Fix for beobachten path by #664

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

README.md

@@ -25,6 +25,7 @@ curl -fsSL https://raw.githubusercontent.com/telemt/telemt/main/install.sh | sh
 - [Quick Start Guide](docs/Quick_start/QUICK_START_GUIDE.en.md)
 - [Инструкция по быстрому запуску](docs/Quick_start/QUICK_START_GUIDE.ru.md)
 
+## Features
 Our implementation of **TLS-fronting** is one of the most deeply debugged, focused, advanced and *almost* **"behaviorally consistent to real"**:  we are confident we have it right - [see evidence on our validation and traces](docs/FAQ.en.md#recognizability-for-dpi-and-crawler)
 
 Our ***Middle-End Pool*** is fastest by design in standard scenarios, compared to other implementations of connecting to the Middle-End Proxy: non dramatically, but usual

README.ru.md

@@ -54,7 +54,6 @@ curl -fsSL https://raw.githubusercontent.com/telemt/telemt/main/install.sh | sh
 - [FAQ EN](docs/FAQ.en.md)
 
 ## Сборка
-
 ```bash
 # Клонируйте репозиторий
 git clone https://github.com/telemt/telemt 
@@ -63,7 +62,6 @@ cd telemt
 # Начните процесс сборки
 cargo build --release
 
-# Устройства с небольшим объёмом оперативной памяти (1 ГБ, например NanoPi Neo3 / Raspberry Pi Zero 2):
 # В текущем release-профиле используется lto = "fat" для максимальной оптимизации (см. Cargo.toml).
 # На системах с малым объёмом RAM (~1 ГБ) можно переопределить это значение на "thin".
 

config.toml

@@ -32,13 +32,13 @@ show = "*"
 port = 443
 # proxy_protocol = false           # Enable if behind HAProxy/nginx with PROXY protocol
 # metrics_port = 9090
-# metrics_listen = "0.0.0.0:9090"  # Listen address for metrics (overrides metrics_port)
-# metrics_whitelist = ["127.0.0.1", "::1", "0.0.0.0/0"]
+# metrics_listen = "127.0.0.1:9090" # Listen address for metrics (overrides metrics_port)
+# metrics_whitelist = ["127.0.0.1/32", "::1/128"]
 
 [server.api]
 enabled = true
-listen = "0.0.0.0:9091"
-whitelist = ["127.0.0.0/8"]
+listen = "127.0.0.1:9091"
+whitelist = ["127.0.0.1/32", "::1/128"]
 minimal_runtime_enabled = false
 minimal_runtime_cache_ttl_ms = 1000
 
@@ -48,9 +48,12 @@ ip = "0.0.0.0"
 
 # === Anti-Censorship & Masking ===
 [censorship]
+# Fake-TLS / SNI masking domain used in generated ee-links.
+# Changing tls_domain invalidates previously generated TLS links.
 tls_domain = "petrovich.ru"
+
 mask = true
-tls_emulation = true        # Fetch real cert lengths and emulate TLS records
+tls_emulation = true         # Fetch real cert lengths and emulate TLS records
 tls_front_dir = "tlsfront"   # Cache directory for TLS emulation
 
 [access.users]

docs/Architecture/API/API.md

@@ -9,12 +9,12 @@ API runtime is configured in `[server.api]`.
 
 | Field | Type | Default | Description |
 | --- | --- | --- | --- |
-| `enabled` | `bool` | `false` | Enables REST API listener. |
-| `listen` | `string` (`IP:PORT`) | `127.0.0.1:9091` | API bind address. |
-| `whitelist` | `CIDR[]` | `127.0.0.1/32, ::1/128` | Source IP allowlist. Empty list means allow all. |
+| `enabled` | `bool` | `true` | Enables REST API listener. |
+| `listen` | `string` (`IP:PORT`) | `0.0.0.0:9091` | API bind address. |
+| `whitelist` | `CIDR[]` | `127.0.0.0/8` | Source IP allowlist. Empty list means allow all. |
 | `auth_header` | `string` | `""` | Exact value for `Authorization` header. Empty disables header auth. |
 | `request_body_limit_bytes` | `usize` | `65536` | Maximum request body size. Must be `> 0`. |
-| `minimal_runtime_enabled` | `bool` | `false` | Enables runtime snapshot endpoints requiring ME pool read-lock aggregation. |
+| `minimal_runtime_enabled` | `bool` | `true` | Enables runtime snapshot endpoints requiring ME pool read-lock aggregation. |
 | `minimal_runtime_cache_ttl_ms` | `u64` | `1000` | Cache TTL for minimal snapshots. `0` disables cache; valid range is `[0, 60000]`. |
 | `runtime_edge_enabled` | `bool` | `false` | Enables runtime edge endpoints with cached aggregation payloads. |
 | `runtime_edge_cache_ttl_ms` | `u64` | `1000` | Cache TTL for runtime edge summary payloads. `0` disables cache. |

docs/Quick_start/OPENBSD_QUICK_START_GUIDE.en.md

@@ -27,7 +27,8 @@ cargo build --release
 ./target/release/telemt --version
 ```
 
-For low-RAM systems, this repository already uses `lto = "thin"` in release profile.
+For low-RAM systems, note that this repository currently uses `lto = "fat"` in release profile.  
+On constrained builders, a local override to `lto = "thin"` may be more practical.
 
 ## 3. Install binary and config
 

docs/Quick_start/QUICK_START_GUIDE.en.md

@@ -110,15 +110,15 @@ show = "*"
 # === Server Binding ===
 [server]
 port = 443
-# proxy_protocol = false           # Enable if behind HAProxy/nginx with PROXY protocol
+# proxy_protocol = false            # Enable if behind HAProxy/nginx with PROXY protocol
 # metrics_port = 9090
-# metrics_listen = "0.0.0.0:9090"  # Listen address for metrics (overrides metrics_port)
-# metrics_whitelist = ["127.0.0.1", "::1", "0.0.0.0/0"]
+# metrics_listen = "127.0.0.1:9090" # Listen address for metrics (overrides metrics_port)
+# metrics_whitelist = ["127.0.0.1/32", "::1/128"]
 
 [server.api]
 enabled = true
-listen = "0.0.0.0:9091"
-whitelist = ["127.0.0.0/8"]
+listen = "127.0.0.1:9091"
+whitelist = ["127.0.0.1/32", "::1/128"]
 minimal_runtime_enabled = false
 minimal_runtime_cache_ttl_ms = 1000
 
@@ -128,9 +128,9 @@ ip = "0.0.0.0"
 
 # === Anti-Censorship & Masking ===
 [censorship]
-tls_domain = "petrovich.ru"
+tls_domain = "petrovich.ru"  # Fake-TLS / SNI masking domain used in generated ee-links
 mask = true
-tls_emulation = true        # Fetch real cert lengths and emulate TLS records
+tls_emulation = true         # Fetch real cert lengths and emulate TLS records
 tls_front_dir = "tlsfront"   # Cache directory for TLS emulation
 
 [access.users]
@@ -141,9 +141,9 @@ hello = "00000000000000000000000000000000"
 then Ctrl+S -> Ctrl+X to save
 
 > [!WARNING]
-> Replace the value of the hello parameter with the value you obtained in step 0.  
-> Additionally, change the value of the tls_domain parameter to a different website.
-> Changing the tls_domain parameter will break all links that use the old domain!
+> Replace the value of the `hello` parameter with the value you obtained in step 0.  
+> Additionally, change the value of the `tls_domain` parameter to a different website.
+> Changing the `tls_domain` parameter will break all links that use the old domain!
 
 ---
 

docs/Quick_start/QUICK_START_GUIDE.ru.md

@@ -103,22 +103,22 @@ tls = true
 [general.links]
 show = "*"
 # show = ["alice", "bob"] # Показывать ссылки только для alice и bob
-# show = "*"              # Показывать ссылки для всех пользователей
-# public_host = "proxy.example.com"  # Хост (IP-адрес или домен) для ссылок tg://
-# public_port = 443                  # Порт для ссылок tg:// (по умолчанию: server.port)
+# show = "*"              # Показывать ссылки для всех пользователей
+# public_host = "proxy.example.com"  # Хост (IP-адрес или домен) для ссылок tg://
+# public_port = 443                  # Порт для ссылок tg:// (по умолчанию: server.port)
 
 # === Привязка сервера ===
 [server]
 port = 443
-# proxy_protocol = false           # Включите, если сервер находится за HAProxy/nginx с протоколом PROXY
+# proxy_protocol = false           # Включите, если сервер находится за HAProxy/nginx с протоколом PROXY
 # metrics_port = 9090
-# metrics_listen = "0.0.0.0:9090"  # Адрес прослушивания для метрик (переопределяет metrics_port)
-# metrics_whitelist = ["127.0.0.1", "::1", "0.0.0.0/0"]
+# metrics_listen = "127.0.0.1:9090"  # Адрес прослушивания для метрик (переопределяет metrics_port)
+# metrics_whitelist = ["127.0.0.1/32", "::1/128"]
 
 [server.api]
 enabled = true
-listen = "0.0.0.0:9091"
-whitelist = ["127.0.0.0/8"]
+listen = "127.0.0.1:9091"
+whitelist = ["127.0.0.1/32", "::1/128"]
 minimal_runtime_enabled = false
 minimal_runtime_cache_ttl_ms = 1000
 
@@ -128,9 +128,9 @@ ip = "0.0.0.0"
 
 # === Обход блокировок и маскировка ===
 [censorship]
-tls_domain = "petrovich.ru"
+tls_domain = "petrovich.ru"  # Домен Fake-TLS / SNI, который будет использоваться в сгенерированных ee-ссылках
 mask = true
-tls_emulation = true        # Получить реальную длину сертификата и эмулировать запись TLS
+tls_emulation = true         # Получить реальную длину сертификата и эмулировать запись TLS
 tls_front_dir = "tlsfront"   # Директория кэша для эмуляции TLS
 
 [access.users]
@@ -141,9 +141,9 @@ hello = "00000000000000000000000000000000"
 Затем нажмите Ctrl+S -> Ctrl+X, чтобы сохранить
 
 > [!WARNING]
-> Замените значение параметра hello на значение, которое вы получили в пункте 0.  
-> Так же замените значение параметра tls_domain на другой сайт.
-> Изменение параметра tls_domain сделает нерабочими все ссылки, использующие старый домен!
+> Замените значение параметра `hello` на значение, которое вы получили в пункте 0.  
+> Так же замените значение параметра `tls_domain` на другой сайт.
+> Изменение параметра `tls_domain` сделает нерабочими все ссылки, использующие старый домен!
 
 ---
 

src/api/mod.rs

@@ -1,6 +1,6 @@
 #![allow(clippy::too_many_arguments)]
 
-use std::convert::Infallible;
+use std::io::{Error as IoError, ErrorKind};
 use std::net::{IpAddr, SocketAddr};
 use std::path::PathBuf;
 use std::sync::Arc;
@@ -16,7 +16,7 @@ use tokio::net::TcpListener;
 use tokio::sync::{Mutex, RwLock, watch};
 use tracing::{debug, info, warn};
 
-use crate::config::ProxyConfig;
+use crate::config::{ApiGrayAction, ProxyConfig};
 use crate::ip_tracker::UserIpTracker;
 use crate::proxy::route_mode::RouteRuntimeController;
 use crate::startup::StartupTracker;
@@ -184,7 +184,9 @@ pub async fn serve(
                 .serve_connection(hyper_util::rt::TokioIo::new(stream), svc)
                 .await
             {
-                debug!(error = %error, "API connection error");
+                if !error.is_user() {
+                    debug!(error = %error, "API connection error");
+                }
             }
         });
     }
@@ -195,7 +197,7 @@ async fn handle(
     peer: SocketAddr,
     shared: Arc<ApiShared>,
     config_rx: watch::Receiver<Arc<ProxyConfig>>,
-) -> Result<Response<Full<Bytes>>, Infallible> {
+) -> Result<Response<Full<Bytes>>, IoError> {
     let request_id = shared.next_request_id();
     let cfg = config_rx.borrow().clone();
     let api_cfg = &cfg.server.api;
@@ -213,14 +215,27 @@ async fn handle(
 
     if !api_cfg.whitelist.is_empty() && !api_cfg.whitelist.iter().any(|net| net.contains(peer.ip()))
     {
-        return Ok(error_response(
-            request_id,
-            ApiFailure::new(
-                StatusCode::FORBIDDEN,
-                "forbidden",
-                "Source IP is not allowed",
+        return match api_cfg.gray_action {
+            ApiGrayAction::Api => Ok(error_response(
+                request_id,
+                ApiFailure::new(
+                    StatusCode::FORBIDDEN,
+                    "forbidden",
+                    "Source IP is not allowed",
+                ),
+            )),
+            ApiGrayAction::Ok200 => Ok(
+                Response::builder()
+                    .status(StatusCode::OK)
+                    .header("content-type", "text/html; charset=utf-8")
+                    .body(Full::new(Bytes::new()))
+                    .unwrap(),
             ),
-        ));
+            ApiGrayAction::Drop => Err(IoError::new(
+                ErrorKind::ConnectionAborted,
+                "api request dropped by gray_action=drop",
+            )),
+        };
     }
 
     if !api_cfg.auth_header.is_empty() {

src/config/hot_reload.rs

@@ -560,6 +560,7 @@ fn warn_non_hot_changes(old: &ProxyConfig, new: &ProxyConfig, non_hot_changed: b
     if old.server.api.enabled != new.server.api.enabled
         || old.server.api.listen != new.server.api.listen
         || old.server.api.whitelist != new.server.api.whitelist
+        || old.server.api.gray_action != new.server.api.gray_action
         || old.server.api.auth_header != new.server.api.auth_header
         || old.server.api.request_body_limit_bytes != new.server.api.request_body_limit_bytes
         || old.server.api.minimal_runtime_enabled != new.server.api.minimal_runtime_enabled

src/config/load.rs

@@ -340,12 +340,29 @@ impl ProxyConfig {
         let update_every_is_explicit = general_table
             .map(|table| table.contains_key("update_every"))
             .unwrap_or(false);
+        let beobachten_is_explicit = general_table
+            .map(|table| table.contains_key("beobachten"))
+            .unwrap_or(false);
+        let beobachten_minutes_is_explicit = general_table
+            .map(|table| table.contains_key("beobachten_minutes"))
+            .unwrap_or(false);
+        let beobachten_flush_secs_is_explicit = general_table
+            .map(|table| table.contains_key("beobachten_flush_secs"))
+            .unwrap_or(false);
+        let beobachten_file_is_explicit = general_table
+            .map(|table| table.contains_key("beobachten_file"))
+            .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 legacy_top_level_beobachten = parsed_toml.get("beobachten").cloned();
+        let legacy_top_level_beobachten_minutes = parsed_toml.get("beobachten_minutes").cloned();
+        let legacy_top_level_beobachten_flush_secs =
+            parsed_toml.get("beobachten_flush_secs").cloned();
+        let legacy_top_level_beobachten_file = parsed_toml.get("beobachten_file").cloned();
         let stun_servers_is_explicit = network_table
             .map(|table| table.contains_key("stun_servers"))
             .unwrap_or(false);
@@ -358,6 +375,63 @@ impl ProxyConfig {
             config.general.update_every = None;
         }
 
+        // Backward compatibility: legacy top-level beobachten* keys.
+        // Prefer `[general].*` when both are present.
+        let mut legacy_beobachten_applied = false;
+        if !beobachten_is_explicit
+            && let Some(value) = legacy_top_level_beobachten.as_ref()
+        {
+            let parsed = value.as_bool().ok_or_else(|| {
+                ProxyError::Config("beobachten (top-level) must be a boolean".to_string())
+            })?;
+            config.general.beobachten = parsed;
+            legacy_beobachten_applied = true;
+        }
+        if !beobachten_minutes_is_explicit
+            && let Some(value) = legacy_top_level_beobachten_minutes.as_ref()
+        {
+            let raw = value.as_integer().ok_or_else(|| {
+                ProxyError::Config("beobachten_minutes (top-level) must be an integer".to_string())
+            })?;
+            let parsed = u64::try_from(raw).map_err(|_| {
+                ProxyError::Config(
+                    "beobachten_minutes (top-level) must be within u64 range".to_string(),
+                )
+            })?;
+            config.general.beobachten_minutes = parsed;
+            legacy_beobachten_applied = true;
+        }
+        if !beobachten_flush_secs_is_explicit
+            && let Some(value) = legacy_top_level_beobachten_flush_secs.as_ref()
+        {
+            let raw = value.as_integer().ok_or_else(|| {
+                ProxyError::Config(
+                    "beobachten_flush_secs (top-level) must be an integer".to_string(),
+                )
+            })?;
+            let parsed = u64::try_from(raw).map_err(|_| {
+                ProxyError::Config(
+                    "beobachten_flush_secs (top-level) must be within u64 range".to_string(),
+                )
+            })?;
+            config.general.beobachten_flush_secs = parsed;
+            legacy_beobachten_applied = true;
+        }
+        if !beobachten_file_is_explicit
+            && let Some(value) = legacy_top_level_beobachten_file.as_ref()
+        {
+            let parsed = value.as_str().ok_or_else(|| {
+                ProxyError::Config("beobachten_file (top-level) must be a string".to_string())
+            })?;
+            config.general.beobachten_file = parsed.to_string();
+            legacy_beobachten_applied = true;
+        }
+        if legacy_beobachten_applied {
+            warn!(
+                "top-level beobachten* keys are deprecated; use general.beobachten* instead"
+            );
+        }
+
         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);
@@ -1289,6 +1363,7 @@ impl ProxyConfig {
                 upstream_type: UpstreamType::Direct {
                     interface: None,
                     bind_addresses: None,
+                    bindtodevice: None,
                 },
                 weight: 1,
                 enabled: true,
@@ -1385,6 +1460,21 @@ mod tests {
     const TEST_SHADOWSOCKS_URL: &str =
         "ss://2022-blake3-aes-256-gcm:MDEyMzQ1Njc4OTAxMjM0NTY3ODkwMTIzNDU2Nzg5MDE=@127.0.0.1:8388";
 
+    fn load_config_from_temp_toml(toml: &str) -> ProxyConfig {
+        let nonce = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap()
+            .as_nanos();
+        let dir = std::env::temp_dir().join(format!("telemt_load_cfg_{nonce}"));
+        std::fs::create_dir_all(&dir).unwrap();
+        let path = dir.join("config.toml");
+        std::fs::write(&path, toml).unwrap();
+        let cfg = ProxyConfig::load(&path).unwrap();
+        let _ = std::fs::remove_file(path);
+        let _ = std::fs::remove_dir(dir);
+        cfg
+    }
+
     #[test]
     fn serde_defaults_remain_unchanged_for_present_sections() {
         let toml = r#"
@@ -1481,6 +1571,7 @@ mod tests {
             cfg.general.rpc_proxy_req_every,
             default_rpc_proxy_req_every()
         );
+        assert_eq!(cfg.general.beobachten_file, default_beobachten_file());
         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());
@@ -1491,6 +1582,7 @@ mod tests {
         assert_eq!(cfg.censorship.unknown_sni_action, UnknownSniAction::Drop);
         assert_eq!(cfg.server.api.listen, default_api_listen());
         assert_eq!(cfg.server.api.whitelist, default_api_whitelist());
+        assert_eq!(cfg.server.api.gray_action, ApiGrayAction::Drop);
         assert_eq!(
             cfg.server.api.request_body_limit_bytes,
             default_api_request_body_limit_bytes()
@@ -1647,6 +1739,7 @@ mod tests {
             default_upstream_connect_failfast_hard_errors()
         );
         assert_eq!(general.rpc_proxy_req_every, default_rpc_proxy_req_every());
+        assert_eq!(general.beobachten_file, default_beobachten_file());
         assert_eq!(general.update_every, default_update_every());
 
         let server = ServerConfig::default();
@@ -1661,6 +1754,7 @@ mod tests {
         );
         assert_eq!(server.api.listen, default_api_listen());
         assert_eq!(server.api.whitelist, default_api_whitelist());
+        assert_eq!(server.api.gray_action, ApiGrayAction::Drop);
         assert_eq!(
             server.api.request_body_limit_bytes,
             default_api_request_body_limit_bytes()
@@ -1808,6 +1902,107 @@ mod tests {
         );
     }
 
+    #[test]
+    fn api_gray_action_parses_and_defaults_to_drop() {
+        let cfg_default: ProxyConfig = toml::from_str(
+            r#"
+            [server]
+            [general]
+            [network]
+            [access]
+            "#,
+        )
+        .unwrap();
+        assert_eq!(cfg_default.server.api.gray_action, ApiGrayAction::Drop);
+
+        let cfg_api: ProxyConfig = toml::from_str(
+            r#"
+            [server]
+            [general]
+            [network]
+            [access]
+            [server.api]
+            gray_action = "api"
+            "#,
+        )
+        .unwrap();
+        assert_eq!(cfg_api.server.api.gray_action, ApiGrayAction::Api);
+
+        let cfg_200: ProxyConfig = toml::from_str(
+            r#"
+            [server]
+            [general]
+            [network]
+            [access]
+            [server.api]
+            gray_action = "200"
+            "#,
+        )
+        .unwrap();
+        assert_eq!(cfg_200.server.api.gray_action, ApiGrayAction::Ok200);
+
+        let cfg_drop: ProxyConfig = toml::from_str(
+            r#"
+            [server]
+            [general]
+            [network]
+            [access]
+            [server.api]
+            gray_action = "drop"
+            "#,
+        )
+        .unwrap();
+        assert_eq!(cfg_drop.server.api.gray_action, ApiGrayAction::Drop);
+    }
+
+    #[test]
+    fn top_level_beobachten_keys_migrate_to_general_when_general_not_explicit() {
+        let cfg = load_config_from_temp_toml(
+            r#"
+            beobachten = false
+            beobachten_minutes = 7
+            beobachten_flush_secs = 3
+            beobachten_file = "tmp/legacy-beob.txt"
+
+            [server]
+            [general]
+            [network]
+            [access]
+            "#,
+        );
+
+        assert!(!cfg.general.beobachten);
+        assert_eq!(cfg.general.beobachten_minutes, 7);
+        assert_eq!(cfg.general.beobachten_flush_secs, 3);
+        assert_eq!(cfg.general.beobachten_file, "tmp/legacy-beob.txt");
+    }
+
+    #[test]
+    fn general_beobachten_keys_have_priority_over_legacy_top_level() {
+        let cfg = load_config_from_temp_toml(
+            r#"
+            beobachten = true
+            beobachten_minutes = 30
+            beobachten_flush_secs = 30
+            beobachten_file = "tmp/legacy-beob.txt"
+
+            [server]
+            [general]
+            beobachten = false
+            beobachten_minutes = 5
+            beobachten_flush_secs = 2
+            beobachten_file = "tmp/general-beob.txt"
+            [network]
+            [access]
+            "#,
+        );
+
+        assert!(!cfg.general.beobachten);
+        assert_eq!(cfg.general.beobachten_minutes, 5);
+        assert_eq!(cfg.general.beobachten_flush_secs, 2);
+        assert_eq!(cfg.general.beobachten_file, "tmp/general-beob.txt");
+    }
+
     #[test]
     fn dc_overrides_allow_string_and_array() {
         let toml = r#"

src/config/types.rs

@@ -1183,6 +1183,13 @@ pub struct ApiConfig {
     #[serde(default = "default_api_whitelist")]
     pub whitelist: Vec<IpNetwork>,
 
+    /// Behavior for requests from source IPs outside `whitelist`.
+    /// - `api`: return structured API forbidden response.
+    /// - `200`: return `200 OK` with an empty body.
+    /// - `drop`: close the connection without HTTP response.
+    #[serde(default)]
+    pub gray_action: ApiGrayAction,
+
     /// Optional static value for `Authorization` header validation.
     /// Empty string disables header auth.
     #[serde(default)]
@@ -1227,6 +1234,7 @@ impl Default for ApiConfig {
             enabled: default_true(),
             listen: default_api_listen(),
             whitelist: default_api_whitelist(),
+            gray_action: ApiGrayAction::default(),
             auth_header: String::new(),
             request_body_limit_bytes: default_api_request_body_limit_bytes(),
             minimal_runtime_enabled: default_api_minimal_runtime_enabled(),
@@ -1240,6 +1248,19 @@ impl Default for ApiConfig {
     }
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
+#[serde(rename_all = "lowercase")]
+pub enum ApiGrayAction {
+    /// Preserve current API behavior for denied source IPs.
+    Api,
+    /// Mimic a plain web endpoint by returning `200 OK` with an empty body.
+    #[serde(rename = "200")]
+    Ok200,
+    /// Drop connection without HTTP response for denied source IPs.
+    #[default]
+    Drop,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
 #[serde(rename_all = "lowercase")]
 pub enum ConntrackMode {
@@ -1856,6 +1877,10 @@ pub enum UpstreamType {
         interface: Option<String>,
         #[serde(default)]
         bind_addresses: Option<Vec<String>>,
+        /// Linux-only hard interface pinning via `SO_BINDTODEVICE`.
+        /// Optional alias: `force_bind`.
+        #[serde(default, alias = "force_bind")]
+        bindtodevice: Option<String>,
     },
     Socks4 {
         address: String,

src/maestro/mod.rs

@@ -81,23 +81,9 @@ pub async fn run() -> std::result::Result<(), Box<dyn std::error::Error>> {
     }
 }
 
-#[cfg(unix)]
-async fn run_inner(
-    daemon_opts: DaemonOptions,
-) -> std::result::Result<(), Box<dyn std::error::Error>> {
-    // Acquire PID file if daemonizing or if explicitly requested
-    // Keep it alive until shutdown (underscore prefix = intentionally kept for RAII cleanup)
-    let _pid_file = if daemon_opts.daemonize || daemon_opts.pid_file.is_some() {
-        let mut pf = PidFile::new(daemon_opts.pid_file_path());
-        if let Err(e) = pf.acquire() {
-            eprintln!("[telemt] {}", e);
-            std::process::exit(1);
-        }
-        Some(pf)
-    } else {
-        None
-    };
-
+// Shared maestro startup and main loop. `drop_after_bind` runs on Unix after listeners are bound
+// (for privilege drop); it is a no-op on other platforms.
+async fn run_telemt_core(drop_after_bind: impl FnOnce()) -> std::result::Result<(), Box<dyn std::error::Error>> {
     let process_started_at = Instant::now();
     let process_started_at_epoch_secs = SystemTime::now()
         .duration_since(UNIX_EPOCH)
@@ -761,17 +747,8 @@ async fn run_inner(
         std::process::exit(1);
     }
 
-    // Drop privileges after binding sockets (which may require root for port < 1024)
-    if daemon_opts.user.is_some() || daemon_opts.group.is_some() {
-        if let Err(e) = drop_privileges(
-            daemon_opts.user.as_deref(),
-            daemon_opts.group.as_deref(),
-            _pid_file.as_ref(),
-        ) {
-            error!(error = %e, "Failed to drop privileges");
-            std::process::exit(1);
-        }
-    }
+    // On Unix, caller supplies privilege drop after bind (may require root for port < 1024).
+    drop_after_bind();
 
     runtime_tasks::apply_runtime_log_filter(
         has_rust_log,
@@ -819,3 +796,43 @@ async fn run_inner(
 
     Ok(())
 }
+
+#[cfg(unix)]
+async fn run_inner(
+    daemon_opts: DaemonOptions,
+) -> std::result::Result<(), Box<dyn std::error::Error>> {
+    // Acquire PID file if daemonizing or if explicitly requested
+    // Keep it alive until shutdown (underscore prefix = intentionally kept for RAII cleanup)
+    let _pid_file = if daemon_opts.daemonize || daemon_opts.pid_file.is_some() {
+        let mut pf = PidFile::new(daemon_opts.pid_file_path());
+        if let Err(e) = pf.acquire() {
+            eprintln!("[telemt] {}", e);
+            std::process::exit(1);
+        }
+        Some(pf)
+    } else {
+        None
+    };
+
+    let user = daemon_opts.user.clone();
+    let group = daemon_opts.group.clone();
+
+    run_telemt_core(|| {
+        if user.is_some() || group.is_some() {
+            if let Err(e) = drop_privileges(
+                user.as_deref(),
+                group.as_deref(),
+                _pid_file.as_ref(),
+            ) {
+                error!(error = %e, "Failed to drop privileges");
+                std::process::exit(1);
+            }
+        }
+    })
+    .await
+}
+
+#[cfg(not(unix))]
+async fn run_inner() -> std::result::Result<(), Box<dyn std::error::Error>> {
+    run_telemt_core(|| {}).await
+}

src/network/probe.rs

@@ -97,6 +97,7 @@ pub async fn run_probe(
         let UpstreamType::Direct {
             interface,
             bind_addresses,
+            ..
         } = &upstream.upstream_type
         else {
             continue;

src/proxy/tests/client_masking_blackhat_campaign_tests.rs

@@ -31,6 +31,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_budget_security_tests.rs

@@ -27,6 +27,7 @@ fn build_harness(config: ProxyConfig) -> PipelineHarness {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_diagnostics_security_tests.rs

@@ -11,6 +11,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_fragmented_classifier_security_tests.rs

@@ -11,6 +11,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_hard_adversarial_tests.rs

@@ -25,6 +25,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_http2_fragmented_preface_security_tests.rs

@@ -11,6 +11,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_prefetch_config_pipeline_integration_security_tests.rs

@@ -11,6 +11,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_prefetch_invariant_security_tests.rs

@@ -38,6 +38,7 @@ fn build_harness(secret_hex: &str, mask_port: u16) -> PipelineHarness {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_probe_evasion_blackhat_tests.rs

@@ -16,6 +16,7 @@ fn make_test_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_redteam_expected_fail_tests.rs

@@ -39,6 +39,7 @@ fn build_harness(secret_hex: &str, mask_port: u16) -> RedTeamHarness {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -229,6 +230,7 @@ async fn redteam_03_masking_duration_must_be_less_than_1ms_when_backend_down() {
                 upstream_type: UpstreamType::Direct {
                     interface: None,
                     bind_addresses: None,
+                    bindtodevice: None,
                 },
                 weight: 1,
                 enabled: true,
@@ -470,6 +472,7 @@ async fn measure_invalid_probe_duration_ms(delay_ms: u64, tls_len: u16, body_sen
                 upstream_type: UpstreamType::Direct {
                     interface: None,
                     bind_addresses: None,
+                    bindtodevice: None,
                 },
                 weight: 1,
                 enabled: true,
@@ -544,6 +547,7 @@ async fn capture_forwarded_probe_len(tls_len: u16, body_sent: usize) -> usize {
                 upstream_type: UpstreamType::Direct {
                     interface: None,
                     bind_addresses: None,
+                    bindtodevice: None,
                 },
                 weight: 1,
                 enabled: true,

src/proxy/tests/client_masking_replay_timing_security_tests.rs

@@ -13,6 +13,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_shape_classifier_fuzz_redteam_expected_fail_tests.rs

@@ -11,6 +11,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_shape_hardening_adversarial_tests.rs

@@ -11,6 +11,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_shape_hardening_redteam_expected_fail_tests.rs

@@ -11,6 +11,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_shape_hardening_security_tests.rs

@@ -11,6 +11,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_masking_stress_adversarial_tests.rs

@@ -25,6 +25,7 @@ fn new_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_security_tests.rs

@@ -332,6 +332,7 @@ async fn relay_task_abort_releases_user_gate_and_ip_reservation() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -446,6 +447,7 @@ async fn relay_cutover_releases_user_gate_and_ip_reservation() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -570,6 +572,7 @@ async fn integration_route_cutover_and_quota_overlap_fails_closed_and_releases_s
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -740,6 +743,7 @@ async fn proxy_protocol_header_is_rejected_when_trust_list_is_empty() {
             upstream_type: crate::config::UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -817,6 +821,7 @@ async fn proxy_protocol_header_from_untrusted_peer_range_is_rejected_under_load(
                 upstream_type: crate::config::UpstreamType::Direct {
                     interface: None,
                     bind_addresses: None,
+                    bindtodevice: None,
                 },
                 weight: 1,
                 enabled: true,
@@ -977,6 +982,7 @@ async fn short_tls_probe_is_masked_through_client_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1065,6 +1071,7 @@ async fn tls12_record_probe_is_masked_through_client_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1151,6 +1158,7 @@ async fn handle_client_stream_increments_connects_all_exactly_once() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1244,6 +1252,7 @@ async fn running_client_handler_increments_connects_all_exactly_once() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1334,6 +1343,7 @@ async fn idle_pooled_connection_closes_cleanly_in_generic_stream_path() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1405,6 +1415,7 @@ async fn idle_pooled_connection_closes_cleanly_in_client_handler_path() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1491,6 +1502,7 @@ async fn partial_tls_header_stall_triggers_handshake_timeout() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1816,6 +1828,7 @@ async fn valid_tls_path_does_not_fall_back_to_mask_backend() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1925,6 +1938,7 @@ async fn valid_tls_with_invalid_mtproto_falls_back_to_mask_backend() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -2032,6 +2046,7 @@ async fn client_handler_tls_bad_mtproto_is_forwarded_to_mask_backend() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -2154,6 +2169,7 @@ async fn alpn_mismatch_tls_probe_is_masked_through_client_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -2247,6 +2263,7 @@ async fn invalid_hmac_tls_probe_is_masked_through_client_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -2346,6 +2363,7 @@ async fn burst_invalid_tls_probes_are_masked_verbatim() {
                 upstream_type: UpstreamType::Direct {
                     interface: None,
                     bind_addresses: None,
+                    bindtodevice: None,
                 },
                 weight: 1,
                 enabled: true,
@@ -3251,6 +3269,7 @@ async fn relay_connect_error_releases_user_and_ip_before_return() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -3812,6 +3831,7 @@ async fn untrusted_proxy_header_source_is_rejected() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -3882,6 +3902,7 @@ async fn empty_proxy_trusted_cidrs_rejects_proxy_header_by_default() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -3979,6 +4000,7 @@ async fn oversized_tls_record_is_masked_in_generic_stream_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -4082,6 +4104,7 @@ async fn oversized_tls_record_is_masked_in_client_handler_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -4199,6 +4222,7 @@ async fn tls_record_len_min_minus_1_is_rejected_in_generic_stream_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -4302,6 +4326,7 @@ async fn tls_record_len_min_minus_1_is_rejected_in_client_handler_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -4408,6 +4433,7 @@ async fn tls_record_len_16384_is_accepted_in_generic_stream_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -4509,6 +4535,7 @@ async fn tls_record_len_16384_is_accepted_in_client_handler_pipeline() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_timing_profile_adversarial_tests.rs

@@ -24,6 +24,7 @@ fn make_test_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_tls_clienthello_size_security_tests.rs

@@ -26,6 +26,7 @@ fn make_test_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_tls_clienthello_truncation_adversarial_tests.rs

@@ -27,6 +27,7 @@ fn make_test_upstream_manager(stats: Arc<Stats>) -> Arc<UpstreamManager> {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/client_tls_mtproto_fallback_security_tests.rs

@@ -41,6 +41,7 @@ fn build_harness(secret_hex: &str, mask_port: u16) -> PipelineHarness {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/proxy/tests/direct_relay_security_tests.rs

@@ -1293,6 +1293,7 @@ async fn direct_relay_abort_midflight_releases_route_gauge() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1400,6 +1401,7 @@ async fn direct_relay_cutover_midflight_releases_route_gauge() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1522,6 +1524,7 @@ async fn direct_relay_cutover_storm_multi_session_keeps_generic_errors_and_relea
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,
@@ -1758,6 +1761,7 @@ async fn negative_direct_relay_dc_connection_refused_fails_fast() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             selected_scope: String::new(),
         }],
@@ -1849,6 +1853,7 @@ async fn adversarial_direct_relay_cutover_integrity() {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             selected_scope: String::new(),
         }],

src/proxy/tests/proxy_shared_state_isolation_tests.rs

@@ -53,6 +53,7 @@ fn new_client_harness() -> ClientHarness {
             upstream_type: UpstreamType::Direct {
                 interface: None,
                 bind_addresses: None,
+                bindtodevice: None,
             },
             weight: 1,
             enabled: true,

src/transport/middle_proxy/ping.rs

@@ -67,6 +67,7 @@ pub fn format_sample_line(sample: &MePingSample) -> String {
 fn format_direct_with_config(
     interface: &Option<String>,
     bind_addresses: &Option<Vec<String>>,
+    bindtodevice: &Option<String>,
 ) -> Option<String> {
     let mut direct_parts: Vec<String> = Vec::new();
     if let Some(dev) = interface.as_deref().filter(|v| !v.is_empty()) {
@@ -75,6 +76,9 @@ fn format_direct_with_config(
     if let Some(src) = bind_addresses.as_ref().filter(|v| !v.is_empty()) {
         direct_parts.push(format!("src={}", src.join(",")));
     }
+    if let Some(device) = bindtodevice.as_deref().filter(|v| !v.is_empty()) {
+        direct_parts.push(format!("bindtodevice={device}"));
+    }
     if direct_parts.is_empty() {
         None
     } else {
@@ -231,8 +235,11 @@ pub async fn format_me_route(
             UpstreamType::Direct {
                 interface,
                 bind_addresses,
+                bindtodevice,
             } => {
-                if let Some(route) = format_direct_with_config(interface, bind_addresses) {
+                if let Some(route) =
+                    format_direct_with_config(interface, bind_addresses, bindtodevice)
+                {
                     route
                 } else {
                     detect_direct_route_details(reports, prefer_ipv6, v4_ok, v6_ok)

src/transport/socket.rs

@@ -158,6 +158,56 @@ pub fn create_outgoing_socket_bound(addr: SocketAddr, bind_addr: Option<IpAddr>)
     Ok(socket)
 }
 
+/// Pin an outgoing socket to a specific Linux network interface via SO_BINDTODEVICE.
+#[cfg(target_os = "linux")]
+pub fn bind_outgoing_socket_to_device(socket: &Socket, device: &str) -> Result<()> {
+    use std::io::{Error, ErrorKind};
+    use std::os::fd::AsRawFd;
+
+    let name = device.trim();
+    if name.is_empty() {
+        return Err(Error::new(
+            ErrorKind::InvalidInput,
+            "bindtodevice must not be empty",
+        ));
+    }
+
+    // The kernel expects an interface name buffer with a trailing NUL.
+    if name.len() >= libc::IFNAMSIZ {
+        return Err(Error::new(
+            ErrorKind::InvalidInput,
+            "bindtodevice exceeds IFNAMSIZ",
+        ));
+    }
+    let mut ifname = [0u8; libc::IFNAMSIZ];
+    ifname[..name.len()].copy_from_slice(name.as_bytes());
+
+    let rc = unsafe {
+        libc::setsockopt(
+            socket.as_raw_fd(),
+            libc::SOL_SOCKET,
+            libc::SO_BINDTODEVICE,
+            ifname.as_ptr().cast::<libc::c_void>(),
+            (name.len() + 1) as libc::socklen_t,
+        )
+    };
+    if rc != 0 {
+        return Err(Error::last_os_error());
+    }
+    debug!("Pinned outgoing socket to interface {}", name);
+    Ok(())
+}
+
+/// Stub for non-Linux targets where SO_BINDTODEVICE is unavailable.
+#[cfg(not(target_os = "linux"))]
+pub fn bind_outgoing_socket_to_device(_socket: &Socket, _device: &str) -> Result<()> {
+    use std::io::{Error, ErrorKind};
+    Err(Error::new(
+        ErrorKind::Unsupported,
+        "bindtodevice is supported only on Linux",
+    ))
+}
+
 /// Get local address of a socket
 #[allow(dead_code)]
 pub fn get_local_addr(stream: &TcpStream) -> Option<SocketAddr> {

src/transport/upstream.rs

@@ -26,7 +26,9 @@ use crate::stats::Stats;
 use crate::transport::shadowsocks::{
     ShadowsocksStream, connect_shadowsocks, sanitize_shadowsocks_url,
 };
-use crate::transport::socket::{create_outgoing_socket_bound, resolve_interface_ip};
+use crate::transport::socket::{
+    bind_outgoing_socket_to_device, create_outgoing_socket_bound, resolve_interface_ip,
+};
 use crate::transport::socks::{connect_socks4, connect_socks5};
 
 /// Number of Telegram datacenters
@@ -928,6 +930,7 @@ impl UpstreamManager {
             UpstreamType::Direct {
                 interface,
                 bind_addresses,
+                bindtodevice,
             } => {
                 let bind_ip = Self::resolve_bind_address(
                     interface,
@@ -943,6 +946,10 @@ impl UpstreamManager {
                 }
 
                 let socket = create_outgoing_socket_bound(target, bind_ip)?;
+                if let Some(device) = bindtodevice.as_deref().filter(|value| !value.is_empty()) {
+                    bind_outgoing_socket_to_device(&socket, device).map_err(ProxyError::Io)?;
+                    debug!(bindtodevice = %device, target = %target, "Pinned socket to interface");
+                }
                 if let Some(ip) = bind_ip {
                     debug!(bind = %ip, target = %target, "Bound outgoing socket");
                 } else if interface.is_some() || bind_addresses.is_some() {
@@ -1209,6 +1216,7 @@ impl UpstreamManager {
                 UpstreamType::Direct {
                     interface,
                     bind_addresses,
+                    bindtodevice,
                 } => {
                     let mut direct_parts = Vec::new();
                     if let Some(dev) = interface.as_deref().filter(|v| !v.is_empty()) {
@@ -1217,6 +1225,9 @@ impl UpstreamManager {
                     if let Some(src) = bind_addresses.as_ref().filter(|v| !v.is_empty()) {
                         direct_parts.push(format!("src={}", src.join(",")));
                     }
+                    if let Some(device) = bindtodevice.as_deref().filter(|v| !v.is_empty()) {
+                        direct_parts.push(format!("bindtodevice={device}"));
+                    }
                     if direct_parts.is_empty() {
                         "direct".to_string()
                     } else {