Some(quota) = config.access.user_data_quota.get(user) {
             if stats.get_user_total_octets(user) >= *quota {
-                return Err(ProxyError::DataQuotaExceeded { user: user.to_string() });
+                return Err(ProxyError::DataQuotaExceeded {
+                    user: user.to_string(),
+                });
             }
         }
 
         Ok(())
     }
-    
-    /// Resolve DC index to a target address.
-    ///
-    /// Matches the C implementation's behavior exactly:
-    ///
-    /// 1. Look up DC in known clusters (standard DCs ±1..±5)
-    /// 2. If not found and `force=1` → fall back to `default_cluster`
-    ///
-    /// In the C code:
-    /// - `proxy-multi.conf` is downloaded from Telegram, contains only DC ±1..±5
-    /// - `default 2;` directive sets the default cluster
-    /// - `mf_cluster_lookup(CurConf, target_dc, 1)` returns default_cluster
-    ///   for any unknown DC (like CDN DC 203)
-    ///
-    /// So DC 203, DC 101, DC -300, etc. all route to the default DC (2).
-    /// There is NO modular arithmetic in the C implementation.
-    fn get_dc_addr_static(dc_idx: i16, config: &ProxyConfig) -> Result<SocketAddr> {
-        let datacenters = if config.general.prefer_ipv6 {
-            &*TG_DATACENTERS_V6
-        } else {
-            &*TG_DATACENTERS_V4
-        };
-    
-        let num_dcs = datacenters.len(); // 5
-    
-        // === Step 1: Check dc_overrides (like C's `proxy_for <dc> <ip>:<port>`) ===
-        let dc_key = dc_idx.to_string();
-        if let Some(addr_str) = config.dc_overrides.get(&dc_key) {
-            match addr_str.parse::<SocketAddr>() {
-                Ok(addr) => {
-                    debug!(dc_idx = dc_idx, addr = %addr, "Using DC override from config");
-                    return Ok(addr);
-                }
-                Err(_) => {
-                    warn!(dc_idx = dc_idx, addr_str = %addr_str,
-                        "Invalid DC override address in config, ignoring");
-                }
-            }
-        }
-    
-        // === Step 2: Standard DCs ±1..±5 — direct lookup ===
-        let abs_dc = dc_idx.unsigned_abs() as usize;
-        if abs_dc >= 1 && abs_dc <= num_dcs {
-            return Ok(SocketAddr::new(datacenters[abs_dc - 1], TG_DATACENTER_PORT));
-        }
-    
-        // === Step 3: Unknown DC — fall back to default_cluster ===
-        // Exactly like C's `mf_cluster_lookup(CurConf, target_dc, force=1)`
-        // which returns `MC->default_cluster` when the DC is not found.
-        // Telegram's proxy-multi.conf uses `default 2;`
-        let default_dc = config.default_dc.unwrap_or(2) as usize;
-        let fallback_idx = if default_dc >= 1 && default_dc <= num_dcs {
-            default_dc - 1
-        } else {
-            1 // DC 2 (index 1) — matches Telegram's `default 2;`
-        };
-    
-        info!(
-            original_dc = dc_idx,
-            fallback_dc = (fallback_idx + 1) as u16,
-            fallback_addr = %datacenters[fallback_idx],
-            "Special DC ---> default_cluster"
-        );
-    
-        Ok(SocketAddr::new(datacenters[fallback_idx], TG_DATACENTER_PORT))
-    }
-    
-    async fn do_tg_handshake_static(
-        mut stream: TcpStream,
-        success: &HandshakeSuccess,
-        config: &ProxyConfig,
-        rng: &SecureRandom,
-    ) -> Result<(CryptoReader<tokio::net::tcp::OwnedReadHalf>, CryptoWriter<tokio::net::tcp::OwnedWriteHalf>)> {
-        let (nonce, tg_enc_key, tg_enc_iv, tg_dec_key, tg_dec_iv) = generate_tg_nonce(
-            success.proto_tag,
-            &success.dec_key,
-            success.dec_iv,
-            rng,
-            config.general.fast_mode,
-        );
-        
-        let encrypted_nonce = encrypt_tg_nonce(&nonce);
-        
-        debug!(
-            peer = %success.peer,
-            nonce_head = %hex::encode(&nonce[..16]),
-            "Sending nonce to Telegram"
-        );
-        
-        stream.write_all(&encrypted_nonce).await?;
-        stream.flush().await?;
-        
-        let (read_half, write_half) = stream.into_split();
-        
-        let decryptor = AesCtr::new(&tg_dec_key, tg_dec_iv);
-        let encryptor = AesCtr::new(&tg_enc_key, tg_enc_iv);
-        
-        Ok((
-            CryptoReader::new(read_half, decryptor),
-            CryptoWriter::new(write_half, encryptor),
-        ))
-    }
 }

src/proxy/direct_relay.rs

@@ -0,0 +1,163 @@
+use std::net::SocketAddr;
+use std::sync::Arc;
+
+use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt};
+use tokio::net::TcpStream;
+use tracing::{debug, info, warn};
+
+use crate::config::ProxyConfig;
+use crate::crypto::SecureRandom;
+use crate::error::Result;
+use crate::protocol::constants::*;
+use crate::proxy::handshake::{HandshakeSuccess, encrypt_tg_nonce_with_ciphers, generate_tg_nonce};
+use crate::proxy::relay::relay_bidirectional;
+use crate::stats::Stats;
+use crate::stream::{BufferPool, CryptoReader, CryptoWriter};
+use crate::transport::UpstreamManager;
+
+pub(crate) async fn handle_via_direct<R, W>(
+    client_reader: CryptoReader<R>,
+    client_writer: CryptoWriter<W>,
+    success: HandshakeSuccess,
+    upstream_manager: Arc<UpstreamManager>,
+    stats: Arc<Stats>,
+    config: Arc<ProxyConfig>,
+    buffer_pool: Arc<BufferPool>,
+    rng: Arc<SecureRandom>,
+) -> Result<()>
+where
+    R: AsyncRead + Unpin + Send + 'static,
+    W: AsyncWrite + Unpin + Send + 'static,
+{
+    let user = &success.user;
+    let dc_addr = get_dc_addr_static(success.dc_idx, &config)?;
+
+    info!(
+        user = %user,
+        peer = %success.peer,
+        dc = success.dc_idx,
+        dc_addr = %dc_addr,
+        proto = ?success.proto_tag,
+        mode = "direct",
+        "Connecting to Telegram DC"
+    );
+
+    let tg_stream = upstream_manager
+        .connect(dc_addr, Some(success.dc_idx))
+        .await?;
+
+    debug!(peer = %success.peer, dc_addr = %dc_addr, "Connected, performing TG handshake");
+
+    let (tg_reader, tg_writer) =
+        do_tg_handshake_static(tg_stream, &success, &config, rng.as_ref()).await?;
+
+    debug!(peer = %success.peer, "TG handshake complete, starting relay");
+
+    stats.increment_user_connects(user);
+    stats.increment_user_curr_connects(user);
+
+    let relay_result = relay_bidirectional(
+        client_reader,
+        client_writer,
+        tg_reader,
+        tg_writer,
+        user,
+        Arc::clone(&stats),
+        buffer_pool,
+    )
+    .await;
+
+    stats.decrement_user_curr_connects(user);
+
+    match &relay_result {
+        Ok(()) => debug!(user = %user, "Direct relay completed"),
+        Err(e) => debug!(user = %user, error = %e, "Direct relay ended with error"),
+    }
+
+    relay_result
+}
+
+fn get_dc_addr_static(dc_idx: i16, config: &ProxyConfig) -> Result<SocketAddr> {
+    let datacenters = if config.general.prefer_ipv6 {
+        &*TG_DATACENTERS_V6
+    } else {
+        &*TG_DATACENTERS_V4
+    };
+
+    let num_dcs = datacenters.len();
+
+    let dc_key = dc_idx.to_string();
+    if let Some(addr_str) = config.dc_overrides.get(&dc_key) {
+        match addr_str.parse::<SocketAddr>() {
+            Ok(addr) => {
+                debug!(dc_idx = dc_idx, addr = %addr, "Using DC override from config");
+                return Ok(addr);
+            }
+            Err(_) => {
+                warn!(dc_idx = dc_idx, addr_str = %addr_str,
+                        "Invalid DC override address in config, ignoring");
+            }
+        }
+    }
+
+    let abs_dc = dc_idx.unsigned_abs() as usize;
+    if abs_dc >= 1 && abs_dc <= num_dcs {
+        return Ok(SocketAddr::new(datacenters[abs_dc - 1], TG_DATACENTER_PORT));
+    }
+
+    let default_dc = config.default_dc.unwrap_or(2) as usize;
+    let fallback_idx = if default_dc >= 1 && default_dc <= num_dcs {
+        default_dc - 1
+    } else {
+        1
+    };
+
+    info!(
+        original_dc = dc_idx,
+        fallback_dc = (fallback_idx + 1) as u16,
+        fallback_addr = %datacenters[fallback_idx],
+        "Special DC ---> default_cluster"
+    );
+
+    Ok(SocketAddr::new(
+        datacenters[fallback_idx],
+        TG_DATACENTER_PORT,
+    ))
+}
+
+async fn do_tg_handshake_static(
+    mut stream: TcpStream,
+    success: &HandshakeSuccess,
+    config: &ProxyConfig,
+    rng: &SecureRandom,
+) -> Result<(
+    CryptoReader<tokio::net::tcp::OwnedReadHalf>,
+    CryptoWriter<tokio::net::tcp::OwnedWriteHalf>,
+)> {
+    let (nonce, _tg_enc_key, _tg_enc_iv, _tg_dec_key, _tg_dec_iv) = generate_tg_nonce(
+        success.proto_tag,
+        success.dc_idx,
+        &success.dec_key,
+        success.dec_iv,
+        rng,
+        config.general.fast_mode,
+    );
+
+    let (encrypted_nonce, tg_encryptor, tg_decryptor) = encrypt_tg_nonce_with_ciphers(&nonce);
+
+    debug!(
+        peer = %success.peer,
+        nonce_head = %hex::encode(&nonce[..16]),
+        "Sending nonce to Telegram"
+    );
+
+    stream.write_all(&encrypted_nonce).await?;
+    stream.flush().await?;
+
+    let (read_half, write_half) = stream.into_split();
+
+    Ok((
+        CryptoReader::new(read_half, tg_decryptor),
+        CryptoWriter::new(write_half, tg_encryptor),
+    ))
+}

src/proxy/handshake.rs

@@ -218,7 +218,6 @@ where
 
         replay_checker.add_handshake(dec_prekey_iv);
 
-        let decryptor = AesCtr::new(&dec_key, dec_iv);
         let encryptor = AesCtr::new(&enc_key, enc_iv);
 
         let success = HandshakeSuccess {
@@ -256,6 +255,7 @@ where
 /// Generate nonce for Telegram connection
 pub fn generate_tg_nonce(
     proto_tag: ProtoTag, 
+    dc_idx: i16,
     client_dec_key: &[u8; 32],
     client_dec_iv: u128,
     rng: &SecureRandom,
@@ -274,6 +274,8 @@ pub fn generate_tg_nonce(
         if RESERVED_NONCE_CONTINUES.contains(&continue_four) { continue; }
 
         nonce[PROTO_TAG_POS..PROTO_TAG_POS + 4].copy_from_slice(&proto_tag.to_bytes());
+        // CRITICAL: write dc_idx so upstream DC knows where to route
+        nonce[DC_IDX_POS..DC_IDX_POS + 2].copy_from_slice(&dc_idx.to_le_bytes());
 
         if fast_mode {
             nonce[SKIP_LEN..SKIP_LEN + KEY_LEN].copy_from_slice(client_dec_key);
@@ -294,19 +296,32 @@ pub fn generate_tg_nonce(
     }
 }
 
-/// Encrypt nonce for sending to Telegram
+/// Encrypt nonce for sending to Telegram and return cipher objects with correct counter state
-pub fn encrypt_tg_nonce(nonce: &[u8; HANDSHAKE_LEN]) -> Vec<u8> {
+pub fn encrypt_tg_nonce_with_ciphers(nonce: &[u8; HANDSHAKE_LEN]) -> (Vec<u8>, AesCtr, AesCtr) {
     let enc_key_iv = &nonce[SKIP_LEN..SKIP_LEN + KEY_LEN + IV_LEN];
-    let key: [u8; 32] = enc_key_iv[..KEY_LEN].try_into().unwrap();
+    let dec_key_iv: Vec<u8> = enc_key_iv.iter().rev().copied().collect();
-    let iv = u128::from_be_bytes(enc_key_iv[KEY_LEN..].try_into().unwrap());
 
-    let mut encryptor = AesCtr::new(&key, iv);
+    let enc_key: [u8; 32] = enc_key_iv[..KEY_LEN].try_into().unwrap();
-    let encrypted_full = encryptor.encrypt(nonce);
+    let enc_iv = u128::from_be_bytes(enc_key_iv[KEY_LEN..].try_into().unwrap());
+
+    let dec_key: [u8; 32] = dec_key_iv[..KEY_LEN].try_into().unwrap();
+    let dec_iv = u128::from_be_bytes(dec_key_iv[KEY_LEN..].try_into().unwrap());
+
+    let mut encryptor = AesCtr::new(&enc_key, enc_iv);
+    let encrypted_full = encryptor.encrypt(nonce);  // counter: 0 → 4
 
     let mut result = nonce[..PROTO_TAG_POS].to_vec();
     result.extend_from_slice(&encrypted_full[PROTO_TAG_POS..]);
 
-    result
+    let decryptor = AesCtr::new(&dec_key, dec_iv);
+
+    (result, encryptor, decryptor)
+}
+
+/// Encrypt nonce for sending to Telegram (legacy function for compatibility)
+pub fn encrypt_tg_nonce(nonce: &[u8; HANDSHAKE_LEN]) -> Vec<u8> {
+    let (encrypted, _, _) = encrypt_tg_nonce_with_ciphers(nonce);
+    encrypted
 }
 
 #[cfg(test)]
@@ -320,7 +335,7 @@ mod tests {
 
         let rng = SecureRandom::new();
         let (nonce, _tg_enc_key, _tg_enc_iv, _tg_dec_key, _tg_dec_iv) = 
-            generate_tg_nonce(ProtoTag::Secure, &client_dec_key, client_dec_iv, &rng, false);
+            generate_tg_nonce(ProtoTag::Secure, 2, &client_dec_key, client_dec_iv, &rng, false);
 
         assert_eq!(nonce.len(), HANDSHAKE_LEN);
 
@@ -335,7 +350,7 @@ mod tests {
 
         let rng = SecureRandom::new();
         let (nonce, _, _, _, _) = 
-            generate_tg_nonce(ProtoTag::Secure, &client_dec_key, client_dec_iv, &rng, false);
+            generate_tg_nonce(ProtoTag::Secure, 2, &client_dec_key, client_dec_iv, &rng, false);
 
         let encrypted = encrypt_tg_nonce(&nonce);
 

src/proxy/masking.rs

@@ -3,6 +3,8 @@
 use std::time::Duration;
 use std::str;
 use tokio::net::TcpStream;
+#[cfg(unix)]
+use tokio::net::UnixStream;
 use tokio::io::{AsyncRead, AsyncWrite, AsyncReadExt, AsyncWriteExt};
 use tokio::time::timeout;
 use tracing::debug;
@@ -45,8 +47,8 @@ fn detect_client_type(data: &[u8]) -> &'static str {
 
 /// Handle a bad client by forwarding to mask host
 pub async fn handle_bad_client<R, W>(
-    mut reader: R,
+    reader: R,
-    mut writer: W,
+    writer: W,
     initial_data: &[u8],
     config: &ProxyConfig,
 )
@@ -62,6 +64,34 @@ where
 
     let client_type = detect_client_type(initial_data);
 
+    // Connect via Unix socket or TCP
+    #[cfg(unix)]
+    if let Some(ref sock_path) = config.censorship.mask_unix_sock {
+        debug!(
+            client_type = client_type,
+            sock = %sock_path,
+            data_len = initial_data.len(),
+            "Forwarding bad client to mask unix socket"
+        );
+
+        let connect_result = timeout(MASK_TIMEOUT, UnixStream::connect(sock_path)).await;
+        match connect_result {
+            Ok(Ok(stream)) => {
+                let (mask_read, mask_write) = stream.into_split();
+                relay_to_mask(reader, writer, mask_read, mask_write, initial_data).await;
+            }
+            Ok(Err(e)) => {
+                debug!(error = %e, "Failed to connect to mask unix socket");
+                consume_client_data(reader).await;
+            }
+            Err(_) => {
+                debug!("Timeout connecting to mask unix socket");
+                consume_client_data(reader).await;
+            }
+        }
+        return;
+    }
+
     let mask_host = config.censorship.mask_host.as_deref()
         .unwrap_or(&config.censorship.tls_domain);
     let mask_port = config.censorship.mask_port;
@@ -76,27 +106,37 @@ where
 
     // Connect to mask host
     let mask_addr = format!("{}:{}", mask_host, mask_port);
-    let connect_result = timeout(
+    let connect_result = timeout(MASK_TIMEOUT, TcpStream::connect(&mask_addr)).await;
-        MASK_TIMEOUT,
+    match connect_result {
-        TcpStream::connect(&mask_addr)
+        Ok(Ok(stream)) => {
-    ).await;
+            let (mask_read, mask_write) = stream.into_split();
-    
+            relay_to_mask(reader, writer, mask_read, mask_write, initial_data).await;
-    let mask_stream = match connect_result {
+        }
-        Ok(Ok(s)) => s,
         Ok(Err(e)) => {
             debug!(error = %e, "Failed to connect to mask host");
             consume_client_data(reader).await;
-            return;
         }
         Err(_) => {
             debug!("Timeout connecting to mask host");
             consume_client_data(reader).await;
-            return;
         }
-    };
+    }
-    
+}
-    let (mut mask_read, mut mask_write) = mask_stream.into_split();
 
+/// Relay traffic between client and mask backend
+async fn relay_to_mask<R, W, MR, MW>(
+    mut reader: R,
+    mut writer: W,
+    mut mask_read: MR,
+    mut mask_write: MW,
+    initial_data: &[u8],
+)
+where
+    R: AsyncRead + Unpin + Send + 'static,
+    W: AsyncWrite + Unpin + Send + 'static,
+    MR: AsyncRead + Unpin + Send + 'static,
+    MW: AsyncWrite + Unpin + Send + 'static,
+{
     // Send initial data to mask host
     if mask_write.write_all(initial_data).await.is_err() {
         return;

src/proxy/middle_relay.rs

@@ -0,0 +1,254 @@
+use std::net::SocketAddr;
+use std::sync::Arc;
+
+use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
+use tracing::{debug, info, trace};
+
+use crate::config::ProxyConfig;
+use crate::error::{ProxyError, Result};
+use crate::protocol::constants::*;
+use crate::proxy::handshake::HandshakeSuccess;
+use crate::stats::Stats;
+use crate::stream::{BufferPool, CryptoReader, CryptoWriter};
+use crate::transport::middle_proxy::{MePool, MeResponse, proto_flags_for_tag};
+
+pub(crate) async fn handle_via_middle_proxy<R, W>(
+    mut crypto_reader: CryptoReader<R>,
+    mut crypto_writer: CryptoWriter<W>,
+    success: HandshakeSuccess,
+    me_pool: Arc<MePool>,
+    stats: Arc<Stats>,
+    _config: Arc<ProxyConfig>,
+    _buffer_pool: Arc<BufferPool>,
+    local_addr: SocketAddr,
+) -> Result<()>
+where
+    R: AsyncRead + Unpin + Send + 'static,
+    W: AsyncWrite + Unpin + Send + 'static,
+{
+    let user = success.user.clone();
+    let peer = success.peer;
+    let proto_tag = success.proto_tag;
+
+    info!(
+        user = %user,
+        peer = %peer,
+        dc = success.dc_idx,
+        proto = ?proto_tag,
+        mode = "middle_proxy",
+        "Routing via Middle-End"
+    );
+
+    let (conn_id, mut me_rx) = me_pool.registry().register().await;
+
+    stats.increment_user_connects(&user);
+    stats.increment_user_curr_connects(&user);
+
+    let proto_flags = proto_flags_for_tag(proto_tag, me_pool.has_proxy_tag());
+    debug!(
+        user = %user,
+        conn_id,
+        proto_flags = format_args!("0x{:08x}", proto_flags),
+        "ME relay started"
+    );
+
+    let translated_local_addr = me_pool.translate_our_addr(local_addr);
+
+    let result: Result<()> = loop {
+        tokio::select! {
+            client_frame = read_client_payload(&mut crypto_reader, proto_tag) => {
+                match client_frame {
+                    Ok(Some(payload)) => {
+                        trace!(conn_id, bytes = payload.len(), "C->ME frame");
+                        stats.add_user_octets_from(&user, payload.len() as u64);
+                        me_pool.send_proxy_req(
+                            conn_id,
+                            success.dc_idx,
+                            peer,
+                            translated_local_addr,
+                            &payload,
+                            proto_flags,
+                        ).await?;
+                    }
+                    Ok(None) => {
+                        debug!(conn_id, "Client EOF");
+                        let _ = me_pool.send_close(conn_id).await;
+                        break Ok(());
+                    }
+                    Err(e) => break Err(e),
+                }
+            }
+            me_msg = me_rx.recv() => {
+                match me_msg {
+                    Some(MeResponse::Data { flags, data }) => {
+                        trace!(conn_id, bytes = data.len(), flags, "ME->C data");
+                        stats.add_user_octets_to(&user, data.len() as u64);
+                        write_client_payload(&mut crypto_writer, proto_tag, flags, &data).await?;
+                    }
+                    Some(MeResponse::Ack(confirm)) => {
+                        trace!(conn_id, confirm, "ME->C quickack");
+                        write_client_ack(&mut crypto_writer, proto_tag, confirm).await?;
+                    }
+                    Some(MeResponse::Close) => {
+                        debug!(conn_id, "ME sent close");
+                        break Ok(());
+                    }
+                    None => {
+                        debug!(conn_id, "ME channel closed");
+                        break Err(ProxyError::Proxy("ME connection lost".into()));
+                    }
+                }
+            }
+        }
+    };
+
+    debug!(user = %user, conn_id, "ME relay cleanup");
+    me_pool.registry().unregister(conn_id).await;
+    stats.decrement_user_curr_connects(&user);
+    result
+}
+
+async fn read_client_payload<R>(
+    client_reader: &mut CryptoReader<R>,
+    proto_tag: ProtoTag,
+) -> Result<Option<Vec<u8>>>
+where
+    R: AsyncRead + Unpin + Send + 'static,
+{
+    let len = match proto_tag {
+        ProtoTag::Abridged => {
+            let mut first = [0u8; 1];
+            match client_reader.read_exact(&mut first).await {
+                Ok(_) => {}
+                Err(e) if e.kind() == std::io::ErrorKind::UnexpectedEof => return Ok(None),
+                Err(e) => return Err(ProxyError::Io(e)),
+            }
+
+            let len_words = if (first[0] & 0x7f) == 0x7f {
+                let mut ext = [0u8; 3];
+                client_reader
+                    .read_exact(&mut ext)
+                    .await
+                    .map_err(ProxyError::Io)?;
+                u32::from_le_bytes([ext[0], ext[1], ext[2], 0]) as usize
+            } else {
+                (first[0] & 0x7f) as usize
+            };
+
+            len_words
+                .checked_mul(4)
+                .ok_or_else(|| ProxyError::Proxy("Abridged frame length overflow".into()))?
+        }
+        ProtoTag::Intermediate | ProtoTag::Secure => {
+            let mut len_buf = [0u8; 4];
+            match client_reader.read_exact(&mut len_buf).await {
+                Ok(_) => {}
+                Err(e) if e.kind() == std::io::ErrorKind::UnexpectedEof => return Ok(None),
+                Err(e) => return Err(ProxyError::Io(e)),
+            }
+            (u32::from_le_bytes(len_buf) & 0x7fff_ffff) as usize
+        }
+    };
+
+    if len > 16 * 1024 * 1024 {
+        return Err(ProxyError::Proxy(format!("Frame too large: {len}")));
+    }
+
+    let mut payload = vec![0u8; len];
+    client_reader
+        .read_exact(&mut payload)
+        .await
+        .map_err(ProxyError::Io)?;
+    Ok(Some(payload))
+}
+
+async fn write_client_payload<W>(
+    client_writer: &mut CryptoWriter<W>,
+    proto_tag: ProtoTag,
+    flags: u32,
+    data: &[u8],
+) -> Result<()>
+where
+    W: AsyncWrite + Unpin + Send + 'static,
+{
+    let quickack = (flags & RPC_FLAG_QUICKACK) != 0;
+
+    match proto_tag {
+        ProtoTag::Abridged => {
+            if data.len() % 4 != 0 {
+                return Err(ProxyError::Proxy(format!(
+                    "Abridged payload must be 4-byte aligned, got {}",
+                    data.len()
+                )));
+            }
+
+            let len_words = data.len() / 4;
+            if len_words < 0x7f {
+                let mut first = len_words as u8;
+                if quickack {
+                    first |= 0x80;
+                }
+                client_writer
+                    .write_all(&[first])
+                    .await
+                    .map_err(ProxyError::Io)?;
+            } else if len_words < (1 << 24) {
+                let mut first = 0x7fu8;
+                if quickack {
+                    first |= 0x80;
+                }
+                let lw = (len_words as u32).to_le_bytes();
+                client_writer
+                    .write_all(&[first, lw[0], lw[1], lw[2]])
+                    .await
+                    .map_err(ProxyError::Io)?;
+            } else {
+                return Err(ProxyError::Proxy(format!(
+                    "Abridged frame too large: {}",
+                    data.len()
+                )));
+            }
+
+            client_writer
+                .write_all(data)
+                .await
+                .map_err(ProxyError::Io)?;
+        }
+        ProtoTag::Intermediate | ProtoTag::Secure => {
+            let mut len = data.len() as u32;
+            if quickack {
+                len |= 0x8000_0000;
+            }
+            client_writer
+                .write_all(&len.to_le_bytes())
+                .await
+                .map_err(ProxyError::Io)?;
+            client_writer
+                .write_all(data)
+                .await
+                .map_err(ProxyError::Io)?;
+        }
+    }
+
+    client_writer.flush().await.map_err(ProxyError::Io)
+}
+
+async fn write_client_ack<W>(
+    client_writer: &mut CryptoWriter<W>,
+    proto_tag: ProtoTag,
+    confirm: u32,
+) -> Result<()>
+where
+    W: AsyncWrite + Unpin + Send + 'static,
+{
+    let bytes = if proto_tag == ProtoTag::Abridged {
+        confirm.to_be_bytes()
+    } else {
+        confirm.to_le_bytes()
+    };
+    client_writer
+        .write_all(&bytes)
+        .await
+        .map_err(ProxyError::Io)?;
+    client_writer.flush().await.map_err(ProxyError::Io)
+}

src/proxy/mod.rs

@@ -1,11 +1,13 @@
 //! Proxy Defs
 
-pub mod handshake;
 pub mod client;
-pub mod relay;
+pub mod direct_relay;
+pub mod handshake;
 pub mod masking;
+pub mod middle_relay;
+pub mod relay;
 
-pub use handshake::*;
 pub use client::ClientHandler;
-pub use relay::*;
+pub use handshake::*;
 pub use masking::*;
+pub use relay::*;

src/transport/middle_proxy.rs

@@ -0,0 +1,925 @@
+//! Middle Proxy RPC Transport
+//!
+//! Implements Telegram Middle-End RPC protocol for routing to ALL DCs (including CDN).
+//!
+//! ## Phase 3 fixes:
+//! - ROOT CAUSE: Use Telegram proxy-secret (binary file) not user secret
+//! - Streaming handshake response (no fixed-size read deadlock)
+//! - Health monitoring + reconnection
+//! - Hex diagnostics for debugging
+
+use std::collections::HashMap;
+use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+use std::sync::Arc;
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::time::Duration;
+use bytes::{Bytes, BytesMut};
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::TcpStream;
+use tokio::sync::{mpsc, Mutex, RwLock};
+use tokio::time::{timeout, Instant};
+use tracing::{debug, info, trace, warn, error};
+
+use crate::crypto::{crc32, derive_middleproxy_keys, AesCbc, SecureRandom};
+use crate::error::{ProxyError, Result};
+use crate::protocol::constants::*;
+
+// ========== Proxy Secret Fetching ==========
+
+/// Fetch the Telegram proxy-secret binary file.
+///
+/// This is NOT the user secret (-S flag, 16 bytes hex for clients).
+/// This is the infrastructure secret (--aes-pwd in C MTProxy),
+/// a binary file of 32-512 bytes used for ME RPC key derivation.
+///
+/// Strategy: try local cache, then download from Telegram.
+pub async fn fetch_proxy_secret(cache_path: Option<&str>) -> Result<Vec<u8>> {
+    let cache = cache_path.unwrap_or("proxy-secret");
+
+    // 1. Try local cache (< 24h old)
+    if let Ok(metadata) = tokio::fs::metadata(cache).await {
+        if let Ok(modified) = metadata.modified() {
+            let age = std::time::SystemTime::now()
+                .duration_since(modified)
+                .unwrap_or(Duration::from_secs(u64::MAX));
+            if age < Duration::from_secs(86400) {
+                if let Ok(data) = tokio::fs::read(cache).await {
+                    if data.len() >= 32 {
+                        info!(
+                            path = cache,
+                            len = data.len(),
+                            age_hours = age.as_secs() / 3600,
+                            "Loaded proxy-secret from cache"
+                        );
+                        return Ok(data);
+                    }
+                    warn!(path = cache, len = data.len(), "Cached proxy-secret too short");
+                }
+            }
+        }
+    }
+
+    // 2. Download from Telegram
+    info!("Downloading proxy-secret from core.telegram.org...");
+    let data = download_proxy_secret().await?;
+
+    // 3. Cache locally (best-effort)
+    if let Err(e) = tokio::fs::write(cache, &data).await {
+        warn!(error = %e, "Failed to cache proxy-secret (non-fatal)");
+    } else {
+        debug!(path = cache, len = data.len(), "Cached proxy-secret");
+    }
+
+    Ok(data)
+}
+
+async fn download_proxy_secret() -> Result<Vec<u8>> {
+    let url = "https://core.telegram.org/getProxySecret";
+    let resp = reqwest::get(url)
+        .await
+        .map_err(|e| ProxyError::Proxy(format!("Failed to download proxy-secret: {}", e)))?;
+
+    if !resp.status().is_success() {
+        return Err(ProxyError::Proxy(format!(
+            "proxy-secret download HTTP {}", resp.status()
+        )));
+    }
+
+    let data = resp.bytes().await
+        .map_err(|e| ProxyError::Proxy(format!("Read proxy-secret body: {}", e)))?
+        .to_vec();
+
+    if data.len() < 32 {
+        return Err(ProxyError::Proxy(format!(
+            "proxy-secret too short: {} bytes (need >= 32)", data.len()
+        )));
+    }
+
+    info!(len = data.len(), "Downloaded proxy-secret OK");
+    Ok(data)
+}
+
+// ========== RPC Frame helpers ==========
+
+/// Build an RPC frame: [len(4) | seq_no(4) | payload | crc32(4)]
+fn build_rpc_frame(seq_no: i32, payload: &[u8]) -> Vec<u8> {
+    let total_len = (4 + 4 + payload.len() + 4) as u32;
+    let mut f = Vec::with_capacity(total_len as usize);
+    f.extend_from_slice(&total_len.to_le_bytes());
+    f.extend_from_slice(&seq_no.to_le_bytes());
+    f.extend_from_slice(payload);
+    let c = crc32(&f);
+    f.extend_from_slice(&c.to_le_bytes());
+    f
+}
+
+/// Read one plaintext RPC frame. Returns (seq_no, payload).
+async fn read_rpc_frame_plaintext(
+    rd: &mut (impl AsyncReadExt + Unpin),
+) -> Result<(i32, Vec<u8>)> {
+    let mut len_buf = [0u8; 4];
+    rd.read_exact(&mut len_buf).await.map_err(ProxyError::Io)?;
+    let total_len = u32::from_le_bytes(len_buf) as usize;
+
+    if total_len < 12 || total_len > (1 << 24) {
+        return Err(ProxyError::InvalidHandshake(
+            format!("Bad RPC frame length: {}", total_len),
+        ));
+    }
+
+    let mut rest = vec![0u8; total_len - 4];
+    rd.read_exact(&mut rest).await.map_err(ProxyError::Io)?;
+
+    let mut full = Vec::with_capacity(total_len);
+    full.extend_from_slice(&len_buf);
+    full.extend_from_slice(&rest);
+
+    let crc_offset = total_len - 4;
+    let expected_crc = u32::from_le_bytes([
+        full[crc_offset], full[crc_offset + 1],
+        full[crc_offset + 2], full[crc_offset + 3],
+    ]);
+    let actual_crc = crc32(&full[..crc_offset]);
+    if expected_crc != actual_crc {
+        return Err(ProxyError::InvalidHandshake(
+            format!("CRC mismatch: 0x{:08x} vs 0x{:08x}", expected_crc, actual_crc),
+        ));
+    }
+
+    let seq_no = i32::from_le_bytes([full[4], full[5], full[6], full[7]]);
+    let payload = full[8..crc_offset].to_vec();
+    Ok((seq_no, payload))
+}
+
+// ========== RPC Nonce (32 bytes payload) ==========
+
+fn build_nonce_payload(key_selector: u32, crypto_ts: u32, nonce: &[u8; 16]) -> [u8; 32] {
+    let mut p = [0u8; 32];
+    p[0..4].copy_from_slice(&RPC_NONCE_U32.to_le_bytes());
+    p[4..8].copy_from_slice(&key_selector.to_le_bytes());
+    p[8..12].copy_from_slice(&RPC_CRYPTO_AES_U32.to_le_bytes());
+    p[12..16].copy_from_slice(&crypto_ts.to_le_bytes());
+    p[16..32].copy_from_slice(nonce);
+    p
+}
+
+fn parse_nonce_payload(d: &[u8]) -> Result<(u32, u32, [u8; 16])> {
+    if d.len() < 32 {
+        return Err(ProxyError::InvalidHandshake(
+            format!("Nonce payload too short: {} bytes", d.len()),
+        ));
+    }
+    let t = u32::from_le_bytes([d[0], d[1], d[2], d[3]]);
+    if t != RPC_NONCE_U32 {
+        return Err(ProxyError::InvalidHandshake(
+            format!("Expected RPC_NONCE 0x{:08x}, got 0x{:08x}", RPC_NONCE_U32, t),
+        ));
+    }
+    let schema = u32::from_le_bytes([d[8], d[9], d[10], d[11]]);
+    let ts = u32::from_le_bytes([d[12], d[13], d[14], d[15]]);
+    let mut nonce = [0u8; 16];
+    nonce.copy_from_slice(&d[16..32]);
+    Ok((schema, ts, nonce))
+}
+
+// ========== RPC Handshake (32 bytes payload) ==========
+
+fn build_handshake_payload(our_ip: u32, our_port: u16, peer_ip: u32, peer_port: u16) -> [u8; 32] {
+    let mut p = [0u8; 32];
+    p[0..4].copy_from_slice(&RPC_HANDSHAKE_U32.to_le_bytes());
+    // flags = 0 at offset 4..8
+
+    // sender_pid: {ip(4), port(2), pid(2), utime(4)} at offset 8..20
+    p[8..12].copy_from_slice(&our_ip.to_le_bytes());
+    p[12..14].copy_from_slice(&our_port.to_le_bytes());
+    let pid = (std::process::id() & 0xFFFF) as u16;
+    p[14..16].copy_from_slice(&pid.to_le_bytes());
+    let utime = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_secs() as u32;
+    p[16..20].copy_from_slice(&utime.to_le_bytes());
+
+    // peer_pid: {ip(4), port(2), pid(2), utime(4)} at offset 20..32
+    p[20..24].copy_from_slice(&peer_ip.to_le_bytes());
+    p[24..26].copy_from_slice(&peer_port.to_le_bytes());
+    p
+}
+
+// ========== CBC helpers ==========
+
+fn cbc_encrypt_padded(key: &[u8; 32], iv: &[u8; 16], plaintext: &[u8]) -> Result<(Vec<u8>, [u8; 16])> {
+    let pad = (16 - (plaintext.len() % 16)) % 16;
+    let mut buf = plaintext.to_vec();
+    let pad_pattern: [u8; 4] = [0x04, 0x00, 0x00, 0x00];
+    for i in 0..pad {
+        buf.push(pad_pattern[i % 4]);
+    }
+    let cipher = AesCbc::new(*key, *iv);
+    cipher.encrypt_in_place(&mut buf)
+        .map_err(|e| ProxyError::Crypto(format!("CBC encrypt: {}", e)))?;
+    let mut new_iv = [0u8; 16];
+    if buf.len() >= 16 {
+        new_iv.copy_from_slice(&buf[buf.len() - 16..]);
+    }
+    Ok((buf, new_iv))
+}
+
+fn cbc_decrypt_inplace(key: &[u8; 32], iv: &[u8; 16], data: &mut [u8]) -> Result<[u8; 16]> {
+    let mut new_iv = [0u8; 16];
+    if data.len() >= 16 {
+        new_iv.copy_from_slice(&data[data.len() - 16..]);
+    }
+    AesCbc::new(*key, *iv)
+        .decrypt_in_place(data)
+        .map_err(|e| ProxyError::Crypto(format!("CBC decrypt: {}", e)))?;
+    Ok(new_iv)
+}
+
+// ========== IPv4 helpers ==========
+
+fn ipv4_to_mapped_v6(ip: Ipv4Addr) -> [u8; 16] {
+    let mut buf = [0u8; 16];
+    buf[10] = 0xFF;
+    buf[11] = 0xFF;
+    let o = ip.octets();
+    buf[12] = o[0]; buf[13] = o[1]; buf[14] = o[2]; buf[15] = o[3];
+    buf
+}
+
+fn addr_to_ip_u32(addr: &SocketAddr) -> u32 {
+    match addr.ip() {
+        IpAddr::V4(v4) => u32::from_be_bytes(v4.octets()),
+        IpAddr::V6(v6) => {
+            if let Some(v4) = v6.to_ipv4_mapped() {
+                u32::from_be_bytes(v4.octets())
+            } else { 0 }
+        }
+    }
+}
+
+// ========== ME Response ==========
+
+#[derive(Debug)]
+pub enum MeResponse {
+    Data(Bytes),
+    Ack(u32),
+    Close,
+}
+
+// ========== Connection Registry ==========
+
+pub struct ConnRegistry {
+    map: RwLock<HashMap<u64, mpsc::Sender<MeResponse>>>,
+    next_id: AtomicU64,
+}
+
+impl ConnRegistry {
+    pub fn new() -> Self {
+        Self {
+            map: RwLock::new(HashMap::new()),
+            next_id: AtomicU64::new(1),
+        }
+    }
+    pub async fn register(&self) -> (u64, mpsc::Receiver<MeResponse>) {
+        let id = self.next_id.fetch_add(1, Ordering::Relaxed);
+        let (tx, rx) = mpsc::channel(256);
+        self.map.write().await.insert(id, tx);
+        (id, rx)
+    }
+    pub async fn unregister(&self, id: u64) {
+        self.map.write().await.remove(&id);
+    }
+    pub async fn route(&self, id: u64, resp: MeResponse) -> bool {
+        let m = self.map.read().await;
+        if let Some(tx) = m.get(&id) {
+            tx.send(resp).await.is_ok()
+        } else { false }
+    }
+}
+
+// ========== RPC Writer (streaming CBC) ==========
+
+struct RpcWriter {
+    writer: tokio::io::WriteHalf<TcpStream>,
+    key: [u8; 32],
+    iv: [u8; 16],
+    seq_no: i32,
+}
+
+impl RpcWriter {
+    async fn send(&mut self, payload: &[u8]) -> Result<()> {
+        let frame = build_rpc_frame(self.seq_no, payload);
+        self.seq_no += 1;
+
+        let pad = (16 - (frame.len() % 16)) % 16;
+        let mut buf = frame;
+        let pad_pattern: [u8; 4] = [0x04, 0x00, 0x00, 0x00];
+        for i in 0..pad {
+            buf.push(pad_pattern[i % 4]);
+        }
+
+        let cipher = AesCbc::new(self.key, self.iv);
+        cipher.encrypt_in_place(&mut buf)
+            .map_err(|e| ProxyError::Crypto(format!("{}", e)))?;
+
+        if buf.len() >= 16 {
+            self.iv.copy_from_slice(&buf[buf.len() - 16..]);
+        }
+        self.writer.write_all(&buf).await.map_err(ProxyError::Io)
+    }
+}
+
+// ========== RPC_PROXY_REQ ==========
+
+
+fn build_proxy_req_payload(
+    conn_id: u64,
+    client_addr: SocketAddr,
+    our_addr: SocketAddr,
+    data: &[u8],
+    proxy_tag: Option<&[u8]>,
+    proto_flags: u32,
+) -> Vec<u8> {
+    // flags are pre-calculated by proto_flags_for_tag
+    // We just need to ensure FLAG_HAS_AD_TAG is set if we have a tag (it is set by default in our new function, but let's be safe)
+    let mut flags = proto_flags;
+
+    // The C code logic:
+    // flags = (transport_flags) | 0x1000 | 0x20000 | 0x8 (if tag)
+    // Our proto_flags_for_tag returns: 0x8 | 0x1000 | 0x20000 | transport_flags
+    // So we are good.
+
+    let b_cap = 128 + data.len();
+    let mut b = Vec::with_capacity(b_cap);
+
+    b.extend_from_slice(&RPC_PROXY_REQ_U32.to_le_bytes());
+    b.extend_from_slice(&flags.to_le_bytes());
+    b.extend_from_slice(&conn_id.to_le_bytes());
+
+    // Client IP (16 bytes IPv4-mapped-v6) + port (4 bytes)
+    match client_addr.ip() {
+        IpAddr::V4(v4) => b.extend_from_slice(&ipv4_to_mapped_v6(v4)),
+        IpAddr::V6(v6) => b.extend_from_slice(&v6.octets()),
+    }
+    b.extend_from_slice(&(client_addr.port() as u32).to_le_bytes());
+
+    // Our IP (16 bytes) + port (4 bytes)
+    match our_addr.ip() {
+        IpAddr::V4(v4) => b.extend_from_slice(&ipv4_to_mapped_v6(v4)),
+        IpAddr::V6(v6) => b.extend_from_slice(&v6.octets()),
+    }
+    b.extend_from_slice(&(our_addr.port() as u32).to_le_bytes());
+
+    // Extra section (proxy_tag)
+    if flags & 12 != 0 {
+        let extra_start = b.len();
+        b.extend_from_slice(&0u32.to_le_bytes()); // placeholder
+
+        if let Some(tag) = proxy_tag {
+            b.extend_from_slice(&TL_PROXY_TAG_U32.to_le_bytes());
+            // TL string encoding
+            if tag.len() < 254 {
+                b.push(tag.len() as u8);
+                b.extend_from_slice(tag);
+                let pad = (4 - ((1 + tag.len()) % 4)) % 4;
+                b.extend(std::iter::repeat(0u8).take(pad));
+            } else {
+                b.push(0xfe);
+                let len_bytes = (tag.len() as u32).to_le_bytes();
+                b.extend_from_slice(&len_bytes[..3]);
+                b.extend_from_slice(tag);
+                let pad = (4 - (tag.len() % 4)) % 4;
+                b.extend(std::iter::repeat(0u8).take(pad));
+            }
+        }
+
+        let extra_bytes = (b.len() - extra_start - 4) as u32;
+        let eb = extra_bytes.to_le_bytes();
+        b[extra_start..extra_start + 4].copy_from_slice(&eb);
+    }
+
+    b.extend_from_slice(data);
+    b
+}
+
+// ========== ME Pool ==========
+
+pub struct MePool {
+    registry: Arc<ConnRegistry>,
+    writers: Arc<RwLock<Vec<Arc<Mutex<RpcWriter>>>>>,
+    rr: AtomicU64,
+    proxy_tag: Option<Vec<u8>>,
+    /// Telegram proxy-secret (binary, 32-512 bytes)
+    proxy_secret: Vec<u8>,
+    pool_size: usize,
+}
+
+impl MePool {
+    pub fn new(proxy_tag: Option<Vec<u8>>, proxy_secret: Vec<u8>) -> Arc<Self> {
+        Arc::new(Self {
+            registry: Arc::new(ConnRegistry::new()),
+            writers: Arc::new(RwLock::new(Vec::new())),
+            rr: AtomicU64::new(0),
+            proxy_tag,
+            proxy_secret,
+            pool_size: 2,
+        })
+    }
+
+    pub fn registry(&self) -> &Arc<ConnRegistry> {
+        &self.registry
+    }
+
+    fn writers_arc(&self) -> Arc<RwLock<Vec<Arc<Mutex<RpcWriter>>>>> {
+        self.writers.clone()
+    }
+
+    /// key_selector = first 4 bytes of proxy-secret as LE u32
+    /// C: main_secret.key_signature via union { char secret[]; int key_signature; }
+    fn key_selector(&self) -> u32 {
+        if self.proxy_secret.len() >= 4 {
+            u32::from_le_bytes([
+                self.proxy_secret[0], self.proxy_secret[1],
+                self.proxy_secret[2], self.proxy_secret[3],
+            ])
+        } else { 0 }
+    }
+
+    pub async fn init(
+        self: &Arc<Self>,
+        pool_size: usize,
+        rng: &SecureRandom,
+    ) -> Result<()> {
+        let addrs = &*TG_MIDDLE_PROXIES_FLAT_V4;
+        let ks = self.key_selector();
+        info!(
+            me_servers = addrs.len(),
+            pool_size,
+            key_selector = format_args!("0x{:08x}", ks),
+            secret_len = self.proxy_secret.len(),
+            "Initializing ME pool"
+        );
+
+        for &(ip, port) in addrs.iter() {
+            for i in 0..pool_size {
+                let addr = SocketAddr::new(ip, port);
+                match self.connect_one(addr, rng).await {
+                    Ok(()) => info!(%addr, idx = i, "ME connected"),
+                    Err(e) => warn!(%addr, idx = i, error = %e, "ME connect failed"),
+                }
+            }
+            if self.writers.read().await.len() >= pool_size {
+                break;
+            }
+        }
+
+        if self.writers.read().await.is_empty() {
+            return Err(ProxyError::Proxy("No ME connections".into()));
+        }
+        Ok(())
+    }
+
+    async fn connect_one(
+        self: &Arc<Self>,
+        addr: SocketAddr,
+        rng: &SecureRandom,
+    ) -> Result<()> {
+        let secret = &self.proxy_secret;
+        if secret.len() < 32 {
+            return Err(ProxyError::Proxy("proxy-secret too short for ME auth".into()));
+        }
+
+        // ===== TCP connect =====
+        let stream = timeout(
+            Duration::from_secs(ME_CONNECT_TIMEOUT_SECS),
+            TcpStream::connect(addr),
+        )
+        .await
+        .map_err(|_| ProxyError::ConnectionTimeout { addr: addr.to_string() })?
+        .map_err(ProxyError::Io)?;
+        stream.set_nodelay(true).ok();
+
+        let local_addr = stream.local_addr().map_err(ProxyError::Io)?;
+        let peer_addr = stream.peer_addr().map_err(ProxyError::Io)?;
+        let (mut rd, mut wr) = tokio::io::split(stream);
+
+        // ===== 1. Send RPC nonce (plaintext, seq=-2) =====
+        let my_nonce: [u8; 16] = rng.bytes(16).try_into().unwrap();
+        let crypto_ts = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs() as u32;
+        let ks = self.key_selector();
+
+        let nonce_payload = build_nonce_payload(ks, crypto_ts, &my_nonce);
+        let nonce_frame = build_rpc_frame(-2, &nonce_payload);
+
+        debug!(
+            %addr,
+            frame_len = nonce_frame.len(),
+            key_sel = format_args!("0x{:08x}", ks),
+            crypto_ts,
+            "Sending nonce"
+        );
+
+        wr.write_all(&nonce_frame).await.map_err(ProxyError::Io)?;
+        wr.flush().await.map_err(ProxyError::Io)?;
+
+        // ===== 2. Read server nonce (plaintext, seq=-2) =====
+        let (srv_seq, srv_nonce_payload) = timeout(
+            Duration::from_secs(ME_HANDSHAKE_TIMEOUT_SECS),
+            read_rpc_frame_plaintext(&mut rd),
+        )
+        .await
+        .map_err(|_| ProxyError::TgHandshakeTimeout)??;
+
+        if srv_seq != -2 {
+            return Err(ProxyError::InvalidHandshake(
+                format!("Expected seq=-2, got {}", srv_seq),
+            ));
+        }
+
+        let (schema, _srv_ts, srv_nonce) = parse_nonce_payload(&srv_nonce_payload)?;
+        if schema != RPC_CRYPTO_AES_U32 {
+            return Err(ProxyError::InvalidHandshake(
+                format!("Unsupported crypto schema: 0x{:x}", schema),
+            ));
+        }
+
+        debug!(%addr, "Nonce exchange OK, deriving keys");
+
+        // ===== 3. Derive AES-256-CBC keys =====
+        // C buffer layout:
+        //   [0..16]  nonce_server (srv_nonce)
+        //   [16..32] nonce_client (my_nonce)
+        //   [32..36] client_timestamp
+        //   [36..40] server_ip
+        //   [40..42] client_port
+        //   [42..48] "CLIENT" or "SERVER"
+        //   [48..52] client_ip
+        //   [52..54] server_port
+        //   [54..54+N] secret (proxy-secret binary)
+        //   [54+N..70+N] nonce_server
+        //   nonce_client(16)
+
+        let ts_bytes = crypto_ts.to_le_bytes();
+        let server_ip = addr_to_ip_u32(&peer_addr);
+        let client_ip = addr_to_ip_u32(&local_addr);
+        let server_ip_bytes = server_ip.to_le_bytes();
+        let client_ip_bytes = client_ip.to_le_bytes();
+        let server_port_bytes = peer_addr.port().to_le_bytes();
+        let client_port_bytes = local_addr.port().to_le_bytes();
+
+        let (wk, wi) = derive_middleproxy_keys(
+            &srv_nonce, &my_nonce, &ts_bytes,
+            Some(&server_ip_bytes), &client_port_bytes,
+            b"CLIENT",
+            Some(&client_ip_bytes), &server_port_bytes,
+            secret, None, None,
+        );
+        let (rk, ri) = derive_middleproxy_keys(
+            &srv_nonce, &my_nonce, &ts_bytes,
+            Some(&server_ip_bytes), &client_port_bytes,
+            b"SERVER",
+            Some(&client_ip_bytes), &server_port_bytes,
+            secret, None, None,
+        );
+
+        debug!(
+            %addr,
+            write_key = %hex::encode(&wk[..8]),
+            read_key = %hex::encode(&rk[..8]),
+            "Keys derived"
+        );
+
+        // ===== 4. Send encrypted handshake (seq=-1) =====
+        let hs_payload = build_handshake_payload(
+            client_ip, local_addr.port(),
+            server_ip, peer_addr.port(),
+        );
+        let hs_frame = build_rpc_frame(-1, &hs_payload);
+        let (encrypted_hs, write_iv) = cbc_encrypt_padded(&wk, &wi, &hs_frame)?;
+        wr.write_all(&encrypted_hs).await.map_err(ProxyError::Io)?;
+        wr.flush().await.map_err(ProxyError::Io)?;
+
+        debug!(%addr, enc_len = encrypted_hs.len(), "Sent encrypted handshake");
+
+        // ===== 5. Read encrypted handshake response (STREAMING) =====
+        // Server sends encrypted handshake. C crypto layer may send partial
+        // blocks (only complete 16-byte blocks get encrypted at a time).
+        // We read incrementally and decrypt block-by-block.
+        let deadline = Instant::now() + Duration::from_secs(ME_HANDSHAKE_TIMEOUT_SECS);
+        let mut enc_buf = BytesMut::with_capacity(256);
+        let mut dec_buf = BytesMut::with_capacity(256);
+        let mut read_iv = ri;
+        let mut handshake_ok = false;
+
+        while Instant::now() < deadline && !handshake_ok {
+            let remaining = deadline - Instant::now();
+            let mut tmp = [0u8; 256];
+            let n = match timeout(remaining, rd.read(&mut tmp)).await {
+                Ok(Ok(0)) => return Err(ProxyError::Io(std::io::Error::new(
+                    std::io::ErrorKind::UnexpectedEof, "ME closed during handshake",
+                ))),
+                Ok(Ok(n)) => n,
+                Ok(Err(e)) => return Err(ProxyError::Io(e)),
+                Err(_) => return Err(ProxyError::TgHandshakeTimeout),
+            };
+            enc_buf.extend_from_slice(&tmp[..n]);
+
+            // Decrypt complete 16-byte blocks
+            let blocks = enc_buf.len() / 16 * 16;
+            if blocks > 0 {
+                let mut chunk = vec![0u8; blocks];
+                chunk.copy_from_slice(&enc_buf[..blocks]);
+                let new_iv = cbc_decrypt_inplace(&rk, &read_iv, &mut chunk)?;
+                read_iv = new_iv;
+                dec_buf.extend_from_slice(&chunk);
+                let _ = enc_buf.split_to(blocks);
+            }
+
+            // Try to parse RPC frame from decrypted data
+            while dec_buf.len() >= 4 {
+                let fl = u32::from_le_bytes([
+                    dec_buf[0], dec_buf[1], dec_buf[2], dec_buf[3],
+                ]) as usize;
+
+                // Skip noop padding
+                if fl == 4 {
+                    let _ = dec_buf.split_to(4);
+                    continue;
+                }
+                if fl < 12 || fl > (1 << 24) {
+                    return Err(ProxyError::InvalidHandshake(
+                        format!("Bad HS response frame len: {}", fl),
+                    ));
+                }
+                if dec_buf.len() < fl {
+                    break; // need more data
+                }
+
+                let frame = dec_buf.split_to(fl);
+
+                // CRC32 check
+                let pe = fl - 4;
+                let ec = u32::from_le_bytes([
+                    frame[pe], frame[pe + 1], frame[pe + 2], frame[pe + 3],
+                ]);
+                let ac = crc32(&frame[..pe]);
+                if ec != ac {
+                    return Err(ProxyError::InvalidHandshake(
+                        format!("HS CRC mismatch: 0x{:08x} vs 0x{:08x}", ec, ac),
+                    ));
+                }
+
+                // Check type
+                let hs_type = u32::from_le_bytes([
+                    frame[8], frame[9], frame[10], frame[11],
+                ]);
+                if hs_type == RPC_HANDSHAKE_ERROR_U32 {
+                    let err_code = if frame.len() >= 16 {
+                        i32::from_le_bytes([frame[12], frame[13], frame[14], frame[15]])
+                    } else { -1 };
+                    return Err(ProxyError::InvalidHandshake(
+                        format!("ME rejected handshake (error={})", err_code),
+                    ));
+                }
+                if hs_type != RPC_HANDSHAKE_U32 {
+                    return Err(ProxyError::InvalidHandshake(
+                        format!("Expected HANDSHAKE 0x{:08x}, got 0x{:08x}", RPC_HANDSHAKE_U32, hs_type),
+                    ));
+                }
+
+                handshake_ok = true;
+                break;
+            }
+        }
+
+        if !handshake_ok {
+            return Err(ProxyError::TgHandshakeTimeout);
+        }
+
+        info!(%addr, "RPC handshake OK");
+
+        // ===== 6. Setup writer + reader =====
+        let rpc_w = Arc::new(Mutex::new(RpcWriter {
+            writer: wr,
+            key: wk,
+            iv: write_iv,
+            seq_no: 0,
+        }));
+        self.writers.write().await.push(rpc_w.clone());
+
+        let reg = self.registry.clone();
+        let w_pong = rpc_w.clone();
+        let w_pool = self.writers_arc();
+        tokio::spawn(async move {
+            if let Err(e) = reader_loop(rd, rk, read_iv, reg, enc_buf, dec_buf, w_pong.clone()).await {
+                warn!(error = %e, "ME reader ended");
+            }
+            // Remove dead writer from pool
+            let mut ws = w_pool.write().await;
+            ws.retain(|w| !Arc::ptr_eq(w, &w_pong));
+            info!(remaining = ws.len(), "Dead ME writer removed from pool");
+        });
+
+        Ok(())
+    }
+
+    pub async fn send_proxy_req(
+        &self,
+        conn_id: u64,
+        client_addr: SocketAddr,
+        our_addr: SocketAddr,
+        data: &[u8],
+        proto_flags: u32,
+    ) -> Result<()> {
+        let payload = build_proxy_req_payload(
+            conn_id, client_addr, our_addr, data,
+            self.proxy_tag.as_deref(), proto_flags,
+        );
+        loop {
+            let ws = self.writers.read().await;
+            if ws.is_empty() {
+                return Err(ProxyError::Proxy("All ME connections dead".into()));
+            }
+            let idx = self.rr.fetch_add(1, Ordering::Relaxed) as usize % ws.len();
+            let w = ws[idx].clone();
+            drop(ws);
+            match w.lock().await.send(&payload).await {
+                Ok(()) => return Ok(()),
+                Err(e) => {
+                    warn!(error = %e, "ME write failed, removing dead conn");
+                    let mut ws = self.writers.write().await;
+                    ws.retain(|o| !Arc::ptr_eq(o, &w));
+                    if ws.is_empty() {
+                        return Err(ProxyError::Proxy("All ME connections dead".into()));
+                    }
+                }
+            }
+        }
+    }
+
+    pub async fn send_close(&self, conn_id: u64) -> Result<()> {
+        let ws = self.writers.read().await;
+        if !ws.is_empty() {
+            let w = ws[0].clone();
+            drop(ws);
+            let mut p = Vec::with_capacity(12);
+            p.extend_from_slice(&RPC_CLOSE_EXT_U32.to_le_bytes());
+            p.extend_from_slice(&conn_id.to_le_bytes());
+            if let Err(e) = w.lock().await.send(&p).await {
+                debug!(error = %e, "ME close write failed");
+                let mut ws = self.writers.write().await;
+                ws.retain(|o| !Arc::ptr_eq(o, &w));
+            }
+        }
+        self.registry.unregister(conn_id).await;
+        Ok(())
+    }
+
+    pub fn connection_count(&self) -> usize {
+        self.writers.try_read().map(|w| w.len()).unwrap_or(0)
+    }
+}
+
+// ========== Reader Loop ==========
+
+async fn reader_loop(
+    mut rd: tokio::io::ReadHalf<TcpStream>,
+    dk: [u8; 32],
+    mut div: [u8; 16],
+    reg: Arc<ConnRegistry>,
+    mut enc_leftover: BytesMut,
+    mut dec: BytesMut,
+    writer: Arc<Mutex<RpcWriter>>,
+) -> Result<()> {
+    let mut raw = enc_leftover;
+    loop {
+        let mut tmp = [0u8; 16384];
+        let n = rd.read(&mut tmp).await.map_err(ProxyError::Io)?;
+        if n == 0 { return Ok(()); }
+        raw.extend_from_slice(&tmp[..n]);
+
+        // Decrypt complete 16-byte blocks
+        let blocks = raw.len() / 16 * 16;
+        if blocks > 0 {
+            let mut new_iv = [0u8; 16];
+            new_iv.copy_from_slice(&raw[blocks - 16..blocks]);
+            let mut chunk = vec![0u8; blocks];
+            chunk.copy_from_slice(&raw[..blocks]);
+            AesCbc::new(dk, div)
+                .decrypt_in_place(&mut chunk)
+                .map_err(|e| ProxyError::Crypto(format!("{}", e)))?;
+            div = new_iv;
+            dec.extend_from_slice(&chunk);
+            let _ = raw.split_to(blocks);
+        }
+
+        // Parse RPC frames
+        while dec.len() >= 12 {
+            let fl = u32::from_le_bytes([dec[0], dec[1], dec[2], dec[3]]) as usize;
+            if fl == 4 { let _ = dec.split_to(4); continue; }
+            if fl < 12 || fl > (1 << 24) {
+                warn!(frame_len = fl, "Invalid RPC frame len");
+                dec.clear();
+                break;
+            }
+            if dec.len() < fl { break; }
+
+            let frame = dec.split_to(fl);
+            let pe = fl - 4;
+            let ec = u32::from_le_bytes([frame[pe], frame[pe+1], frame[pe+2], frame[pe+3]]);
+            if crc32(&frame[..pe]) != ec {
+                warn!("CRC mismatch in data frame");
+                continue;
+            }
+
+            let payload = &frame[8..pe];
+            if payload.len() < 4 { continue; }
+            let pt = u32::from_le_bytes([payload[0], payload[1], payload[2], payload[3]]);
+            let body = &payload[4..];
+
+            if pt == RPC_PROXY_ANS_U32 && body.len() >= 12 {
+                let flags = u32::from_le_bytes(body[0..4].try_into().unwrap());
+                let cid = u64::from_le_bytes(body[4..12].try_into().unwrap());
+                let data = Bytes::copy_from_slice(&body[12..]);
+                trace!(cid, len = data.len(), flags, "ANS");
+                reg.route(cid, MeResponse::Data(data)).await;
+            } else if pt == RPC_SIMPLE_ACK_U32 && body.len() >= 12 {
+                let cid = u64::from_le_bytes(body[0..8].try_into().unwrap());
+                let cfm = u32::from_le_bytes(body[8..12].try_into().unwrap());
+                trace!(cid, cfm, "ACK");
+                reg.route(cid, MeResponse::Ack(cfm)).await;
+            } else if pt == RPC_CLOSE_EXT_U32 && body.len() >= 8 {
+                let cid = u64::from_le_bytes(body[0..8].try_into().unwrap());
+                debug!(cid, "CLOSE_EXT from ME");
+                reg.route(cid, MeResponse::Close).await;
+                reg.unregister(cid).await;
+            } else if pt == RPC_CLOSE_CONN_U32 && body.len() >= 8 {
+                let cid = u64::from_le_bytes(body[0..8].try_into().unwrap());
+                debug!(cid, "CLOSE_CONN from ME");
+                reg.route(cid, MeResponse::Close).await;
+                reg.unregister(cid).await;
+            } else if pt == RPC_PING_U32 && body.len() >= 8 {
+                let ping_id = i64::from_le_bytes(body[0..8].try_into().unwrap());
+                trace!(ping_id, "RPC_PING -> PONG");
+                let mut pong = Vec::with_capacity(12);
+                pong.extend_from_slice(&RPC_PONG_U32.to_le_bytes());
+                pong.extend_from_slice(&ping_id.to_le_bytes());
+                if let Err(e) = writer.lock().await.send(&pong).await {
+                    warn!(error = %e, "PONG send failed");
+                    break;
+                }
+            } else {
+                debug!(rpc_type = format_args!("0x{:08x}", pt), len = body.len(), "Unknown RPC");
+            }
+        }
+    }
+}
+
+// ========== Proto flags ==========
+
+/// Map ProtoTag to C-compatible RPC_PROXY_REQ transport flags.
+/// C: RPC_F_COMPACT(0x40000000)=abridged, RPC_F_MEDIUM(0x20000000)=intermediate/secure
+/// The 0x1000(magic) and 0x8(proxy_tag) are added inside build_proxy_req_payload.
+
+pub fn proto_flags_for_tag(tag: crate::protocol::constants::ProtoTag) -> u32 {
+    use crate::protocol::constants::*;
+    let mut flags = RPC_FLAG_HAS_AD_TAG | RPC_FLAG_MAGIC | RPC_FLAG_EXTMODE2;
+    match tag {
+        ProtoTag::Abridged     => flags | RPC_FLAG_ABRIDGED,
+        ProtoTag::Intermediate => flags | RPC_FLAG_INTERMEDIATE,
+        ProtoTag::Secure       => flags | RPC_FLAG_PAD | RPC_FLAG_INTERMEDIATE,
+    }
+}
+
+
+// ========== Health Monitor (Phase 4) ==========
+
+pub async fn me_health_monitor(
+    pool: Arc<MePool>,
+    rng: Arc<SecureRandom>,
+    min_connections: usize,
+) {
+    loop {
+        tokio::time::sleep(Duration::from_secs(30)).await;
+        let current = pool.writers.read().await.len();
+        if current < min_connections {
+            warn!(current, min = min_connections, "ME pool below minimum, reconnecting...");
+            let addrs = TG_MIDDLE_PROXIES_FLAT_V4.clone();
+            for &(ip, port) in addrs.iter() {
+                let needed = min_connections.saturating_sub(pool.writers.read().await.len());
+                if needed == 0 { break; }
+                for _ in 0..needed {
+                    let addr = SocketAddr::new(ip, port);
+                    match pool.connect_one(addr, &rng).await {
+                        Ok(()) => info!(%addr, "ME reconnected"),
+                        Err(e) => debug!(%addr, error = %e, "ME reconnect failed"),
+                    }
+                }
+            }
+        }
+    }
+}

src/transport/middle_proxy/codec.rs

@@ -0,0 +1,179 @@
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+
+use crate::crypto::{AesCbc, crc32};
+use crate::error::{ProxyError, Result};
+use crate::protocol::constants::*;
+
+pub(crate) fn build_rpc_frame(seq_no: i32, payload: &[u8]) -> Vec<u8> {
+    let total_len = (4 + 4 + payload.len() + 4) as u32;
+    let mut frame = Vec::with_capacity(total_len as usize);
+    frame.extend_from_slice(&total_len.to_le_bytes());
+    frame.extend_from_slice(&seq_no.to_le_bytes());
+    frame.extend_from_slice(payload);
+    let c = crc32(&frame);
+    frame.extend_from_slice(&c.to_le_bytes());
+    frame
+}
+
+pub(crate) async fn read_rpc_frame_plaintext(
+    rd: &mut (impl AsyncReadExt + Unpin),
+) -> Result<(i32, Vec<u8>)> {
+    let mut len_buf = [0u8; 4];
+    rd.read_exact(&mut len_buf).await.map_err(ProxyError::Io)?;
+    let total_len = u32::from_le_bytes(len_buf) as usize;
+
+    if !(12..=(1 << 24)).contains(&total_len) {
+        return Err(ProxyError::InvalidHandshake(format!(
+            "Bad RPC frame length: {total_len}"
+        )));
+    }
+
+    let mut rest = vec![0u8; total_len - 4];
+    rd.read_exact(&mut rest).await.map_err(ProxyError::Io)?;
+
+    let mut full = Vec::with_capacity(total_len);
+    full.extend_from_slice(&len_buf);
+    full.extend_from_slice(&rest);
+
+    let crc_offset = total_len - 4;
+    let expected_crc = u32::from_le_bytes(full[crc_offset..crc_offset + 4].try_into().unwrap());
+    let actual_crc = crc32(&full[..crc_offset]);
+    if expected_crc != actual_crc {
+        return Err(ProxyError::InvalidHandshake(format!(
+            "CRC mismatch: 0x{expected_crc:08x} vs 0x{actual_crc:08x}"
+        )));
+    }
+
+    let seq_no = i32::from_le_bytes(full[4..8].try_into().unwrap());
+    let payload = full[8..crc_offset].to_vec();
+    Ok((seq_no, payload))
+}
+
+pub(crate) fn build_nonce_payload(key_selector: u32, crypto_ts: u32, nonce: &[u8; 16]) -> [u8; 32] {
+    let mut p = [0u8; 32];
+    p[0..4].copy_from_slice(&RPC_NONCE_U32.to_le_bytes());
+    p[4..8].copy_from_slice(&key_selector.to_le_bytes());
+    p[8..12].copy_from_slice(&RPC_CRYPTO_AES_U32.to_le_bytes());
+    p[12..16].copy_from_slice(&crypto_ts.to_le_bytes());
+    p[16..32].copy_from_slice(nonce);
+    p
+}
+
+pub(crate) fn parse_nonce_payload(d: &[u8]) -> Result<(u32, u32, u32, [u8; 16])> {
+    if d.len() < 32 {
+        return Err(ProxyError::InvalidHandshake(format!(
+            "Nonce payload too short: {} bytes",
+            d.len()
+        )));
+    }
+
+    let t = u32::from_le_bytes(d[0..4].try_into().unwrap());
+    if t != RPC_NONCE_U32 {
+        return Err(ProxyError::InvalidHandshake(format!(
+            "Expected RPC_NONCE 0x{RPC_NONCE_U32:08x}, got 0x{t:08x}"
+        )));
+    }
+
+    let key_select = u32::from_le_bytes(d[4..8].try_into().unwrap());
+    let schema = u32::from_le_bytes(d[8..12].try_into().unwrap());
+    let ts = u32::from_le_bytes(d[12..16].try_into().unwrap());
+    let mut nonce = [0u8; 16];
+    nonce.copy_from_slice(&d[16..32]);
+    Ok((key_select, schema, ts, nonce))
+}
+
+pub(crate) fn build_handshake_payload(
+    our_ip: [u8; 4],
+    our_port: u16,
+    peer_ip: [u8; 4],
+    peer_port: u16,
+) -> [u8; 32] {
+    let mut p = [0u8; 32];
+    p[0..4].copy_from_slice(&RPC_HANDSHAKE_U32.to_le_bytes());
+
+    // Keep C memory layout compatibility for PID IPv4 bytes.
+    p[8..12].copy_from_slice(&our_ip);
+    p[12..14].copy_from_slice(&our_port.to_le_bytes());
+    let pid = (std::process::id() & 0xffff) as u16;
+    p[14..16].copy_from_slice(&pid.to_le_bytes());
+    let utime = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_secs() as u32;
+    p[16..20].copy_from_slice(&utime.to_le_bytes());
+
+    p[20..24].copy_from_slice(&peer_ip);
+    p[24..26].copy_from_slice(&peer_port.to_le_bytes());
+    p
+}
+
+pub(crate) fn cbc_encrypt_padded(
+    key: &[u8; 32],
+    iv: &[u8; 16],
+    plaintext: &[u8],
+) -> Result<(Vec<u8>, [u8; 16])> {
+    let pad = (16 - (plaintext.len() % 16)) % 16;
+    let mut buf = plaintext.to_vec();
+    let pad_pattern: [u8; 4] = [0x04, 0x00, 0x00, 0x00];
+    for i in 0..pad {
+        buf.push(pad_pattern[i % 4]);
+    }
+
+    let cipher = AesCbc::new(*key, *iv);
+    cipher
+        .encrypt_in_place(&mut buf)
+        .map_err(|e| ProxyError::Crypto(format!("CBC encrypt: {e}")))?;
+
+    let mut new_iv = [0u8; 16];
+    if buf.len() >= 16 {
+        new_iv.copy_from_slice(&buf[buf.len() - 16..]);
+    }
+    Ok((buf, new_iv))
+}
+
+pub(crate) fn cbc_decrypt_inplace(
+    key: &[u8; 32],
+    iv: &[u8; 16],
+    data: &mut [u8],
+) -> Result<[u8; 16]> {
+    let mut new_iv = [0u8; 16];
+    if data.len() >= 16 {
+        new_iv.copy_from_slice(&data[data.len() - 16..]);
+    }
+
+    AesCbc::new(*key, *iv)
+        .decrypt_in_place(data)
+        .map_err(|e| ProxyError::Crypto(format!("CBC decrypt: {e}")))?;
+    Ok(new_iv)
+}
+
+pub(crate) struct RpcWriter {
+    pub(crate) writer: tokio::io::WriteHalf<tokio::net::TcpStream>,
+    pub(crate) key: [u8; 32],
+    pub(crate) iv: [u8; 16],
+    pub(crate) seq_no: i32,
+}
+
+impl RpcWriter {
+    pub(crate) async fn send(&mut self, payload: &[u8]) -> Result<()> {
+        let frame = build_rpc_frame(self.seq_no, payload);
+        self.seq_no += 1;
+
+        let pad = (16 - (frame.len() % 16)) % 16;
+        let mut buf = frame;
+        let pad_pattern: [u8; 4] = [0x04, 0x00, 0x00, 0x00];
+        for i in 0..pad {
+            buf.push(pad_pattern[i % 4]);
+        }
+
+        let cipher = AesCbc::new(self.key, self.iv);
+        cipher
+            .encrypt_in_place(&mut buf)
+            .map_err(|e| ProxyError::Crypto(format!("{e}")))?;
+
+        if buf.len() >= 16 {
+            self.iv.copy_from_slice(&buf[buf.len() - 16..]);
+        }
+        self.writer.write_all(&buf).await.map_err(ProxyError::Io)
+    }
+}

src/transport/middle_proxy/health.rs

@@ -0,0 +1,38 @@
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::time::Duration;
+
+use tracing::{debug, info, warn};
+
+use crate::crypto::SecureRandom;
+use crate::protocol::constants::TG_MIDDLE_PROXIES_FLAT_V4;
+
+use super::MePool;
+
+pub async fn me_health_monitor(pool: Arc<MePool>, rng: Arc<SecureRandom>, min_connections: usize) {
+    loop {
+        tokio::time::sleep(Duration::from_secs(30)).await;
+        let current = pool.connection_count();
+        if current < min_connections {
+            warn!(
+                current,
+                min = min_connections,
+                "ME pool below minimum, reconnecting..."
+            );
+            let addrs = TG_MIDDLE_PROXIES_FLAT_V4.clone();
+            for &(ip, port) in addrs.iter() {
+                let needed = min_connections.saturating_sub(pool.connection_count());
+                if needed == 0 {
+                    break;
+                }
+                for _ in 0..needed {
+                    let addr = SocketAddr::new(ip, port);
+                    match pool.connect_one(addr, &rng).await {
+                        Ok(()) => info!(%addr, "ME reconnected"),
+                        Err(e) => debug!(%addr, error = %e, "ME reconnect failed"),
+                    }
+                }
+            }
+        }
+    }
+}

src/transport/middle_proxy/mod.rs

@@ -0,0 +1,26 @@
+//! Middle Proxy RPC transport.
+
+mod codec;
+mod health;
+mod pool;
+mod pool_nat;
+mod reader;
+mod registry;
+mod send;
+mod secret;
+mod wire;
+
+use bytes::Bytes;
+
+pub use health::me_health_monitor;
+pub use pool::MePool;
+pub use registry::ConnRegistry;
+pub use secret::fetch_proxy_secret;
+pub use wire::proto_flags_for_tag;
+
+#[derive(Debug)]
+pub enum MeResponse {
+    Data { flags: u32, data: Bytes },
+    Ack(u32),
+    Close,
+}

src/transport/middle_proxy/pool.rs

@@ -0,0 +1,499 @@
+use std::net::{IpAddr, SocketAddr};
+use std::sync::Arc;
+use std::sync::OnceLock;
+use std::sync::atomic::AtomicU64;
+use std::time::Duration;
+
+use bytes::BytesMut;
+use rand::Rng;
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::TcpStream;
+use tokio::sync::{Mutex, RwLock};
+use tokio::time::{Instant, timeout};
+use tracing::{debug, info, warn};
+
+use crate::crypto::{SecureRandom, build_middleproxy_prekey, derive_middleproxy_keys, sha256};
+use crate::error::{ProxyError, Result};
+use crate::protocol::constants::*;
+
+use super::ConnRegistry;
+use super::codec::{
+    RpcWriter, build_handshake_payload, build_nonce_payload, build_rpc_frame, cbc_decrypt_inplace,
+    cbc_encrypt_padded, parse_nonce_payload, read_rpc_frame_plaintext,
+};
+use super::reader::reader_loop;
+use super::wire::{IpMaterial, extract_ip_material};
+
+const ME_ACTIVE_PING_SECS: u64 = 25;
+const ME_ACTIVE_PING_JITTER_SECS: i64 = 5;
+
+pub struct MePool {
+    pub(super) registry: Arc<ConnRegistry>,
+    pub(super) writers: Arc<RwLock<Vec<(SocketAddr, Arc<Mutex<RpcWriter>>)>>> ,
+    pub(super) rr: AtomicU64,
+    pub(super) proxy_tag: Option<Vec<u8>>,
+    proxy_secret: Vec<u8>,
+    pub(super) nat_ip_cfg: Option<IpAddr>,
+    pub(super) nat_ip_detected: OnceLock<IpAddr>,
+    pub(super) nat_probe: bool,
+    pub(super) nat_stun: Option<String>,
+    pool_size: usize,
+}
+
+impl MePool {
+    pub fn new(
+        proxy_tag: Option<Vec<u8>>,
+        proxy_secret: Vec<u8>,
+        nat_ip: Option<IpAddr>,
+        nat_probe: bool,
+        nat_stun: Option<String>,
+    ) -> Arc<Self> {
+        Arc::new(Self {
+            registry: Arc::new(ConnRegistry::new()),
+            writers: Arc::new(RwLock::new(Vec::new())),
+            rr: AtomicU64::new(0),
+            proxy_tag,
+            proxy_secret,
+            nat_ip_cfg: nat_ip,
+            nat_ip_detected: OnceLock::new(),
+            nat_probe,
+            nat_stun,
+            pool_size: 2,
+        })
+    }
+
+    pub fn has_proxy_tag(&self) -> bool {
+        self.proxy_tag.is_some()
+    }
+
+    pub fn translate_our_addr(&self, addr: SocketAddr) -> SocketAddr {
+        let ip = self.translate_ip_for_nat(addr.ip());
+        SocketAddr::new(ip, addr.port())
+    }
+
+    pub fn registry(&self) -> &Arc<ConnRegistry> {
+        &self.registry
+    }
+
+    fn writers_arc(&self) -> Arc<RwLock<Vec<(SocketAddr, Arc<Mutex<RpcWriter>>)>>>
+    {
+        self.writers.clone()
+    }
+
+    fn key_selector(&self) -> u32 {
+        if self.proxy_secret.len() >= 4 {
+            u32::from_le_bytes([
+                self.proxy_secret[0],
+                self.proxy_secret[1],
+                self.proxy_secret[2],
+                self.proxy_secret[3],
+            ])
+        } else {
+            0
+        }
+    }
+
+    pub async fn init(self: &Arc<Self>, pool_size: usize, rng: &SecureRandom) -> Result<()> {
+        let addrs = &*TG_MIDDLE_PROXIES_FLAT_V4;
+        let ks = self.key_selector();
+        info!(
+            me_servers = addrs.len(),
+            pool_size,
+            key_selector = format_args!("0x{ks:08x}"),
+            secret_len = self.proxy_secret.len(),
+            "Initializing ME pool"
+        );
+
+        for &(ip, port) in addrs.iter() {
+            for i in 0..pool_size {
+                let addr = SocketAddr::new(ip, port);
+                match self.connect_one(addr, rng).await {
+                    Ok(()) => info!(%addr, idx = i, "ME connected"),
+                    Err(e) => warn!(%addr, idx = i, error = %e, "ME connect failed"),
+                }
+            }
+            if self.writers.read().await.len() >= pool_size {
+                break;
+            }
+        }
+
+        if self.writers.read().await.is_empty() {
+            return Err(ProxyError::Proxy("No ME connections".into()));
+        }
+        Ok(())
+    }
+
+    pub(crate) async fn connect_one(
+        self: &Arc<Self>,
+        addr: SocketAddr,
+        rng: &SecureRandom,
+    ) -> Result<()> {
+        let secret = &self.proxy_secret;
+        if secret.len() < 32 {
+            return Err(ProxyError::Proxy(
+                "proxy-secret too short for ME auth".into(),
+            ));
+        }
+
+        let stream = timeout(
+            Duration::from_secs(ME_CONNECT_TIMEOUT_SECS),
+            TcpStream::connect(addr),
+        )
+        .await
+        .map_err(|_| ProxyError::ConnectionTimeout {
+            addr: addr.to_string(),
+        })?
+        .map_err(ProxyError::Io)?;
+        stream.set_nodelay(true).ok();
+
+        let local_addr = stream.local_addr().map_err(ProxyError::Io)?;
+        let peer_addr = stream.peer_addr().map_err(ProxyError::Io)?;
+        let _ = self.maybe_detect_nat_ip(local_addr.ip()).await;
+        let reflected = if self.nat_probe {
+            self.maybe_reflect_public_addr().await
+        } else {
+            None
+        };
+        let local_addr_nat = self.translate_our_addr_with_reflection(local_addr, reflected);
+        let peer_addr_nat =
+            SocketAddr::new(self.translate_ip_for_nat(peer_addr.ip()), peer_addr.port());
+        let (mut rd, mut wr) = tokio::io::split(stream);
+
+        let my_nonce: [u8; 16] = rng.bytes(16).try_into().unwrap();
+        let crypto_ts = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs() as u32;
+
+        let ks = self.key_selector();
+        let nonce_payload = build_nonce_payload(ks, crypto_ts, &my_nonce);
+        let nonce_frame = build_rpc_frame(-2, &nonce_payload);
+        let dump = hex_dump(&nonce_frame[..nonce_frame.len().min(44)]);
+        info!(
+            key_selector = format_args!("0x{ks:08x}"),
+            crypto_ts,
+            frame_len = nonce_frame.len(),
+            nonce_frame_hex = %dump,
+            "Sending ME nonce frame"
+        );
+        wr.write_all(&nonce_frame).await.map_err(ProxyError::Io)?;
+        wr.flush().await.map_err(ProxyError::Io)?;
+
+        let (srv_seq, srv_nonce_payload) = timeout(
+            Duration::from_secs(ME_HANDSHAKE_TIMEOUT_SECS),
+            read_rpc_frame_plaintext(&mut rd),
+        )
+        .await
+        .map_err(|_| ProxyError::TgHandshakeTimeout)??;
+
+        if srv_seq != -2 {
+            return Err(ProxyError::InvalidHandshake(format!(
+                "Expected seq=-2, got {srv_seq}"
+            )));
+        }
+
+        let (srv_key_select, schema, srv_ts, srv_nonce) = parse_nonce_payload(&srv_nonce_payload)?;
+        if schema != RPC_CRYPTO_AES_U32 {
+            warn!(schema = format_args!("0x{schema:08x}"), "Unsupported ME crypto schema");
+            return Err(ProxyError::InvalidHandshake(format!(
+                "Unsupported crypto schema: 0x{schema:x}"
+            )));
+        }
+
+        if srv_key_select != ks {
+            return Err(ProxyError::InvalidHandshake(format!(
+                "Server key_select 0x{srv_key_select:08x} != client 0x{ks:08x}"
+            )));
+        }
+
+        let skew = crypto_ts.abs_diff(srv_ts);
+        if skew > 30 {
+            return Err(ProxyError::InvalidHandshake(format!(
+                "nonce crypto_ts skew too large: client={crypto_ts}, server={srv_ts}, skew={skew}s"
+            )));
+        }
+
+        info!(
+            %local_addr,
+            %local_addr_nat,
+            reflected_ip = reflected.map(|r| r.ip()).as_ref().map(ToString::to_string),
+            %peer_addr,
+            %peer_addr_nat,
+            key_selector = format_args!("0x{ks:08x}"),
+            crypto_schema = format_args!("0x{schema:08x}"),
+            skew_secs = skew,
+            "ME key derivation parameters"
+        );
+
+        let ts_bytes = crypto_ts.to_le_bytes();
+        let server_port_bytes = peer_addr_nat.port().to_le_bytes();
+        let client_port_bytes = local_addr_nat.port().to_le_bytes();
+
+        let server_ip = extract_ip_material(peer_addr_nat);
+        let client_ip = extract_ip_material(local_addr_nat);
+
+        let (srv_ip_opt, clt_ip_opt, clt_v6_opt, srv_v6_opt, hs_our_ip, hs_peer_ip) =
+            match (server_ip, client_ip) {
+                (IpMaterial::V4(srv), IpMaterial::V4(clt)) => {
+                    (Some(srv), Some(clt), None, None, clt, srv)
+                }
+                (IpMaterial::V6(srv), IpMaterial::V6(clt)) => {
+                    let zero = [0u8; 4];
+                    (None, None, Some(clt), Some(srv), zero, zero)
+                }
+                _ => {
+                    return Err(ProxyError::InvalidHandshake(
+                        "mixed IPv4/IPv6 endpoints are not supported for ME key derivation"
+                            .to_string(),
+                    ));
+                }
+            };
+
+        let diag_level: u8 = std::env::var("ME_DIAG")
+            .ok()
+            .and_then(|v| v.parse().ok())
+            .unwrap_or(0);
+
+        let prekey_client = build_middleproxy_prekey(
+            &srv_nonce,
+            &my_nonce,
+            &ts_bytes,
+            srv_ip_opt.as_ref().map(|x| &x[..]),
+            &client_port_bytes,
+            b"CLIENT",
+            clt_ip_opt.as_ref().map(|x| &x[..]),
+            &server_port_bytes,
+            secret,
+            clt_v6_opt.as_ref(),
+            srv_v6_opt.as_ref(),
+        );
+        let prekey_server = build_middleproxy_prekey(
+            &srv_nonce,
+            &my_nonce,
+            &ts_bytes,
+            srv_ip_opt.as_ref().map(|x| &x[..]),
+            &client_port_bytes,
+            b"SERVER",
+            clt_ip_opt.as_ref().map(|x| &x[..]),
+            &server_port_bytes,
+            secret,
+            clt_v6_opt.as_ref(),
+            srv_v6_opt.as_ref(),
+        );
+
+        let (wk, wi) = derive_middleproxy_keys(
+            &srv_nonce,
+            &my_nonce,
+            &ts_bytes,
+            srv_ip_opt.as_ref().map(|x| &x[..]),
+            &client_port_bytes,
+            b"CLIENT",
+            clt_ip_opt.as_ref().map(|x| &x[..]),
+            &server_port_bytes,
+            secret,
+            clt_v6_opt.as_ref(),
+            srv_v6_opt.as_ref(),
+        );
+        let (rk, ri) = derive_middleproxy_keys(
+            &srv_nonce,
+            &my_nonce,
+            &ts_bytes,
+            srv_ip_opt.as_ref().map(|x| &x[..]),
+            &client_port_bytes,
+            b"SERVER",
+            clt_ip_opt.as_ref().map(|x| &x[..]),
+            &server_port_bytes,
+            secret,
+            clt_v6_opt.as_ref(),
+            srv_v6_opt.as_ref(),
+        );
+
+        let hs_payload =
+            build_handshake_payload(hs_our_ip, local_addr.port(), hs_peer_ip, peer_addr.port());
+        let hs_frame = build_rpc_frame(-1, &hs_payload);
+        if diag_level >= 1 {
+            info!(
+                write_key = %hex_dump(&wk),
+                write_iv = %hex_dump(&wi),
+                read_key = %hex_dump(&rk),
+                read_iv = %hex_dump(&ri),
+                srv_ip = %srv_ip_opt.map(|ip| hex_dump(&ip)).unwrap_or_default(),
+                clt_ip = %clt_ip_opt.map(|ip| hex_dump(&ip)).unwrap_or_default(),
+                srv_port = %hex_dump(&server_port_bytes),
+                clt_port = %hex_dump(&client_port_bytes),
+                crypto_ts = %hex_dump(&ts_bytes),
+                nonce_srv = %hex_dump(&srv_nonce),
+                nonce_clt = %hex_dump(&my_nonce),
+                prekey_sha256_client = %hex_dump(&sha256(&prekey_client)),
+                prekey_sha256_server = %hex_dump(&sha256(&prekey_server)),
+                hs_plain = %hex_dump(&hs_frame),
+                proxy_secret_sha256 = %hex_dump(&sha256(secret)),
+                "ME diag: derived keys and handshake plaintext"
+            );
+        }
+        if diag_level >= 2 {
+            info!(
+                prekey_client = %hex_dump(&prekey_client),
+                prekey_server = %hex_dump(&prekey_server),
+                "ME diag: full prekey buffers"
+            );
+        }
+
+        let (encrypted_hs, write_iv) = cbc_encrypt_padded(&wk, &wi, &hs_frame)?;
+        if diag_level >= 1 {
+            info!(
+                hs_cipher = %hex_dump(&encrypted_hs),
+                "ME diag: handshake ciphertext"
+            );
+        }
+        wr.write_all(&encrypted_hs).await.map_err(ProxyError::Io)?;
+        wr.flush().await.map_err(ProxyError::Io)?;
+
+        let deadline = Instant::now() + Duration::from_secs(ME_HANDSHAKE_TIMEOUT_SECS);
+        let mut enc_buf = BytesMut::with_capacity(256);
+        let mut dec_buf = BytesMut::with_capacity(256);
+        let mut read_iv = ri;
+        let mut handshake_ok = false;
+
+        while Instant::now() < deadline && !handshake_ok {
+            let remaining = deadline - Instant::now();
+            let mut tmp = [0u8; 256];
+            let n = match timeout(remaining, rd.read(&mut tmp)).await {
+                Ok(Ok(0)) => {
+                    return Err(ProxyError::Io(std::io::Error::new(
+                        std::io::ErrorKind::UnexpectedEof,
+                        "ME closed during handshake",
+                    )));
+                }
+                Ok(Ok(n)) => n,
+                Ok(Err(e)) => return Err(ProxyError::Io(e)),
+                Err(_) => return Err(ProxyError::TgHandshakeTimeout),
+            };
+
+            enc_buf.extend_from_slice(&tmp[..n]);
+
+            let blocks = enc_buf.len() / 16 * 16;
+            if blocks > 0 {
+                let mut chunk = vec![0u8; blocks];
+                chunk.copy_from_slice(&enc_buf[..blocks]);
+                read_iv = cbc_decrypt_inplace(&rk, &read_iv, &mut chunk)?;
+                dec_buf.extend_from_slice(&chunk);
+                let _ = enc_buf.split_to(blocks);
+            }
+
+            while dec_buf.len() >= 4 {
+                let fl = u32::from_le_bytes(dec_buf[0..4].try_into().unwrap()) as usize;
+
+                if fl == 4 {
+                    let _ = dec_buf.split_to(4);
+                    continue;
+                }
+                if !(12..=(1 << 24)).contains(&fl) {
+                    return Err(ProxyError::InvalidHandshake(format!(
+                        "Bad HS response frame len: {fl}"
+                    )));
+                }
+                if dec_buf.len() < fl {
+                    break;
+                }
+
+                let frame = dec_buf.split_to(fl);
+                let pe = fl - 4;
+                let ec = u32::from_le_bytes(frame[pe..pe + 4].try_into().unwrap());
+                let ac = crate::crypto::crc32(&frame[..pe]);
+                if ec != ac {
+                    return Err(ProxyError::InvalidHandshake(format!(
+                        "HS CRC mismatch: 0x{ec:08x} vs 0x{ac:08x}"
+                    )));
+                }
+
+                let hs_type = u32::from_le_bytes(frame[8..12].try_into().unwrap());
+                if hs_type == RPC_HANDSHAKE_ERROR_U32 {
+                    let err_code = if frame.len() >= 16 {
+                        i32::from_le_bytes(frame[12..16].try_into().unwrap())
+                    } else {
+                        -1
+                    };
+                    return Err(ProxyError::InvalidHandshake(format!(
+                        "ME rejected handshake (error={err_code})"
+                    )));
+                }
+                if hs_type != RPC_HANDSHAKE_U32 {
+                    return Err(ProxyError::InvalidHandshake(format!(
+                        "Expected HANDSHAKE 0x{RPC_HANDSHAKE_U32:08x}, got 0x{hs_type:08x}"
+                    )));
+                }
+
+                handshake_ok = true;
+                break;
+            }
+        }
+
+        if !handshake_ok {
+            return Err(ProxyError::TgHandshakeTimeout);
+        }
+
+        info!(%addr, "RPC handshake OK");
+
+        let rpc_w = Arc::new(Mutex::new(RpcWriter {
+            writer: wr,
+            key: wk,
+            iv: write_iv,
+            seq_no: 0,
+        }));
+        self.writers.write().await.push((addr, rpc_w.clone()));
+
+        let reg = self.registry.clone();
+        let w_pong = rpc_w.clone();
+        let w_pool = self.writers_arc();
+        let w_ping = rpc_w.clone();
+        let w_pool_ping = self.writers_arc();
+        tokio::spawn(async move {
+            if let Err(e) =
+                reader_loop(rd, rk, read_iv, reg, enc_buf, dec_buf, w_pong.clone()).await
+            {
+                warn!(error = %e, "ME reader ended");
+            }
+            let mut ws = w_pool.write().await;
+            ws.retain(|(_, w)| !Arc::ptr_eq(w, &w_pong));
+            info!(remaining = ws.len(), "Dead ME writer removed from pool");
+        });
+        tokio::spawn(async move {
+            let mut ping_id: i64 = rand::random::<i64>();
+            loop {
+                let jitter = rand::rng()
+                    .random_range(-ME_ACTIVE_PING_JITTER_SECS..=ME_ACTIVE_PING_JITTER_SECS);
+                let wait = (ME_ACTIVE_PING_SECS as i64 + jitter).max(5) as u64;
+                tokio::time::sleep(Duration::from_secs(wait)).await;
+                let mut p = Vec::with_capacity(12);
+                p.extend_from_slice(&RPC_PING_U32.to_le_bytes());
+                p.extend_from_slice(&ping_id.to_le_bytes());
+                ping_id = ping_id.wrapping_add(1);
+                if let Err(e) = w_ping.lock().await.send(&p).await {
+                    debug!(error = %e, "Active ME ping failed, removing dead writer");
+                    let mut ws = w_pool_ping.write().await;
+                    ws.retain(|(_, w)| !Arc::ptr_eq(w, &w_ping));
+                    break;
+                }
+            }
+        });
+
+        Ok(())
+    }
+
+}
+
+fn hex_dump(data: &[u8]) -> String {
+    const MAX: usize = 64;
+    let mut out = String::with_capacity(data.len() * 2 + 3);
+    for (i, b) in data.iter().take(MAX).enumerate() {
+        if i > 0 {
+            out.push(' ');
+        }
+        out.push_str(&format!("{b:02x}"));
+    }
+    if data.len() > MAX {
+        out.push_str(" …");
+    }
+    out
+}

src/transport/middle_proxy/pool_nat.rs

@@ -0,0 +1,200 @@
+use std::net::{IpAddr, Ipv4Addr};
+
+use tracing::{info, warn};
+
+use crate::error::{ProxyError, Result};
+
+use super::MePool;
+
+impl MePool {
+    pub(super) fn translate_ip_for_nat(&self, ip: IpAddr) -> IpAddr {
+        let nat_ip = self
+            .nat_ip_cfg
+            .or_else(|| self.nat_ip_detected.get().copied());
+
+        let Some(nat_ip) = nat_ip else {
+            return ip;
+        };
+
+        match (ip, nat_ip) {
+            (IpAddr::V4(src), IpAddr::V4(dst))
+                if is_privateish(IpAddr::V4(src))
+                    || src.is_loopback()
+                    || src.is_unspecified() =>
+            {
+                IpAddr::V4(dst)
+            }
+            (IpAddr::V6(src), IpAddr::V6(dst)) if src.is_loopback() || src.is_unspecified() => {
+                IpAddr::V6(dst)
+            }
+            (orig, _) => orig,
+        }
+    }
+
+    pub(super) fn translate_our_addr_with_reflection(
+        &self,
+        addr: std::net::SocketAddr,
+        reflected: Option<std::net::SocketAddr>,
+    ) -> std::net::SocketAddr {
+        let ip = if let Some(r) = reflected {
+            // Use reflected IP (not port) only when local address is non-public.
+            if is_privateish(addr.ip()) || addr.ip().is_loopback() || addr.ip().is_unspecified() {
+                r.ip()
+            } else {
+                self.translate_ip_for_nat(addr.ip())
+            }
+        } else {
+            self.translate_ip_for_nat(addr.ip())
+        };
+
+        // Keep the kernel-assigned TCP source port; STUN port can differ.
+        std::net::SocketAddr::new(ip, addr.port())
+    }
+
+    pub(super) async fn maybe_detect_nat_ip(&self, local_ip: IpAddr) -> Option<IpAddr> {
+        if self.nat_ip_cfg.is_some() {
+            return self.nat_ip_cfg;
+        }
+
+        if !(is_privateish(local_ip) || local_ip.is_loopback() || local_ip.is_unspecified()) {
+            return None;
+        }
+
+        if let Some(ip) = self.nat_ip_detected.get().copied() {
+            return Some(ip);
+        }
+
+        match fetch_public_ipv4().await {
+            Ok(Some(ip)) => {
+                let _ = self.nat_ip_detected.set(IpAddr::V4(ip));
+                info!(public_ip = %ip, "Auto-detected public IP for NAT translation");
+                Some(IpAddr::V4(ip))
+            }
+            Ok(None) => None,
+            Err(e) => {
+                warn!(error = %e, "Failed to auto-detect public IP");
+                None
+            }
+        }
+    }
+
+    pub(super) async fn maybe_reflect_public_addr(&self) -> Option<std::net::SocketAddr> {
+        let stun_addr = self
+            .nat_stun
+            .clone()
+            .unwrap_or_else(|| "stun.l.google.com:19302".to_string());
+        match fetch_stun_binding(&stun_addr).await {
+            Ok(sa) => {
+                if let Some(sa) = sa {
+                    info!(%sa, "NAT probe: reflected address");
+                }
+                sa
+            }
+            Err(e) => {
+                warn!(error = %e, "NAT probe failed");
+                None
+            }
+        }
+    }
+}
+
+async fn fetch_public_ipv4() -> Result<Option<Ipv4Addr>> {
+    let res = reqwest::get("https://checkip.amazonaws.com").await.map_err(|e| {
+        ProxyError::Proxy(format!("public IP detection request failed: {e}"))
+    })?;
+
+    let text = res.text().await.map_err(|e| {
+        ProxyError::Proxy(format!("public IP detection read failed: {e}"))
+    })?;
+
+    let ip = text.trim().parse().ok();
+    Ok(ip)
+}
+
+async fn fetch_stun_binding(stun_addr: &str) -> Result<Option<std::net::SocketAddr>> {
+    use rand::RngCore;
+    use tokio::net::UdpSocket;
+
+    let socket = UdpSocket::bind("0.0.0.0:0")
+        .await
+        .map_err(|e| ProxyError::Proxy(format!("STUN bind failed: {e}")))?;
+    socket
+        .connect(stun_addr)
+        .await
+        .map_err(|e| ProxyError::Proxy(format!("STUN connect failed: {e}")))?;
+
+    // Build minimal Binding Request.
+    let mut req = vec![0u8; 20];
+    req[0..2].copy_from_slice(&0x0001u16.to_be_bytes()); // Binding Request
+    req[2..4].copy_from_slice(&0u16.to_be_bytes()); // length
+    req[4..8].copy_from_slice(&0x2112A442u32.to_be_bytes()); // magic cookie
+    rand::thread_rng().fill_bytes(&mut req[8..20]);
+
+    socket
+        .send(&req)
+        .await
+        .map_err(|e| ProxyError::Proxy(format!("STUN send failed: {e}")))?;
+
+    let mut buf = [0u8; 128];
+    let n = socket
+        .recv(&mut buf)
+        .await
+        .map_err(|e| ProxyError::Proxy(format!("STUN recv failed: {e}")))?;
+    if n < 20 {
+        return Ok(None);
+    }
+
+    // Parse attributes.
+    let mut idx = 20;
+    while idx + 4 <= n {
+        let atype = u16::from_be_bytes(buf[idx..idx + 2].try_into().unwrap());
+        let alen = u16::from_be_bytes(buf[idx + 2..idx + 4].try_into().unwrap()) as usize;
+        idx += 4;
+        if idx + alen > n {
+            break;
+        }
+        match atype {
+            0x0020 /* XOR-MAPPED-ADDRESS */ | 0x0001 /* MAPPED-ADDRESS */ => {
+                if alen < 8 {
+                    break;
+                }
+                let family = buf[idx + 1];
+                if family != 0x01 {
+                    // only IPv4 supported here
+                    break;
+                }
+                let port_bytes = [buf[idx + 2], buf[idx + 3]];
+                let ip_bytes = [buf[idx + 4], buf[idx + 5], buf[idx + 6], buf[idx + 7]];
+
+                let (port, ip) = if atype == 0x0020 {
+                    let magic = 0x2112A442u32.to_be_bytes();
+                    let port = u16::from_be_bytes(port_bytes) ^ ((magic[0] as u16) << 8 | magic[1] as u16);
+                    let ip = [
+                        ip_bytes[0] ^ magic[0],
+                        ip_bytes[1] ^ magic[1],
+                        ip_bytes[2] ^ magic[2],
+                        ip_bytes[3] ^ magic[3],
+                    ];
+                    (port, ip)
+                } else {
+                    (u16::from_be_bytes(port_bytes), ip_bytes)
+                };
+                return Ok(Some(std::net::SocketAddr::new(
+                    IpAddr::V4(Ipv4Addr::new(ip[0], ip[1], ip[2], ip[3])),
+                    port,
+                )));
+            }
+            _ => {}
+        }
+        idx += (alen + 3) & !3; // 4-byte alignment
+    }
+
+    Ok(None)
+}
+
+fn is_privateish(ip: IpAddr) -> bool {
+    match ip {
+        IpAddr::V4(v4) => v4.is_private() || v4.is_link_local(),
+        IpAddr::V6(v6) => v6.is_unique_local(),
+    }
+}

src/transport/middle_proxy/reader.rs

@@ -0,0 +1,141 @@
+use std::sync::Arc;
+
+use bytes::{Bytes, BytesMut};
+use tokio::io::AsyncReadExt;
+use tokio::net::TcpStream;
+use tokio::sync::Mutex;
+use tracing::{debug, trace, warn};
+
+use crate::crypto::{AesCbc, crc32};
+use crate::error::{ProxyError, Result};
+use crate::protocol::constants::*;
+
+use super::codec::RpcWriter;
+use super::{ConnRegistry, MeResponse};
+
+pub(crate) async fn reader_loop(
+    mut rd: tokio::io::ReadHalf<TcpStream>,
+    dk: [u8; 32],
+    mut div: [u8; 16],
+    reg: Arc<ConnRegistry>,
+    enc_leftover: BytesMut,
+    mut dec: BytesMut,
+    writer: Arc<Mutex<RpcWriter>>,
+) -> Result<()> {
+    let mut raw = enc_leftover;
+
+    loop {
+        let mut tmp = [0u8; 16_384];
+        let n = rd.read(&mut tmp).await.map_err(ProxyError::Io)?;
+        if n == 0 {
+            return Ok(());
+        }
+        raw.extend_from_slice(&tmp[..n]);
+
+        let blocks = raw.len() / 16 * 16;
+        if blocks > 0 {
+            let mut new_iv = [0u8; 16];
+            new_iv.copy_from_slice(&raw[blocks - 16..blocks]);
+
+            let mut chunk = vec![0u8; blocks];
+            chunk.copy_from_slice(&raw[..blocks]);
+            AesCbc::new(dk, div)
+                .decrypt_in_place(&mut chunk)
+                .map_err(|e| ProxyError::Crypto(format!("{e}")))?;
+            div = new_iv;
+            dec.extend_from_slice(&chunk);
+            let _ = raw.split_to(blocks);
+        }
+
+        while dec.len() >= 12 {
+            let fl = u32::from_le_bytes(dec[0..4].try_into().unwrap()) as usize;
+            if fl == 4 {
+                let _ = dec.split_to(4);
+                continue;
+            }
+            if !(12..=(1 << 24)).contains(&fl) {
+                warn!(frame_len = fl, "Invalid RPC frame len");
+                dec.clear();
+                break;
+            }
+            if dec.len() < fl {
+                break;
+            }
+
+            let frame = dec.split_to(fl);
+            let pe = fl - 4;
+            let ec = u32::from_le_bytes(frame[pe..pe + 4].try_into().unwrap());
+            if crc32(&frame[..pe]) != ec {
+                warn!("CRC mismatch in data frame");
+                continue;
+            }
+
+            let payload = &frame[8..pe];
+            if payload.len() < 4 {
+                continue;
+            }
+
+            let pt = u32::from_le_bytes(payload[0..4].try_into().unwrap());
+            let body = &payload[4..];
+
+            if pt == RPC_PROXY_ANS_U32 && body.len() >= 12 {
+                let flags = u32::from_le_bytes(body[0..4].try_into().unwrap());
+                let cid = u64::from_le_bytes(body[4..12].try_into().unwrap());
+                let data = Bytes::copy_from_slice(&body[12..]);
+                trace!(cid, flags, len = data.len(), "RPC_PROXY_ANS");
+
+                let routed = reg.route(cid, MeResponse::Data { flags, data }).await;
+                if !routed {
+                    reg.unregister(cid).await;
+                    send_close_conn(&writer, cid).await;
+                }
+            } else if pt == RPC_SIMPLE_ACK_U32 && body.len() >= 12 {
+                let cid = u64::from_le_bytes(body[0..8].try_into().unwrap());
+                let cfm = u32::from_le_bytes(body[8..12].try_into().unwrap());
+                trace!(cid, cfm, "RPC_SIMPLE_ACK");
+
+                let routed = reg.route(cid, MeResponse::Ack(cfm)).await;
+                if !routed {
+                    reg.unregister(cid).await;
+                    send_close_conn(&writer, cid).await;
+                }
+            } else if pt == RPC_CLOSE_EXT_U32 && body.len() >= 8 {
+                let cid = u64::from_le_bytes(body[0..8].try_into().unwrap());
+                debug!(cid, "RPC_CLOSE_EXT from ME");
+                reg.route(cid, MeResponse::Close).await;
+                reg.unregister(cid).await;
+            } else if pt == RPC_CLOSE_CONN_U32 && body.len() >= 8 {
+                let cid = u64::from_le_bytes(body[0..8].try_into().unwrap());
+                debug!(cid, "RPC_CLOSE_CONN from ME");
+                reg.route(cid, MeResponse::Close).await;
+                reg.unregister(cid).await;
+            } else if pt == RPC_PING_U32 && body.len() >= 8 {
+                let ping_id = i64::from_le_bytes(body[0..8].try_into().unwrap());
+                trace!(ping_id, "RPC_PING -> RPC_PONG");
+                let mut pong = Vec::with_capacity(12);
+                pong.extend_from_slice(&RPC_PONG_U32.to_le_bytes());
+                pong.extend_from_slice(&ping_id.to_le_bytes());
+                if let Err(e) = writer.lock().await.send(&pong).await {
+                    warn!(error = %e, "PONG send failed");
+                    break;
+                }
+            } else {
+                debug!(
+                    rpc_type = format_args!("0x{pt:08x}"),
+                    len = body.len(),
+                    "Unknown RPC"
+                );
+            }
+        }
+    }
+}
+
+async fn send_close_conn(writer: &Arc<Mutex<RpcWriter>>, conn_id: u64) {
+    let mut p = Vec::with_capacity(12);
+    p.extend_from_slice(&RPC_CLOSE_CONN_U32.to_le_bytes());
+    p.extend_from_slice(&conn_id.to_le_bytes());
+
+    if let Err(e) = writer.lock().await.send(&p).await {
+        debug!(conn_id, error = %e, "Failed to send RPC_CLOSE_CONN");
+    }
+}

src/transport/middle_proxy/registry.rs

@@ -0,0 +1,42 @@
+use std::collections::HashMap;
+use std::sync::atomic::{AtomicU64, Ordering};
+
+use tokio::sync::{RwLock, mpsc};
+
+use super::MeResponse;
+
+pub struct ConnRegistry {
+    map: RwLock<HashMap<u64, mpsc::Sender<MeResponse>>>,
+    next_id: AtomicU64,
+}
+
+impl ConnRegistry {
+    pub fn new() -> Self {
+        // Avoid fully predictable conn_id sequence from 1.
+        let start = rand::random::<u64>() | 1;
+        Self {
+            map: RwLock::new(HashMap::new()),
+            next_id: AtomicU64::new(start),
+        }
+    }
+
+    pub async fn register(&self) -> (u64, mpsc::Receiver<MeResponse>) {
+        let id = self.next_id.fetch_add(1, Ordering::Relaxed);
+        let (tx, rx) = mpsc::channel(256);
+        self.map.write().await.insert(id, tx);
+        (id, rx)
+    }
+
+    pub async fn unregister(&self, id: u64) {
+        self.map.write().await.remove(&id);
+    }
+
+    pub async fn route(&self, id: u64, resp: MeResponse) -> bool {
+        let m = self.map.read().await;
+        if let Some(tx) = m.get(&id) {
+            tx.send(resp).await.is_ok()
+        } else {
+            false
+        }
+    }
+}

src/transport/middle_proxy/secret.rs

@@ -0,0 +1,81 @@
+use std::time::Duration;
+
+use tracing::{debug, info, warn};
+
+use crate::error::{ProxyError, Result};
+
+/// Fetch Telegram proxy-secret binary.
+pub async fn fetch_proxy_secret(cache_path: Option<&str>) -> Result<Vec<u8>> {
+    let cache = cache_path.unwrap_or("proxy-secret");
+
+    // 1) Try fresh download first.
+    match download_proxy_secret().await {
+        Ok(data) => {
+            if let Err(e) = tokio::fs::write(cache, &data).await {
+                warn!(error = %e, "Failed to cache proxy-secret (non-fatal)");
+            } else {
+                debug!(path = cache, len = data.len(), "Cached proxy-secret");
+            }
+            return Ok(data);
+        }
+        Err(download_err) => {
+            warn!(error = %download_err, "Proxy-secret download failed, trying cache/file fallback");
+            // Fall through to cache/file.
+        }
+    }
+
+    // 2) Fallback to cache/file regardless of age; require len>=32.
+    match tokio::fs::read(cache).await {
+        Ok(data) if data.len() >= 32 => {
+            let age_hours = tokio::fs::metadata(cache)
+                .await
+                .ok()
+                .and_then(|m| m.modified().ok())
+                .and_then(|m| std::time::SystemTime::now().duration_since(m).ok())
+                .map(|d| d.as_secs() / 3600);
+            info!(
+                path = cache,
+                len = data.len(),
+                age_hours,
+                "Loaded proxy-secret from cache/file after download failure"
+            );
+            Ok(data)
+        }
+        Ok(data) => Err(ProxyError::Proxy(format!(
+            "Cached proxy-secret too short: {} bytes (need >= 32)",
+            data.len()
+        ))),
+        Err(e) => Err(ProxyError::Proxy(format!(
+            "Failed to read proxy-secret cache after download failure: {e}"
+        ))),
+    }
+}
+
+async fn download_proxy_secret() -> Result<Vec<u8>> {
+    let resp = reqwest::get("https://core.telegram.org/getProxySecret")
+        .await
+        .map_err(|e| ProxyError::Proxy(format!("Failed to download proxy-secret: {e}")))?;
+
+    if !resp.status().is_success() {
+        return Err(ProxyError::Proxy(format!(
+            "proxy-secret download HTTP {}",
+            resp.status()
+        )));
+    }
+
+    let data = resp
+        .bytes()
+        .await
+        .map_err(|e| ProxyError::Proxy(format!("Read proxy-secret body: {e}")))?
+        .to_vec();
+
+    if data.len() < 32 {
+        return Err(ProxyError::Proxy(format!(
+            "proxy-secret too short: {} bytes (need >= 32)",
+            data.len()
+        )));
+    }
+
+    info!(len = data.len(), "Downloaded proxy-secret OK");
+    Ok(data)
+}

src/transport/middle_proxy/send.rs

@@ -0,0 +1,146 @@
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::sync::atomic::Ordering;
+
+use tokio::sync::Mutex;
+use tracing::{debug, warn};
+
+use crate::error::{ProxyError, Result};
+use crate::protocol::constants::{RPC_CLOSE_EXT_U32, TG_MIDDLE_PROXIES_V4};
+
+use super::MePool;
+use super::codec::RpcWriter;
+use super::wire::build_proxy_req_payload;
+
+impl MePool {
+    pub async fn send_proxy_req(
+        &self,
+        conn_id: u64,
+        target_dc: i16,
+        client_addr: SocketAddr,
+        our_addr: SocketAddr,
+        data: &[u8],
+        proto_flags: u32,
+    ) -> Result<()> {
+        let payload = build_proxy_req_payload(
+            conn_id,
+            client_addr,
+            our_addr,
+            data,
+            self.proxy_tag.as_deref(),
+            proto_flags,
+        );
+
+        loop {
+            let ws = self.writers.read().await;
+            if ws.is_empty() {
+                return Err(ProxyError::Proxy("All ME connections dead".into()));
+            }
+            let writers: Vec<(SocketAddr, Arc<Mutex<RpcWriter>>)> = ws.iter().cloned().collect();
+            drop(ws);
+
+            let candidate_indices = candidate_indices_for_dc(&writers, target_dc);
+            if candidate_indices.is_empty() {
+                return Err(ProxyError::Proxy("No ME writers available for target DC".into()));
+            }
+            let start = self.rr.fetch_add(1, Ordering::Relaxed) as usize % candidate_indices.len();
+
+            // Prefer immediately available writer to avoid waiting on stalled connection.
+            for offset in 0..candidate_indices.len() {
+                let cidx = (start + offset) % candidate_indices.len();
+                let idx = candidate_indices[cidx];
+                let w = writers[idx].1.clone();
+                if let Ok(mut guard) = w.try_lock() {
+                    let send_res = guard.send(&payload).await;
+                    drop(guard);
+                    match send_res {
+                        Ok(()) => return Ok(()),
+                        Err(e) => {
+                            warn!(error = %e, "ME write failed, removing dead conn");
+                            let mut ws = self.writers.write().await;
+                            ws.retain(|(_, o)| !Arc::ptr_eq(o, &w));
+                            if ws.is_empty() {
+                                return Err(ProxyError::Proxy("All ME connections dead".into()));
+                            }
+                            continue;
+                        }
+                    }
+                }
+            }
+
+            // All writers are currently busy, wait for the selected one.
+            let w = writers[candidate_indices[start]].1.clone();
+            match w.lock().await.send(&payload).await {
+                Ok(()) => return Ok(()),
+                Err(e) => {
+                    warn!(error = %e, "ME write failed, removing dead conn");
+                    let mut ws = self.writers.write().await;
+                    ws.retain(|(_, o)| !Arc::ptr_eq(o, &w));
+                    if ws.is_empty() {
+                        return Err(ProxyError::Proxy("All ME connections dead".into()));
+                    }
+                }
+            }
+        }
+    }
+
+    pub async fn send_close(&self, conn_id: u64) -> Result<()> {
+        let ws = self.writers.read().await;
+        if !ws.is_empty() {
+            let w = ws[0].1.clone();
+            drop(ws);
+            let mut p = Vec::with_capacity(12);
+            p.extend_from_slice(&RPC_CLOSE_EXT_U32.to_le_bytes());
+            p.extend_from_slice(&conn_id.to_le_bytes());
+            if let Err(e) = w.lock().await.send(&p).await {
+                debug!(error = %e, "ME close write failed");
+                let mut ws = self.writers.write().await;
+                ws.retain(|(_, o)| !Arc::ptr_eq(o, &w));
+            }
+        }
+
+        self.registry.unregister(conn_id).await;
+        Ok(())
+    }
+
+    pub fn connection_count(&self) -> usize {
+        self.writers.try_read().map(|w| w.len()).unwrap_or(0)
+    }
+}
+
+fn candidate_indices_for_dc(
+    writers: &[(SocketAddr, Arc<Mutex<RpcWriter>>)],
+    target_dc: i16,
+) -> Vec<usize> {
+    let mut preferred = Vec::<SocketAddr>::new();
+    let key = target_dc as i32;
+    if let Some(v) = TG_MIDDLE_PROXIES_V4.get(&key) {
+        preferred.extend(v.iter().map(|(ip, port)| SocketAddr::new(*ip, *port)));
+    }
+    if preferred.is_empty() {
+        let abs = key.abs();
+        if let Some(v) = TG_MIDDLE_PROXIES_V4.get(&abs) {
+            preferred.extend(v.iter().map(|(ip, port)| SocketAddr::new(*ip, *port)));
+        }
+    }
+    if preferred.is_empty() {
+        let abs = key.abs();
+        if let Some(v) = TG_MIDDLE_PROXIES_V4.get(&-abs) {
+            preferred.extend(v.iter().map(|(ip, port)| SocketAddr::new(*ip, *port)));
+        }
+    }
+    if preferred.is_empty() {
+        return (0..writers.len()).collect();
+    }
+
+    let mut out = Vec::new();
+    for (idx, (addr, _)) in writers.iter().enumerate() {
+        if preferred.iter().any(|p| p == addr) {
+            out.push(idx);
+        }
+    }
+    if out.is_empty() {
+        return (0..writers.len()).collect();
+    }
+    out
+}

src/transport/middle_proxy/wire.rs

@@ -0,0 +1,106 @@
+use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+
+use crate::protocol::constants::*;
+
+#[derive(Clone, Copy)]
+pub(crate) enum IpMaterial {
+    V4([u8; 4]),
+    V6([u8; 16]),
+}
+
+pub(crate) fn extract_ip_material(addr: SocketAddr) -> IpMaterial {
+    match addr.ip() {
+        IpAddr::V4(v4) => IpMaterial::V4(v4.octets()),
+        IpAddr::V6(v6) => {
+            if let Some(v4) = v6.to_ipv4_mapped() {
+                IpMaterial::V4(v4.octets())
+            } else {
+                IpMaterial::V6(v6.octets())
+            }
+        }
+    }
+}
+
+fn ipv4_to_mapped_v6_c_compat(ip: Ipv4Addr) -> [u8; 16] {
+    let mut buf = [0u8; 16];
+
+    // Matches tl_store_long(0) + tl_store_int(-0x10000).
+    buf[8..12].copy_from_slice(&(-0x10000i32).to_le_bytes());
+
+    // Matches tl_store_int(htonl(remote_ip_host_order)).
+    let host_order = u32::from_ne_bytes(ip.octets());
+    let network_order = host_order.to_be();
+    buf[12..16].copy_from_slice(&network_order.to_le_bytes());
+
+    buf
+}
+
+fn append_mapped_addr_and_port(buf: &mut Vec<u8>, addr: SocketAddr) {
+    match addr.ip() {
+        IpAddr::V4(v4) => buf.extend_from_slice(&ipv4_to_mapped_v6_c_compat(v4)),
+        IpAddr::V6(v6) => buf.extend_from_slice(&v6.octets()),
+    }
+    buf.extend_from_slice(&(addr.port() as u32).to_le_bytes());
+}
+
+pub(crate) fn build_proxy_req_payload(
+    conn_id: u64,
+    client_addr: SocketAddr,
+    our_addr: SocketAddr,
+    data: &[u8],
+    proxy_tag: Option<&[u8]>,
+    proto_flags: u32,
+) -> Vec<u8> {
+    let mut b = Vec::with_capacity(128 + data.len());
+
+    b.extend_from_slice(&RPC_PROXY_REQ_U32.to_le_bytes());
+    b.extend_from_slice(&proto_flags.to_le_bytes());
+    b.extend_from_slice(&conn_id.to_le_bytes());
+
+    append_mapped_addr_and_port(&mut b, client_addr);
+    append_mapped_addr_and_port(&mut b, our_addr);
+
+    if proto_flags & 12 != 0 {
+        let extra_start = b.len();
+        b.extend_from_slice(&0u32.to_le_bytes());
+
+        if let Some(tag) = proxy_tag {
+            b.extend_from_slice(&TL_PROXY_TAG_U32.to_le_bytes());
+
+            if tag.len() < 254 {
+                b.push(tag.len() as u8);
+                b.extend_from_slice(tag);
+                let pad = (4 - ((1 + tag.len()) % 4)) % 4;
+                b.extend(std::iter::repeat_n(0u8, pad));
+            } else {
+                b.push(0xfe);
+                let len_bytes = (tag.len() as u32).to_le_bytes();
+                b.extend_from_slice(&len_bytes[..3]);
+                b.extend_from_slice(tag);
+                let pad = (4 - (tag.len() % 4)) % 4;
+                b.extend(std::iter::repeat_n(0u8, pad));
+            }
+        }
+
+        let extra_bytes = (b.len() - extra_start - 4) as u32;
+        b[extra_start..extra_start + 4].copy_from_slice(&extra_bytes.to_le_bytes());
+    }
+
+    b.extend_from_slice(data);
+    b
+}
+
+pub fn proto_flags_for_tag(tag: crate::protocol::constants::ProtoTag, has_proxy_tag: bool) -> u32 {
+    use crate::protocol::constants::ProtoTag;
+
+    let mut flags = RPC_FLAG_MAGIC | RPC_FLAG_EXTMODE2;
+    if has_proxy_tag {
+        flags |= RPC_FLAG_HAS_AD_TAG;
+    }
+
+    match tag {
+        ProtoTag::Abridged => flags | RPC_FLAG_ABRIDGED,
+        ProtoTag::Intermediate => flags | RPC_FLAG_INTERMEDIATE,
+        ProtoTag::Secure => flags | RPC_FLAG_PAD | RPC_FLAG_INTERMEDIATE,
+    }
+}

src/transport/mod.rs

@@ -10,4 +10,5 @@ pub use pool::ConnectionPool;
 pub use proxy_protocol::{ProxyProtocolInfo, parse_proxy_protocol};
 pub use socket::*;
 pub use socks::*;
-pub use upstream::{UpstreamManager, StartupPingResult, DcPingResult};
+pub use upstream::{DcPingResult, StartupPingResult, UpstreamManager};
+pub mod middle_proxy;

src/transport/upstream.rs

@@ -1,4 +1,6 @@
 //! Upstream Management with per-DC latency-weighted selection
+//! 
+//! IPv6/IPv4 connectivity checks with configurable preference.
 
 use std::net::{SocketAddr, IpAddr};
 use std::sync::Arc;
@@ -18,6 +20,9 @@ use crate::transport::socks::{connect_socks4, connect_socks5};
 /// Number of Telegram datacenters
 const NUM_DCS: usize = 5;
 
+/// Timeout for individual DC ping attempt
+const DC_PING_TIMEOUT_SECS: u64 = 5;
+
 // ============= RTT Tracking =============
 
 #[derive(Debug, Clone, Copy)]
@@ -43,6 +48,29 @@ impl LatencyEma {
     }
 }
 
+// ============= Per-DC IP Preference Tracking =============
+
+/// Tracks which IP version works for each DC
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum IpPreference {
+    /// Not yet tested
+    Unknown,
+    /// IPv6 works
+    PreferV6,
+    /// Only IPv4 works (IPv6 failed)
+    PreferV4,
+    /// Both work
+    BothWork,
+    /// Both failed
+    Unavailable,
+}
+
+impl Default for IpPreference {
+    fn default() -> Self {
+        Self::Unknown
+    }
+}
+
 // ============= Upstream State =============
 
 #[derive(Debug)]
@@ -53,6 +81,8 @@ struct UpstreamState {
     last_check: std::time::Instant,
     /// Per-DC latency EMA (index 0 = DC1, index 4 = DC5)
     dc_latency: [LatencyEma; NUM_DCS],
+    /// Per-DC IP version preference (learned from connectivity tests)
+    dc_ip_pref: [IpPreference; NUM_DCS],
 }
 
 impl UpstreamState {
@@ -63,16 +93,11 @@ impl UpstreamState {
             fails: 0,
             last_check: std::time::Instant::now(),
             dc_latency: [LatencyEma::new(0.3); NUM_DCS],
+            dc_ip_pref: [IpPreference::Unknown; NUM_DCS],
         }
     }
 
     /// Map DC index to latency array slot (0..NUM_DCS).
-    ///
-    /// Matches the C implementation's `mf_cluster_lookup` behavior:
-    /// - Standard DCs ±1..±5 → direct mapping to array index 0..4
-    /// - Unknown DCs (CDN, media, etc.) → default DC slot (index 1 = DC 2)
-    ///   This matches Telegram's `default 2;` in proxy-multi.conf.
-    /// - There is NO modular arithmetic in the C implementation.
     fn dc_array_idx(dc_idx: i16) -> Option<usize> {
         let abs_dc = dc_idx.unsigned_abs() as usize;
         if abs_dc == 0 {
@@ -82,21 +107,18 @@ impl UpstreamState {
             Some(abs_dc - 1)
         } else {
             // Unknown DC → default cluster (DC 2, index 1)
-            // Same as C: mf_cluster_lookup returns default_cluster
             Some(1)
         }
     }
 
     /// Get latency for a specific DC, falling back to average across all known DCs
     fn effective_latency(&self, dc_idx: Option<i16>) -> Option<f64> {
-        // Try DC-specific latency first
         if let Some(di) = dc_idx.and_then(Self::dc_array_idx) {
             if let Some(ms) = self.dc_latency[di].get() {
                 return Some(ms);
             }
         }
 
-        // Fallback: average of all known DC latencies
         let (sum, count) = self.dc_latency.iter()
             .filter_map(|l| l.get())
             .fold((0.0, 0u32), |(s, c), v| (s + v, c + 1));
@@ -114,11 +136,14 @@ pub struct DcPingResult {
     pub error: Option<String>,
 }
 
-/// Result of startup ping for one upstream
+/// Result of startup ping for one upstream (separate v6/v4 results)
 #[derive(Debug, Clone)]
 pub struct StartupPingResult {
-    pub results: Vec<DcPingResult>,
+    pub v6_results: Vec<DcPingResult>,
+    pub v4_results: Vec<DcPingResult>,
     pub upstream_name: String,
+    /// True if both IPv6 and IPv4 have at least one working DC
+    pub both_available: bool,
 }
 
 // ============= Upstream Manager =============
@@ -141,15 +166,6 @@ impl UpstreamManager {
     }
 
     /// Select upstream using latency-weighted random selection.
-    ///
-    /// `effective_weight = config_weight × latency_factor`
-    ///
-    /// where `latency_factor = 1000 / latency_ms` if latency is known,
-    /// or `1.0` if no latency data is available.
-    ///
-    /// This means a 50ms upstream gets factor 20, a 200ms upstream gets
-    /// factor 5 — the faster route is 4× more likely to be chosen
-    /// (all else being equal).
     async fn select_upstream(&self, dc_idx: Option<i16>) -> Option<usize> {
         let upstreams = self.upstreams.read().await;
         if upstreams.is_empty() {
@@ -163,7 +179,6 @@ impl UpstreamManager {
             .collect();
 
         if healthy.is_empty() {
-            // All unhealthy — pick any
             return Some(rand::rng().gen_range(0..upstreams.len()));
         }
 
@@ -171,7 +186,6 @@ impl UpstreamManager {
             return Some(healthy[0]);
         }
 
-        // Calculate latency-weighted scores
         let weights: Vec<(usize, f64)> = healthy.iter().map(|&i| {
             let base = upstreams[i].config.weight as f64;
             let latency_factor = upstreams[i].effective_latency(dc_idx)
@@ -207,9 +221,6 @@ impl UpstreamManager {
     }
 
     /// Connect to target through a selected upstream.
-    ///
-    /// `dc_idx` is used for latency-based upstream selection and RTT tracking.
-    /// Pass `None` if DC index is unknown.
     pub async fn connect(&self, target: SocketAddr, dc_idx: Option<i16>) -> Result<TcpStream> {
         let idx = self.select_upstream(dc_idx).await
             .ok_or_else(|| ProxyError::Config("No upstreams available".to_string()))?;
@@ -232,7 +243,6 @@ impl UpstreamManager {
                     u.healthy = true;
                     u.fails = 0;
 
-                    // Store per-DC latency
                     if let Some(di) = dc_idx.and_then(UpstreamState::dc_array_idx) {
                         u.dc_latency[di].update(rtt_ms);
                     }
@@ -336,9 +346,10 @@ impl UpstreamManager {
         }
     }
 
-    // ============= Startup Ping =============
+    // ============= Startup Ping (test both IPv6 and IPv4) =============
 
     /// Ping all Telegram DCs through all upstreams.
+    /// Tests BOTH IPv6 and IPv4, returns separate results for each.
     pub async fn ping_all_dcs(&self, prefer_ipv6: bool) -> Vec<StartupPingResult> {
         let upstreams: Vec<(usize, UpstreamConfig)> = {
             let guard = self.upstreams.read().await;
@@ -347,8 +358,6 @@ impl UpstreamManager {
                 .collect()
         };
 
-        let datacenters = if prefer_ipv6 { &*TG_DATACENTERS_V6 } else { &*TG_DATACENTERS_V4 };
-        
         let mut all_results = Vec::new();
 
         for (upstream_idx, upstream_config) in &upstreams {
@@ -360,50 +369,115 @@ impl UpstreamManager {
                 UpstreamType::Socks5 { address, .. } => format!("socks5://{}", address),
             };
 
-            let mut dc_results = Vec::new();
+            let mut v6_results = Vec::new();
+            let mut v4_results = Vec::new();
 
-            for (dc_zero_idx, dc_ip) in datacenters.iter().enumerate() {
+            // === Ping IPv6 first ===
-                let dc_addr = SocketAddr::new(*dc_ip, TG_DATACENTER_PORT);
+            for dc_zero_idx in 0..NUM_DCS {
+                let dc_v6 = TG_DATACENTERS_V6[dc_zero_idx];
+                let addr_v6 = SocketAddr::new(dc_v6, TG_DATACENTER_PORT);
 
-                let ping_result = tokio::time::timeout(
+                let result = tokio::time::timeout(
-                    Duration::from_secs(5),
+                    Duration::from_secs(DC_PING_TIMEOUT_SECS),
-                    self.ping_single_dc(upstream_config, dc_addr)
+                    self.ping_single_dc(&upstream_config, addr_v6)
                 ).await;
 
-                let result = match ping_result {
+                let ping_result = match result {
                     Ok(Ok(rtt_ms)) => {
-                        // Store per-DC latency
                         let mut guard = self.upstreams.write().await;
                         if let Some(u) = guard.get_mut(*upstream_idx) {
                             u.dc_latency[dc_zero_idx].update(rtt_ms);
                         }
                         DcPingResult {
                             dc_idx: dc_zero_idx + 1,
-                            dc_addr,
+                            dc_addr: addr_v6,
                             rtt_ms: Some(rtt_ms),
                             error: None,
                         }
                     }
                     Ok(Err(e)) => DcPingResult {
                         dc_idx: dc_zero_idx + 1,
-                        dc_addr,
+                        dc_addr: addr_v6,
                         rtt_ms: None,
                         error: Some(e.to_string()),
                     },
                     Err(_) => DcPingResult {
                         dc_idx: dc_zero_idx + 1,
-                        dc_addr,
+                        dc_addr: addr_v6,
                         rtt_ms: None,
-                        error: Some("timeout (5s)".to_string()),
+                        error: Some("timeout".to_string()),
                     },
                 };
+                v6_results.push(ping_result);
+            }
 
-                dc_results.push(result);
+            // === Then ping IPv4 ===
+            for dc_zero_idx in 0..NUM_DCS {
+                let dc_v4 = TG_DATACENTERS_V4[dc_zero_idx];
+                let addr_v4 = SocketAddr::new(dc_v4, TG_DATACENTER_PORT);
+
+                let result = tokio::time::timeout(
+                    Duration::from_secs(DC_PING_TIMEOUT_SECS),
+                    self.ping_single_dc(&upstream_config, addr_v4)
+                ).await;
+
+                let ping_result = match result {
+                    Ok(Ok(rtt_ms)) => {
+                        let mut guard = self.upstreams.write().await;
+                        if let Some(u) = guard.get_mut(*upstream_idx) {
+                            u.dc_latency[dc_zero_idx].update(rtt_ms);
+                        }
+                        DcPingResult {
+                            dc_idx: dc_zero_idx + 1,
+                            dc_addr: addr_v4,
+                            rtt_ms: Some(rtt_ms),
+                            error: None,
+                        }
+                    }
+                    Ok(Err(e)) => DcPingResult {
+                        dc_idx: dc_zero_idx + 1,
+                        dc_addr: addr_v4,
+                        rtt_ms: None,
+                        error: Some(e.to_string()),
+                    },
+                    Err(_) => DcPingResult {
+                        dc_idx: dc_zero_idx + 1,
+                        dc_addr: addr_v4,
+                        rtt_ms: None,
+                        error: Some("timeout".to_string()),
+                    },
+                };
+                v4_results.push(ping_result);
+            }
+
+            // Check if both IP versions have at least one working DC
+            let v6_has_working = v6_results.iter().any(|r| r.rtt_ms.is_some());
+            let v4_has_working = v4_results.iter().any(|r| r.rtt_ms.is_some());
+            let both_available = v6_has_working && v4_has_working;
+
+            // Update IP preference for each DC
+            {
+                let mut guard = self.upstreams.write().await;
+                if let Some(u) = guard.get_mut(*upstream_idx) {
+                    for dc_zero_idx in 0..NUM_DCS {
+                        let v6_ok = v6_results[dc_zero_idx].rtt_ms.is_some();
+                        let v4_ok = v4_results[dc_zero_idx].rtt_ms.is_some();
+
+                        u.dc_ip_pref[dc_zero_idx] = match (v6_ok, v4_ok) {
+                            (true, true) => IpPreference::BothWork,
+                            (true, false) => IpPreference::PreferV6,
+                            (false, true) => IpPreference::PreferV4,
+                            (false, false) => IpPreference::Unavailable,
+                        };
+                    }
+                }
             }
 
             all_results.push(StartupPingResult {
-                results: dc_results,
+                v6_results,
+                v4_results,
                 upstream_name,
+                both_available,
             });
         }
 
@@ -419,19 +493,30 @@ impl UpstreamManager {
     // ============= Health Checks =============
 
     /// Background health check: rotates through DCs, 30s interval.
+    /// Uses preferred IP version based on config.
     pub async fn run_health_checks(&self, prefer_ipv6: bool) {
-        let datacenters = if prefer_ipv6 { &*TG_DATACENTERS_V6 } else { &*TG_DATACENTERS_V4 };
         let mut dc_rotation = 0usize;
 
         loop {
             tokio::time::sleep(Duration::from_secs(30)).await;
 
-            let dc_zero_idx = dc_rotation % datacenters.len();
+            let dc_zero_idx = dc_rotation % NUM_DCS;
             dc_rotation += 1;
 
-            let check_target = SocketAddr::new(datacenters[dc_zero_idx], TG_DATACENTER_PORT);
+            let dc_addr = if prefer_ipv6 {
+                SocketAddr::new(TG_DATACENTERS_V6[dc_zero_idx], TG_DATACENTER_PORT)
+            } else {
+                SocketAddr::new(TG_DATACENTERS_V4[dc_zero_idx], TG_DATACENTER_PORT)
+            };
+
+            let fallback_addr = if prefer_ipv6 {
+                SocketAddr::new(TG_DATACENTERS_V4[dc_zero_idx], TG_DATACENTER_PORT)
+            } else {
+                SocketAddr::new(TG_DATACENTERS_V6[dc_zero_idx], TG_DATACENTER_PORT)
+            };
 
             let count = self.upstreams.read().await.len();
+
             for i in 0..count {
                 let config = {
                     let guard = self.upstreams.read().await;
@@ -441,48 +526,102 @@ impl UpstreamManager {
                 let start = Instant::now();
                 let result = tokio::time::timeout(
                     Duration::from_secs(10),
-                    self.connect_via_upstream(&config, check_target)
+                    self.connect_via_upstream(&config, dc_addr)
                 ).await;
 
-                let mut guard = self.upstreams.write().await;
-                let u = &mut guard[i];
-                
                 match result {
                     Ok(Ok(_stream)) => {
                         let rtt_ms = start.elapsed().as_secs_f64() * 1000.0;
+                        let mut guard = self.upstreams.write().await;
+                        let u = &mut guard[i];
                         u.dc_latency[dc_zero_idx].update(rtt_ms);
 
                         if !u.healthy {
                             info!(
-                                rtt = format!("{:.0}ms", rtt_ms),
+                                rtt = format!("{:.0} ms", rtt_ms),
                                 dc = dc_zero_idx + 1,
                                 "Upstream recovered"
                             );
                         }
                         u.healthy = true;
                         u.fails = 0;
+                        u.last_check = std::time::Instant::now();
                     }
-                    Ok(Err(e)) => {
+                    Ok(Err(_)) | Err(_) => {
-                        u.fails += 1;
+                        // Try fallback
-                        debug!(dc = dc_zero_idx + 1, fails = u.fails,
+                        debug!(dc = dc_zero_idx + 1, "Health check failed, trying fallback");
-                            "Health check failed: {}", e);
+
-                        if u.fails > 3 {
+                        let start2 = Instant::now();
-                            u.healthy = false;
+                        let result2 = tokio::time::timeout(
-                            warn!("Upstream unhealthy (fails)");
+                            Duration::from_secs(10),
-                        }
+                            self.connect_via_upstream(&config, fallback_addr)
-                    }
+                        ).await;
-                    Err(_) => {
+
-                        u.fails += 1;
+                        let mut guard = self.upstreams.write().await;
-                        debug!(dc = dc_zero_idx + 1, fails = u.fails,
+                        let u = &mut guard[i];
-                            "Health check timeout");
+
-                        if u.fails > 3 {
+                        match result2 {
-                            u.healthy = false;
+                            Ok(Ok(_stream)) => {
-                            warn!("Upstream unhealthy (timeout)");
+                                let rtt_ms = start2.elapsed().as_secs_f64() * 1000.0;
+                                u.dc_latency[dc_zero_idx].update(rtt_ms);
+
+                                if !u.healthy {
+                                    info!(
+                                        rtt = format!("{:.0} ms", rtt_ms),
+                                        dc = dc_zero_idx + 1,
+                                        "Upstream recovered (fallback)"
+                                    );
+                                }
+                                u.healthy = true;
+                                u.fails = 0;
+                            }
+                            Ok(Err(e)) => {
+                                u.fails += 1;
+                                debug!(dc = dc_zero_idx + 1, fails = u.fails,
+                                    "Health check failed (both): {}", e);
+                                if u.fails > 3 {
+                                    u.healthy = false;
+                                    warn!("Upstream unhealthy (fails)");
+                                }
+                            }
+                            Err(_) => {
+                                u.fails += 1;
+                                debug!(dc = dc_zero_idx + 1, fails = u.fails,
+                                    "Health check timeout (both)");
+                                if u.fails > 3 {
+                                    u.healthy = false;
+                                    warn!("Upstream unhealthy (timeout)");
+                                }
+                            }
                         }
+                        u.last_check = std::time::Instant::now();
                     }
                 }
-                u.last_check = std::time::Instant::now();
             }
         }
     }
+
+    /// Get the preferred IP for a DC (for use by other components)
+    pub async fn get_dc_ip_preference(&self, dc_idx: i16) -> Option<IpPreference> {
+        let guard = self.upstreams.read().await;
+        if guard.is_empty() {
+            return None;
+        }
+
+        UpstreamState::dc_array_idx(dc_idx)
+            .map(|idx| guard[0].dc_ip_pref[idx])
+    }
+
+    /// Get preferred DC address based on config preference
+    pub async fn get_dc_addr(&self, dc_idx: i16, prefer_ipv6: bool) -> Option<SocketAddr> {
+        let arr_idx = UpstreamState::dc_array_idx(dc_idx)?;
+
+        let ip = if prefer_ipv6 {
+            TG_DATACENTERS_V6[arr_idx]
+        } else {
+            TG_DATACENTERS_V4[arr_idx]
+        };
+
+        Some(SocketAddr::new(ip, TG_DATACENTER_PORT))
+    }
 }