STUN Fixes + ME Pool tweaks: merge pull request #260 from telemt/flow-mep

STUN Fixes + ME Pool tweaks

.gitignore

@@ -19,7 +19,5 @@ target
 #  and can be added to the global gitignore or merged into this file.  For a more nuclear
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
 #.idea/
-*.rs
+
-target
+proxy-secret
-Cargo.lock
-src

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "telemt"
-version = "3.0.15"
+version = "3.1.2"
 edition = "2024"
 
 [dependencies]

README.md

@@ -2,6 +2,8 @@
 
 **Telemt** is a fast, secure, and feature-rich server written in Rust: it fully implements the official Telegram proxy algo and adds many production-ready improvements such as connection pooling, replay protection, detailed statistics, masking from "prying" eyes
 
+[**Telemt Chat in Telegram**](https://t.me/telemtrs)
+
 ## NEWS and EMERGENCY
 ### ✈️ Telemt 3 is released!
 <table>
@@ -10,28 +12,18 @@
 
 ### 🇷🇺 RU
 
-#### Драфтинг LTS и текущие улучшения
+#### Релиз 3.0.15 — 25 февраля
 
-С 21 февраля мы начали подготовку LTS-версии.
+25 февраля мы выпустили версию **3.0.15**
 
-Мы внимательно анализируем весь доступный фидбек.  
+Мы предполагаем, что она станет завершающей версией поколения 3.0 и уже сейчас мы рассматриваем её как **LTS-кандидата** для версии **3.1.0**!
-Наша цель — сделать LTS-кандидаты максимально стабильными, тщательно отлаженными и готовыми к long-run и highload production-сценариям.
 
----
+После нескольких дней детального анализа особенностей работы Middle-End мы спроектировали и реализовали продуманный режим **ротации ME Writer**. Данный режим позволяет поддерживать стабильно высокую производительность в long-run сценариях без возникновения ошибок, связанных с некорректной конфигурацией прокси
 
-#### Улучшения от 23 февраля
+Будем рады вашему фидбеку и предложениям по улучшению — особенно в части **статистики** и **UX**
-
-23 февраля были внесены улучшения производительности в режимах **DC** и **Middle-End (ME)**, с акцентом на обратный канал (путь клиент → DC / ME).
-
-Дополнительно реализован ряд изменений, направленных на повышение устойчивости системы:
-
-- Смягчение сетевой нестабильности  
-- Повышение устойчивости к десинхронизации криптографии  
-- Снижение дрейфа сессий при неблагоприятных условиях  
-- Улучшение обработки ошибок в edge-case транспортных сценариях  
 
 Релиз:  
-[3.0.12](https://github.com/telemt/telemt/releases/tag/3.0.12)
+[3.0.15](https://github.com/telemt/telemt/releases/tag/3.0.15)
 
 ---
 
@@ -48,28 +40,18 @@
 
 ### 🇬🇧 EN
 
-#### LTS Drafting and Ongoing Improvements
+#### Release 3.0.15 — February 25
 
-Starting February 21, we began drafting the upcoming LTS version.
+On February 25, we released version **3.0.15**
 
-We are carefully reviewing and analyzing all available feedback.  
+We expect this to become the final release of the 3.0 generation and at this point, we already see it as a strong **LTS candidate** for the upcoming **3.1.0** release!
-The goal is to ensure that LTS candidates are максимально stable, thoroughly debugged, and ready for long-run and high-load production scenarios.
 
----
+After several days of deep analysis of Middle-End behavior, we designed and implemented a well-engineered **ME Writer rotation mode**. This mode enables sustained high throughput in long-run scenarios while preventing proxy misconfiguration errors
 
-#### February 23 Improvements
+We are looking forward to your feedback and improvement proposals — especially regarding **statistics** and **UX**
-
-On February 23, we introduced performance improvements for both **DC** and **Middle-End (ME)** modes, specifically optimizing the reverse channel (client → DC / ME data path).
-
-Additionally, we implemented a set of robustness enhancements designed to:
-
-- Mitigate network-related instability
-- Improve resilience against cryptographic desynchronization
-- Reduce session drift under adverse conditions
-- Improve error handling in edge-case transport scenarios
 
 Release:  
-[3.0.12](https://github.com/telemt/telemt/releases/tag/3.0.12)
+[3.0.15](https://github.com/telemt/telemt/releases/tag/3.0.15)
 
 ---
 

config.full.toml

@@ -0,0 +1,205 @@
+# Telemt full config with default values.
+# Examples are kept in comments after '#'.
+
+# Top-level legacy field.
+show_link = [] # example: "*" or ["alice", "bob"]
+# default_dc = 2 # example: default DC for unmapped non-standard DCs
+
+[general]
+fast_mode = true
+use_middle_proxy = false
+# ad_tag = "00000000000000000000000000000000" # example
+# proxy_secret_path = "proxy-secret" # example custom path
+# middle_proxy_nat_ip = "203.0.113.10" # example public NAT IP override
+middle_proxy_nat_probe = true
+# middle_proxy_nat_stun = "stun.l.google.com:19302" # example
+# middle_proxy_nat_stun_servers = [] # example: ["stun1.l.google.com:19302", "stun2.l.google.com:19302"]
+middle_proxy_pool_size = 8
+middle_proxy_warm_standby = 16
+me_keepalive_enabled = true
+me_keepalive_interval_secs = 25
+me_keepalive_jitter_secs = 5
+me_keepalive_payload_random = true
+crypto_pending_buffer = 262144
+max_client_frame = 16777216
+desync_all_full = false
+beobachten = true
+beobachten_minutes = 10
+beobachten_flush_secs = 15
+beobachten_file = "cache/beobachten.txt"
+hardswap = true
+me_warmup_stagger_enabled = true
+me_warmup_step_delay_ms = 500
+me_warmup_step_jitter_ms = 300
+me_reconnect_max_concurrent_per_dc = 8
+me_reconnect_backoff_base_ms = 500
+me_reconnect_backoff_cap_ms = 30000
+me_reconnect_fast_retry_count = 12
+stun_iface_mismatch_ignore = false
+unknown_dc_log_path = "unknown-dc.txt" # to disable: set to null
+log_level = "normal" # debug | verbose | normal | silent
+disable_colors = false
+fast_mode_min_tls_record = 0
+update_every = 300
+me_reinit_every_secs = 900
+me_hardswap_warmup_delay_min_ms = 1000
+me_hardswap_warmup_delay_max_ms = 2000
+me_hardswap_warmup_extra_passes = 3
+me_hardswap_warmup_pass_backoff_base_ms = 500
+me_config_stable_snapshots = 2
+me_config_apply_cooldown_secs = 300
+proxy_secret_stable_snapshots = 2
+proxy_secret_rotate_runtime = true
+proxy_secret_len_max = 256
+me_pool_drain_ttl_secs = 90
+me_pool_min_fresh_ratio = 0.8
+me_reinit_drain_timeout_secs = 120
+# Legacy compatibility fields used when update_every is omitted.
+proxy_secret_auto_reload_secs = 3600
+proxy_config_auto_reload_secs = 3600
+ntp_check = true
+ntp_servers = ["pool.ntp.org"] # example: ["pool.ntp.org", "time.cloudflare.com"]
+auto_degradation_enabled = true
+degradation_min_unavailable_dc_groups = 2
+
+[general.modes]
+classic = false
+secure = false
+tls = true
+
+[general.links]
+show ="*" # example: "*" or ["alice", "bob"]
+# public_host = "proxy.example.com" # example explicit host/IP for tg:// links
+# public_port = 443 # example explicit port for tg:// links
+
+[network]
+ipv4 = true
+ipv6 = false # set true to enable IPv6
+prefer = 4 # 4 or 6
+multipath = false
+stun_servers = [
+  "stun.l.google.com:5349",
+  "stun1.l.google.com:3478",
+  "stun.gmx.net:3478",
+  "stun.l.google.com:19302",
+  "stun.1und1.de:3478",
+  "stun1.l.google.com:19302",
+  "stun2.l.google.com:19302",
+  "stun3.l.google.com:19302",
+  "stun4.l.google.com:19302",
+  "stun.services.mozilla.com:3478",
+  "stun.stunprotocol.org:3478",
+  "stun.nextcloud.com:3478",
+  "stun.voip.eutelia.it:3478",
+]
+stun_tcp_fallback = true
+http_ip_detect_urls = ["https://ifconfig.me/ip", "https://api.ipify.org"]
+cache_public_ip_path = "cache/public_ip.txt"
+
+[server]
+port = 443
+listen_addr_ipv4 = "0.0.0.0"
+listen_addr_ipv6 = "::"
+# listen_unix_sock = "/var/run/telemt.sock" # example
+# listen_unix_sock_perm = "0660" # example unix socket mode
+# listen_tcp = true # example explicit override (auto-detected when omitted)
+proxy_protocol = false
+# metrics_port = 9090 # example
+metrics_whitelist = ["127.0.0.1/32", "::1/128"]
+# Example explicit listeners (default: omitted, auto-generated from listen_addr_*):
+# [[server.listeners]]
+# ip = "0.0.0.0"
+# announce = "proxy-v4.example.com"
+# # announce_ip = "203.0.113.10" # deprecated alias
+# proxy_protocol = false
+# reuse_allow = false
+#
+# [[server.listeners]]
+# ip = "::"
+# announce = "proxy-v6.example.com"
+# proxy_protocol = false
+# reuse_allow = false
+
+[timeouts]
+client_handshake = 15
+tg_connect = 10
+client_keepalive = 60
+client_ack = 300
+me_one_retry = 3
+me_one_timeout_ms = 1500
+
+[censorship]
+tls_domain = "petrovich.ru"
+# tls_domains = ["example.com", "cdn.example.net"] # Additional domains for EE links
+mask = true
+# mask_host = "www.google.com" # example, defaults to tls_domain when both mask_host/mask_unix_sock are unset
+# mask_unix_sock = "/var/run/nginx.sock" # example, mutually exclusive with mask_host
+mask_port = 443
+# mask_proxy_protocol = 0 # Send PROXY protocol header to mask_host: 0 = off, 1 = v1 (text), 2 = v2 (binary)
+fake_cert_len = 2048 # if tls_emulation=false and default value is used, loader may randomize this value at runtime
+tls_emulation = true
+tls_front_dir = "tlsfront"
+server_hello_delay_min_ms = 0
+server_hello_delay_max_ms = 0
+tls_new_session_tickets = 0
+tls_full_cert_ttl_secs = 90
+alpn_enforce = true
+
+[access]
+replay_check_len = 65536
+replay_window_secs = 1800
+ignore_time_skew = false
+
+[access.users]
+# format: "username" = "32_hex_chars_secret"
+hello = "00000000000000000000000000000000"
+# alice = "11111111111111111111111111111111" # example
+
+[access.user_max_tcp_conns]
+# alice = 100 # example
+
+[access.user_expirations]
+# alice = "2078-01-01T00:00:00Z" # example
+
+[access.user_data_quota]
+# hello = 10737418240 # example bytes
+# alice = 10737418240 # example bytes
+
+[access.user_max_unique_ips]
+# hello = 10 # example
+# alice = 100 # example
+
+# Default behavior if [[upstreams]] is omitted: loader injects one direct upstream.
+# Example explicit upstreams:
+# [[upstreams]]
+# type = "direct"
+# interface = "eth0"
+# bind_addresses = ["192.0.2.10"]
+# weight = 1
+# enabled = true
+# scopes = "*"
+#
+# [[upstreams]]
+# type = "socks4"
+# address = "198.51.100.20:1080"
+# interface = "eth0"
+# user_id = "telemt"
+# weight = 1
+# enabled = true
+# scopes = "*"
+#
+# [[upstreams]]
+# type = "socks5"
+# address = "198.51.100.30:1080"
+# interface = "eth0"
+# username = "proxy-user"
+# password = "proxy-pass"
+# weight = 1
+# enabled = true
+# scopes = "*"
+
+# === DC Address Overrides ===
+# [dc_overrides]
+# "201" = "149.154.175.50:443" # example
+# "202" = ["149.154.167.51:443", "149.154.175.100:443"] # example
+# "203" = "91.105.192.100:443" # loader auto-adds this one when omitted

config.toml

@@ -1,11 +1,11 @@
+### Telemt Based Config.toml
+# We believe that these settings are sufficient for most scenarios 
+# where cutting-egde methods and parameters or special solutions are not needed
+
 # === General Settings ===
 [general]
-fast_mode = true
+use_middle_proxy = false
-use_middle_proxy = true
 # ad_tag = "00000000000000000000000000000000"
-# Path to proxy-secret binary (auto-downloaded if missing).
-proxy_secret_path = "proxy-secret"
-# disable_colors = false  # Disable colored output in logs (useful for files/systemd)
 
 # === Log Level ===
 # Log level: debug | verbose | normal | silent
@@ -13,51 +13,6 @@ proxy_secret_path = "proxy-secret"
 # RUST_LOG env var takes absolute priority over all of these
 log_level = "normal"
 
-# === Middle Proxy - ME ===
-# Public IP override for ME KDF when behind NAT; leave unset to auto-detect.
-# middle_proxy_nat_ip = "203.0.113.10"
-# Enable STUN probing to discover public IP:port for ME.
-middle_proxy_nat_probe = true
-# Primary STUN server (host:port); defaults to Telegram STUN when empty.
-middle_proxy_nat_stun = "stun.l.google.com:19302"
-# Optional fallback STUN servers list.
-middle_proxy_nat_stun_servers = ["stun1.l.google.com:19302", "stun2.l.google.com:19302"]
-# Desired number of concurrent ME writers in pool.
-middle_proxy_pool_size = 8
-# Pre-initialized warm-standby ME connections kept idle.
-middle_proxy_warm_standby = 8
-# Ignore STUN/interface mismatch and keep ME enabled even if IP differs.
-stun_iface_mismatch_ignore = false
-# Keepalive padding frames - fl==4
-me_keepalive_enabled = true
-me_keepalive_interval_secs = 25           # Period between keepalives
-me_keepalive_jitter_secs = 5              # Jitter added to interval
-me_keepalive_payload_random = true        # Randomize 4-byte payload (vs zeros)
-# Stagger extra ME connections on warmup to de-phase lifecycles.
-me_warmup_stagger_enabled = true
-me_warmup_step_delay_ms = 500             # Base delay between extra connects
-me_warmup_step_jitter_ms = 300            # Jitter for warmup delay
-# Reconnect policy knobs.
-me_reconnect_max_concurrent_per_dc = 4    # Parallel reconnects per DC - EXPERIMENTAL! UNSTABLE!
-me_reconnect_backoff_base_ms = 500        # Backoff start
-me_reconnect_backoff_cap_ms = 30000       # Backoff cap
-me_reconnect_fast_retry_count = 11        # Quick retries before backoff
-update_every = 7200                       # Resolve the active updater interval for ME infrastructure refresh tasks.
-crypto_pending_buffer = 262144            # Max pending ciphertext buffer per client writer (bytes). Controls FakeTLS backpressure vs throughput.
-max_client_frame = 16777216               # Maximum allowed client MTProto frame size (bytes).
-desync_all_full = false                   # Emit full crypto-desync forensic logs for every event. When false, full forensic details are emitted once per key window.
-auto_degradation_enabled = true           # Enable auto-degradation from ME to Direct-DC.
-degradation_min_unavailable_dc_groups = 2 # Minimum unavailable ME DC groups before degrading.
-hardswap = true                           # Enable C-like hard-swap for ME pool generations. When true, Telemt prewarms a new generation and switches once full coverage is reached.
-me_pool_drain_ttl_secs = 90               # Drain-TTL in seconds for stale ME writers after endpoint map changes. During TTL, stale writers may be used only as fallback for new bindings.
-me_pool_min_fresh_ratio = 0.8             # Minimum desired-DC coverage ratio required before draining stale writers. Range: 0.0..=1.0.
-me_reinit_drain_timeout_secs = 120        # Drain timeout in seconds for stale ME writers after endpoint map changes. Set to 0 to keep stale writers draining indefinitely (no force-close).
-me_config_stable_snapshots = 2            # Number of identical getProxyConfig snapshots required before applying ME map updates.
-me_config_apply_cooldown_secs = 300       # Cooldown in seconds between applied ME map updates.
-proxy_secret_rotate_runtime = true        # Enable runtime proxy-secret rotation from getProxySecret.
-proxy_secret_stable_snapshots = 2         # Number of identical getProxySecret snapshots required before runtime secret rotation.
-proxy_secret_len_max = 256                # Maximum allowed proxy-secret length in bytes for startup and runtime refresh.
-
 [general.modes]
 classic = false
 secure = false
@@ -70,93 +25,24 @@ show = "*"
 # public_host = "proxy.example.com"  # Host (IP or domain) for tg:// links
 # public_port = 443                  # Port for tg:// links (default: server.port)
 
-# === Network Parameters ===
-[network]
-# Enable/disable families: true/false/auto(None)
-ipv4 = true
-ipv6 = false # UNSTABLE WITH ME
-# prefer = 4 or 6
-prefer = 4
-multipath = false # EXPERIMENTAL!
-
 # === Server Binding ===
 [server]
 port = 443
-listen_addr_ipv4 = "0.0.0.0"
-listen_addr_ipv6 = "::"
-# listen_unix_sock = "/var/run/telemt.sock" # Unix socket
-# listen_unix_sock_perm = "0666" # Socket file permissions
 # proxy_protocol = false           # Enable if behind HAProxy/nginx with PROXY protocol
 # metrics_port = 9090
-# metrics_whitelist = ["127.0.0.1", "::1"]
+# metrics_whitelist = ["127.0.0.1", "::1", "0.0.0.0/0"]
 
 # Listen on multiple interfaces/IPs - IPv4
 [[server.listeners]]
 ip = "0.0.0.0"
 
-# Listen on multiple interfaces/IPs - IPv6
-[[server.listeners]]
-ip = "::"
-
-# === Timeouts (in seconds) ===
-[timeouts]
-client_handshake = 30
-tg_connect = 10
-client_keepalive = 60
-client_ack = 300
-# Quick ME reconnects for single-address DCs (count and per-attempt timeout, ms).
-me_one_retry = 12
-me_one_timeout_ms = 1200
-
 # === Anti-Censorship & Masking ===
 [censorship]
 tls_domain = "petrovich.ru"
-# tls_domains = ["example.com", "cdn.example.net"] # Additional domains for EE links
 mask = true
-mask_port = 443
+tls_emulation = true        # Fetch real cert lengths and emulate TLS records
-# mask_host = "petrovich.ru" # Defaults to tls_domain if not set
+tls_front_dir = "tlsfront"   # Cache directory for TLS emulation
-# mask_unix_sock = "/var/run/nginx.sock" # Unix socket (mutually exclusive with mask_host)
-fake_cert_len = 2048
-# tls_emulation = false        # Fetch real cert lengths and emulate TLS records
-# tls_front_dir = "tlsfront"   # Cache directory for TLS emulation
-
-# === Access Control & Users ===
-[access]
-replay_check_len = 65536
-replay_window_secs = 1800
-ignore_time_skew = false
 
 [access.users]
 # format: "username" = "32_hex_chars_secret"
 hello = "00000000000000000000000000000000"
-
-# [access.user_max_tcp_conns]
-# hello = 50
-
-# [access.user_max_unique_ips]
-# hello = 5
-
-# [access.user_data_quota]
-# hello = 1073741824 # 1 GB
-
-# [access.user_expirations]
-# format: username = "[year]-[month]-[day]T[hour]:[minute]:[second]Z" UTC
-# hello = "2027-01-01T00:00:00Z"
-
-# === Upstreams & Routing ===
-[[upstreams]]
-type = "direct"
-enabled = true
-weight = 10
-# interface = "192.168.1.100"           # Bind outgoing to specific IP or iface name
-# bind_addresses = ["192.168.1.100"]    # List for round-robin binding (family must match target)
-
-# [[upstreams]]
-# type = "socks5"
-# address = "127.0.0.1:1080"
-# enabled = false
-# weight = 1
-
-# === DC Address Overrides ===
-# [dc_overrides]
-# "203" = "91.105.192.100:443"

src/config/defaults.rs

@@ -3,6 +3,15 @@ use ipnetwork::IpNetwork;
 use serde::Deserialize;
 
 // Helper defaults kept private to the config module.
+const DEFAULT_NETWORK_IPV6: Option<bool> = Some(false);
+const DEFAULT_STUN_TCP_FALLBACK: bool = true;
+const DEFAULT_MIDDLE_PROXY_WARM_STANDBY: usize = 16;
+const DEFAULT_ME_RECONNECT_MAX_CONCURRENT_PER_DC: u32 = 8;
+const DEFAULT_ME_RECONNECT_FAST_RETRY_COUNT: u32 = 16;
+const DEFAULT_LISTEN_ADDR_IPV6: &str = "::";
+const DEFAULT_ACCESS_USER: &str = "default";
+const DEFAULT_ACCESS_SECRET: &str = "00000000000000000000000000000000";
+
 pub(crate) fn default_true() -> bool {
     true
 }
@@ -12,7 +21,7 @@ pub(crate) fn default_port() -> u16 {
 }
 
 pub(crate) fn default_tls_domain() -> String {
-    "www.google.com".to_string()
+    "petrovich.ru".to_string()
 }
 
 pub(crate) fn default_mask_port() -> u16 {
@@ -36,7 +45,7 @@ pub(crate) fn default_replay_window_secs() -> u64 {
 }
 
 pub(crate) fn default_handshake_timeout() -> u64 {
-    15
+    30
 }
 
 pub(crate) fn default_connect_timeout() -> u64 {
@@ -51,17 +60,21 @@ pub(crate) fn default_ack_timeout() -> u64 {
     300
 }
 pub(crate) fn default_me_one_retry() -> u8 {
-    3
+    12
 }
 
 pub(crate) fn default_me_one_timeout() -> u64 {
-    1500
+    1200
 }
 
 pub(crate) fn default_listen_addr() -> String {
     "0.0.0.0".to_string()
 }
 
+pub(crate) fn default_listen_addr_ipv4() -> Option<String> {
+    Some(default_listen_addr())
+}
+
 pub(crate) fn default_weight() -> u16 {
     1
 }
@@ -77,6 +90,14 @@ pub(crate) fn default_prefer_4() -> u8 {
     4
 }
 
+pub(crate) fn default_network_ipv6() -> Option<bool> {
+    DEFAULT_NETWORK_IPV6
+}
+
+pub(crate) fn default_stun_tcp_fallback() -> bool {
+    DEFAULT_STUN_TCP_FALLBACK
+}
+
 pub(crate) fn default_unknown_dc_log_path() -> Option<String> {
     Some("unknown-dc.txt".to_string())
 }
@@ -85,6 +106,26 @@ pub(crate) fn default_pool_size() -> usize {
     8
 }
 
+pub(crate) fn default_proxy_secret_path() -> Option<String> {
+    Some("proxy-secret".to_string())
+}
+
+pub(crate) fn default_middle_proxy_nat_stun() -> Option<String> {
+    None
+}
+
+pub(crate) fn default_middle_proxy_nat_stun_servers() -> Vec<String> {
+    Vec::new()
+}
+
+pub(crate) fn default_stun_nat_probe_concurrency() -> usize {
+    8
+}
+
+pub(crate) fn default_middle_proxy_warm_standby() -> usize {
+    DEFAULT_MIDDLE_PROXY_WARM_STANDBY
+}
+
 pub(crate) fn default_keepalive_interval() -> u64 {
     25
 }
@@ -109,6 +150,14 @@ pub(crate) fn default_reconnect_backoff_cap_ms() -> u64 {
     30_000
 }
 
+pub(crate) fn default_me_reconnect_max_concurrent_per_dc() -> u32 {
+    DEFAULT_ME_RECONNECT_MAX_CONCURRENT_PER_DC
+}
+
+pub(crate) fn default_me_reconnect_fast_retry_count() -> u32 {
+    DEFAULT_ME_RECONNECT_FAST_RETRY_COUNT
+}
+
 pub(crate) fn default_crypto_pending_buffer() -> usize {
     256 * 1024
 }
@@ -121,6 +170,18 @@ pub(crate) fn default_desync_all_full() -> bool {
     false
 }
 
+pub(crate) fn default_beobachten_minutes() -> u64 {
+    10
+}
+
+pub(crate) fn default_beobachten_flush_secs() -> u64 {
+    15
+}
+
+pub(crate) fn default_beobachten_file() -> String {
+    "cache/beobachten.txt".to_string()
+}
+
 pub(crate) fn default_tls_new_session_tickets() -> u8 {
     0
 }
@@ -179,7 +240,11 @@ pub(crate) fn default_proxy_config_reload_secs() -> u64 {
 }
 
 pub(crate) fn default_update_every_secs() -> u64 {
-    30 * 60
+    5 * 60
+}
+
+pub(crate) fn default_update_every() -> Option<u64> {
+    Some(default_update_every_secs())
 }
 
 pub(crate) fn default_me_reinit_every_secs() -> u64 {
@@ -254,6 +319,21 @@ pub(crate) fn default_degradation_min_unavailable_dc_groups() -> u8 {
     2
 }
 
+pub(crate) fn default_listen_addr_ipv6() -> String {
+    DEFAULT_LISTEN_ADDR_IPV6.to_string()
+}
+
+pub(crate) fn default_listen_addr_ipv6_opt() -> Option<String> {
+    Some(default_listen_addr_ipv6())
+}
+
+pub(crate) fn default_access_users() -> HashMap<String, String> {
+    HashMap::from([(
+        DEFAULT_ACCESS_USER.to_string(),
+        DEFAULT_ACCESS_SECRET.to_string(),
+    )])
+}
+
 // Custom deserializer helpers
 
 #[derive(Deserialize)]

src/config/hot_reload.rs

@@ -96,6 +96,9 @@ fn warn_non_hot_changes(old: &ProxyConfig, new: &ProxyConfig) {
     if old.general.use_middle_proxy != new.general.use_middle_proxy {
         warn!("config reload: use_middle_proxy changed; restart required");
     }
+    if old.general.stun_nat_probe_concurrency != new.general.stun_nat_probe_concurrency {
+        warn!("config reload: general.stun_nat_probe_concurrency changed; restart required");
+    }
 }
 
 /// Resolve the public host for link generation — mirrors the logic in main.rs.

src/config/load.rs

@@ -65,6 +65,16 @@ fn validate_network_cfg(net: &mut NetworkConfig) -> Result<()> {
     Ok(())
 }
 
+fn push_unique_nonempty(target: &mut Vec<String>, value: String) {
+    let trimmed = value.trim();
+    if trimmed.is_empty() {
+        return;
+    }
+    if !target.iter().any(|existing| existing == trimmed) {
+        target.push(trimmed.to_string());
+    }
+}
+
 // ============= Main Config =============
 
 #[derive(Debug, Clone, Serialize, Deserialize, Default)]
@@ -116,8 +126,63 @@ impl ProxyConfig {
         let base_dir = path.as_ref().parent().unwrap_or(Path::new("."));
         let processed = preprocess_includes(&content, base_dir, 0)?;
 
-        let mut config: ProxyConfig =
+        let parsed_toml: toml::Value =
             toml::from_str(&processed).map_err(|e| ProxyError::Config(e.to_string()))?;
+        let general_table = parsed_toml
+            .get("general")
+            .and_then(|value| value.as_table());
+        let network_table = parsed_toml
+            .get("network")
+            .and_then(|value| value.as_table());
+        let update_every_is_explicit = general_table
+            .map(|table| table.contains_key("update_every"))
+            .unwrap_or(false);
+        let legacy_secret_is_explicit = general_table
+            .map(|table| table.contains_key("proxy_secret_auto_reload_secs"))
+            .unwrap_or(false);
+        let legacy_config_is_explicit = general_table
+            .map(|table| table.contains_key("proxy_config_auto_reload_secs"))
+            .unwrap_or(false);
+        let stun_servers_is_explicit = network_table
+            .map(|table| table.contains_key("stun_servers"))
+            .unwrap_or(false);
+
+        let mut config: ProxyConfig =
+            parsed_toml.try_into().map_err(|e| ProxyError::Config(e.to_string()))?;
+
+        if !update_every_is_explicit && (legacy_secret_is_explicit || legacy_config_is_explicit) {
+            config.general.update_every = None;
+        }
+
+        let legacy_nat_stun = config.general.middle_proxy_nat_stun.take();
+        let legacy_nat_stun_servers = std::mem::take(&mut config.general.middle_proxy_nat_stun_servers);
+        let legacy_nat_stun_used = legacy_nat_stun.is_some() || !legacy_nat_stun_servers.is_empty();
+        if stun_servers_is_explicit {
+            let mut explicit_stun_servers = Vec::new();
+            for stun in std::mem::take(&mut config.network.stun_servers) {
+                push_unique_nonempty(&mut explicit_stun_servers, stun);
+            }
+            config.network.stun_servers = explicit_stun_servers;
+
+            if legacy_nat_stun_used {
+                warn!("general.middle_proxy_nat_stun and general.middle_proxy_nat_stun_servers are ignored because network.stun_servers is explicitly set");
+            }
+        } else {
+            // Keep the default STUN pool unless network.stun_servers is explicitly overridden.
+            let mut unified_stun_servers = default_stun_servers();
+            if let Some(stun) = legacy_nat_stun {
+                push_unique_nonempty(&mut unified_stun_servers, stun);
+            }
+            for stun in legacy_nat_stun_servers {
+                push_unique_nonempty(&mut unified_stun_servers, stun);
+            }
+
+            config.network.stun_servers = unified_stun_servers;
+
+            if legacy_nat_stun_used {
+                warn!("general.middle_proxy_nat_stun and general.middle_proxy_nat_stun_servers are deprecated; use network.stun_servers");
+            }
+        }
 
         if let Some(update_every) = config.general.update_every {
             if update_every == 0 {
@@ -147,12 +212,36 @@ impl ProxyConfig {
             }
         }
 
+        if config.general.stun_nat_probe_concurrency == 0 {
+            return Err(ProxyError::Config(
+                "general.stun_nat_probe_concurrency must be > 0".to_string(),
+            ));
+        }
+
         if config.general.me_reinit_every_secs == 0 {
             return Err(ProxyError::Config(
                 "general.me_reinit_every_secs must be > 0".to_string(),
             ));
         }
 
+        if config.general.beobachten_minutes == 0 {
+            return Err(ProxyError::Config(
+                "general.beobachten_minutes must be > 0".to_string(),
+            ));
+        }
+
+        if config.general.beobachten_flush_secs == 0 {
+            return Err(ProxyError::Config(
+                "general.beobachten_flush_secs must be > 0".to_string(),
+            ));
+        }
+
+        if config.general.beobachten_file.trim().is_empty() {
+            return Err(ProxyError::Config(
+                "general.beobachten_file cannot be empty".to_string(),
+            ));
+        }
+
         if config.general.me_hardswap_warmup_delay_max_ms == 0 {
             return Err(ProxyError::Config(
                 "general.me_hardswap_warmup_delay_max_ms must be > 0".to_string(),
@@ -409,6 +498,64 @@ impl ProxyConfig {
 mod tests {
     use super::*;
 
+    #[test]
+    fn serde_defaults_remain_unchanged_for_present_sections() {
+        let toml = r#"
+            [network]
+            [general]
+            [server]
+            [access]
+        "#;
+        let cfg: ProxyConfig = toml::from_str(toml).unwrap();
+
+        assert_eq!(cfg.network.ipv6, default_network_ipv6());
+        assert_eq!(cfg.network.stun_tcp_fallback, default_stun_tcp_fallback());
+        assert_eq!(
+            cfg.general.middle_proxy_warm_standby,
+            default_middle_proxy_warm_standby()
+        );
+        assert_eq!(
+            cfg.general.me_reconnect_max_concurrent_per_dc,
+            default_me_reconnect_max_concurrent_per_dc()
+        );
+        assert_eq!(
+            cfg.general.me_reconnect_fast_retry_count,
+            default_me_reconnect_fast_retry_count()
+        );
+        assert_eq!(cfg.general.update_every, default_update_every());
+        assert_eq!(cfg.server.listen_addr_ipv4, default_listen_addr_ipv4());
+        assert_eq!(cfg.server.listen_addr_ipv6, default_listen_addr_ipv6_opt());
+        assert_eq!(cfg.access.users, default_access_users());
+    }
+
+    #[test]
+    fn impl_defaults_are_sourced_from_default_helpers() {
+        let network = NetworkConfig::default();
+        assert_eq!(network.ipv6, default_network_ipv6());
+        assert_eq!(network.stun_tcp_fallback, default_stun_tcp_fallback());
+
+        let general = GeneralConfig::default();
+        assert_eq!(
+            general.middle_proxy_warm_standby,
+            default_middle_proxy_warm_standby()
+        );
+        assert_eq!(
+            general.me_reconnect_max_concurrent_per_dc,
+            default_me_reconnect_max_concurrent_per_dc()
+        );
+        assert_eq!(
+            general.me_reconnect_fast_retry_count,
+            default_me_reconnect_fast_retry_count()
+        );
+        assert_eq!(general.update_every, default_update_every());
+
+        let server = ServerConfig::default();
+        assert_eq!(server.listen_addr_ipv6, Some(default_listen_addr_ipv6()));
+
+        let access = AccessConfig::default();
+        assert_eq!(access.users, default_access_users());
+    }
+
     #[test]
     fn dc_overrides_allow_string_and_array() {
         let toml = r#"
@@ -512,6 +659,26 @@ mod tests {
         let _ = std::fs::remove_file(path);
     }
 
+    #[test]
+    fn stun_nat_probe_concurrency_zero_is_rejected() {
+        let toml = r#"
+            [general]
+            stun_nat_probe_concurrency = 0
+
+            [censorship]
+            tls_domain = "example.com"
+
+            [access.users]
+            user = "00000000000000000000000000000000"
+        "#;
+        let dir = std::env::temp_dir();
+        let path = dir.join("telemt_stun_nat_probe_concurrency_zero_test.toml");
+        std::fs::write(&path, toml).unwrap();
+        let err = ProxyConfig::load(&path).unwrap_err().to_string();
+        assert!(err.contains("general.stun_nat_probe_concurrency must be > 0"));
+        let _ = std::fs::remove_file(path);
+    }
+
     #[test]
     fn me_reinit_every_default_is_set() {
         let toml = r#"

src/config/types.rs

@@ -76,7 +76,7 @@ impl Default for ProxyModes {
         Self {
             classic: false,
             secure: false,
-            tls: true,
+            tls: default_true(),
         }
     }
 }
@@ -87,7 +87,7 @@ pub struct NetworkConfig {
     pub ipv4: bool,
 
     /// None = auto-detect IPv6 availability.
-    #[serde(default)]
+    #[serde(default = "default_network_ipv6")]
     pub ipv6: Option<bool>,
 
     /// 4 or 6.
@@ -102,7 +102,7 @@ pub struct NetworkConfig {
     pub stun_servers: Vec<String>,
 
     /// Enable TCP STUN fallback when UDP is blocked.
-    #[serde(default)]
+    #[serde(default = "default_stun_tcp_fallback")]
     pub stun_tcp_fallback: bool,
 
     /// HTTP-based public IP detection endpoints (fallback after STUN).
@@ -117,12 +117,12 @@ pub struct NetworkConfig {
 impl Default for NetworkConfig {
     fn default() -> Self {
         Self {
-            ipv4: true,
+            ipv4: default_true(),
-            ipv6: Some(false),
+            ipv6: default_network_ipv6(),
-            prefer: 4,
+            prefer: default_prefer_4(),
             multipath: false,
             stun_servers: default_stun_servers(),
-            stun_tcp_fallback: true,
+            stun_tcp_fallback: default_stun_tcp_fallback(),
             http_ip_detect_urls: default_http_ip_detect_urls(),
             cache_public_ip_path: default_cache_public_ip_path(),
         }
@@ -140,7 +140,7 @@ pub struct GeneralConfig {
     #[serde(default = "default_true")]
     pub fast_mode: bool,
 
-    #[serde(default)]
+    #[serde(default = "default_true")]
     pub use_middle_proxy: bool,
 
     #[serde(default)]
@@ -148,7 +148,7 @@ pub struct GeneralConfig {
 
     /// Path to proxy-secret binary file (auto-downloaded if absent).
     /// Infrastructure secret from https://core.telegram.org/getProxySecret.
-    #[serde(default)]
+    #[serde(default = "default_proxy_secret_path")]
     pub proxy_secret_path: Option<String>,
 
     /// Public IP override for middle-proxy NAT environments.
@@ -157,23 +157,29 @@ pub struct GeneralConfig {
     pub middle_proxy_nat_ip: Option<IpAddr>,
 
     /// Enable STUN-based NAT probing to discover public IP:port for ME KDF.
-    #[serde(default)]
+    #[serde(default = "default_true")]
     pub middle_proxy_nat_probe: bool,
 
-    /// Optional STUN server address (host:port) for NAT probing.
+    /// Deprecated legacy single STUN server for NAT probing.
-    #[serde(default)]
+    /// Use `network.stun_servers` instead.
+    #[serde(default = "default_middle_proxy_nat_stun")]
     pub middle_proxy_nat_stun: Option<String>,
 
-    /// Optional list of STUN servers for NAT probing fallback.
+    /// Deprecated legacy STUN list for NAT probing fallback.
-    #[serde(default)]
+    /// Use `network.stun_servers` instead.
+    #[serde(default = "default_middle_proxy_nat_stun_servers")]
     pub middle_proxy_nat_stun_servers: Vec<String>,
 
+    /// Maximum number of concurrent STUN probes during NAT detection.
+    #[serde(default = "default_stun_nat_probe_concurrency")]
+    pub stun_nat_probe_concurrency: usize,
+
     /// Desired size of active Middle-Proxy writer pool.
     #[serde(default = "default_pool_size")]
     pub middle_proxy_pool_size: usize,
 
     /// Number of warm standby ME connections kept pre-initialized.
-    #[serde(default)]
+    #[serde(default = "default_middle_proxy_warm_standby")]
     pub middle_proxy_warm_standby: usize,
 
     /// Enable ME keepalive padding frames.
@@ -206,6 +212,22 @@ pub struct GeneralConfig {
     #[serde(default = "default_desync_all_full")]
     pub desync_all_full: bool,
 
+    /// Enable per-IP forensic observation buckets for scanners and handshake failures.
+    #[serde(default = "default_true")]
+    pub beobachten: bool,
+
+    /// Observation retention window in minutes for per-IP forensic buckets.
+    #[serde(default = "default_beobachten_minutes")]
+    pub beobachten_minutes: u64,
+
+    /// Snapshot flush interval in seconds for beob output file.
+    #[serde(default = "default_beobachten_flush_secs")]
+    pub beobachten_flush_secs: u64,
+
+    /// Snapshot file path for beob output.
+    #[serde(default = "default_beobachten_file")]
+    pub beobachten_file: String,
+
     /// Enable C-like hard-swap for ME pool generations.
     /// When true, Telemt prewarms a new generation and switches once full coverage is reached.
     #[serde(default = "default_hardswap")]
@@ -224,7 +246,7 @@ pub struct GeneralConfig {
     pub me_warmup_step_jitter_ms: u64,
 
     /// Max concurrent reconnect attempts per DC.
-    #[serde(default)]
+    #[serde(default = "default_me_reconnect_max_concurrent_per_dc")]
     pub me_reconnect_max_concurrent_per_dc: u32,
 
     /// Base backoff in ms for reconnect.
@@ -236,7 +258,7 @@ pub struct GeneralConfig {
     pub me_reconnect_backoff_cap_ms: u64,
 
     /// Fast retry attempts before backoff.
-    #[serde(default)]
+    #[serde(default = "default_me_reconnect_fast_retry_count")]
     pub me_reconnect_fast_retry_count: u32,
 
     /// Ignore STUN/interface IP mismatch (keep using Middle Proxy even if NAT detected).
@@ -264,7 +286,7 @@ pub struct GeneralConfig {
 
     /// Unified ME updater interval in seconds for getProxyConfig/getProxyConfigV6/getProxySecret.
     /// When omitted, effective value falls back to legacy proxy_*_auto_reload_secs fields.
-    #[serde(default)]
+    #[serde(default = "default_update_every")]
     pub update_every: Option<u64>,
 
     /// Periodic ME pool reinitialization interval in seconds.
@@ -354,27 +376,28 @@ impl Default for GeneralConfig {
         Self {
             modes: ProxyModes::default(),
             prefer_ipv6: false,
-            fast_mode: true,
+            fast_mode: default_true(),
-            use_middle_proxy: false,
+            use_middle_proxy: default_true(),
             ad_tag: None,
-            proxy_secret_path: None,
+            proxy_secret_path: default_proxy_secret_path(),
             middle_proxy_nat_ip: None,
-            middle_proxy_nat_probe: false,
+            middle_proxy_nat_probe: default_true(),
-            middle_proxy_nat_stun: None,
+            middle_proxy_nat_stun: default_middle_proxy_nat_stun(),
-            middle_proxy_nat_stun_servers: Vec::new(),
+            middle_proxy_nat_stun_servers: default_middle_proxy_nat_stun_servers(),
+            stun_nat_probe_concurrency: default_stun_nat_probe_concurrency(),
             middle_proxy_pool_size: default_pool_size(),
-            middle_proxy_warm_standby: 16,
+            middle_proxy_warm_standby: default_middle_proxy_warm_standby(),
-            me_keepalive_enabled: true,
+            me_keepalive_enabled: default_true(),
             me_keepalive_interval_secs: default_keepalive_interval(),
             me_keepalive_jitter_secs: default_keepalive_jitter(),
-            me_keepalive_payload_random: true,
+            me_keepalive_payload_random: default_true(),
-            me_warmup_stagger_enabled: true,
+            me_warmup_stagger_enabled: default_true(),
             me_warmup_step_delay_ms: default_warmup_step_delay_ms(),
             me_warmup_step_jitter_ms: default_warmup_step_jitter_ms(),
-            me_reconnect_max_concurrent_per_dc: 8,
+            me_reconnect_max_concurrent_per_dc: default_me_reconnect_max_concurrent_per_dc(),
             me_reconnect_backoff_base_ms: default_reconnect_backoff_base_ms(),
             me_reconnect_backoff_cap_ms: default_reconnect_backoff_cap_ms(),
-            me_reconnect_fast_retry_count: 8,
+            me_reconnect_fast_retry_count: default_me_reconnect_fast_retry_count(),
             stun_iface_mismatch_ignore: false,
             unknown_dc_log_path: default_unknown_dc_log_path(),
             log_level: LogLevel::Normal,
@@ -383,9 +406,13 @@ impl Default for GeneralConfig {
             crypto_pending_buffer: default_crypto_pending_buffer(),
             max_client_frame: default_max_client_frame(),
             desync_all_full: default_desync_all_full(),
+            beobachten: default_true(),
+            beobachten_minutes: default_beobachten_minutes(),
+            beobachten_flush_secs: default_beobachten_flush_secs(),
+            beobachten_file: default_beobachten_file(),
             hardswap: default_hardswap(),
             fast_mode_min_tls_record: default_fast_mode_min_tls_record(),
-            update_every: Some(default_update_every_secs()),
+            update_every: default_update_every(),
             me_reinit_every_secs: default_me_reinit_every_secs(),
             me_hardswap_warmup_delay_min_ms: default_me_hardswap_warmup_delay_min_ms(),
             me_hardswap_warmup_delay_max_ms: default_me_hardswap_warmup_delay_max_ms(),
@@ -403,7 +430,7 @@ impl Default for GeneralConfig {
             proxy_config_auto_reload_secs: default_proxy_config_reload_secs(),
             ntp_check: default_ntp_check(),
             ntp_servers: default_ntp_servers(),
-            auto_degradation_enabled: true,
+            auto_degradation_enabled: default_true(),
             degradation_min_unavailable_dc_groups: default_degradation_min_unavailable_dc_groups(),
         }
     }
@@ -430,11 +457,11 @@ impl GeneralConfig {
 }
 
 /// `[general.links]` — proxy link generation settings.
-#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct LinksConfig {
     /// List of usernames whose tg:// links to display at startup.
     /// `"*"` = all users, `["alice", "bob"]` = specific users.
-    #[serde(default)]
+    #[serde(default = "default_links_show")]
     pub show: ShowLink,
 
     /// Public hostname/IP for tg:// link generation (overrides detected IP).
@@ -446,15 +473,25 @@ pub struct LinksConfig {
     pub public_port: Option<u16>,
 }
 
+impl Default for LinksConfig {
+    fn default() -> Self {
+        Self {
+            show: default_links_show(),
+            public_host: None,
+            public_port: None,
+        }
+    }
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ServerConfig {
     #[serde(default = "default_port")]
     pub port: u16,
 
-    #[serde(default)]
+    #[serde(default = "default_listen_addr_ipv4")]
     pub listen_addr_ipv4: Option<String>,
 
-    #[serde(default)]
+    #[serde(default = "default_listen_addr_ipv6_opt")]
     pub listen_addr_ipv6: Option<String>,
 
     #[serde(default)]
@@ -489,8 +526,8 @@ impl Default for ServerConfig {
     fn default() -> Self {
         Self {
             port: default_port(),
-            listen_addr_ipv4: Some(default_listen_addr()),
+            listen_addr_ipv4: default_listen_addr_ipv4(),
-            listen_addr_ipv6: Some("::".to_string()),
+            listen_addr_ipv6: default_listen_addr_ipv6_opt(),
             listen_unix_sock: None,
             listen_unix_sock_perm: None,
             listen_tcp: None,
@@ -563,7 +600,7 @@ pub struct AntiCensorshipConfig {
     pub fake_cert_len: usize,
 
     /// Enable TLS certificate emulation using cached real certificates.
-    #[serde(default)]
+    #[serde(default = "default_true")]
     pub tls_emulation: bool,
 
     /// Directory to store TLS front cache (on disk).
@@ -591,6 +628,12 @@ pub struct AntiCensorshipConfig {
     /// Enforce ALPN echo of client preference.
     #[serde(default = "default_alpn_enforce")]
     pub alpn_enforce: bool,
+
+    /// Send PROXY protocol header when connecting to mask_host.
+    /// 0 = disabled, 1 = v1 (text), 2 = v2 (binary).
+    /// Allows the backend to see the real client IP.
+    #[serde(default)]
+    pub mask_proxy_protocol: u8,
 }
 
 impl Default for AntiCensorshipConfig {
@@ -598,25 +641,26 @@ impl Default for AntiCensorshipConfig {
         Self {
             tls_domain: default_tls_domain(),
             tls_domains: Vec::new(),
-            mask: true,
+            mask: default_true(),
             mask_host: None,
             mask_port: default_mask_port(),
             mask_unix_sock: None,
             fake_cert_len: default_fake_cert_len(),
-            tls_emulation: false,
+            tls_emulation: true,
             tls_front_dir: default_tls_front_dir(),
             server_hello_delay_min_ms: default_server_hello_delay_min_ms(),
             server_hello_delay_max_ms: default_server_hello_delay_max_ms(),
             tls_new_session_tickets: default_tls_new_session_tickets(),
             tls_full_cert_ttl_secs: default_tls_full_cert_ttl_secs(),
             alpn_enforce: default_alpn_enforce(),
+            mask_proxy_protocol: 0,
         }
     }
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct AccessConfig {
-    #[serde(default)]
+    #[serde(default = "default_access_users")]
     pub users: HashMap<String, String>,
 
     #[serde(default)]
@@ -643,13 +687,8 @@ pub struct AccessConfig {
 
 impl Default for AccessConfig {
     fn default() -> Self {
-        let mut users = HashMap::new();
-        users.insert(
-            "default".to_string(),
-            "00000000000000000000000000000000".to_string(),
-        );
         Self {
-            users,
+            users: default_access_users(),
             user_max_tcp_conns: HashMap::new(),
             user_expirations: HashMap::new(),
             user_data_quota: HashMap::new(),
@@ -731,7 +770,7 @@ pub struct ListenerConfig {
 /// In TOML, this can be:
 /// - `show_link = "*"`          — show links for all users
 /// - `show_link = ["a", "b"]`   — show links for specific users
-/// - omitted                    — show no links (default)
+/// - omitted                    — default depends on the owning config field
 #[derive(Debug, Clone, Default)]
 pub enum ShowLink {
     /// Don't show any links (default when omitted).
@@ -743,6 +782,10 @@ pub enum ShowLink {
     Specific(Vec<String>),
 }
 
+fn default_links_show() -> ShowLink {
+    ShowLink::All
+}
+
 impl ShowLink {
     /// Returns true if no links should be shown.
     pub fn is_empty(&self) -> bool {

src/main.rs

@@ -35,6 +35,7 @@ use crate::crypto::SecureRandom;
 use crate::ip_tracker::UserIpTracker;
 use crate::network::probe::{decide_network_capabilities, log_probe_result, run_probe};
 use crate::proxy::ClientHandler;
+use crate::stats::beobachten::BeobachtenStore;
 use crate::stats::{ReplayChecker, Stats};
 use crate::stream::BufferPool;
 use crate::transport::middle_proxy::{
@@ -159,6 +160,15 @@ fn print_proxy_links(host: &str, port: u16, config: &ProxyConfig) {
     info!(target: "telemt::links", "------------------------");
 }
 
+async fn write_beobachten_snapshot(path: &str, payload: &str) -> std::io::Result<()> {
+    if let Some(parent) = std::path::Path::new(path).parent()
+        && !parent.as_os_str().is_empty()
+    {
+        tokio::fs::create_dir_all(parent).await?;
+    }
+    tokio::fs::write(path, payload).await
+}
+
 #[tokio::main]
 async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
     let (config_path, cli_silent, cli_log_level) = parse_cli();
@@ -244,10 +254,137 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
         warn!("Using default tls_domain. Consider setting a custom domain.");
     }
 
+    let upstream_manager = Arc::new(UpstreamManager::new(config.upstreams.clone()));
+
+    let mut tls_domains = Vec::with_capacity(1 + config.censorship.tls_domains.len());
+    tls_domains.push(config.censorship.tls_domain.clone());
+    for d in &config.censorship.tls_domains {
+        if !tls_domains.contains(d) {
+            tls_domains.push(d.clone());
+        }
+    }
+
+    // Start TLS front fetching in background immediately, in parallel with STUN probing.
+    let tls_cache: Option<Arc<TlsFrontCache>> = if config.censorship.tls_emulation {
+        let cache = Arc::new(TlsFrontCache::new(
+            &tls_domains,
+            config.censorship.fake_cert_len,
+            &config.censorship.tls_front_dir,
+        ));
+        cache.load_from_disk().await;
+
+        let port = config.censorship.mask_port;
+        let proxy_protocol = config.censorship.mask_proxy_protocol;
+        let mask_host = config
+            .censorship
+            .mask_host
+            .clone()
+            .unwrap_or_else(|| config.censorship.tls_domain.clone());
+        let fetch_timeout = Duration::from_secs(5);
+
+        let cache_initial = cache.clone();
+        let domains_initial = tls_domains.clone();
+        let host_initial = mask_host.clone();
+        let upstream_initial = upstream_manager.clone();
+        tokio::spawn(async move {
+            let mut join = tokio::task::JoinSet::new();
+            for domain in domains_initial {
+                let cache_domain = cache_initial.clone();
+                let host_domain = host_initial.clone();
+                let upstream_domain = upstream_initial.clone();
+                join.spawn(async move {
+                    match crate::tls_front::fetcher::fetch_real_tls(
+                        &host_domain,
+                        port,
+                        &domain,
+                        fetch_timeout,
+                        Some(upstream_domain),
+                        proxy_protocol,
+                    )
+                    .await
+                    {
+                        Ok(res) => cache_domain.update_from_fetch(&domain, res).await,
+                        Err(e) => {
+                            warn!(domain = %domain, error = %e, "TLS emulation initial fetch failed")
+                        }
+                    }
+                });
+            }
+            while let Some(res) = join.join_next().await {
+                if let Err(e) = res {
+                    warn!(error = %e, "TLS emulation initial fetch task join failed");
+                }
+            }
+        });
+
+        let cache_timeout = cache.clone();
+        let domains_timeout = tls_domains.clone();
+        let fake_cert_len = config.censorship.fake_cert_len;
+        tokio::spawn(async move {
+            tokio::time::sleep(fetch_timeout).await;
+            for domain in domains_timeout {
+                let cached = cache_timeout.get(&domain).await;
+                if cached.domain == "default" {
+                    warn!(
+                        domain = %domain,
+                        timeout_secs = fetch_timeout.as_secs(),
+                        fake_cert_len,
+                        "TLS-front fetch not ready within timeout; using cache/default fake cert fallback"
+                    );
+                }
+            }
+        });
+
+        // Periodic refresh with jitter.
+        let cache_refresh = cache.clone();
+        let domains_refresh = tls_domains.clone();
+        let host_refresh = mask_host.clone();
+        let upstream_refresh = upstream_manager.clone();
+        tokio::spawn(async move {
+            loop {
+                let base_secs = rand::rng().random_range(4 * 3600..=6 * 3600);
+                let jitter_secs = rand::rng().random_range(0..=7200);
+                tokio::time::sleep(Duration::from_secs(base_secs + jitter_secs)).await;
+
+                let mut join = tokio::task::JoinSet::new();
+                for domain in domains_refresh.clone() {
+                    let cache_domain = cache_refresh.clone();
+                    let host_domain = host_refresh.clone();
+                    let upstream_domain = upstream_refresh.clone();
+                    join.spawn(async move {
+                        match crate::tls_front::fetcher::fetch_real_tls(
+                            &host_domain,
+                            port,
+                            &domain,
+                            fetch_timeout,
+                            Some(upstream_domain),
+                            proxy_protocol,
+                        )
+                        .await
+                        {
+                            Ok(res) => cache_domain.update_from_fetch(&domain, res).await,
+                            Err(e) => warn!(domain = %domain, error = %e, "TLS emulation refresh failed"),
+                        }
+                    });
+                }
+
+                while let Some(res) = join.join_next().await {
+                    if let Err(e) = res {
+                        warn!(error = %e, "TLS emulation refresh task join failed");
+                    }
+                }
+            }
+        });
+
+        Some(cache)
+    } else {
+        None
+    };
+
     let probe = run_probe(
         &config.network,
-        config.general.middle_proxy_nat_stun.clone(),
         config.general.middle_proxy_nat_probe,
+        config.general.stun_nat_probe_concurrency,
     )
     .await?;
     let decision = decide_network_capabilities(&config.network, &probe);
@@ -256,6 +393,7 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
     let prefer_ipv6 = decision.prefer_ipv6();
     let mut use_middle_proxy = config.general.use_middle_proxy && (decision.ipv4_me || decision.ipv6_me);
     let stats = Arc::new(Stats::new());
+    let beobachten = Arc::new(BeobachtenStore::new());
     let rng = Arc::new(SecureRandom::new());
 
     // IP Tracker initialization
@@ -347,8 +485,9 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
                     proxy_secret,
                     config.general.middle_proxy_nat_ip,
                     config.general.middle_proxy_nat_probe,
-                    config.general.middle_proxy_nat_stun.clone(),
+                    None,
-                    config.general.middle_proxy_nat_stun_servers.clone(),
+                    config.network.stun_servers.clone(),
+                    config.general.stun_nat_probe_concurrency,
                     probe.detected_ipv6,
                     config.timeouts.me_one_retry,
                     config.timeouts.me_one_timeout_ms,
@@ -380,6 +519,7 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
                 );
 
                 let pool_size = config.general.middle_proxy_pool_size.max(1);
+                loop {
                     match pool.init(pool_size, &rng).await {
                         Ok(()) => {
                             info!("Middle-End pool initialized successfully");
@@ -395,11 +535,17 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
                                 .await;
                             });
 
-                        Some(pool)
+                            break Some(pool);
                         }
                         Err(e) => {
-                        error!(error = %e, "Failed to initialize ME pool. Falling back to direct mode.");
+                            warn!(
-                        None
+                                error = %e,
+                                retry_in_secs = 2,
+                                "ME pool is not ready yet; retrying startup initialization"
+                            );
+                            pool.reset_stun_state();
+                            tokio::time::sleep(Duration::from_secs(2)).await;
+                        }
                     }
                 }
             }
@@ -431,77 +577,8 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
         Duration::from_secs(config.access.replay_window_secs),
     ));
 
-    let upstream_manager = Arc::new(UpstreamManager::new(config.upstreams.clone()));
     let buffer_pool = Arc::new(BufferPool::with_config(16 * 1024, 4096));
 
-    // TLS front cache (optional emulation)
-    let mut tls_domains = Vec::with_capacity(1 + config.censorship.tls_domains.len());
-    tls_domains.push(config.censorship.tls_domain.clone());
-    for d in &config.censorship.tls_domains {
-        if !tls_domains.contains(d) {
-            tls_domains.push(d.clone());
-        }
-    }
-
-    let tls_cache: Option<Arc<TlsFrontCache>> = if config.censorship.tls_emulation {
-        let cache = Arc::new(TlsFrontCache::new(
-            &tls_domains,
-            config.censorship.fake_cert_len,
-            &config.censorship.tls_front_dir,
-        ));
-
-        cache.load_from_disk().await;
-
-        let port = config.censorship.mask_port;
-        let mask_host = config.censorship.mask_host.clone()
-            .unwrap_or_else(|| config.censorship.tls_domain.clone());
-        // Initial synchronous fetch to warm cache before serving clients.
-        for domain in tls_domains.clone() {
-            match crate::tls_front::fetcher::fetch_real_tls(
-                &mask_host,
-                port,
-                &domain,
-                Duration::from_secs(5),
-                Some(upstream_manager.clone()),
-            )
-            .await
-            {
-                Ok(res) => cache.update_from_fetch(&domain, res).await,
-                Err(e) => warn!(domain = %domain, error = %e, "TLS emulation fetch failed"),
-            }
-        }
-
-        // Periodic refresh with jitter.
-        let cache_clone = cache.clone();
-        let domains = tls_domains.clone();
-        let upstream_for_task = upstream_manager.clone();
-        tokio::spawn(async move {
-            loop {
-                let base_secs = rand::rng().random_range(4 * 3600..=6 * 3600);
-                let jitter_secs = rand::rng().random_range(0..=7200);
-                tokio::time::sleep(Duration::from_secs(base_secs + jitter_secs)).await;
-                for domain in &domains {
-                    match crate::tls_front::fetcher::fetch_real_tls(
-                        &mask_host,
-                        port,
-                        domain,
-                        Duration::from_secs(5),
-                        Some(upstream_for_task.clone()),
-                    )
-                    .await
-                    {
-                        Ok(res) => cache_clone.update_from_fetch(domain, res).await,
-                        Err(e) => warn!(domain = %domain, error = %e, "TLS emulation refresh failed"),
-                    }
-                }
-            }
-        });
-
-        Some(cache)
-    } else {
-        None
-    };
-
     // Middle-End ping before DC connectivity
     if let Some(ref pool) = me_pool {
         let me_results = run_me_ping(pool, &rng).await;
@@ -595,9 +672,9 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
 				info!("  IPv4 in use / IPv6 is fallback");
 			}
 		} else if v6_works && !v4_works {
-			info!("  IPv6 only / IPv4 unavailable)");
+			info!("  IPv6 only / IPv4 unavailable");
 		} else if v4_works && !v6_works {
-			info!("  IPv4 only / IPv6 unavailable)");
+			info!("  IPv4 only / IPv6 unavailable");
 		} else if !v6_works && !v4_works {
 			info!("  No DC connectivity");
 		}
@@ -666,14 +743,8 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
         rc_clone.run_periodic_cleanup().await;
     });
 
-    let detected_ip_v4: Option<std::net::IpAddr> = probe
+    let detected_ip_v4: Option<std::net::IpAddr> = probe.detected_ipv4.map(std::net::IpAddr::V4);
-        .reflected_ipv4
+    let detected_ip_v6: Option<std::net::IpAddr> = probe.detected_ipv6.map(std::net::IpAddr::V6);
-        .map(|s| s.ip())
-        .or_else(|| probe.detected_ipv4.map(std::net::IpAddr::V4));
-    let detected_ip_v6: Option<std::net::IpAddr> = probe
-        .reflected_ipv6
-        .map(|s| s.ip())
-        .or_else(|| probe.detected_ipv6.map(std::net::IpAddr::V6));
     debug!(
         "Detected IPs: v4={:?} v6={:?}",
         detected_ip_v4, detected_ip_v6
@@ -692,6 +763,26 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
         detected_ip_v6,
     );
 
+    let beobachten_writer = beobachten.clone();
+    let config_rx_beobachten = config_rx.clone();
+    tokio::spawn(async move {
+        loop {
+            let cfg = config_rx_beobachten.borrow().clone();
+            let sleep_secs = cfg.general.beobachten_flush_secs.max(1);
+
+            if cfg.general.beobachten {
+                let ttl = Duration::from_secs(cfg.general.beobachten_minutes.saturating_mul(60));
+                let path = cfg.general.beobachten_file.clone();
+                let snapshot = beobachten_writer.snapshot_text(ttl);
+                if let Err(e) = write_beobachten_snapshot(&path, &snapshot).await {
+                    warn!(error = %e, path = %path, "Failed to flush beobachten snapshot");
+                }
+            }
+
+            tokio::time::sleep(Duration::from_secs(sleep_secs)).await;
+        }
+    });
+
     if let Some(ref pool) = me_pool {
         let pool_clone = pool.clone();
         let rng_clone = rng.clone();
@@ -860,6 +951,7 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
         let me_pool = me_pool.clone();
         let tls_cache = tls_cache.clone();
         let ip_tracker = ip_tracker.clone();
+        let beobachten = beobachten.clone();
         let max_connections_unix = max_connections.clone();
 
         tokio::spawn(async move {
@@ -887,6 +979,7 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
                         let me_pool = me_pool.clone();
                         let tls_cache = tls_cache.clone();
                         let ip_tracker = ip_tracker.clone();
+                        let beobachten = beobachten.clone();
                         let proxy_protocol_enabled = config.server.proxy_protocol;
 
                         tokio::spawn(async move {
@@ -894,7 +987,7 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
                             if let Err(e) = crate::proxy::client::handle_client_stream(
                                 stream, fake_peer, config, stats,
                                 upstream_manager, replay_checker, buffer_pool, rng,
-                                me_pool, tls_cache, ip_tracker, proxy_protocol_enabled,
+                                me_pool, tls_cache, ip_tracker, beobachten, proxy_protocol_enabled,
                             ).await {
                                 debug!(error = %e, "Unix socket connection error");
                             }
@@ -942,9 +1035,11 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
 
     if let Some(port) = config.server.metrics_port {
         let stats = stats.clone();
+        let beobachten = beobachten.clone();
+        let config_rx_metrics = config_rx.clone();
         let whitelist = config.server.metrics_whitelist.clone();
         tokio::spawn(async move {
-            metrics::serve(port, stats, whitelist).await;
+            metrics::serve(port, stats, beobachten, config_rx_metrics, whitelist).await;
         });
     }
 
@@ -958,6 +1053,7 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
         let me_pool = me_pool.clone();
         let tls_cache = tls_cache.clone();
         let ip_tracker = ip_tracker.clone();
+        let beobachten = beobachten.clone();
         let max_connections_tcp = max_connections.clone();
 
         tokio::spawn(async move {
@@ -980,6 +1076,7 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
                         let me_pool = me_pool.clone();
                         let tls_cache = tls_cache.clone();
                         let ip_tracker = ip_tracker.clone();
+                        let beobachten = beobachten.clone();
                         let proxy_protocol_enabled = listener_proxy_protocol;
 
                         tokio::spawn(async move {
@@ -996,6 +1093,7 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
                                 me_pool,
                                 tls_cache,
                                 ip_tracker,
+                                beobachten,
                                 proxy_protocol_enabled,
                             )
                             .run()

src/metrics.rs

@@ -1,6 +1,7 @@
 use std::convert::Infallible;
 use std::net::SocketAddr;
 use std::sync::Arc;
+use std::time::Duration;
 
 use http_body_util::Full;
 use hyper::body::Bytes;
@@ -11,9 +12,17 @@ use ipnetwork::IpNetwork;
 use tokio::net::TcpListener;
 use tracing::{info, warn, debug};
 
+use crate::config::ProxyConfig;
+use crate::stats::beobachten::BeobachtenStore;
 use crate::stats::Stats;
 
-pub async fn serve(port: u16, stats: Arc<Stats>, whitelist: Vec<IpNetwork>) {
+pub async fn serve(
+    port: u16,
+    stats: Arc<Stats>,
+    beobachten: Arc<BeobachtenStore>,
+    config_rx: tokio::sync::watch::Receiver<Arc<ProxyConfig>>,
+    whitelist: Vec<IpNetwork>,
+) {
     let addr = SocketAddr::from(([0, 0, 0, 0], port));
     let listener = match TcpListener::bind(addr).await {
         Ok(l) => l,
@@ -22,7 +31,7 @@ pub async fn serve(port: u16, stats: Arc<Stats>, whitelist: Vec<IpNetwork>) {
             return;
         }
     };
-    info!("Metrics endpoint: http://{}/metrics", addr);
+    info!("Metrics endpoint: http://{}/metrics and /beobachten", addr);
 
     loop {
         let (stream, peer) = match listener.accept().await {
@@ -39,10 +48,14 @@ pub async fn serve(port: u16, stats: Arc<Stats>, whitelist: Vec<IpNetwork>) {
         }
 
         let stats = stats.clone();
+        let beobachten = beobachten.clone();
+        let config_rx_conn = config_rx.clone();
         tokio::spawn(async move {
             let svc = service_fn(move |req| {
                 let stats = stats.clone();
-                async move { handle(req, &stats) }
+                let beobachten = beobachten.clone();
+                let config = config_rx_conn.borrow().clone();
+                async move { handle(req, &stats, &beobachten, &config) }
             });
             if let Err(e) = http1::Builder::new()
                 .serve_connection(hyper_util::rt::TokioIo::new(stream), svc)
@@ -54,24 +67,48 @@ pub async fn serve(port: u16, stats: Arc<Stats>, whitelist: Vec<IpNetwork>) {
     }
 }
 
-fn handle<B>(req: Request<B>, stats: &Stats) -> Result<Response<Full<Bytes>>, Infallible> {
+fn handle<B>(
-    if req.uri().path() != "/metrics" {
+    req: Request<B>,
-        let resp = Response::builder()
+    stats: &Stats,
-            .status(StatusCode::NOT_FOUND)
+    beobachten: &BeobachtenStore,
-            .body(Full::new(Bytes::from("Not Found\n")))
+    config: &ProxyConfig,
-            .unwrap();
+) -> Result<Response<Full<Bytes>>, Infallible> {
-        return Ok(resp);
+    if req.uri().path() == "/metrics" {
-    }
-
         let body = render_metrics(stats);
         let resp = Response::builder()
             .status(StatusCode::OK)
             .header("content-type", "text/plain; version=0.0.4; charset=utf-8")
             .body(Full::new(Bytes::from(body)))
             .unwrap();
+        return Ok(resp);
+    }
+
+    if req.uri().path() == "/beobachten" {
+        let body = render_beobachten(beobachten, config);
+        let resp = Response::builder()
+            .status(StatusCode::OK)
+            .header("content-type", "text/plain; charset=utf-8")
+            .body(Full::new(Bytes::from(body)))
+            .unwrap();
+        return Ok(resp);
+    }
+
+    let resp = Response::builder()
+        .status(StatusCode::NOT_FOUND)
+        .body(Full::new(Bytes::from("Not Found\n")))
+        .unwrap();
     Ok(resp)
 }
 
+fn render_beobachten(beobachten: &BeobachtenStore, config: &ProxyConfig) -> String {
+    if !config.general.beobachten {
+        return "beobachten disabled\n".to_string();
+    }
+
+    let ttl = Duration::from_secs(config.general.beobachten_minutes.saturating_mul(60));
+    beobachten.snapshot_text(ttl)
+}
+
 fn render_metrics(stats: &Stats) -> String {
     use std::fmt::Write;
     let mut out = String::with_capacity(4096);
@@ -199,6 +236,95 @@ fn render_metrics(stats: &Stats) -> String {
         stats.get_pool_stale_pick_total()
     );
 
+    let _ = writeln!(out, "# HELP telemt_me_writer_removed_total Total ME writer removals");
+    let _ = writeln!(out, "# TYPE telemt_me_writer_removed_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_me_writer_removed_total {}",
+        stats.get_me_writer_removed_total()
+    );
+
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_writer_removed_unexpected_total Unexpected ME writer removals that triggered refill"
+    );
+    let _ = writeln!(out, "# TYPE telemt_me_writer_removed_unexpected_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_me_writer_removed_unexpected_total {}",
+        stats.get_me_writer_removed_unexpected_total()
+    );
+
+    let _ = writeln!(out, "# HELP telemt_me_refill_triggered_total Immediate ME refill runs started");
+    let _ = writeln!(out, "# TYPE telemt_me_refill_triggered_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_me_refill_triggered_total {}",
+        stats.get_me_refill_triggered_total()
+    );
+
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_refill_skipped_inflight_total Immediate ME refill skips due to inflight dedup"
+    );
+    let _ = writeln!(out, "# TYPE telemt_me_refill_skipped_inflight_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_me_refill_skipped_inflight_total {}",
+        stats.get_me_refill_skipped_inflight_total()
+    );
+
+    let _ = writeln!(out, "# HELP telemt_me_refill_failed_total Immediate ME refill failures");
+    let _ = writeln!(out, "# TYPE telemt_me_refill_failed_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_me_refill_failed_total {}",
+        stats.get_me_refill_failed_total()
+    );
+
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_writer_restored_same_endpoint_total Refilled ME writer restored on the same endpoint"
+    );
+    let _ = writeln!(out, "# TYPE telemt_me_writer_restored_same_endpoint_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_me_writer_restored_same_endpoint_total {}",
+        stats.get_me_writer_restored_same_endpoint_total()
+    );
+
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_writer_restored_fallback_total Refilled ME writer restored via fallback endpoint"
+    );
+    let _ = writeln!(out, "# TYPE telemt_me_writer_restored_fallback_total counter");
+    let _ = writeln!(
+        out,
+        "telemt_me_writer_restored_fallback_total {}",
+        stats.get_me_writer_restored_fallback_total()
+    );
+
+    let unresolved_writer_losses = stats
+        .get_me_writer_removed_unexpected_total()
+        .saturating_sub(
+            stats
+                .get_me_writer_restored_same_endpoint_total()
+                .saturating_add(stats.get_me_writer_restored_fallback_total()),
+        );
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_writer_removed_unexpected_minus_restored_total Unexpected writer removals not yet compensated by restore"
+    );
+    let _ = writeln!(
+        out,
+        "# TYPE telemt_me_writer_removed_unexpected_minus_restored_total gauge"
+    );
+    let _ = writeln!(
+        out,
+        "telemt_me_writer_removed_unexpected_minus_restored_total {}",
+        unresolved_writer_losses
+    );
+
     let _ = writeln!(out, "# HELP telemt_user_connections_total Per-user total connections");
     let _ = writeln!(out, "# TYPE telemt_user_connections_total counter");
     let _ = writeln!(out, "# HELP telemt_user_connections_current Per-user active connections");
@@ -229,6 +355,7 @@ fn render_metrics(stats: &Stats) -> String {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::net::IpAddr;
     use http_body_util::BodyExt;
 
     #[test]
@@ -277,11 +404,17 @@ mod tests {
         assert!(output.contains("# TYPE telemt_connections_total counter"));
         assert!(output.contains("# TYPE telemt_connections_bad_total counter"));
         assert!(output.contains("# TYPE telemt_handshake_timeouts_total counter"));
+        assert!(output.contains("# TYPE telemt_me_writer_removed_total counter"));
+        assert!(output.contains(
+            "# TYPE telemt_me_writer_removed_unexpected_minus_restored_total gauge"
+        ));
     }
 
     #[tokio::test]
     async fn test_endpoint_integration() {
         let stats = Arc::new(Stats::new());
+        let beobachten = Arc::new(BeobachtenStore::new());
+        let mut config = ProxyConfig::default();
         stats.increment_connects_all();
         stats.increment_connects_all();
         stats.increment_connects_all();
@@ -290,16 +423,34 @@ mod tests {
             .uri("/metrics")
             .body(())
             .unwrap();
-        let resp = handle(req, &stats).unwrap();
+        let resp = handle(req, &stats, &beobachten, &config).unwrap();
         assert_eq!(resp.status(), StatusCode::OK);
         let body = resp.into_body().collect().await.unwrap().to_bytes();
         assert!(std::str::from_utf8(body.as_ref()).unwrap().contains("telemt_connections_total 3"));
 
+        config.general.beobachten = true;
+        config.general.beobachten_minutes = 10;
+        beobachten.record(
+            "TLS-scanner",
+            "203.0.113.10".parse::<IpAddr>().unwrap(),
+            Duration::from_secs(600),
+        );
+        let req_beob = Request::builder()
+            .uri("/beobachten")
+            .body(())
+            .unwrap();
+        let resp_beob = handle(req_beob, &stats, &beobachten, &config).unwrap();
+        assert_eq!(resp_beob.status(), StatusCode::OK);
+        let body_beob = resp_beob.into_body().collect().await.unwrap().to_bytes();
+        let beob_text = std::str::from_utf8(body_beob.as_ref()).unwrap();
+        assert!(beob_text.contains("[TLS-scanner]"));
+        assert!(beob_text.contains("203.0.113.10-1"));
+
         let req404 = Request::builder()
             .uri("/other")
             .body(())
             .unwrap();
-        let resp404 = handle(req404, &stats).unwrap();
+        let resp404 = handle(req404, &stats, &beobachten, &config).unwrap();
         assert_eq!(resp404.status(), StatusCode::NOT_FOUND);
     }
 }

src/network/probe.rs

@@ -1,12 +1,16 @@
 #![allow(dead_code)]
 
+use std::collections::HashMap;
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, UdpSocket};
+use std::time::Duration;
 
-use tracing::{info, warn};
+use tokio::task::JoinSet;
+use tokio::time::timeout;
+use tracing::{debug, info, warn};
 
 use crate::config::NetworkConfig;
 use crate::error::Result;
-use crate::network::stun::{stun_probe_dual, DualStunResult, IpFamily};
+use crate::network::stun::{stun_probe_dual, DualStunResult, IpFamily, StunProbeResult};
 
 #[derive(Debug, Clone, Default)]
 pub struct NetworkProbe {
@@ -49,7 +53,13 @@ impl NetworkDecision {
     }
 }
 
-pub async fn run_probe(config: &NetworkConfig, stun_addr: Option<String>, nat_probe: bool) -> Result<NetworkProbe> {
+const STUN_BATCH_TIMEOUT: Duration = Duration::from_secs(5);
+
+pub async fn run_probe(
+    config: &NetworkConfig,
+    nat_probe: bool,
+    stun_nat_probe_concurrency: usize,
+) -> Result<NetworkProbe> {
     let mut probe = NetworkProbe::default();
 
     probe.detected_ipv4 = detect_local_ip_v4();
@@ -58,14 +68,17 @@ pub async fn run_probe(config: &NetworkConfig, stun_addr: Option<String>, nat_pr
     probe.ipv4_is_bogon = probe.detected_ipv4.map(is_bogon_v4).unwrap_or(false);
     probe.ipv6_is_bogon = probe.detected_ipv6.map(is_bogon_v6).unwrap_or(false);
 
-    let stun_server = stun_addr.unwrap_or_else(|| "stun.l.google.com:19302".to_string());
     let stun_res = if nat_probe {
-        match stun_probe_dual(&stun_server).await {
+        let servers = collect_stun_servers(config);
-            Ok(res) => res,
+        if servers.is_empty() {
-            Err(e) => {
+            warn!("STUN probe is enabled but network.stun_servers is empty");
-                warn!(error = %e, "STUN probe failed, continuing without reflection");
             DualStunResult::default()
-            }
+        } else {
+            probe_stun_servers_parallel(
+                &servers,
+                stun_nat_probe_concurrency.max(1),
+            )
+            .await
         }
     } else {
         DualStunResult::default()
@@ -73,6 +86,17 @@ pub async fn run_probe(config: &NetworkConfig, stun_addr: Option<String>, nat_pr
     probe.reflected_ipv4 = stun_res.v4.map(|r| r.reflected_addr);
     probe.reflected_ipv6 = stun_res.v6.map(|r| r.reflected_addr);
 
+    // If STUN is blocked but IPv4 is private, try HTTP public-IP fallback.
+    if nat_probe
+        && probe.reflected_ipv4.is_none()
+        && probe.detected_ipv4.map(is_bogon_v4).unwrap_or(false)
+    {
+        if let Some(public_ip) = detect_public_ipv4_http(&config.http_ip_detect_urls).await {
+            probe.reflected_ipv4 = Some(SocketAddr::new(IpAddr::V4(public_ip), 0));
+            info!(public_ip = %public_ip, "STUN unavailable, using HTTP public IPv4 fallback");
+        }
+    }
+
     probe.ipv4_nat_detected = match (probe.detected_ipv4, probe.reflected_ipv4) {
         (Some(det), Some(reflected)) => det != reflected.ip(),
         _ => false,
@@ -94,6 +118,111 @@ pub async fn run_probe(config: &NetworkConfig, stun_addr: Option<String>, nat_pr
     Ok(probe)
 }
 
+async fn detect_public_ipv4_http(urls: &[String]) -> Option<Ipv4Addr> {
+    let client = reqwest::Client::builder()
+        .timeout(Duration::from_secs(3))
+        .build()
+        .ok()?;
+
+    for url in urls {
+        let response = match client.get(url).send().await {
+            Ok(response) => response,
+            Err(_) => continue,
+        };
+
+        let body = match response.text().await {
+            Ok(body) => body,
+            Err(_) => continue,
+        };
+
+        let Ok(ip) = body.trim().parse::<Ipv4Addr>() else {
+            continue;
+        };
+        if !is_bogon_v4(ip) {
+            return Some(ip);
+        }
+    }
+
+    None
+}
+
+fn collect_stun_servers(config: &NetworkConfig) -> Vec<String> {
+    let mut out = Vec::new();
+    for s in &config.stun_servers {
+        if !s.is_empty() && !out.contains(s) {
+            out.push(s.clone());
+        }
+    }
+    out
+}
+
+async fn probe_stun_servers_parallel(
+    servers: &[String],
+    concurrency: usize,
+) -> DualStunResult {
+    let mut join_set = JoinSet::new();
+    let mut next_idx = 0usize;
+    let mut best_v4_by_ip: HashMap<IpAddr, (usize, StunProbeResult)> = HashMap::new();
+    let mut best_v6_by_ip: HashMap<IpAddr, (usize, StunProbeResult)> = HashMap::new();
+
+    while next_idx < servers.len() || !join_set.is_empty() {
+        while next_idx < servers.len() && join_set.len() < concurrency {
+            let stun_addr = servers[next_idx].clone();
+            next_idx += 1;
+            join_set.spawn(async move {
+                let res = timeout(STUN_BATCH_TIMEOUT, stun_probe_dual(&stun_addr)).await;
+                (stun_addr, res)
+            });
+        }
+
+        let Some(task) = join_set.join_next().await else {
+            break;
+        };
+
+        match task {
+            Ok((stun_addr, Ok(Ok(result)))) => {
+                if let Some(v4) = result.v4 {
+                    let entry = best_v4_by_ip.entry(v4.reflected_addr.ip()).or_insert((0, v4));
+                    entry.0 += 1;
+                }
+                if let Some(v6) = result.v6 {
+                    let entry = best_v6_by_ip.entry(v6.reflected_addr.ip()).or_insert((0, v6));
+                    entry.0 += 1;
+                }
+                if result.v4.is_some() || result.v6.is_some() {
+                    debug!(stun = %stun_addr, "STUN server responded within probe timeout");
+                }
+            }
+            Ok((stun_addr, Ok(Err(e)))) => {
+                debug!(error = %e, stun = %stun_addr, "STUN probe failed");
+            }
+            Ok((stun_addr, Err(_))) => {
+                debug!(stun = %stun_addr, "STUN probe timeout");
+            }
+            Err(e) => {
+                debug!(error = %e, "STUN probe task join failed");
+            }
+        }
+    }
+
+    let mut out = DualStunResult::default();
+    if let Some((_, best)) = best_v4_by_ip
+        .into_values()
+        .max_by_key(|(count, _)| *count)
+    {
+        info!("STUN-Quorum reached, IP: {}", best.reflected_addr.ip());
+        out.v4 = Some(best);
+    }
+    if let Some((_, best)) = best_v6_by_ip
+        .into_values()
+        .max_by_key(|(count, _)| *count)
+    {
+        info!("STUN-Quorum reached, IP: {}", best.reflected_addr.ip());
+        out.v6 = Some(best);
+    }
+    out
+}
+
 pub fn decide_network_capabilities(config: &NetworkConfig, probe: &NetworkProbe) -> NetworkDecision {
     let ipv4_dc = config.ipv4 && probe.detected_ipv4.is_some();
     let ipv6_dc = config.ipv6.unwrap_or(probe.detected_ipv6.is_some()) && probe.detected_ipv6.is_some();

src/proxy/client.rs

@@ -1,7 +1,7 @@
 //! Client Handler
 
 use std::future::Future;
-use std::net::SocketAddr;
+use std::net::{IpAddr, SocketAddr};
 use std::pin::Pin;
 use std::sync::Arc;
 use std::time::Duration;
@@ -27,6 +27,7 @@ use crate::error::{HandshakeResult, ProxyError, Result};
 use crate::ip_tracker::UserIpTracker;
 use crate::protocol::constants::*;
 use crate::protocol::tls;
+use crate::stats::beobachten::BeobachtenStore;
 use crate::stats::{ReplayChecker, Stats};
 use crate::stream::{BufferPool, CryptoReader, CryptoWriter};
 use crate::transport::middle_proxy::MePool;
@@ -39,6 +40,36 @@ use crate::proxy::handshake::{HandshakeSuccess, handle_mtproto_handshake, handle
 use crate::proxy::masking::handle_bad_client;
 use crate::proxy::middle_relay::handle_via_middle_proxy;
 
+fn beobachten_ttl(config: &ProxyConfig) -> Duration {
+    Duration::from_secs(config.general.beobachten_minutes.saturating_mul(60))
+}
+
+fn record_beobachten_class(
+    beobachten: &BeobachtenStore,
+    config: &ProxyConfig,
+    peer_ip: IpAddr,
+    class: &str,
+) {
+    if !config.general.beobachten {
+        return;
+    }
+    beobachten.record(class, peer_ip, beobachten_ttl(config));
+}
+
+fn record_handshake_failure_class(
+    beobachten: &BeobachtenStore,
+    config: &ProxyConfig,
+    peer_ip: IpAddr,
+    error: &ProxyError,
+) {
+    let class = if error.to_string().contains("expected 64 bytes, got 0") {
+        "expected_64_got_0"
+    } else {
+        "other"
+    };
+    record_beobachten_class(beobachten, config, peer_ip, class);
+}
+
 pub async fn handle_client_stream<S>(
     mut stream: S,
     peer: SocketAddr,
@@ -51,6 +82,7 @@ pub async fn handle_client_stream<S>(
     me_pool: Option<Arc<MePool>>,
     tls_cache: Option<Arc<TlsFrontCache>>,
     ip_tracker: Arc<UserIpTracker>,
+    beobachten: Arc<BeobachtenStore>,
     proxy_protocol_enabled: bool,
 ) -> Result<()>
 where
@@ -73,6 +105,7 @@ where
             Err(e) => {
                 stats.increment_connects_bad();
                 warn!(peer = %peer, error = %e, "Invalid PROXY protocol header");
+                record_beobachten_class(&beobachten, &config, peer.ip(), "other");
                 return Err(e);
             }
         }
@@ -82,6 +115,9 @@ where
 
     let handshake_timeout = Duration::from_secs(config.timeouts.client_handshake);
     let stats_for_timeout = stats.clone();
+    let config_for_timeout = config.clone();
+    let beobachten_for_timeout = beobachten.clone();
+    let peer_for_timeout = real_peer.ip();
 
     // For non-TCP streams, use a synthetic local address
     let local_addr: SocketAddr = format!("0.0.0.0:{}", config.server.port)
@@ -103,7 +139,15 @@ where
                 debug!(peer = %real_peer, tls_len = tls_len, "TLS handshake too short");
                 stats.increment_connects_bad();
                 let (reader, writer) = tokio::io::split(stream);
-                handle_bad_client(reader, writer, &first_bytes, &config).await;
+                handle_bad_client(
+                    reader,
+                    writer,
+                    &first_bytes,
+                    real_peer,
+                    &config,
+                    &beobachten,
+                )
+                .await;
                 return Ok(HandshakeOutcome::Handled);
             }
 
@@ -120,7 +164,15 @@ where
                 HandshakeResult::Success(result) => result,
                 HandshakeResult::BadClient { reader, writer } => {
                     stats.increment_connects_bad();
-                    handle_bad_client(reader, writer, &handshake, &config).await;
+                    handle_bad_client(
+                        reader,
+                        writer,
+                        &handshake,
+                        real_peer,
+                        &config,
+                        &beobachten,
+                    )
+                    .await;
                     return Ok(HandshakeOutcome::Handled);
                 }
                 HandshakeResult::Error(e) => return Err(e),
@@ -156,7 +208,15 @@ where
                 debug!(peer = %real_peer, "Non-TLS modes disabled");
                 stats.increment_connects_bad();
                 let (reader, writer) = tokio::io::split(stream);
-                handle_bad_client(reader, writer, &first_bytes, &config).await;
+                handle_bad_client(
+                    reader,
+                    writer,
+                    &first_bytes,
+                    real_peer,
+                    &config,
+                    &beobachten,
+                )
+                .await;
                 return Ok(HandshakeOutcome::Handled);
             }
 
@@ -173,7 +233,15 @@ where
                 HandshakeResult::Success(result) => result,
                 HandshakeResult::BadClient { reader, writer } => {
                     stats.increment_connects_bad();
-                    handle_bad_client(reader, writer, &handshake, &config).await;
+                    handle_bad_client(
+                        reader,
+                        writer,
+                        &handshake,
+                        real_peer,
+                        &config,
+                        &beobachten,
+                    )
+                    .await;
                     return Ok(HandshakeOutcome::Handled);
                 }
                 HandshakeResult::Error(e) => return Err(e),
@@ -200,11 +268,23 @@ where
         Ok(Ok(outcome)) => outcome,
         Ok(Err(e)) => {
             debug!(peer = %peer, error = %e, "Handshake failed");
+            record_handshake_failure_class(
+                &beobachten_for_timeout,
+                &config_for_timeout,
+                peer_for_timeout,
+                &e,
+            );
             return Err(e);
         }
         Err(_) => {
             stats_for_timeout.increment_handshake_timeouts();
             debug!(peer = %peer, "Handshake timeout");
+            record_beobachten_class(
+                &beobachten_for_timeout,
+                &config_for_timeout,
+                peer_for_timeout,
+                "other",
+            );
             return Err(ProxyError::TgHandshakeTimeout);
         }
     };
@@ -230,6 +310,7 @@ pub struct RunningClientHandler {
     me_pool: Option<Arc<MePool>>,
     tls_cache: Option<Arc<TlsFrontCache>>,
     ip_tracker: Arc<UserIpTracker>,
+    beobachten: Arc<BeobachtenStore>,
     proxy_protocol_enabled: bool,
 }
 
@@ -246,6 +327,7 @@ impl ClientHandler {
         me_pool: Option<Arc<MePool>>,
         tls_cache: Option<Arc<TlsFrontCache>>,
         ip_tracker: Arc<UserIpTracker>,
+        beobachten: Arc<BeobachtenStore>,
         proxy_protocol_enabled: bool,
     ) -> RunningClientHandler {
         RunningClientHandler {
@@ -260,6 +342,7 @@ impl ClientHandler {
             me_pool,
             tls_cache,
             ip_tracker,
+            beobachten,
             proxy_protocol_enabled,
         }
     }
@@ -284,17 +367,32 @@ impl RunningClientHandler {
 
         let handshake_timeout = Duration::from_secs(self.config.timeouts.client_handshake);
         let stats = self.stats.clone();
+        let config_for_timeout = self.config.clone();
+        let beobachten_for_timeout = self.beobachten.clone();
+        let peer_for_timeout = peer.ip();
 
         // Phase 1: handshake (with timeout)
         let outcome = match timeout(handshake_timeout, self.do_handshake()).await {
             Ok(Ok(outcome)) => outcome,
             Ok(Err(e)) => {
                 debug!(peer = %peer, error = %e, "Handshake failed");
+                record_handshake_failure_class(
+                    &beobachten_for_timeout,
+                    &config_for_timeout,
+                    peer_for_timeout,
+                    &e,
+                );
                 return Err(e);
             }
             Err(_) => {
                 stats.increment_handshake_timeouts();
                 debug!(peer = %peer, "Handshake timeout");
+                record_beobachten_class(
+                    &beobachten_for_timeout,
+                    &config_for_timeout,
+                    peer_for_timeout,
+                    "other",
+                );
                 return Err(ProxyError::TgHandshakeTimeout);
             }
         };
@@ -321,6 +419,12 @@ impl RunningClientHandler {
                 Err(e) => {
                     self.stats.increment_connects_bad();
                     warn!(peer = %self.peer, error = %e, "Invalid PROXY protocol header");
+                    record_beobachten_class(
+                        &self.beobachten,
+                        &self.config,
+                        self.peer.ip(),
+                        "other",
+                    );
                     return Err(e);
                 }
             }
@@ -354,7 +458,15 @@ impl RunningClientHandler {
             debug!(peer = %peer, tls_len = tls_len, "TLS handshake too short");
             self.stats.increment_connects_bad();
             let (reader, writer) = self.stream.into_split();
-            handle_bad_client(reader, writer, &first_bytes, &self.config).await;
+            handle_bad_client(
+                reader,
+                writer,
+                &first_bytes,
+                peer,
+                &self.config,
+                &self.beobachten,
+            )
+            .await;
             return Ok(HandshakeOutcome::Handled);
         }
 
@@ -385,7 +497,15 @@ impl RunningClientHandler {
             HandshakeResult::Success(result) => result,
             HandshakeResult::BadClient { reader, writer } => {
                 stats.increment_connects_bad();
-                handle_bad_client(reader, writer, &handshake, &config).await;
+                handle_bad_client(
+                    reader,
+                    writer,
+                    &handshake,
+                    peer,
+                    &config,
+                    &self.beobachten,
+                )
+                .await;
                 return Ok(HandshakeOutcome::Handled);
             }
             HandshakeResult::Error(e) => return Err(e),
@@ -446,7 +566,15 @@ impl RunningClientHandler {
             debug!(peer = %peer, "Non-TLS modes disabled");
             self.stats.increment_connects_bad();
             let (reader, writer) = self.stream.into_split();
-            handle_bad_client(reader, writer, &first_bytes, &self.config).await;
+            handle_bad_client(
+                reader,
+                writer,
+                &first_bytes,
+                peer,
+                &self.config,
+                &self.beobachten,
+            )
+            .await;
             return Ok(HandshakeOutcome::Handled);
         }
 
@@ -476,7 +604,15 @@ impl RunningClientHandler {
             HandshakeResult::Success(result) => result,
             HandshakeResult::BadClient { reader, writer } => {
                 stats.increment_connects_bad();
-                handle_bad_client(reader, writer, &handshake, &config).await;
+                handle_bad_client(
+                    reader,
+                    writer,
+                    &handshake,
+                    peer,
+                    &config,
+                    &self.beobachten,
+                )
+                .await;
                 return Ok(HandshakeOutcome::Handled);
             }
             HandshakeResult::Error(e) => return Err(e),

src/proxy/masking.rs

@@ -1,6 +1,7 @@
 //! Masking - forward unrecognized traffic to mask host
 
 use std::str;
+use std::net::SocketAddr;
 use std::time::Duration;
 use tokio::net::TcpStream;
 #[cfg(unix)]
@@ -9,6 +10,8 @@ use tokio::io::{AsyncRead, AsyncWrite, AsyncReadExt, AsyncWriteExt};
 use tokio::time::timeout;
 use tracing::debug;
 use crate::config::ProxyConfig;
+use crate::stats::beobachten::BeobachtenStore;
+use crate::transport::proxy_protocol::{ProxyProtocolV1Builder, ProxyProtocolV2Builder};
 
 const MASK_TIMEOUT: Duration = Duration::from_secs(5);
 /// Maximum duration for the entire masking relay.
@@ -50,20 +53,26 @@ pub async fn handle_bad_client<R, W>(
     reader: R,
     writer: W,
     initial_data: &[u8],
+    peer: SocketAddr,
     config: &ProxyConfig,
+    beobachten: &BeobachtenStore,
 )
 where
     R: AsyncRead + Unpin + Send + 'static,
     W: AsyncWrite + Unpin + Send + 'static,
 {
+    let client_type = detect_client_type(initial_data);
+    if config.general.beobachten {
+        let ttl = Duration::from_secs(config.general.beobachten_minutes.saturating_mul(60));
+        beobachten.record(client_type, peer.ip(), ttl);
+    }
+
     if !config.censorship.mask {
         // Masking disabled, just consume data
         consume_client_data(reader).await;
         return;
     }
 
-    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 {
@@ -111,7 +120,37 @@ where
     let connect_result = timeout(MASK_TIMEOUT, TcpStream::connect(&mask_addr)).await;
     match connect_result {
         Ok(Ok(stream)) => {
-            let (mask_read, mask_write) = stream.into_split();
+            let proxy_header: Option<Vec<u8>> = match config.censorship.mask_proxy_protocol {
+                0 => None,
+                version => {
+                    let header = if let Ok(local_addr) = stream.local_addr() {
+                        match version {
+                            2 => ProxyProtocolV2Builder::new().with_addrs(peer, local_addr).build(),
+                            _ => match (peer, local_addr) {
+                                (SocketAddr::V4(src), SocketAddr::V4(dst)) =>
+                                    ProxyProtocolV1Builder::new().tcp4(src.into(), dst.into()).build(),
+                                (SocketAddr::V6(src), SocketAddr::V6(dst)) =>
+                                    ProxyProtocolV1Builder::new().tcp6(src.into(), dst.into()).build(),
+                                _ =>
+                                    ProxyProtocolV1Builder::new().build(),
+                            },
+                        }
+                    } else {
+                        match version {
+                            2 => ProxyProtocolV2Builder::new().build(),
+                            _ => ProxyProtocolV1Builder::new().build(),
+                        }
+                    };
+                    Some(header)
+                }
+            };
+
+            let (mask_read, mut mask_write) = stream.into_split();
+            if let Some(header) = proxy_header {
+                if mask_write.write_all(&header).await.is_err() {
+                    return;
+                }
+            }
             if timeout(MASK_RELAY_TIMEOUT, relay_to_mask(reader, writer, mask_read, mask_write, initial_data)).await.is_err() {
                 debug!("Mask relay timed out");
             }

src/stats/beobachten.rs

@@ -0,0 +1,117 @@
+//! Per-IP forensic buckets for scanner and handshake failure observation.
+
+use std::collections::{BTreeMap, HashMap};
+use std::net::IpAddr;
+use std::time::{Duration, Instant};
+
+use parking_lot::Mutex;
+
+const CLEANUP_INTERVAL: Duration = Duration::from_secs(30);
+
+#[derive(Default)]
+struct BeobachtenInner {
+    entries: HashMap<(String, IpAddr), BeobachtenEntry>,
+    last_cleanup: Option<Instant>,
+}
+
+#[derive(Clone, Copy)]
+struct BeobachtenEntry {
+    tries: u64,
+    last_seen: Instant,
+}
+
+/// In-memory, TTL-scoped per-IP counters keyed by source class.
+pub struct BeobachtenStore {
+    inner: Mutex<BeobachtenInner>,
+}
+
+impl Default for BeobachtenStore {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl BeobachtenStore {
+    pub fn new() -> Self {
+        Self {
+            inner: Mutex::new(BeobachtenInner::default()),
+        }
+    }
+
+    pub fn record(&self, class: &str, ip: IpAddr, ttl: Duration) {
+        if class.is_empty() || ttl.is_zero() {
+            return;
+        }
+
+        let now = Instant::now();
+        let mut guard = self.inner.lock();
+        Self::cleanup_if_needed(&mut guard, now, ttl);
+
+        let key = (class.to_string(), ip);
+        let entry = guard.entries.entry(key).or_insert(BeobachtenEntry {
+            tries: 0,
+            last_seen: now,
+        });
+        entry.tries = entry.tries.saturating_add(1);
+        entry.last_seen = now;
+    }
+
+    pub fn snapshot_text(&self, ttl: Duration) -> String {
+        if ttl.is_zero() {
+            return "beobachten disabled\n".to_string();
+        }
+
+        let now = Instant::now();
+        let mut guard = self.inner.lock();
+        Self::cleanup(&mut guard, now, ttl);
+        guard.last_cleanup = Some(now);
+
+        let mut grouped = BTreeMap::<String, Vec<(IpAddr, u64)>>::new();
+        for ((class, ip), entry) in &guard.entries {
+            grouped
+                .entry(class.clone())
+                .or_default()
+                .push((*ip, entry.tries));
+        }
+
+        if grouped.is_empty() {
+            return "empty\n".to_string();
+        }
+
+        let mut out = String::with_capacity(grouped.len() * 64);
+        for (class, entries) in &mut grouped {
+            out.push('[');
+            out.push_str(class);
+            out.push_str("]\n");
+
+            entries.sort_by(|(ip_a, tries_a), (ip_b, tries_b)| {
+                tries_b
+                    .cmp(tries_a)
+                    .then_with(|| ip_a.to_string().cmp(&ip_b.to_string()))
+            });
+
+            for (ip, tries) in entries {
+                out.push_str(&format!("{ip}-{tries}\n"));
+            }
+        }
+
+        out
+    }
+
+    fn cleanup_if_needed(inner: &mut BeobachtenInner, now: Instant, ttl: Duration) {
+        let should_cleanup = match inner.last_cleanup {
+            Some(last) => now.saturating_duration_since(last) >= CLEANUP_INTERVAL,
+            None => true,
+        };
+        if should_cleanup {
+            Self::cleanup(inner, now, ttl);
+            inner.last_cleanup = Some(now);
+        }
+    }
+
+    fn cleanup(inner: &mut BeobachtenInner, now: Instant, ttl: Duration) {
+        inner.entries.retain(|_, entry| {
+            now.saturating_duration_since(entry.last_seen) <= ttl
+        });
+    }
+}

src/stats/mod.rs

@@ -2,6 +2,8 @@
 
 #![allow(dead_code)]
 
+pub mod beobachten;
+
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::time::{Instant, Duration};
 use dashmap::DashMap;
@@ -43,6 +45,13 @@ pub struct Stats {
     pool_drain_active: AtomicU64,
     pool_force_close_total: AtomicU64,
     pool_stale_pick_total: AtomicU64,
+    me_writer_removed_total: AtomicU64,
+    me_writer_removed_unexpected_total: AtomicU64,
+    me_refill_triggered_total: AtomicU64,
+    me_refill_skipped_inflight_total: AtomicU64,
+    me_refill_failed_total: AtomicU64,
+    me_writer_restored_same_endpoint_total: AtomicU64,
+    me_writer_restored_fallback_total: AtomicU64,
     user_stats: DashMap<String, UserStats>,
     start_time: parking_lot::RwLock<Option<Instant>>,
 }
@@ -142,6 +151,27 @@ impl Stats {
     pub fn increment_pool_stale_pick_total(&self) {
         self.pool_stale_pick_total.fetch_add(1, Ordering::Relaxed);
     }
+    pub fn increment_me_writer_removed_total(&self) {
+        self.me_writer_removed_total.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_me_writer_removed_unexpected_total(&self) {
+        self.me_writer_removed_unexpected_total.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_me_refill_triggered_total(&self) {
+        self.me_refill_triggered_total.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_me_refill_skipped_inflight_total(&self) {
+        self.me_refill_skipped_inflight_total.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_me_refill_failed_total(&self) {
+        self.me_refill_failed_total.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_me_writer_restored_same_endpoint_total(&self) {
+        self.me_writer_restored_same_endpoint_total.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_me_writer_restored_fallback_total(&self) {
+        self.me_writer_restored_fallback_total.fetch_add(1, Ordering::Relaxed);
+    }
     pub fn get_connects_all(&self) -> u64 { self.connects_all.load(Ordering::Relaxed) }
     pub fn get_connects_bad(&self) -> u64 { self.connects_bad.load(Ordering::Relaxed) }
     pub fn get_me_keepalive_sent(&self) -> u64 { self.me_keepalive_sent.load(Ordering::Relaxed) }
@@ -195,6 +225,27 @@ impl Stats {
     pub fn get_pool_stale_pick_total(&self) -> u64 {
         self.pool_stale_pick_total.load(Ordering::Relaxed)
     }
+    pub fn get_me_writer_removed_total(&self) -> u64 {
+        self.me_writer_removed_total.load(Ordering::Relaxed)
+    }
+    pub fn get_me_writer_removed_unexpected_total(&self) -> u64 {
+        self.me_writer_removed_unexpected_total.load(Ordering::Relaxed)
+    }
+    pub fn get_me_refill_triggered_total(&self) -> u64 {
+        self.me_refill_triggered_total.load(Ordering::Relaxed)
+    }
+    pub fn get_me_refill_skipped_inflight_total(&self) -> u64 {
+        self.me_refill_skipped_inflight_total.load(Ordering::Relaxed)
+    }
+    pub fn get_me_refill_failed_total(&self) -> u64 {
+        self.me_refill_failed_total.load(Ordering::Relaxed)
+    }
+    pub fn get_me_writer_restored_same_endpoint_total(&self) -> u64 {
+        self.me_writer_restored_same_endpoint_total.load(Ordering::Relaxed)
+    }
+    pub fn get_me_writer_restored_fallback_total(&self) -> u64 {
+        self.me_writer_restored_fallback_total.load(Ordering::Relaxed)
+    }
     
     pub fn increment_user_connects(&self, user: &str) {
         self.user_stats.entry(user.to_string()).or_default()

src/tls_front/fetcher.rs

@@ -19,6 +19,7 @@ use x509_parser::certificate::X509Certificate;
 
 use crate::crypto::SecureRandom;
 use crate::protocol::constants::{TLS_RECORD_APPLICATION, TLS_RECORD_HANDSHAKE};
+use crate::transport::proxy_protocol::{ProxyProtocolV1Builder, ProxyProtocolV2Builder};
 use crate::tls_front::types::{
     ParsedCertificateInfo,
     ParsedServerHello,
@@ -366,6 +367,7 @@ async fn fetch_via_raw_tls(
     port: u16,
     sni: &str,
     connect_timeout: Duration,
+    proxy_protocol: u8,
 ) -> Result<TlsFetchResult> {
     let addr = format!("{host}:{port}");
     let mut stream = timeout(connect_timeout, TcpStream::connect(addr)).await??;
@@ -373,6 +375,13 @@ async fn fetch_via_raw_tls(
     let rng = SecureRandom::new();
     let client_hello = build_client_hello(sni, &rng);
     timeout(connect_timeout, async {
+        if proxy_protocol > 0 {
+            let header = match proxy_protocol {
+                2 => ProxyProtocolV2Builder::new().build(),
+                _ => ProxyProtocolV1Builder::new().build(),
+            };
+            stream.write_all(&header).await?;
+        }
         stream.write_all(&client_hello).await?;
         stream.flush().await?;
         Ok::<(), std::io::Error>(())
@@ -424,9 +433,10 @@ async fn fetch_via_rustls(
     sni: &str,
     connect_timeout: Duration,
     upstream: Option<std::sync::Arc<crate::transport::UpstreamManager>>,
+    proxy_protocol: u8,
 ) -> Result<TlsFetchResult> {
     // rustls handshake path for certificate and basic negotiated metadata.
-    let stream = if let Some(manager) = upstream {
+    let mut stream = if let Some(manager) = upstream {
         // Resolve host to SocketAddr
         if let Ok(mut addrs) = tokio::net::lookup_host((host, port)).await {
             if let Some(addr) = addrs.find(|a| a.is_ipv4()) {
@@ -447,6 +457,15 @@ async fn fetch_via_rustls(
         timeout(connect_timeout, TcpStream::connect((host, port))).await??
     };
 
+    if proxy_protocol > 0 {
+        let header = match proxy_protocol {
+            2 => ProxyProtocolV2Builder::new().build(),
+            _ => ProxyProtocolV1Builder::new().build(),
+        };
+        stream.write_all(&header).await?;
+        stream.flush().await?;
+    }
+
     let config = build_client_config();
     let connector = TlsConnector::from(config);
 
@@ -527,8 +546,9 @@ pub async fn fetch_real_tls(
     sni: &str,
     connect_timeout: Duration,
     upstream: Option<std::sync::Arc<crate::transport::UpstreamManager>>,
+    proxy_protocol: u8,
 ) -> Result<TlsFetchResult> {
-    let raw_result = match fetch_via_raw_tls(host, port, sni, connect_timeout).await {
+    let raw_result = match fetch_via_raw_tls(host, port, sni, connect_timeout, proxy_protocol).await {
         Ok(res) => Some(res),
         Err(e) => {
             warn!(sni = %sni, error = %e, "Raw TLS fetch failed");
@@ -536,7 +556,7 @@ pub async fn fetch_real_tls(
         }
     };
 
-    match fetch_via_rustls(host, port, sni, connect_timeout, upstream).await {
+    match fetch_via_rustls(host, port, sni, connect_timeout, upstream, proxy_protocol).await {
         Ok(rustls_result) => {
             if let Some(mut raw) = raw_result {
                 raw.cert_info = rustls_result.cert_info;

src/transport/middle_proxy/health.rs

@@ -22,6 +22,7 @@ pub async fn me_health_monitor(pool: Arc<MePool>, rng: Arc<SecureRandom>, _min_c
     let mut inflight: HashMap<(i32, IpFamily), usize> = HashMap::new();
     loop {
         tokio::time::sleep(Duration::from_secs(HEALTH_INTERVAL_SECS)).await;
+        pool.prune_closed_writers().await;
         check_family(
             IpFamily::V4,
             &pool,

src/transport/middle_proxy/mod.rs

@@ -1,17 +1,22 @@
 //! Middle Proxy RPC transport.
 
 mod codec;
+mod config_updater;
 mod handshake;
 mod health;
 mod pool;
+mod pool_config;
+mod pool_init;
 mod pool_nat;
+mod pool_refill;
+mod pool_reinit;
+mod pool_writer;
 mod ping;
 mod reader;
 mod registry;
+mod rotation;
 mod send;
 mod secret;
-mod rotation;
-mod config_updater;
 mod wire;
 
 use bytes::Bytes;

src/transport/middle_proxy/pool_config.rs

@@ -0,0 +1,81 @@
+use std::collections::HashMap;
+use std::net::IpAddr;
+use std::sync::Arc;
+use std::time::Duration;
+
+use tracing::warn;
+
+use super::pool::MePool;
+
+impl MePool {
+    pub async fn update_proxy_maps(
+        &self,
+        new_v4: HashMap<i32, Vec<(IpAddr, u16)>>,
+        new_v6: Option<HashMap<i32, Vec<(IpAddr, u16)>>>,
+    ) -> bool {
+        let mut changed = false;
+        {
+            let mut guard = self.proxy_map_v4.write().await;
+            if !new_v4.is_empty() && *guard != new_v4 {
+                *guard = new_v4;
+                changed = true;
+            }
+        }
+        if let Some(v6) = new_v6 {
+            let mut guard = self.proxy_map_v6.write().await;
+            if !v6.is_empty() && *guard != v6 {
+                *guard = v6;
+                changed = true;
+            }
+        }
+        // Ensure negative DC entries mirror positives when absent (Telegram convention).
+        {
+            let mut guard = self.proxy_map_v4.write().await;
+            let keys: Vec<i32> = guard.keys().cloned().collect();
+            for k in keys.iter().cloned().filter(|k| *k > 0) {
+                if !guard.contains_key(&-k)
+                    && let Some(addrs) = guard.get(&k).cloned()
+                {
+                    guard.insert(-k, addrs);
+                }
+            }
+        }
+        {
+            let mut guard = self.proxy_map_v6.write().await;
+            let keys: Vec<i32> = guard.keys().cloned().collect();
+            for k in keys.iter().cloned().filter(|k| *k > 0) {
+                if !guard.contains_key(&-k)
+                    && let Some(addrs) = guard.get(&k).cloned()
+                {
+                    guard.insert(-k, addrs);
+                }
+            }
+        }
+        changed
+    }
+
+    pub async fn update_secret(self: &Arc<Self>, new_secret: Vec<u8>) -> bool {
+        if new_secret.len() < 32 {
+            warn!(len = new_secret.len(), "proxy-secret update ignored (too short)");
+            return false;
+        }
+        let mut guard = self.proxy_secret.write().await;
+        if *guard != new_secret {
+            *guard = new_secret;
+            drop(guard);
+            self.reconnect_all().await;
+            return true;
+        }
+        false
+    }
+
+    pub async fn reconnect_all(self: &Arc<Self>) {
+        let ws = self.writers.read().await.clone();
+        for w in ws {
+            if let Ok(()) = self.connect_one(w.addr, self.rng.as_ref()).await {
+                self.mark_writer_draining(w.id).await;
+                tokio::time::sleep(Duration::from_secs(2)).await;
+            }
+        }
+    }
+}

src/transport/middle_proxy/pool_init.rs

@@ -0,0 +1,201 @@
+use std::collections::{HashMap, HashSet};
+use std::net::{IpAddr, SocketAddr};
+use std::sync::Arc;
+
+use rand::Rng;
+use rand::seq::SliceRandom;
+use tracing::{debug, info, warn};
+
+use crate::crypto::SecureRandom;
+use crate::error::{ProxyError, Result};
+
+use super::pool::MePool;
+
+impl MePool {
+    pub async fn init(self: &Arc<Self>, pool_size: usize, rng: &Arc<SecureRandom>) -> Result<()> {
+        let family_order = self.family_order();
+        let ks = self.key_selector().await;
+        info!(
+            me_servers = self.proxy_map_v4.read().await.len(),
+            pool_size,
+            key_selector = format_args!("0x{ks:08x}"),
+            secret_len = self.proxy_secret.read().await.len(),
+            "Initializing ME pool"
+        );
+
+        for family in family_order {
+            let map = self.proxy_map_for_family(family).await;
+            let mut grouped_dc_addrs: HashMap<i32, Vec<(IpAddr, u16)>> = HashMap::new();
+            for (dc, addrs) in map {
+                if addrs.is_empty() {
+                    continue;
+                }
+                grouped_dc_addrs.entry(dc.abs()).or_default().extend(addrs);
+            }
+            let mut dc_addrs: Vec<(i32, Vec<(IpAddr, u16)>)> = grouped_dc_addrs
+                .into_iter()
+                .map(|(dc, mut addrs)| {
+                    addrs.sort_unstable();
+                    addrs.dedup();
+                    (dc, addrs)
+                })
+                .collect();
+            dc_addrs.sort_unstable_by_key(|(dc, _)| *dc);
+
+            // Ensure at least one live writer per DC group; run missing DCs in parallel.
+            let mut join = tokio::task::JoinSet::new();
+            for (dc, addrs) in dc_addrs.iter().cloned() {
+                if addrs.is_empty() {
+                    continue;
+                }
+                let endpoints: HashSet<SocketAddr> = addrs
+                    .iter()
+                    .map(|(ip, port)| SocketAddr::new(*ip, *port))
+                    .collect();
+                if self.active_writer_count_for_endpoints(&endpoints).await > 0 {
+                    continue;
+                }
+                let pool = Arc::clone(self);
+                let rng_clone = Arc::clone(rng);
+                join.spawn(async move { pool.connect_primary_for_dc(dc, addrs, rng_clone).await });
+            }
+            while join.join_next().await.is_some() {}
+
+            let mut missing_dcs = Vec::new();
+            for (dc, addrs) in &dc_addrs {
+                let endpoints: HashSet<SocketAddr> = addrs
+                    .iter()
+                    .map(|(ip, port)| SocketAddr::new(*ip, *port))
+                    .collect();
+                if self.active_writer_count_for_endpoints(&endpoints).await == 0 {
+                    missing_dcs.push(*dc);
+                }
+            }
+            if !missing_dcs.is_empty() {
+                return Err(ProxyError::Proxy(format!(
+                    "ME init incomplete: no live writers for DC groups {missing_dcs:?}"
+                )));
+            }
+
+            // Warm reserve writers asynchronously so startup does not block after first working pool is ready.
+            let pool = Arc::clone(self);
+            let rng_clone = Arc::clone(rng);
+            let dc_addrs_bg = dc_addrs.clone();
+            tokio::spawn(async move {
+                if pool.me_warmup_stagger_enabled {
+                    for (dc, addrs) in &dc_addrs_bg {
+                        for (ip, port) in addrs {
+                            if pool.connection_count() >= pool_size {
+                                break;
+                            }
+                            let addr = SocketAddr::new(*ip, *port);
+                            let jitter = rand::rng()
+                                .random_range(0..=pool.me_warmup_step_jitter.as_millis() as u64);
+                            let delay_ms = pool.me_warmup_step_delay.as_millis() as u64 + jitter;
+                            tokio::time::sleep(std::time::Duration::from_millis(delay_ms)).await;
+                            if let Err(e) = pool.connect_one(addr, rng_clone.as_ref()).await {
+                                debug!(%addr, dc = %dc, error = %e, "Extra ME connect failed (staggered)");
+                            }
+                        }
+                    }
+                } else {
+                    for (dc, addrs) in &dc_addrs_bg {
+                        for (ip, port) in addrs {
+                            if pool.connection_count() >= pool_size {
+                                break;
+                            }
+                            let addr = SocketAddr::new(*ip, *port);
+                            if let Err(e) = pool.connect_one(addr, rng_clone.as_ref()).await {
+                                debug!(%addr, dc = %dc, error = %e, "Extra ME connect failed");
+                            }
+                        }
+                        if pool.connection_count() >= pool_size {
+                            break;
+                        }
+                    }
+                }
+                debug!(
+                    target_pool_size = pool_size,
+                    current_pool_size = pool.connection_count(),
+                    "Background ME reserve warmup finished"
+                );
+            });
+
+            if !self.decision.effective_multipath && self.connection_count() > 0 {
+                break;
+            }
+        }
+
+        if self.writers.read().await.is_empty() {
+            return Err(ProxyError::Proxy("No ME connections".into()));
+        }
+        info!(
+            active_writers = self.connection_count(),
+            "ME primary pool ready; reserve warmup continues in background"
+        );
+        Ok(())
+    }
+
+    async fn connect_primary_for_dc(
+        self: Arc<Self>,
+        dc: i32,
+        mut addrs: Vec<(IpAddr, u16)>,
+        rng: Arc<SecureRandom>,
+    ) -> bool {
+        if addrs.is_empty() {
+            return false;
+        }
+        addrs.shuffle(&mut rand::rng());
+        if addrs.len() > 1 {
+            let concurrency = 2usize;
+            let mut join = tokio::task::JoinSet::new();
+            let mut next_idx = 0usize;
+
+            while next_idx < addrs.len() || !join.is_empty() {
+                while next_idx < addrs.len() && join.len() < concurrency {
+                    let (ip, port) = addrs[next_idx];
+                    next_idx += 1;
+                    let addr = SocketAddr::new(ip, port);
+                    let pool = Arc::clone(&self);
+                    let rng_clone = Arc::clone(&rng);
+                    join.spawn(async move {
+                        (addr, pool.connect_one(addr, rng_clone.as_ref()).await)
+                    });
+                }
+
+                let Some(res) = join.join_next().await else {
+                    break;
+                };
+                match res {
+                    Ok((addr, Ok(()))) => {
+                        info!(%addr, dc = %dc, "ME connected");
+                        join.abort_all();
+                        while join.join_next().await.is_some() {}
+                        return true;
+                    }
+                    Ok((addr, Err(e))) => {
+                        warn!(%addr, dc = %dc, error = %e, "ME connect failed, trying next");
+                    }
+                    Err(e) => {
+                        warn!(dc = %dc, error = %e, "ME connect task failed");
+                    }
+                }
+            }
+            warn!(dc = %dc, "All ME servers for DC failed at init");
+            return false;
+        }
+
+        for (ip, port) in addrs {
+            let addr = SocketAddr::new(ip, port);
+            match self.connect_one(addr, rng.as_ref()).await {
+                Ok(()) => {
+                    info!(%addr, dc = %dc, "ME connected");
+                    return true;
+                }
+                Err(e) => warn!(%addr, dc = %dc, error = %e, "ME connect failed, trying next"),
+            }
+        }
+        warn!(dc = %dc, "All ME servers for DC failed at init");
+        false
+    }
+}

src/transport/middle_proxy/pool_nat.rs

@@ -1,7 +1,10 @@
+use std::collections::HashMap;
 use std::net::{IpAddr, Ipv4Addr};
 use std::time::Duration;
 
-use tracing::{info, warn};
+use tokio::task::JoinSet;
+use tokio::time::timeout;
+use tracing::{debug, info, warn};
 
 use crate::error::{ProxyError, Result};
 use crate::network::probe::is_bogon;
@@ -10,9 +13,19 @@ use crate::network::stun::{stun_probe_dual, IpFamily, StunProbeResult};
 use super::MePool;
 use std::time::Instant;
 
+const STUN_BATCH_TIMEOUT: Duration = Duration::from_secs(5);
+
 #[allow(dead_code)]
 pub async fn stun_probe(stun_addr: Option<String>) -> Result<crate::network::stun::DualStunResult> {
-    let stun_addr = stun_addr.unwrap_or_else(|| "stun.l.google.com:19302".to_string());
+    let stun_addr = stun_addr.unwrap_or_else(|| {
+        crate::config::defaults::default_stun_servers()
+            .into_iter()
+            .next()
+            .unwrap_or_default()
+    });
+    if stun_addr.is_empty() {
+        return Err(ProxyError::Proxy("STUN server is not configured".to_string()));
+    }
     stun_probe_dual(&stun_addr).await
 }
 
@@ -22,6 +35,101 @@ pub async fn detect_public_ip() -> Option<IpAddr> {
 }
 
 impl MePool {
+    fn configured_stun_servers(&self) -> Vec<String> {
+        if !self.nat_stun_servers.is_empty() {
+            return self.nat_stun_servers.clone();
+        }
+        if let Some(s) = &self.nat_stun
+            && !s.trim().is_empty()
+        {
+            return vec![s.clone()];
+        }
+        Vec::new()
+    }
+
+    async fn probe_stun_batch_for_family(
+        &self,
+        servers: &[String],
+        family: IpFamily,
+        attempt: u8,
+    ) -> (Vec<String>, Option<std::net::SocketAddr>) {
+        let mut join_set = JoinSet::new();
+        let mut next_idx = 0usize;
+        let mut live_servers = Vec::new();
+        let mut best_by_ip: HashMap<IpAddr, (usize, std::net::SocketAddr)> = HashMap::new();
+        let concurrency = self.nat_probe_concurrency.max(1);
+
+        while next_idx < servers.len() || !join_set.is_empty() {
+            while next_idx < servers.len() && join_set.len() < concurrency {
+                let stun_addr = servers[next_idx].clone();
+                next_idx += 1;
+                join_set.spawn(async move {
+                    let res = timeout(STUN_BATCH_TIMEOUT, stun_probe_dual(&stun_addr)).await;
+                    (stun_addr, res)
+                });
+            }
+
+            let Some(task) = join_set.join_next().await else {
+                break;
+            };
+
+            match task {
+                Ok((stun_addr, Ok(Ok(res)))) => {
+                    let picked: Option<StunProbeResult> = match family {
+                        IpFamily::V4 => res.v4,
+                        IpFamily::V6 => res.v6,
+                    };
+
+                    if let Some(result) = picked {
+                        live_servers.push(stun_addr.clone());
+                        let entry = best_by_ip
+                            .entry(result.reflected_addr.ip())
+                            .or_insert((0, result.reflected_addr));
+                        entry.0 += 1;
+                        debug!(
+                            local = %result.local_addr,
+                            reflected = %result.reflected_addr,
+                            family = ?family,
+                            stun = %stun_addr,
+                            "NAT probe: reflected address"
+                        );
+                    }
+                }
+                Ok((stun_addr, Ok(Err(e)))) => {
+                    debug!(
+                        error = %e,
+                        stun = %stun_addr,
+                        attempt = attempt + 1,
+                        "NAT probe failed, trying next server"
+                    );
+                }
+                Ok((stun_addr, Err(_))) => {
+                    debug!(
+                        stun = %stun_addr,
+                        attempt = attempt + 1,
+                        "NAT probe timeout, trying next server"
+                    );
+                }
+                Err(e) => {
+                    debug!(
+                        error = %e,
+                        attempt = attempt + 1,
+                        "NAT probe task join failed"
+                    );
+                }
+            }
+        }
+
+        live_servers.sort_unstable();
+        live_servers.dedup();
+        let best_reflected = best_by_ip
+            .into_values()
+            .max_by_key(|(count, _)| *count)
+            .map(|(_, addr)| addr);
+
+        (live_servers, best_reflected)
+    }
+
     pub(super) fn translate_ip_for_nat(&self, ip: IpAddr) -> IpAddr {
         let nat_ip = self
             .nat_ip_cfg
@@ -128,39 +236,51 @@ impl MePool {
         }
 
         let attempt = self.nat_probe_attempts.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
-        let servers = if !self.nat_stun_servers.is_empty() {
+        let configured_servers = self.configured_stun_servers();
-            self.nat_stun_servers.clone()
+        let live_snapshot = self.nat_stun_live_servers.read().await.clone();
-        } else if let Some(s) = &self.nat_stun {
+        let primary_servers = if live_snapshot.is_empty() {
-            vec![s.clone()]
+            configured_servers.clone()
         } else {
-            vec!["stun.l.google.com:19302".to_string()]
+            live_snapshot
         };
 
-        for stun_addr in servers {
+        let (mut live_servers, mut selected_reflected) = self
-            match stun_probe_dual(&stun_addr).await {
+            .probe_stun_batch_for_family(&primary_servers, family, attempt)
-                Ok(res) => {
+            .await;
-                    let picked: Option<StunProbeResult> = match family {
+
-                        IpFamily::V4 => res.v4,
+        if selected_reflected.is_none() && !configured_servers.is_empty() && primary_servers != configured_servers {
-                        IpFamily::V6 => res.v6,
+            let (rediscovered_live, rediscovered_reflected) = self
-                    };
+                .probe_stun_batch_for_family(&configured_servers, family, attempt)
-                    if let Some(result) = picked {
+                .await;
-                        info!(local = %result.local_addr, reflected = %result.reflected_addr, family = ?family, stun = %stun_addr, "NAT probe: reflected address");
+            live_servers = rediscovered_live;
+            selected_reflected = rediscovered_reflected;
+        }
+
+        let live_server_count = live_servers.len();
+        if !live_servers.is_empty() {
+            *self.nat_stun_live_servers.write().await = live_servers;
+        } else {
+            self.nat_stun_live_servers.write().await.clear();
+        }
+
+        if let Some(reflected_addr) = selected_reflected {
             self.nat_probe_attempts.store(0, std::sync::atomic::Ordering::Relaxed);
+            info!(
+                family = ?family,
+                live_servers = live_server_count,
+                "STUN-Quorum reached, IP: {}",
+                reflected_addr.ip()
+            );
             if let Ok(mut cache) = self.nat_reflection_cache.try_lock() {
                 let slot = match family {
                     IpFamily::V4 => &mut cache.v4,
                     IpFamily::V6 => &mut cache.v6,
                 };
-                            *slot = Some((Instant::now(), result.reflected_addr));
+                *slot = Some((Instant::now(), reflected_addr));
-                        }
-                        return Some(result.reflected_addr);
-                    }
-                }
-                Err(e) => {
-                    warn!(error = %e, stun = %stun_addr, attempt = attempt + 1, "NAT probe failed, trying next server");
-                }
             }
+            return Some(reflected_addr);
         }
+
         let backoff = Duration::from_secs(60 * 2u64.pow((attempt as u32).min(6)));
         *self.stun_backoff_until.write().await = Some(Instant::now() + backoff);
         None

src/transport/middle_proxy/pool_refill.rs

@@ -0,0 +1,159 @@
+use std::collections::HashSet;
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::sync::atomic::Ordering;
+
+use tracing::{debug, info, warn};
+
+use crate::crypto::SecureRandom;
+
+use super::pool::MePool;
+
+impl MePool {
+    pub(super) async fn connect_endpoints_round_robin(
+        self: &Arc<Self>,
+        endpoints: &[SocketAddr],
+        rng: &SecureRandom,
+    ) -> bool {
+        if endpoints.is_empty() {
+            return false;
+        }
+        let start = (self.rr.fetch_add(1, Ordering::Relaxed) as usize) % endpoints.len();
+        for offset in 0..endpoints.len() {
+            let idx = (start + offset) % endpoints.len();
+            let addr = endpoints[idx];
+            match self.connect_one(addr, rng).await {
+                Ok(()) => return true,
+                Err(e) => debug!(%addr, error = %e, "ME connect failed during round-robin warmup"),
+            }
+        }
+        false
+    }
+
+    async fn endpoints_for_same_dc(&self, addr: SocketAddr) -> Vec<SocketAddr> {
+        let mut target_dc = HashSet::<i32>::new();
+        let mut endpoints = HashSet::<SocketAddr>::new();
+
+        if self.decision.ipv4_me {
+            let map = self.proxy_map_v4.read().await.clone();
+            for (dc, addrs) in &map {
+                if addrs
+                    .iter()
+                    .any(|(ip, port)| SocketAddr::new(*ip, *port) == addr)
+                {
+                    target_dc.insert(dc.abs());
+                }
+            }
+            for dc in &target_dc {
+                for key in [*dc, -*dc] {
+                    if let Some(addrs) = map.get(&key) {
+                        for (ip, port) in addrs {
+                            endpoints.insert(SocketAddr::new(*ip, *port));
+                        }
+                    }
+                }
+            }
+        }
+
+        if self.decision.ipv6_me {
+            let map = self.proxy_map_v6.read().await.clone();
+            for (dc, addrs) in &map {
+                if addrs
+                    .iter()
+                    .any(|(ip, port)| SocketAddr::new(*ip, *port) == addr)
+                {
+                    target_dc.insert(dc.abs());
+                }
+            }
+            for dc in &target_dc {
+                for key in [*dc, -*dc] {
+                    if let Some(addrs) = map.get(&key) {
+                        for (ip, port) in addrs {
+                            endpoints.insert(SocketAddr::new(*ip, *port));
+                        }
+                    }
+                }
+            }
+        }
+
+        let mut sorted: Vec<SocketAddr> = endpoints.into_iter().collect();
+        sorted.sort_unstable();
+        sorted
+    }
+
+    async fn refill_writer_after_loss(self: &Arc<Self>, addr: SocketAddr) -> bool {
+        let fast_retries = self.me_reconnect_fast_retry_count.max(1);
+
+        for attempt in 0..fast_retries {
+            self.stats.increment_me_reconnect_attempt();
+            match self.connect_one(addr, self.rng.as_ref()).await {
+                Ok(()) => {
+                    self.stats.increment_me_reconnect_success();
+                    self.stats.increment_me_writer_restored_same_endpoint_total();
+                    info!(
+                        %addr,
+                        attempt = attempt + 1,
+                        "ME writer restored on the same endpoint"
+                    );
+                    return true;
+                }
+                Err(e) => {
+                    debug!(
+                        %addr,
+                        attempt = attempt + 1,
+                        error = %e,
+                        "ME immediate same-endpoint reconnect failed"
+                    );
+                }
+            }
+        }
+
+        let dc_endpoints = self.endpoints_for_same_dc(addr).await;
+        if dc_endpoints.is_empty() {
+            self.stats.increment_me_refill_failed_total();
+            return false;
+        }
+
+        for attempt in 0..fast_retries {
+            self.stats.increment_me_reconnect_attempt();
+            if self
+                .connect_endpoints_round_robin(&dc_endpoints, self.rng.as_ref())
+                .await
+            {
+                self.stats.increment_me_reconnect_success();
+                self.stats.increment_me_writer_restored_fallback_total();
+                info!(
+                    %addr,
+                    attempt = attempt + 1,
+                    "ME writer restored via DC fallback endpoint"
+                );
+                return true;
+            }
+        }
+
+        self.stats.increment_me_refill_failed_total();
+        false
+    }
+
+    pub(crate) fn trigger_immediate_refill(self: &Arc<Self>, addr: SocketAddr) {
+        let pool = Arc::clone(self);
+        tokio::spawn(async move {
+            {
+                let mut guard = pool.refill_inflight.lock().await;
+                if !guard.insert(addr) {
+                    pool.stats.increment_me_refill_skipped_inflight_total();
+                    return;
+                }
+            }
+            pool.stats.increment_me_refill_triggered_total();
+
+            let restored = pool.refill_writer_after_loss(addr).await;
+            if !restored {
+                warn!(%addr, "ME immediate refill failed");
+            }
+
+            let mut guard = pool.refill_inflight.lock().await;
+            guard.remove(&addr);
+        });
+    }
+}

src/transport/middle_proxy/pool_reinit.rs

@@ -0,0 +1,383 @@
+use std::collections::{HashMap, HashSet};
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::sync::atomic::Ordering;
+use std::time::Duration;
+
+use rand::Rng;
+use rand::seq::SliceRandom;
+use tracing::{debug, info, warn};
+
+use crate::crypto::SecureRandom;
+
+use super::pool::MePool;
+
+impl MePool {
+    fn coverage_ratio(
+        desired_by_dc: &HashMap<i32, HashSet<SocketAddr>>,
+        active_writer_addrs: &HashSet<SocketAddr>,
+    ) -> (f32, Vec<i32>) {
+        if desired_by_dc.is_empty() {
+            return (1.0, Vec::new());
+        }
+
+        let mut missing_dc = Vec::<i32>::new();
+        let mut covered = 0usize;
+        for (dc, endpoints) in desired_by_dc {
+            if endpoints.is_empty() {
+                continue;
+            }
+            if endpoints
+                .iter()
+                .any(|addr| active_writer_addrs.contains(addr))
+            {
+                covered += 1;
+            } else {
+                missing_dc.push(*dc);
+            }
+        }
+
+        missing_dc.sort_unstable();
+        let total = desired_by_dc.len().max(1);
+        let ratio = (covered as f32) / (total as f32);
+        (ratio, missing_dc)
+    }
+
+    pub async fn reconcile_connections(self: &Arc<Self>, rng: &SecureRandom) {
+        let writers = self.writers.read().await;
+        let current: HashSet<SocketAddr> = writers
+            .iter()
+            .filter(|w| !w.draining.load(Ordering::Relaxed))
+            .map(|w| w.addr)
+            .collect();
+        drop(writers);
+
+        for family in self.family_order() {
+            let map = self.proxy_map_for_family(family).await;
+            for (_dc, addrs) in &map {
+                let dc_addrs: Vec<SocketAddr> = addrs
+                    .iter()
+                    .map(|(ip, port)| SocketAddr::new(*ip, *port))
+                    .collect();
+                if !dc_addrs.iter().any(|a| current.contains(a)) {
+                    let mut shuffled = dc_addrs.clone();
+                    shuffled.shuffle(&mut rand::rng());
+                    for addr in shuffled {
+                        if self.connect_one(addr, rng).await.is_ok() {
+                            break;
+                        }
+                    }
+                }
+            }
+            if !self.decision.effective_multipath && !current.is_empty() {
+                break;
+            }
+        }
+    }
+
+    async fn desired_dc_endpoints(&self) -> HashMap<i32, HashSet<SocketAddr>> {
+        let mut out: HashMap<i32, HashSet<SocketAddr>> = HashMap::new();
+
+        if self.decision.ipv4_me {
+            let map_v4 = self.proxy_map_v4.read().await.clone();
+            for (dc, addrs) in map_v4 {
+                let entry = out.entry(dc.abs()).or_default();
+                for (ip, port) in addrs {
+                    entry.insert(SocketAddr::new(ip, port));
+                }
+            }
+        }
+
+        if self.decision.ipv6_me {
+            let map_v6 = self.proxy_map_v6.read().await.clone();
+            for (dc, addrs) in map_v6 {
+                let entry = out.entry(dc.abs()).or_default();
+                for (ip, port) in addrs {
+                    entry.insert(SocketAddr::new(ip, port));
+                }
+            }
+        }
+
+        out
+    }
+
+    pub(super) fn required_writers_for_dc(endpoint_count: usize) -> usize {
+        endpoint_count.max(3)
+    }
+
+    fn hardswap_warmup_connect_delay_ms(&self) -> u64 {
+        let min_ms = self.me_hardswap_warmup_delay_min_ms.load(Ordering::Relaxed);
+        let max_ms = self.me_hardswap_warmup_delay_max_ms.load(Ordering::Relaxed);
+        let (min_ms, max_ms) = if min_ms <= max_ms {
+            (min_ms, max_ms)
+        } else {
+            (max_ms, min_ms)
+        };
+        if min_ms == max_ms {
+            return min_ms;
+        }
+        rand::rng().random_range(min_ms..=max_ms)
+    }
+
+    fn hardswap_warmup_backoff_ms(&self, pass_idx: usize) -> u64 {
+        let base_ms = self
+            .me_hardswap_warmup_pass_backoff_base_ms
+            .load(Ordering::Relaxed);
+        let cap_ms = (self.me_reconnect_backoff_cap.as_millis() as u64).max(base_ms);
+        let shift = (pass_idx as u32).min(20);
+        let scaled = base_ms.saturating_mul(1u64 << shift);
+        let core = scaled.min(cap_ms);
+        let jitter = (core / 2).max(1);
+        core.saturating_add(rand::rng().random_range(0..=jitter))
+    }
+
+    async fn fresh_writer_count_for_endpoints(
+        &self,
+        generation: u64,
+        endpoints: &HashSet<SocketAddr>,
+    ) -> usize {
+        let ws = self.writers.read().await;
+        ws.iter()
+            .filter(|w| !w.draining.load(Ordering::Relaxed))
+            .filter(|w| w.generation == generation)
+            .filter(|w| endpoints.contains(&w.addr))
+            .count()
+    }
+
+    pub(super) async fn active_writer_count_for_endpoints(
+        &self,
+        endpoints: &HashSet<SocketAddr>,
+    ) -> usize {
+        let ws = self.writers.read().await;
+        ws.iter()
+            .filter(|w| !w.draining.load(Ordering::Relaxed))
+            .filter(|w| endpoints.contains(&w.addr))
+            .count()
+    }
+
+    async fn warmup_generation_for_all_dcs(
+        self: &Arc<Self>,
+        rng: &SecureRandom,
+        generation: u64,
+        desired_by_dc: &HashMap<i32, HashSet<SocketAddr>>,
+    ) {
+        let extra_passes = self
+            .me_hardswap_warmup_extra_passes
+            .load(Ordering::Relaxed)
+            .min(10) as usize;
+        let total_passes = 1 + extra_passes;
+
+        for (dc, endpoints) in desired_by_dc {
+            if endpoints.is_empty() {
+                continue;
+            }
+
+            let mut endpoint_list: Vec<SocketAddr> = endpoints.iter().copied().collect();
+            endpoint_list.sort_unstable();
+            let required = Self::required_writers_for_dc(endpoint_list.len());
+            let mut completed = false;
+            let mut last_fresh_count = self
+                .fresh_writer_count_for_endpoints(generation, endpoints)
+                .await;
+
+            for pass_idx in 0..total_passes {
+                if last_fresh_count >= required {
+                    completed = true;
+                    break;
+                }
+
+                let missing = required.saturating_sub(last_fresh_count);
+                debug!(
+                    dc = *dc,
+                    pass = pass_idx + 1,
+                    total_passes,
+                    fresh_count = last_fresh_count,
+                    required,
+                    missing,
+                    endpoint_count = endpoint_list.len(),
+                    "ME hardswap warmup pass started"
+                );
+
+                for attempt_idx in 0..missing {
+                    let delay_ms = self.hardswap_warmup_connect_delay_ms();
+                    tokio::time::sleep(Duration::from_millis(delay_ms)).await;
+
+                    let connected = self.connect_endpoints_round_robin(&endpoint_list, rng).await;
+                    debug!(
+                        dc = *dc,
+                        pass = pass_idx + 1,
+                        total_passes,
+                        attempt = attempt_idx + 1,
+                        delay_ms,
+                        connected,
+                        "ME hardswap warmup connect attempt finished"
+                    );
+                }
+
+                last_fresh_count = self
+                    .fresh_writer_count_for_endpoints(generation, endpoints)
+                    .await;
+                if last_fresh_count >= required {
+                    completed = true;
+                    info!(
+                        dc = *dc,
+                        pass = pass_idx + 1,
+                        total_passes,
+                        fresh_count = last_fresh_count,
+                        required,
+                        "ME hardswap warmup floor reached for DC"
+                    );
+                    break;
+                }
+
+                if pass_idx + 1 < total_passes {
+                    let backoff_ms = self.hardswap_warmup_backoff_ms(pass_idx);
+                    debug!(
+                        dc = *dc,
+                        pass = pass_idx + 1,
+                        total_passes,
+                        fresh_count = last_fresh_count,
+                        required,
+                        backoff_ms,
+                        "ME hardswap warmup pass incomplete, delaying next pass"
+                    );
+                    tokio::time::sleep(Duration::from_millis(backoff_ms)).await;
+                }
+            }
+
+            if !completed {
+                warn!(
+                    dc = *dc,
+                    fresh_count = last_fresh_count,
+                    required,
+                    endpoint_count = endpoint_list.len(),
+                    total_passes,
+                    "ME warmup stopped: unable to reach required writer floor for DC"
+                );
+            }
+        }
+    }
+
+    pub async fn zero_downtime_reinit_after_map_change(self: &Arc<Self>, rng: &SecureRandom) {
+        let desired_by_dc = self.desired_dc_endpoints().await;
+        if desired_by_dc.is_empty() {
+            warn!("ME endpoint map is empty; skipping stale writer drain");
+            return;
+        }
+
+        let previous_generation = self.current_generation();
+        let generation = self.generation.fetch_add(1, Ordering::Relaxed) + 1;
+        let hardswap = self.hardswap.load(Ordering::Relaxed);
+
+        if hardswap {
+            self.warmup_generation_for_all_dcs(rng, generation, &desired_by_dc)
+                .await;
+        } else {
+            self.reconcile_connections(rng).await;
+        }
+
+        let writers = self.writers.read().await;
+        let active_writer_addrs: HashSet<SocketAddr> = writers
+            .iter()
+            .filter(|w| !w.draining.load(Ordering::Relaxed))
+            .map(|w| w.addr)
+            .collect();
+        let min_ratio = Self::permille_to_ratio(
+            self.me_pool_min_fresh_ratio_permille
+                .load(Ordering::Relaxed),
+        );
+        let (coverage_ratio, missing_dc) = Self::coverage_ratio(&desired_by_dc, &active_writer_addrs);
+        if !hardswap && coverage_ratio < min_ratio {
+            warn!(
+                previous_generation,
+                generation,
+                coverage_ratio = format_args!("{coverage_ratio:.3}"),
+                min_ratio = format_args!("{min_ratio:.3}"),
+                missing_dc = ?missing_dc,
+                "ME reinit coverage below threshold; keeping stale writers"
+            );
+            return;
+        }
+
+        if hardswap {
+            let mut fresh_missing_dc = Vec::<(i32, usize, usize)>::new();
+            for (dc, endpoints) in &desired_by_dc {
+                if endpoints.is_empty() {
+                    continue;
+                }
+                let required = Self::required_writers_for_dc(endpoints.len());
+                let fresh_count = writers
+                    .iter()
+                    .filter(|w| !w.draining.load(Ordering::Relaxed))
+                    .filter(|w| w.generation == generation)
+                    .filter(|w| endpoints.contains(&w.addr))
+                    .count();
+                if fresh_count < required {
+                    fresh_missing_dc.push((*dc, fresh_count, required));
+                }
+            }
+            if !fresh_missing_dc.is_empty() {
+                warn!(
+                    previous_generation,
+                    generation,
+                    missing_dc = ?fresh_missing_dc,
+                    "ME hardswap pending: fresh generation coverage incomplete"
+                );
+                return;
+            }
+        } else if !missing_dc.is_empty() {
+            warn!(
+                missing_dc = ?missing_dc,
+                // Keep stale writers alive when fresh coverage is incomplete.
+                "ME reinit coverage incomplete; keeping stale writers"
+            );
+            return;
+        }
+
+        let desired_addrs: HashSet<SocketAddr> = desired_by_dc
+            .values()
+            .flat_map(|set| set.iter().copied())
+            .collect();
+
+        let stale_writer_ids: Vec<u64> = writers
+            .iter()
+            .filter(|w| !w.draining.load(Ordering::Relaxed))
+            .filter(|w| {
+                if hardswap {
+                    w.generation < generation
+                } else {
+                    !desired_addrs.contains(&w.addr)
+                }
+            })
+            .map(|w| w.id)
+            .collect();
+        drop(writers);
+
+        if stale_writer_ids.is_empty() {
+            debug!("ME reinit cycle completed with no stale writers");
+            return;
+        }
+
+        let drain_timeout = self.force_close_timeout();
+        let drain_timeout_secs = drain_timeout.map(|d| d.as_secs()).unwrap_or(0);
+        info!(
+            stale_writers = stale_writer_ids.len(),
+            previous_generation,
+            generation,
+            hardswap,
+            coverage_ratio = format_args!("{coverage_ratio:.3}"),
+            min_ratio = format_args!("{min_ratio:.3}"),
+            drain_timeout_secs,
+            "ME reinit cycle covered; draining stale writers"
+        );
+        self.stats.increment_pool_swap_total();
+        for writer_id in stale_writer_ids {
+            self.mark_writer_draining_with_timeout(writer_id, drain_timeout, !hardswap)
+                .await;
+        }
+    }
+
+    pub async fn zero_downtime_reinit_periodic(self: &Arc<Self>, rng: &SecureRandom) {
+        self.zero_downtime_reinit_after_map_change(rng).await;
+    }
+}

src/transport/middle_proxy/pool_writer.rs

@@ -0,0 +1,366 @@
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
+use std::time::{Duration, Instant};
+
+use bytes::BytesMut;
+use rand::Rng;
+use tokio::sync::mpsc;
+use tokio_util::sync::CancellationToken;
+use tracing::{debug, info, warn};
+
+use crate::crypto::SecureRandom;
+use crate::error::{ProxyError, Result};
+use crate::protocol::constants::RPC_PING_U32;
+
+use super::codec::{RpcWriter, WriterCommand};
+use super::pool::{MePool, MeWriter};
+use super::reader::reader_loop;
+use super::registry::BoundConn;
+
+const ME_ACTIVE_PING_SECS: u64 = 25;
+const ME_ACTIVE_PING_JITTER_SECS: i64 = 5;
+const ME_IDLE_KEEPALIVE_MAX_SECS: u64 = 5;
+
+impl MePool {
+    pub(crate) async fn prune_closed_writers(self: &Arc<Self>) {
+        let closed_writer_ids: Vec<u64> = {
+            let ws = self.writers.read().await;
+            ws.iter().filter(|w| w.tx.is_closed()).map(|w| w.id).collect()
+        };
+        if closed_writer_ids.is_empty() {
+            return;
+        }
+
+        for writer_id in closed_writer_ids {
+            if self.registry.is_writer_empty(writer_id).await {
+                let _ = self.remove_writer_only(writer_id).await;
+            } else {
+                let _ = self.remove_writer_and_close_clients(writer_id).await;
+            }
+        }
+    }
+
+    pub(crate) async fn connect_one(self: &Arc<Self>, addr: SocketAddr, rng: &SecureRandom) -> Result<()> {
+        let secret_len = self.proxy_secret.read().await.len();
+        if secret_len < 32 {
+            return Err(ProxyError::Proxy("proxy-secret too short for ME auth".into()));
+        }
+
+        let (stream, _connect_ms) = self.connect_tcp(addr).await?;
+        let hs = self.handshake_only(stream, addr, rng).await?;
+
+        let writer_id = self.next_writer_id.fetch_add(1, Ordering::Relaxed);
+        let generation = self.current_generation();
+        let cancel = CancellationToken::new();
+        let degraded = Arc::new(AtomicBool::new(false));
+        let draining = Arc::new(AtomicBool::new(false));
+        let draining_started_at_epoch_secs = Arc::new(AtomicU64::new(0));
+        let allow_drain_fallback = Arc::new(AtomicBool::new(false));
+        let (tx, mut rx) = mpsc::channel::<WriterCommand>(4096);
+        let mut rpc_writer = RpcWriter {
+            writer: hs.wr,
+            key: hs.write_key,
+            iv: hs.write_iv,
+            seq_no: 0,
+            crc_mode: hs.crc_mode,
+        };
+        let cancel_wr = cancel.clone();
+        tokio::spawn(async move {
+            loop {
+                tokio::select! {
+                    cmd = rx.recv() => {
+                        match cmd {
+                            Some(WriterCommand::Data(payload)) => {
+                                if rpc_writer.send(&payload).await.is_err() { break; }
+                            }
+                            Some(WriterCommand::DataAndFlush(payload)) => {
+                                if rpc_writer.send_and_flush(&payload).await.is_err() { break; }
+                            }
+                            Some(WriterCommand::Close) | None => break,
+                        }
+                    }
+                    _ = cancel_wr.cancelled() => break,
+                }
+            }
+        });
+        let writer = MeWriter {
+            id: writer_id,
+            addr,
+            generation,
+            tx: tx.clone(),
+            cancel: cancel.clone(),
+            degraded: degraded.clone(),
+            draining: draining.clone(),
+            draining_started_at_epoch_secs: draining_started_at_epoch_secs.clone(),
+            allow_drain_fallback: allow_drain_fallback.clone(),
+        };
+        self.writers.write().await.push(writer.clone());
+        self.conn_count.fetch_add(1, Ordering::Relaxed);
+        self.writer_available.notify_one();
+
+        let reg = self.registry.clone();
+        let writers_arc = self.writers_arc();
+        let ping_tracker = self.ping_tracker.clone();
+        let ping_tracker_reader = ping_tracker.clone();
+        let rtt_stats = self.rtt_stats.clone();
+        let stats_reader = self.stats.clone();
+        let stats_ping = self.stats.clone();
+        let pool = Arc::downgrade(self);
+        let cancel_ping = cancel.clone();
+        let tx_ping = tx.clone();
+        let ping_tracker_ping = ping_tracker.clone();
+        let cleanup_done = Arc::new(AtomicBool::new(false));
+        let cleanup_for_reader = cleanup_done.clone();
+        let cleanup_for_ping = cleanup_done.clone();
+        let keepalive_enabled = self.me_keepalive_enabled;
+        let keepalive_interval = self.me_keepalive_interval;
+        let keepalive_jitter = self.me_keepalive_jitter;
+        let cancel_reader_token = cancel.clone();
+        let cancel_ping_token = cancel_ping.clone();
+
+        tokio::spawn(async move {
+            let res = reader_loop(
+                hs.rd,
+                hs.read_key,
+                hs.read_iv,
+                hs.crc_mode,
+                reg.clone(),
+                BytesMut::new(),
+                BytesMut::new(),
+                tx.clone(),
+                ping_tracker_reader,
+                rtt_stats.clone(),
+                stats_reader,
+                writer_id,
+                degraded.clone(),
+                cancel_reader_token.clone(),
+            )
+            .await;
+            if let Some(pool) = pool.upgrade()
+                && cleanup_for_reader
+                    .compare_exchange(false, true, Ordering::AcqRel, Ordering::Relaxed)
+                    .is_ok()
+            {
+                pool.remove_writer_and_close_clients(writer_id).await;
+            }
+            if let Err(e) = res {
+                warn!(error = %e, "ME reader ended");
+            }
+            let mut ws = writers_arc.write().await;
+            ws.retain(|w| w.id != writer_id);
+            info!(remaining = ws.len(), "Dead ME writer removed from pool");
+        });
+
+        let pool_ping = Arc::downgrade(self);
+        tokio::spawn(async move {
+            let mut ping_id: i64 = rand::random::<i64>();
+            let idle_interval_cap = Duration::from_secs(ME_IDLE_KEEPALIVE_MAX_SECS);
+            // Per-writer jittered start to avoid phase sync.
+            let startup_jitter = if keepalive_enabled {
+                let mut interval = keepalive_interval;
+                if let Some(pool) = pool_ping.upgrade() {
+                    if pool.registry.is_writer_empty(writer_id).await {
+                        interval = interval.min(idle_interval_cap);
+                    }
+                } else {
+                    return;
+                }
+                let jitter_cap_ms = interval.as_millis() / 2;
+                let effective_jitter_ms = keepalive_jitter.as_millis().min(jitter_cap_ms).max(1);
+                Duration::from_millis(rand::rng().random_range(0..=effective_jitter_ms as u64))
+            } else {
+                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;
+                Duration::from_secs(wait)
+            };
+            tokio::select! {
+                _ = cancel_ping_token.cancelled() => return,
+                _ = tokio::time::sleep(startup_jitter) => {}
+            }
+            loop {
+                let wait = if keepalive_enabled {
+                    let mut interval = keepalive_interval;
+                    if let Some(pool) = pool_ping.upgrade() {
+                        if pool.registry.is_writer_empty(writer_id).await {
+                            interval = interval.min(idle_interval_cap);
+                        }
+                    } else {
+                        break;
+                    }
+                    let jitter_cap_ms = interval.as_millis() / 2;
+                    let effective_jitter_ms = keepalive_jitter.as_millis().min(jitter_cap_ms).max(1);
+                    interval + Duration::from_millis(rand::rng().random_range(0..=effective_jitter_ms as u64))
+                } else {
+                    let jitter = rand::rng().random_range(-ME_ACTIVE_PING_JITTER_SECS..=ME_ACTIVE_PING_JITTER_SECS);
+                    let secs = (ME_ACTIVE_PING_SECS as i64 + jitter).max(5) as u64;
+                    Duration::from_secs(secs)
+                };
+                tokio::select! {
+                    _ = cancel_ping_token.cancelled() => {
+                        break;
+                    }
+                    _ = tokio::time::sleep(wait) => {}
+                }
+                let sent_id = ping_id;
+                let mut p = Vec::with_capacity(12);
+                p.extend_from_slice(&RPC_PING_U32.to_le_bytes());
+                p.extend_from_slice(&sent_id.to_le_bytes());
+                {
+                    let mut tracker = ping_tracker_ping.lock().await;
+                    let before = tracker.len();
+                    tracker.retain(|_, (ts, _)| ts.elapsed() < Duration::from_secs(120));
+                    let expired = before.saturating_sub(tracker.len());
+                    if expired > 0 {
+                        stats_ping.increment_me_keepalive_timeout_by(expired as u64);
+                    }
+                    tracker.insert(sent_id, (std::time::Instant::now(), writer_id));
+                }
+                ping_id = ping_id.wrapping_add(1);
+                stats_ping.increment_me_keepalive_sent();
+                if tx_ping.send(WriterCommand::DataAndFlush(p)).await.is_err() {
+                    stats_ping.increment_me_keepalive_failed();
+                    debug!("ME ping failed, removing dead writer");
+                    cancel_ping.cancel();
+                    if let Some(pool) = pool_ping.upgrade()
+                        && cleanup_for_ping
+                            .compare_exchange(false, true, Ordering::AcqRel, Ordering::Relaxed)
+                            .is_ok()
+                    {
+                        pool.remove_writer_and_close_clients(writer_id).await;
+                    }
+                    break;
+                }
+            }
+        });
+
+        Ok(())
+    }
+
+    pub(crate) async fn remove_writer_and_close_clients(self: &Arc<Self>, writer_id: u64) {
+        let conns = self.remove_writer_only(writer_id).await;
+        for bound in conns {
+            let _ = self.registry.route(bound.conn_id, super::MeResponse::Close).await;
+            let _ = self.registry.unregister(bound.conn_id).await;
+        }
+    }
+
+    async fn remove_writer_only(self: &Arc<Self>, writer_id: u64) -> Vec<BoundConn> {
+        let mut close_tx: Option<mpsc::Sender<WriterCommand>> = None;
+        let mut removed_addr: Option<SocketAddr> = None;
+        let mut trigger_refill = false;
+        {
+            let mut ws = self.writers.write().await;
+            if let Some(pos) = ws.iter().position(|w| w.id == writer_id) {
+                let w = ws.remove(pos);
+                let was_draining = w.draining.load(Ordering::Relaxed);
+                if was_draining {
+                    self.stats.decrement_pool_drain_active();
+                }
+                self.stats.increment_me_writer_removed_total();
+                w.cancel.cancel();
+                removed_addr = Some(w.addr);
+                trigger_refill = !was_draining;
+                if trigger_refill {
+                    self.stats.increment_me_writer_removed_unexpected_total();
+                }
+                close_tx = Some(w.tx.clone());
+                self.conn_count.fetch_sub(1, Ordering::Relaxed);
+            }
+        }
+        if let Some(tx) = close_tx {
+            let _ = tx.send(WriterCommand::Close).await;
+        }
+        if trigger_refill
+            && let Some(addr) = removed_addr
+        {
+            self.trigger_immediate_refill(addr);
+        }
+        self.rtt_stats.lock().await.remove(&writer_id);
+        self.registry.writer_lost(writer_id).await
+    }
+
+    pub(crate) async fn mark_writer_draining_with_timeout(
+        self: &Arc<Self>,
+        writer_id: u64,
+        timeout: Option<Duration>,
+        allow_drain_fallback: bool,
+    ) {
+        let timeout = timeout.filter(|d| !d.is_zero());
+        let found = {
+            let mut ws = self.writers.write().await;
+            if let Some(w) = ws.iter_mut().find(|w| w.id == writer_id) {
+                let already_draining = w.draining.swap(true, Ordering::Relaxed);
+                w.allow_drain_fallback
+                    .store(allow_drain_fallback, Ordering::Relaxed);
+                w.draining_started_at_epoch_secs
+                    .store(Self::now_epoch_secs(), Ordering::Relaxed);
+                if !already_draining {
+                    self.stats.increment_pool_drain_active();
+                }
+                w.draining.store(true, Ordering::Relaxed);
+                true
+            } else {
+                false
+            }
+        };
+
+        if !found {
+            return;
+        }
+
+        let timeout_secs = timeout.map(|d| d.as_secs()).unwrap_or(0);
+        debug!(
+            writer_id,
+            timeout_secs,
+            allow_drain_fallback,
+            "ME writer marked draining"
+        );
+
+        let pool = Arc::downgrade(self);
+        tokio::spawn(async move {
+            let deadline = timeout.map(|t| Instant::now() + t);
+            while let Some(p) = pool.upgrade() {
+                if let Some(deadline_at) = deadline
+                    && Instant::now() >= deadline_at
+                {
+                    warn!(writer_id, "Drain timeout, force-closing");
+                    p.stats.increment_pool_force_close_total();
+                    let _ = p.remove_writer_and_close_clients(writer_id).await;
+                    break;
+                }
+                if p.registry.is_writer_empty(writer_id).await {
+                    let _ = p.remove_writer_only(writer_id).await;
+                    break;
+                }
+                tokio::time::sleep(Duration::from_secs(1)).await;
+            }
+        });
+    }
+
+    pub(crate) async fn mark_writer_draining(self: &Arc<Self>, writer_id: u64) {
+        self.mark_writer_draining_with_timeout(writer_id, Some(Duration::from_secs(300)), false)
+            .await;
+    }
+
+    pub(super) fn writer_accepts_new_binding(&self, writer: &MeWriter) -> bool {
+        if !writer.draining.load(Ordering::Relaxed) {
+            return true;
+        }
+        if !writer.allow_drain_fallback.load(Ordering::Relaxed) {
+            return false;
+        }
+
+        let ttl_secs = self.me_pool_drain_ttl_secs.load(Ordering::Relaxed);
+        if ttl_secs == 0 {
+            return true;
+        }
+
+        let started = writer.draining_started_at_epoch_secs.load(Ordering::Relaxed);
+        if started == 0 {
+            return false;
+        }
+
+        Self::now_epoch_secs().saturating_sub(started) <= ttl_secs
+    }
+}

src/transport/proxy_protocol.rs

@@ -233,14 +233,12 @@ async fn parse_v2<R: AsyncRead + Unpin>(
 }
 
 /// Builder for PROXY protocol v1 header
-#[allow(dead_code)]
 pub struct ProxyProtocolV1Builder {
     family: &'static str,
     src_addr: Option<SocketAddr>,
     dst_addr: Option<SocketAddr>,
 }
 
-#[allow(dead_code)]
 impl ProxyProtocolV1Builder {
     pub fn new() -> Self {
         Self {
@@ -288,13 +286,17 @@ impl Default for ProxyProtocolV1Builder {
 }
 
 /// Builder for PROXY protocol v2 header
-#[allow(dead_code)]
 pub struct ProxyProtocolV2Builder {
     src: Option<SocketAddr>,
     dst: Option<SocketAddr>,
 }
 
-#[allow(dead_code)]
+impl Default for ProxyProtocolV2Builder {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl ProxyProtocolV2Builder {
     pub fn new() -> Self {
         Self { src: None, dst: None }