Middle-End protocol hardening

- Secure framing / hot-path fix: enforced a single length + padding contract across the framing layer. Replaced legacy runtime `len % 4` recovery with strict validation to eliminate undefined behavior paths.

- ME RPC aligned with C reference contract: handshake now includes `flags + sender_pid + peer_pid`. Added negotiated CRC mode (CRC32 / CRC32C) and applied the negotiated mode consistently in read/write paths.

- Sequence fail-fast semantics: immediate connection termination on first sequence mismatch with dedicated counter increment.

- Keepalive reworked to RPC ping/pong: removed raw CBC keepalive frames. Introduced stale ping tracker with proper timeout accounting.

- Route/backpressure observability improvements: increased per-connection route queue to 4096. Added `RouteResult` with explicit failure reasons (NoConn, ChannelClosed, QueueFull) and per-reason counters.

- Direct-DC secure mode-gate relaxation: removed TLS/secure conflict in Direct-DC handshake path.

src/config/defaults.rs

@@ -37,7 +37,7 @@ pub(crate) fn default_replay_window_secs() -> u64 {
 }
 
 pub(crate) fn default_handshake_timeout() -> u64 {
-    30
+    15
 }
 
 pub(crate) fn default_connect_timeout() -> u64 {
@@ -52,11 +52,11 @@ pub(crate) fn default_ack_timeout() -> u64 {
     300
 }
 pub(crate) fn default_me_one_retry() -> u8 {
-    12
+    3
 }
 
 pub(crate) fn default_me_one_timeout() -> u64 {
-    1200
+    1500
 }
 
 pub(crate) fn default_listen_addr() -> String {
@@ -83,7 +83,7 @@ pub(crate) fn default_unknown_dc_log_path() -> Option<String> {
 }
 
 pub(crate) fn default_pool_size() -> usize {
-    16
+    2
 }
 
 pub(crate) fn default_keepalive_interval() -> u64 {
@@ -207,4 +207,4 @@ where
         }
     }
     Ok(out)
-}
+}

src/config/types.rs

@@ -118,7 +118,7 @@ impl Default for NetworkConfig {
     fn default() -> Self {
         Self {
             ipv4: true,
-            ipv6: Some(false),
+            ipv6: None,
             prefer: 4,
             multipath: false,
             stun_servers: default_stun_servers(),
@@ -140,7 +140,7 @@ pub struct GeneralConfig {
     #[serde(default = "default_true")]
     pub fast_mode: bool,
 
-    #[serde(default = "default_true")]
+    #[serde(default)]
     pub use_middle_proxy: bool,
 
     #[serde(default)]
@@ -157,7 +157,7 @@ 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 = "default_true")]
+    #[serde(default)]
     pub middle_proxy_nat_probe: bool,
 
     /// Optional STUN server address (host:port) for NAT probing.
@@ -283,15 +283,15 @@ impl Default for GeneralConfig {
             modes: ProxyModes::default(),
             prefer_ipv6: false,
             fast_mode: true,
-            use_middle_proxy: true,
+            use_middle_proxy: false,
             ad_tag: None,
             proxy_secret_path: None,
             middle_proxy_nat_ip: None,
-            middle_proxy_nat_probe: true,
+            middle_proxy_nat_probe: false,
             middle_proxy_nat_stun: None,
             middle_proxy_nat_stun_servers: Vec::new(),
             middle_proxy_pool_size: default_pool_size(),
-            middle_proxy_warm_standby: 8,
+            middle_proxy_warm_standby: 0,
             me_keepalive_enabled: true,
             me_keepalive_interval_secs: default_keepalive_interval(),
             me_keepalive_jitter_secs: default_keepalive_jitter(),
@@ -302,7 +302,7 @@ impl Default for GeneralConfig {
             me_reconnect_max_concurrent_per_dc: 1,
             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: 11,
+            me_reconnect_fast_retry_count: 1,
             stun_iface_mismatch_ignore: false,
             unknown_dc_log_path: default_unknown_dc_log_path(),
             log_level: LogLevel::Normal,
@@ -455,7 +455,7 @@ pub struct AntiCensorshipConfig {
     pub fake_cert_len: usize,
 
     /// Enable TLS certificate emulation using cached real certificates.
-    #[serde(default = "default_true")]
+    #[serde(default)]
     pub tls_emulation: bool,
 
     /// Directory to store TLS front cache (on disk).
@@ -489,7 +489,7 @@ impl Default for AntiCensorshipConfig {
             mask_port: default_mask_port(),
             mask_unix_sock: None,
             fake_cert_len: default_fake_cert_len(),
-            tls_emulation: true,
+            tls_emulation: false,
             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(),
@@ -619,9 +619,9 @@ pub struct ListenerConfig {
 /// - omitted                    — show no links (default)
 #[derive(Debug, Clone)]
 pub enum ShowLink {
-    /// Don't show any links.
+    /// Don't show any links (default when omitted).
     None,
-    /// Show links for all configured users (default).
+    /// Show links for all configured users.
     All,
     /// Show links for specific users.
     Specific(Vec<String>),
@@ -629,7 +629,7 @@ pub enum ShowLink {
 
 impl Default for ShowLink {
     fn default() -> Self {
-        ShowLink::All
+        ShowLink::None
     }
 }
 

src/crypto/hash.rs

@@ -55,6 +55,11 @@ pub fn crc32(data: &[u8]) -> u32 {
     crc32fast::hash(data)
 }
 
+/// CRC32C (Castagnoli)
+pub fn crc32c(data: &[u8]) -> u32 {
+    crc32c::crc32c(data)
+}
+
 /// Build the exact prekey buffer used by Telegram Middle Proxy KDF.
 ///
 /// Returned buffer layout (IPv4):

src/crypto/mod.rs

@@ -5,5 +5,8 @@ pub mod hash;
 pub mod random;
 
 pub use aes::{AesCtr, AesCbc};
-pub use hash::{sha256, sha256_hmac, sha1, md5, crc32, derive_middleproxy_keys, build_middleproxy_prekey};
+pub use hash::{
+    build_middleproxy_prekey, crc32, crc32c, derive_middleproxy_keys, md5, sha1, sha256,
+    sha256_hmac,
+};
 pub use random::SecureRandom;

src/metrics.rs

@@ -100,6 +100,14 @@ fn render_metrics(stats: &Stats) -> String {
     let _ = writeln!(out, "# TYPE telemt_me_keepalive_failed_total counter");
     let _ = writeln!(out, "telemt_me_keepalive_failed_total {}", stats.get_me_keepalive_failed());
 
+    let _ = writeln!(out, "# HELP telemt_me_keepalive_pong_total ME keepalive pong replies");
+    let _ = writeln!(out, "# TYPE telemt_me_keepalive_pong_total counter");
+    let _ = writeln!(out, "telemt_me_keepalive_pong_total {}", stats.get_me_keepalive_pong());
+
+    let _ = writeln!(out, "# HELP telemt_me_keepalive_timeout_total ME keepalive ping timeouts");
+    let _ = writeln!(out, "# TYPE telemt_me_keepalive_timeout_total counter");
+    let _ = writeln!(out, "telemt_me_keepalive_timeout_total {}", stats.get_me_keepalive_timeout());
+
     let _ = writeln!(out, "# HELP telemt_me_reconnect_attempts_total ME reconnect attempts");
     let _ = writeln!(out, "# TYPE telemt_me_reconnect_attempts_total counter");
     let _ = writeln!(out, "telemt_me_reconnect_attempts_total {}", stats.get_me_reconnect_attempts());
@@ -108,6 +116,30 @@ fn render_metrics(stats: &Stats) -> String {
     let _ = writeln!(out, "# TYPE telemt_me_reconnect_success_total counter");
     let _ = writeln!(out, "telemt_me_reconnect_success_total {}", stats.get_me_reconnect_success());
 
+    let _ = writeln!(out, "# HELP telemt_me_crc_mismatch_total ME CRC mismatches");
+    let _ = writeln!(out, "# TYPE telemt_me_crc_mismatch_total counter");
+    let _ = writeln!(out, "telemt_me_crc_mismatch_total {}", stats.get_me_crc_mismatch());
+
+    let _ = writeln!(out, "# HELP telemt_me_seq_mismatch_total ME sequence mismatches");
+    let _ = writeln!(out, "# TYPE telemt_me_seq_mismatch_total counter");
+    let _ = writeln!(out, "telemt_me_seq_mismatch_total {}", stats.get_me_seq_mismatch());
+
+    let _ = writeln!(out, "# HELP telemt_me_route_drop_no_conn_total ME route drops: no conn");
+    let _ = writeln!(out, "# TYPE telemt_me_route_drop_no_conn_total counter");
+    let _ = writeln!(out, "telemt_me_route_drop_no_conn_total {}", stats.get_me_route_drop_no_conn());
+
+    let _ = writeln!(out, "# HELP telemt_me_route_drop_channel_closed_total ME route drops: channel closed");
+    let _ = writeln!(out, "# TYPE telemt_me_route_drop_channel_closed_total counter");
+    let _ = writeln!(out, "telemt_me_route_drop_channel_closed_total {}", stats.get_me_route_drop_channel_closed());
+
+    let _ = writeln!(out, "# HELP telemt_me_route_drop_queue_full_total ME route drops: queue full");
+    let _ = writeln!(out, "# TYPE telemt_me_route_drop_queue_full_total counter");
+    let _ = writeln!(out, "telemt_me_route_drop_queue_full_total {}", stats.get_me_route_drop_queue_full());
+
+    let _ = writeln!(out, "# HELP telemt_secure_padding_invalid_total Invalid secure frame lengths");
+    let _ = writeln!(out, "# TYPE telemt_secure_padding_invalid_total counter");
+    let _ = writeln!(out, "telemt_secure_padding_invalid_total {}", stats.get_secure_padding_invalid());
+
     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");

src/protocol/constants.rs

@@ -156,17 +156,37 @@ pub const MAX_TLS_RECORD_SIZE: usize = 16384;
 /// RFC 8446 §5.2 allows up to 16384 + 256 bytes of ciphertext
 pub const MAX_TLS_CHUNK_SIZE: usize = 16384 + 256;
 
-/// Generate padding length for Secure Intermediate protocol.
-/// Total (data + padding) must not be divisible by 4 per MTProto spec.
-pub fn secure_padding_len(data_len: usize, rng: &SecureRandom) -> usize {
-    let rem = data_len % 4;
-    match rem {
-        0 => (rng.range(3) + 1) as usize,           // {1, 2, 3}
-        1 => rng.range(3) as usize,                 // {0, 1, 2}
-        2 => [0usize, 1, 3][rng.range(3) as usize], // {0, 1, 3}
-        3 => [0usize, 2, 3][rng.range(3) as usize], // {0, 2, 3}
-        _ => unreachable!(),
+/// Secure Intermediate payload is expected to be 4-byte aligned.
+pub fn is_valid_secure_payload_len(data_len: usize) -> bool {
+    data_len % 4 == 0
+}
+
+/// Compute Secure Intermediate payload length from wire length.
+///
+/// Returns `None` for invalid Secure lengths (e.g. divisible by 4).
+pub fn secure_payload_len_from_wire_len(wire_len: usize) -> Option<usize> {
+    if wire_len < 4 {
+        return None;
     }
+    let padding_len = wire_len % 4;
+    if padding_len == 0 || wire_len < padding_len {
+        return None;
+    }
+    let payload_len = wire_len - padding_len;
+    if !is_valid_secure_payload_len(payload_len) {
+        return None;
+    }
+    Some(payload_len)
+}
+
+/// Generate padding length for Secure Intermediate protocol.
+/// Data must be 4-byte aligned; padding is 1..=3 so total is never divisible by 4.
+pub fn secure_padding_len(data_len: usize, rng: &SecureRandom) -> usize {
+    debug_assert!(
+        is_valid_secure_payload_len(data_len),
+        "Secure payload must be 4-byte aligned, got {data_len}"
+    );
+    (rng.range(3) + 1) as usize
 }
 
 // ============= Timeouts =============
@@ -300,6 +320,10 @@ pub mod rpc_flags {
         pub const FLAG_ABRIDGED: u32      = 0x40000000;
         pub const FLAG_QUICKACK: u32      = 0x80000000;
     }
+
+    pub mod rpc_crypto_flags {
+        pub const USE_CRC32C: u32 = 0x800;
+    }
     
     pub const ME_CONNECT_TIMEOUT_SECS: u64 = 5;
     pub const ME_HANDSHAKE_TIMEOUT_SECS: u64 = 10;
@@ -339,7 +363,7 @@ mod tests {
     #[test]
     fn secure_padding_never_produces_aligned_total() {
         let rng = SecureRandom::new();
-        for data_len in 0..1000 {
+        for data_len in (0..1000).step_by(4) {
             for _ in 0..100 {
                 let padding = secure_padding_len(data_len, &rng);
                 assert!(
@@ -355,4 +379,22 @@ mod tests {
             }
         }
     }
+
+    #[test]
+    fn secure_wire_len_roundtrip_for_aligned_payload() {
+        for payload_len in (4..4096).step_by(4) {
+            for padding in 1..=3usize {
+                let wire_len = payload_len + padding;
+                let recovered = secure_payload_len_from_wire_len(wire_len);
+                assert_eq!(recovered, Some(payload_len));
+            }
+        }
+    }
+
+    #[test]
+    fn secure_wire_len_rejects_aligned_totals() {
+        for wire_len in (0..1024).step_by(4) {
+            assert_eq!(secure_payload_len_from_wire_len(wire_len), None);
+        }
+    }
 }

src/proxy/handshake.rs

@@ -253,7 +253,11 @@ where
 
         let mode_ok = match proto_tag {
             ProtoTag::Secure => {
-                if is_tls { config.general.modes.tls } else { config.general.modes.secure }
+                if is_tls {
+                    config.general.modes.tls || config.general.modes.secure
+                } else {
+                    config.general.modes.secure || config.general.modes.tls
+                }
             }
             ProtoTag::Intermediate | ProtoTag::Abridged => config.general.modes.classic,
         };

src/proxy/middle_relay.rs

@@ -165,6 +165,7 @@ where
             frame_limit,
             &user,
             &mut frame_counter,
+            &stats,
         ).await {
             Ok(Some((payload, quickack))) => {
                 trace!(conn_id, bytes = payload.len(), "C->ME frame");
@@ -238,6 +239,7 @@ async fn read_client_payload<R>(
     max_frame: usize,
     user: &str,
     frame_counter: &mut u64,
+    stats: &Stats,
 ) -> Result<Option<(Vec<u8>, bool)>>
 where
     R: AsyncRead + Unpin + Send + 'static,
@@ -326,18 +328,29 @@ where
             )));
         }
 
+        let secure_payload_len = if proto_tag == ProtoTag::Secure {
+            match secure_payload_len_from_wire_len(len) {
+                Some(payload_len) => payload_len,
+                None => {
+                    stats.increment_secure_padding_invalid();
+                    return Err(ProxyError::Proxy(format!(
+                        "Invalid secure frame length: {len}"
+                    )));
+                }
+            }
+        } else {
+            len
+        };
+
         let mut payload = vec![0u8; len];
         client_reader
             .read_exact(&mut payload)
             .await
             .map_err(ProxyError::Io)?;
 
-        // Secure Intermediate: remove random padding (last len%4 bytes)
+        // Secure Intermediate: strip validated trailing padding bytes.
         if proto_tag == ProtoTag::Secure {
-            let rem = len % 4;
-            if rem != 0 && payload.len() >= rem {
-                payload.truncate(len - rem);
-            }
+            payload.truncate(secure_payload_len);
         }
         *frame_counter += 1;
         return Ok(Some((payload, quickack)));
@@ -400,6 +413,12 @@ where
         }
         ProtoTag::Intermediate | ProtoTag::Secure => {
             let padding_len = if proto_tag == ProtoTag::Secure {
+                if !is_valid_secure_payload_len(data.len()) {
+                    return Err(ProxyError::Proxy(format!(
+                        "Secure payload must be 4-byte aligned, got {}",
+                        data.len()
+                    )));
+                }
                 secure_padding_len(data.len(), rng)
             } else {
                 0

src/stats/mod.rs

@@ -21,8 +21,16 @@ pub struct Stats {
     handshake_timeouts: AtomicU64,
     me_keepalive_sent: AtomicU64,
     me_keepalive_failed: AtomicU64,
+    me_keepalive_pong: AtomicU64,
+    me_keepalive_timeout: AtomicU64,
     me_reconnect_attempts: AtomicU64,
     me_reconnect_success: AtomicU64,
+    me_crc_mismatch: AtomicU64,
+    me_seq_mismatch: AtomicU64,
+    me_route_drop_no_conn: AtomicU64,
+    me_route_drop_channel_closed: AtomicU64,
+    me_route_drop_queue_full: AtomicU64,
+    secure_padding_invalid: AtomicU64,
     user_stats: DashMap<String, UserStats>,
     start_time: parking_lot::RwLock<Option<Instant>>,
 }
@@ -49,14 +57,45 @@ impl Stats {
     pub fn increment_handshake_timeouts(&self) { self.handshake_timeouts.fetch_add(1, Ordering::Relaxed); }
     pub fn increment_me_keepalive_sent(&self) { self.me_keepalive_sent.fetch_add(1, Ordering::Relaxed); }
     pub fn increment_me_keepalive_failed(&self) { self.me_keepalive_failed.fetch_add(1, Ordering::Relaxed); }
+    pub fn increment_me_keepalive_pong(&self) { self.me_keepalive_pong.fetch_add(1, Ordering::Relaxed); }
+    pub fn increment_me_keepalive_timeout(&self) { self.me_keepalive_timeout.fetch_add(1, Ordering::Relaxed); }
+    pub fn increment_me_keepalive_timeout_by(&self, value: u64) {
+        self.me_keepalive_timeout.fetch_add(value, Ordering::Relaxed);
+    }
     pub fn increment_me_reconnect_attempt(&self) { self.me_reconnect_attempts.fetch_add(1, Ordering::Relaxed); }
     pub fn increment_me_reconnect_success(&self) { self.me_reconnect_success.fetch_add(1, Ordering::Relaxed); }
+    pub fn increment_me_crc_mismatch(&self) { self.me_crc_mismatch.fetch_add(1, Ordering::Relaxed); }
+    pub fn increment_me_seq_mismatch(&self) { self.me_seq_mismatch.fetch_add(1, Ordering::Relaxed); }
+    pub fn increment_me_route_drop_no_conn(&self) { self.me_route_drop_no_conn.fetch_add(1, Ordering::Relaxed); }
+    pub fn increment_me_route_drop_channel_closed(&self) {
+        self.me_route_drop_channel_closed.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_me_route_drop_queue_full(&self) {
+        self.me_route_drop_queue_full.fetch_add(1, Ordering::Relaxed);
+    }
+    pub fn increment_secure_padding_invalid(&self) {
+        self.secure_padding_invalid.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) }
     pub fn get_me_keepalive_failed(&self) -> u64 { self.me_keepalive_failed.load(Ordering::Relaxed) }
+    pub fn get_me_keepalive_pong(&self) -> u64 { self.me_keepalive_pong.load(Ordering::Relaxed) }
+    pub fn get_me_keepalive_timeout(&self) -> u64 { self.me_keepalive_timeout.load(Ordering::Relaxed) }
     pub fn get_me_reconnect_attempts(&self) -> u64 { self.me_reconnect_attempts.load(Ordering::Relaxed) }
     pub fn get_me_reconnect_success(&self) -> u64 { self.me_reconnect_success.load(Ordering::Relaxed) }
+    pub fn get_me_crc_mismatch(&self) -> u64 { self.me_crc_mismatch.load(Ordering::Relaxed) }
+    pub fn get_me_seq_mismatch(&self) -> u64 { self.me_seq_mismatch.load(Ordering::Relaxed) }
+    pub fn get_me_route_drop_no_conn(&self) -> u64 { self.me_route_drop_no_conn.load(Ordering::Relaxed) }
+    pub fn get_me_route_drop_channel_closed(&self) -> u64 {
+        self.me_route_drop_channel_closed.load(Ordering::Relaxed)
+    }
+    pub fn get_me_route_drop_queue_full(&self) -> u64 {
+        self.me_route_drop_queue_full.load(Ordering::Relaxed)
+    }
+    pub fn get_secure_padding_invalid(&self) -> u64 {
+        self.secure_padding_invalid.load(Ordering::Relaxed)
+    }
     
     pub fn increment_user_connects(&self, user: &str) {
         self.user_stats.entry(user.to_string()).or_default()

src/stream/frame_codec.rs

@@ -8,7 +8,9 @@ use std::io::{self, Error, ErrorKind};
 use std::sync::Arc;
 use tokio_util::codec::{Decoder, Encoder};
 
-use crate::protocol::constants::{ProtoTag, secure_padding_len};
+use crate::protocol::constants::{
+    ProtoTag, is_valid_secure_payload_len, secure_padding_len, secure_payload_len_from_wire_len,
+};
 use crate::crypto::SecureRandom;
 use super::frame::{Frame, FrameMeta, FrameCodec as FrameCodecTrait};
 
@@ -274,13 +276,13 @@ fn decode_secure(src: &mut BytesMut, max_size: usize) -> io::Result<Option<Frame
         return Ok(None);
     }
     
-    // Calculate padding (indicated by length not divisible by 4)
-    let padding_len = len % 4;
-    let data_len = if padding_len != 0 {
-        len - padding_len
-    } else {
-        len
-    };
+    let data_len = secure_payload_len_from_wire_len(len).ok_or_else(|| {
+        Error::new(
+            ErrorKind::InvalidData,
+            format!("invalid secure frame length: {len}"),
+        )
+    })?;
+    let padding_len = len - data_len;
     
     meta.padding_len = padding_len as u8;
     
@@ -303,6 +305,13 @@ fn encode_secure(frame: &Frame, dst: &mut BytesMut, rng: &SecureRandom) -> io::R
         return Ok(());
     }
     
+    if !is_valid_secure_payload_len(data.len()) {
+        return Err(Error::new(
+            ErrorKind::InvalidData,
+            format!("secure payload must be 4-byte aligned, got {}", data.len()),
+        ));
+    }
+
     // Generate padding that keeps total length non-divisible by 4.
     let padding_len = secure_padding_len(data.len(), rng);
     

src/stream/frame_stream.rs

@@ -232,11 +232,13 @@ impl<R: AsyncRead + Unpin> SecureIntermediateFrameReader<R> {
         let mut data = vec![0u8; len];
         self.upstream.read_exact(&mut data).await?;
         
-        // Strip padding (not aligned to 4)
-        if len % 4 != 0 {
-            let actual_len = len - (len % 4);
-            data.truncate(actual_len);
-        }
+        let payload_len = secure_payload_len_from_wire_len(len).ok_or_else(|| {
+            Error::new(
+                ErrorKind::InvalidData,
+                format!("Invalid secure frame length: {len}"),
+            )
+        })?;
+        data.truncate(payload_len);
         
         Ok((Bytes::from(data), meta))
     }
@@ -267,6 +269,13 @@ impl<W: AsyncWrite + Unpin> SecureIntermediateFrameWriter<W> {
             return Ok(());
         }
         
+        if !is_valid_secure_payload_len(data.len()) {
+            return Err(Error::new(
+                ErrorKind::InvalidData,
+                format!("Secure payload must be 4-byte aligned, got {}", data.len()),
+            ));
+        }
+
         // Add padding so total length is never divisible by 4 (MTProto Secure)
         let padding_len = secure_padding_len(data.len(), &self.rng);
         let padding = self.rng.bytes(padding_len);
@@ -550,9 +559,7 @@ mod tests {
         writer.flush().await.unwrap();
         
         let (received, _meta) = reader.read_frame().await.unwrap();
-        // Received should have padding stripped to align to 4
-        let expected_len = (data.len() / 4) * 4;
-        assert_eq!(received.len(), expected_len);
+        assert_eq!(received.len(), data.len());
     }
     
     #[tokio::test]

src/transport/middle_proxy/codec.rs

@@ -1,6 +1,6 @@
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 
-use crate::crypto::{AesCbc, crc32};
+use crate::crypto::{AesCbc, crc32, crc32c};
 use crate::error::{ProxyError, Result};
 use crate::protocol::constants::*;
 
@@ -8,17 +8,46 @@ use crate::protocol::constants::*;
 pub(crate) enum WriterCommand {
     Data(Vec<u8>),
     DataAndFlush(Vec<u8>),
-    Keepalive,
     Close,
 }
 
-pub(crate) fn build_rpc_frame(seq_no: i32, payload: &[u8]) -> Vec<u8> {
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum RpcChecksumMode {
+    Crc32,
+    Crc32c,
+}
+
+impl RpcChecksumMode {
+    pub(crate) fn from_handshake_flags(flags: u32) -> Self {
+        if (flags & rpc_crypto_flags::USE_CRC32C) != 0 {
+            Self::Crc32c
+        } else {
+            Self::Crc32
+        }
+    }
+
+    pub(crate) fn advertised_flags(self) -> u32 {
+        match self {
+            Self::Crc32 => 0,
+            Self::Crc32c => rpc_crypto_flags::USE_CRC32C,
+        }
+    }
+}
+
+pub(crate) fn rpc_crc(mode: RpcChecksumMode, data: &[u8]) -> u32 {
+    match mode {
+        RpcChecksumMode::Crc32 => crc32(data),
+        RpcChecksumMode::Crc32c => crc32c(data),
+    }
+}
+
+pub(crate) fn build_rpc_frame(seq_no: i32, payload: &[u8], crc_mode: RpcChecksumMode) -> Vec<u8> {
     let total_len = (4 + 4 + payload.len() + 4) as u32;
     let mut frame = Vec::with_capacity(total_len as usize);
     frame.extend_from_slice(&total_len.to_le_bytes());
     frame.extend_from_slice(&seq_no.to_le_bytes());
     frame.extend_from_slice(payload);
-    let c = crc32(&frame);
+    let c = rpc_crc(crc_mode, &frame);
     frame.extend_from_slice(&c.to_le_bytes());
     frame
 }
@@ -45,7 +74,7 @@ pub(crate) async fn read_rpc_frame_plaintext(
 
     let crc_offset = total_len - 4;
     let expected_crc = u32::from_le_bytes(full[crc_offset..crc_offset + 4].try_into().unwrap());
-    let actual_crc = crc32(&full[..crc_offset]);
+    let actual_crc = rpc_crc(RpcChecksumMode::Crc32, &full[..crc_offset]);
     if expected_crc != actual_crc {
         return Err(ProxyError::InvalidHandshake(format!(
             "CRC mismatch: 0x{expected_crc:08x} vs 0x{actual_crc:08x}"
@@ -95,24 +124,52 @@ pub(crate) fn build_handshake_payload(
     our_port: u16,
     peer_ip: [u8; 4],
     peer_port: u16,
+    flags: u32,
 ) -> [u8; 32] {
     let mut p = [0u8; 32];
     p[0..4].copy_from_slice(&RPC_HANDSHAKE_U32.to_le_bytes());
+    p[4..8].copy_from_slice(&flags.to_le_bytes());
 
-    // Keep C memory layout compatibility for PID IPv4 bytes.
+    // process_id sender_pid
     p[8..12].copy_from_slice(&our_ip);
     p[12..14].copy_from_slice(&our_port.to_le_bytes());
-    let pid = (std::process::id() & 0xffff) as u16;
-    p[14..16].copy_from_slice(&pid.to_le_bytes());
+    p[14..16].copy_from_slice(&process_pid16().to_le_bytes());
+    p[16..20].copy_from_slice(&process_utime().to_le_bytes());
+
+    // process_id peer_pid
+    p[20..24].copy_from_slice(&peer_ip);
+    p[24..26].copy_from_slice(&peer_port.to_le_bytes());
+    p[26..28].copy_from_slice(&0u16.to_le_bytes());
+    p[28..32].copy_from_slice(&0u32.to_le_bytes());
+    p
+}
+
+pub(crate) fn parse_handshake_flags(payload: &[u8]) -> Result<u32> {
+    if payload.len() != 32 {
+        return Err(ProxyError::InvalidHandshake(format!(
+            "Bad handshake payload len: {}",
+            payload.len()
+        )));
+    }
+    let hs_type = u32::from_le_bytes(payload[0..4].try_into().unwrap());
+    if hs_type != RPC_HANDSHAKE_U32 {
+        return Err(ProxyError::InvalidHandshake(format!(
+            "Expected HANDSHAKE 0x{RPC_HANDSHAKE_U32:08x}, got 0x{hs_type:08x}"
+        )));
+    }
+    Ok(u32::from_le_bytes(payload[4..8].try_into().unwrap()))
+}
+
+fn process_pid16() -> u16 {
+    (std::process::id() & 0xffff) as u16
+}
+
+fn process_utime() -> u32 {
     let utime = std::time::SystemTime::now()
         .duration_since(std::time::UNIX_EPOCH)
         .unwrap_or_default()
         .as_secs() as u32;
-    p[16..20].copy_from_slice(&utime.to_le_bytes());
-
-    p[20..24].copy_from_slice(&peer_ip);
-    p[24..26].copy_from_slice(&peer_port.to_le_bytes());
-    p
+    utime
 }
 
 pub(crate) fn cbc_encrypt_padded(
@@ -160,11 +217,12 @@ pub(crate) struct RpcWriter {
     pub(crate) key: [u8; 32],
     pub(crate) iv: [u8; 16],
     pub(crate) seq_no: i32,
+    pub(crate) crc_mode: RpcChecksumMode,
 }
 
 impl RpcWriter {
     pub(crate) async fn send(&mut self, payload: &[u8]) -> Result<()> {
-        let frame = build_rpc_frame(self.seq_no, payload);
+        let frame = build_rpc_frame(self.seq_no, payload, self.crc_mode);
         self.seq_no += 1;
 
         let pad = (16 - (frame.len() % 16)) % 16;
@@ -189,27 +247,4 @@ impl RpcWriter {
         self.send(payload).await?;
         self.writer.flush().await.map_err(ProxyError::Io)
     }
-
-    /// Sends a 4-byte keepalive marker directly into the CBC stream.
-    /// This is not an RPC frame and must not consume sequence numbers.
-    pub(crate) async fn send_keepalive(&mut self) -> Result<()> {
-        let mut buf = [0u8; 16];
-        for i in 0..4 {
-            let start = i * 4;
-            let end = start + 4;
-            buf[start..end].copy_from_slice(&PADDING_FILLER);
-        }
-
-        let cipher = AesCbc::new(self.key, self.iv);
-        let mut v = buf.to_vec();
-        cipher
-            .encrypt_in_place(&mut v)
-            .map_err(|e| ProxyError::Crypto(format!("{e}")))?;
-
-        if v.len() >= 16 {
-            self.iv.copy_from_slice(&v[v.len() - 16..]);
-        }
-        self.writer.write_all(&v).await.map_err(ProxyError::Io)?;
-        self.writer.flush().await.map_err(ProxyError::Io)
-    }
 }

src/transport/middle_proxy/handshake.rs

@@ -18,13 +18,14 @@ use crate::crypto::{SecureRandom, build_middleproxy_prekey, derive_middleproxy_k
 use crate::error::{ProxyError, Result};
 use crate::network::IpFamily;
 use crate::protocol::constants::{
-    ME_CONNECT_TIMEOUT_SECS, ME_HANDSHAKE_TIMEOUT_SECS, RPC_CRYPTO_AES_U32, RPC_HANDSHAKE_ERROR_U32,
-    RPC_HANDSHAKE_U32, RPC_PING_U32, RPC_PONG_U32, RPC_NONCE_U32,
+    ME_CONNECT_TIMEOUT_SECS, ME_HANDSHAKE_TIMEOUT_SECS, RPC_CRYPTO_AES_U32,
+    RPC_HANDSHAKE_ERROR_U32, rpc_crypto_flags,
 };
 
 use super::codec::{
-    build_handshake_payload, build_nonce_payload, build_rpc_frame, cbc_decrypt_inplace,
-    cbc_encrypt_padded, parse_nonce_payload, read_rpc_frame_plaintext,
+    RpcChecksumMode, build_handshake_payload, build_nonce_payload, build_rpc_frame,
+    cbc_decrypt_inplace, cbc_encrypt_padded, parse_handshake_flags, parse_nonce_payload,
+    read_rpc_frame_plaintext, rpc_crc,
 };
 use super::wire::{extract_ip_material, IpMaterial};
 use super::MePool;
@@ -37,6 +38,7 @@ pub(crate) struct HandshakeOutput {
     pub read_iv: [u8; 16],
     pub write_key: [u8; 32],
     pub write_iv: [u8; 16],
+    pub crc_mode: RpcChecksumMode,
     pub handshake_ms: f64,
 }
 
@@ -146,7 +148,7 @@ impl MePool {
 
         let ks = self.key_selector().await;
         let nonce_payload = build_nonce_payload(ks, crypto_ts, &my_nonce);
-        let nonce_frame = build_rpc_frame(-2, &nonce_payload);
+        let nonce_frame = build_rpc_frame(-2, &nonce_payload, RpcChecksumMode::Crc32);
         let dump = hex_dump(&nonce_frame[..nonce_frame.len().min(44)]);
         debug!(
             key_selector = format_args!("0x{ks:08x}"),
@@ -284,8 +286,15 @@ impl MePool {
             srv_v6_opt.as_ref(),
         );
 
-        let hs_payload = build_handshake_payload(hs_our_ip, local_addr.port(), hs_peer_ip, peer_addr.port());
-        let hs_frame = build_rpc_frame(-1, &hs_payload);
+        let requested_crc_mode = RpcChecksumMode::Crc32c;
+        let hs_payload = build_handshake_payload(
+            hs_our_ip,
+            local_addr.port(),
+            hs_peer_ip,
+            peer_addr.port(),
+            requested_crc_mode.advertised_flags(),
+        );
+        let hs_frame = build_rpc_frame(-1, &hs_payload, RpcChecksumMode::Crc32);
         if diag_level >= 1 {
             info!(
                 write_key = %hex_dump(&wk),
@@ -314,7 +323,7 @@ impl MePool {
             );
         }
 
-        let (encrypted_hs, mut write_iv) = cbc_encrypt_padded(&wk, &wi, &hs_frame)?;
+        let (encrypted_hs, write_iv) = cbc_encrypt_padded(&wk, &wi, &hs_frame)?;
         if diag_level >= 1 {
             info!(
                 hs_cipher = %hex_dump(&encrypted_hs),
@@ -328,6 +337,7 @@ impl MePool {
         let mut enc_buf = BytesMut::with_capacity(256);
         let mut dec_buf = BytesMut::with_capacity(256);
         let mut read_iv = ri;
+        let mut negotiated_crc_mode = RpcChecksumMode::Crc32;
         let mut handshake_ok = false;
 
         while Instant::now() < deadline && !handshake_ok {
@@ -375,17 +385,23 @@ impl MePool {
                 let frame = dec_buf.split_to(fl);
                 let pe = fl - 4;
                 let ec = u32::from_le_bytes(frame[pe..pe + 4].try_into().unwrap());
-                let ac = crate::crypto::crc32(&frame[..pe]);
+                let ac = rpc_crc(RpcChecksumMode::Crc32, &frame[..pe]);
                 if ec != ac {
                     return Err(ProxyError::InvalidHandshake(format!(
                         "HS CRC mismatch: 0x{ec:08x} vs 0x{ac:08x}"
                     )));
                 }
 
-                let hs_type = u32::from_le_bytes(frame[8..12].try_into().unwrap());
+                let hs_payload = &frame[8..pe];
+                if hs_payload.len() < 4 {
+                    return Err(ProxyError::InvalidHandshake(
+                        "Handshake payload too short".to_string(),
+                    ));
+                }
+                let hs_type = u32::from_le_bytes(hs_payload[0..4].try_into().unwrap());
                 if hs_type == RPC_HANDSHAKE_ERROR_U32 {
-                    let err_code = if frame.len() >= 16 {
-                        i32::from_le_bytes(frame[12..16].try_into().unwrap())
+                    let err_code = if hs_payload.len() >= 8 {
+                        i32::from_le_bytes(hs_payload[4..8].try_into().unwrap())
                     } else {
                         -1
                     };
@@ -393,11 +409,21 @@ impl MePool {
                         "ME rejected handshake (error={err_code})"
                     )));
                 }
-                if hs_type != RPC_HANDSHAKE_U32 {
+                let hs_flags = parse_handshake_flags(hs_payload)?;
+                if hs_flags & 0xff != 0 {
                     return Err(ProxyError::InvalidHandshake(format!(
-                        "Expected HANDSHAKE 0x{RPC_HANDSHAKE_U32:08x}, got 0x{hs_type:08x}"
+                        "Unsupported handshake flags: 0x{hs_flags:08x}"
                     )));
                 }
+                negotiated_crc_mode = if (hs_flags & requested_crc_mode.advertised_flags()) != 0 {
+                    RpcChecksumMode::from_handshake_flags(hs_flags)
+                } else if (hs_flags & rpc_crypto_flags::USE_CRC32C) != 0 {
+                    return Err(ProxyError::InvalidHandshake(format!(
+                        "Peer negotiated unsupported CRC flags: 0x{hs_flags:08x}"
+                    )));
+                } else {
+                    RpcChecksumMode::Crc32
+                };
 
                 handshake_ok = true;
                 break;
@@ -418,6 +444,7 @@ impl MePool {
             read_iv,
             write_key: wk,
             write_iv,
+            crc_mode: negotiated_crc_mode,
             handshake_ms,
         })
     }

src/transport/middle_proxy/pool.rs

@@ -17,10 +17,9 @@ use crate::network::IpFamily;
 use crate::protocol::constants::*;
 
 use super::ConnRegistry;
-use super::registry::{BoundConn, ConnMeta};
+use super::registry::BoundConn;
 use super::codec::{RpcWriter, WriterCommand};
 use super::reader::reader_loop;
-use super::MeResponse;
 const ME_ACTIVE_PING_SECS: u64 = 25;
 const ME_ACTIVE_PING_JITTER_SECS: i64 = 5;
 
@@ -417,12 +416,12 @@ impl MePool {
         let draining = Arc::new(AtomicBool::new(false));
         let (tx, mut rx) = mpsc::channel::<WriterCommand>(4096);
         let tx_for_keepalive = tx.clone();
-        let stats = self.stats.clone();
         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 {
@@ -436,17 +435,6 @@ impl MePool {
                             Some(WriterCommand::DataAndFlush(payload)) => {
                                 if rpc_writer.send_and_flush(&payload).await.is_err() { break; }
                             }
-                            Some(WriterCommand::Keepalive) => {
-                                match rpc_writer.send_keepalive().await {
-                                    Ok(()) => {
-                                        stats.increment_me_keepalive_sent();
-                                    }
-                                    Err(_) => {
-                                        stats.increment_me_keepalive_failed();
-                                        break;
-                                    }
-                                }
-                            }
                             Some(WriterCommand::Close) | None => break,
                         }
                     }
@@ -469,7 +457,11 @@ impl MePool {
         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 stats_keepalive = self.stats.clone();
         let pool = Arc::downgrade(self);
         let cancel_ping = cancel.clone();
         let tx_ping = tx.clone();
@@ -489,12 +481,14 @@ impl MePool {
                 hs.rd,
                 hs.read_key,
                 hs.read_iv,
+                hs.crc_mode,
                 reg.clone(),
                 BytesMut::new(),
                 BytesMut::new(),
                 tx.clone(),
-                ping_tracker.clone(),
+                ping_tracker_reader,
                 rtt_stats.clone(),
+                stats_reader,
                 writer_id,
                 degraded.clone(),
                 cancel_reader_token.clone(),
@@ -535,7 +529,12 @@ impl MePool {
                 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);
@@ -558,18 +557,37 @@ impl MePool {
         if keepalive_enabled {
             let tx_keepalive = tx_for_keepalive;
             let cancel_keepalive = cancel_keepalive_token;
+            let ping_tracker_keepalive = ping_tracker.clone();
             tokio::spawn(async move {
                 // Per-writer jittered start to avoid phase sync.
                 let jitter_cap_ms = keepalive_interval.as_millis() / 2;
                 let effective_jitter_ms = keepalive_jitter.as_millis().min(jitter_cap_ms).max(1);
                 let initial_jitter_ms = rand::rng().random_range(0..=effective_jitter_ms as u64);
                 tokio::time::sleep(Duration::from_millis(initial_jitter_ms)).await;
+                let mut ping_id: i64 = rand::random::<i64>();
                 loop {
                     tokio::select! {
                         _ = cancel_keepalive.cancelled() => break,
                         _ = tokio::time::sleep(keepalive_interval + Duration::from_millis(rand::rng().random_range(0..=effective_jitter_ms as u64))) => {}
                     }
-                    if tx_keepalive.send(WriterCommand::Keepalive).await.is_err() {
+                    let sent_id = ping_id;
+                    ping_id = ping_id.wrapping_add(1);
+                    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_keepalive.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_keepalive.increment_me_keepalive_timeout_by(expired as u64);
+                        }
+                        tracker.insert(sent_id, (std::time::Instant::now(), writer_id));
+                    }
+                    stats_keepalive.increment_me_keepalive_sent();
+                    if tx_keepalive.send(WriterCommand::DataAndFlush(p)).await.is_err() {
+                        stats_keepalive.increment_me_keepalive_failed();
                         break;
                     }
                 }

src/transport/middle_proxy/reader.rs

@@ -10,30 +10,33 @@ use tokio::sync::{Mutex, mpsc};
 use tokio_util::sync::CancellationToken;
 use tracing::{debug, trace, warn};
 
-use crate::crypto::{AesCbc, crc32};
+use crate::crypto::AesCbc;
 use crate::error::{ProxyError, Result};
 use crate::protocol::constants::*;
+use crate::stats::Stats;
 
-use super::codec::WriterCommand;
+use super::codec::{RpcChecksumMode, WriterCommand, rpc_crc};
+use super::registry::RouteResult;
 use super::{ConnRegistry, MeResponse};
 
 pub(crate) async fn reader_loop(
     mut rd: tokio::io::ReadHalf<TcpStream>,
     dk: [u8; 32],
     mut div: [u8; 16],
+    crc_mode: RpcChecksumMode,
     reg: Arc<ConnRegistry>,
     enc_leftover: BytesMut,
     mut dec: BytesMut,
     tx: mpsc::Sender<WriterCommand>,
     ping_tracker: Arc<Mutex<HashMap<i64, (Instant, u64)>>>,
     rtt_stats: Arc<Mutex<HashMap<u64, (f64, f64)>>>,
+    stats: Arc<Stats>,
     _writer_id: u64,
     degraded: Arc<AtomicBool>,
     cancel: CancellationToken,
 ) -> Result<()> {
     let mut raw = enc_leftover;
     let mut expected_seq: i32 = 0;
-    let mut seq_mismatch = 0u32;
 
     loop {
         let mut tmp = [0u8; 16_384];
@@ -79,8 +82,9 @@ pub(crate) async fn reader_loop(
             let frame = dec.split_to(fl);
             let pe = fl - 4;
             let ec = u32::from_le_bytes(frame[pe..pe + 4].try_into().unwrap());
-            let actual_crc = crc32(&frame[..pe]);
+            let actual_crc = rpc_crc(crc_mode, &frame[..pe]);
             if actual_crc != ec {
+                stats.increment_me_crc_mismatch();
                 warn!(
                     frame_len = fl,
                     expected_crc = format_args!("0x{ec:08x}"),
@@ -92,15 +96,14 @@ pub(crate) async fn reader_loop(
 
             let seq_no = i32::from_le_bytes(frame[4..8].try_into().unwrap());
             if seq_no != expected_seq {
+                stats.increment_me_seq_mismatch();
                 warn!(seq_no, expected = expected_seq, "ME RPC seq mismatch");
-                seq_mismatch += 1;
-                if seq_mismatch > 10 {
-                    return Err(ProxyError::Proxy("Too many seq mismatches".into()));
-                }
-                expected_seq = seq_no.wrapping_add(1);
-            } else {
-                expected_seq = expected_seq.wrapping_add(1);
+                return Err(ProxyError::SeqNoMismatch {
+                    expected: expected_seq,
+                    got: seq_no,
+                });
             }
+            expected_seq = expected_seq.wrapping_add(1);
 
             let payload = &frame[8..pe];
             if payload.len() < 4 {
@@ -117,7 +120,13 @@ pub(crate) async fn reader_loop(
                 trace!(cid, flags, len = data.len(), "RPC_PROXY_ANS");
 
                 let routed = reg.route(cid, MeResponse::Data { flags, data }).await;
-                if !routed {
+                if !matches!(routed, RouteResult::Routed) {
+                    match routed {
+                        RouteResult::NoConn => stats.increment_me_route_drop_no_conn(),
+                        RouteResult::ChannelClosed => stats.increment_me_route_drop_channel_closed(),
+                        RouteResult::QueueFull => stats.increment_me_route_drop_queue_full(),
+                        RouteResult::Routed => {}
+                    }
                     reg.unregister(cid).await;
                     send_close_conn(&tx, cid).await;
                 }
@@ -127,7 +136,13 @@ pub(crate) async fn reader_loop(
                 trace!(cid, cfm, "RPC_SIMPLE_ACK");
 
                 let routed = reg.route(cid, MeResponse::Ack(cfm)).await;
-                if !routed {
+                if !matches!(routed, RouteResult::Routed) {
+                    match routed {
+                        RouteResult::NoConn => stats.increment_me_route_drop_no_conn(),
+                        RouteResult::ChannelClosed => stats.increment_me_route_drop_channel_closed(),
+                        RouteResult::QueueFull => stats.increment_me_route_drop_queue_full(),
+                        RouteResult::Routed => {}
+                    }
                     reg.unregister(cid).await;
                     send_close_conn(&tx, cid).await;
                 }
@@ -153,6 +168,7 @@ pub(crate) async fn reader_loop(
                 }
             } else if pt == RPC_PONG_U32 && body.len() >= 8 {
                 let ping_id = i64::from_le_bytes(body[0..8].try_into().unwrap());
+                stats.increment_me_keepalive_pong();
                 if let Some((sent, wid)) = {
                     let mut guard = ping_tracker.lock().await;
                     guard.remove(&ping_id)

src/transport/middle_proxy/registry.rs

@@ -1,13 +1,23 @@
 use std::collections::{HashMap, HashSet};
 use std::net::SocketAddr;
 use std::sync::atomic::{AtomicU64, Ordering};
-use std::sync::Arc;
 
-use tokio::sync::{mpsc, Mutex, RwLock};
+use tokio::sync::{mpsc, RwLock};
+use tokio::sync::mpsc::error::TrySendError;
 
 use super::codec::WriterCommand;
 use super::MeResponse;
 
+const ROUTE_CHANNEL_CAPACITY: usize = 4096;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum RouteResult {
+    Routed,
+    NoConn,
+    ChannelClosed,
+    QueueFull,
+}
+
 #[derive(Clone)]
 pub struct ConnMeta {
     pub target_dc: i16,
@@ -64,7 +74,7 @@ impl ConnRegistry {
 
     pub async fn register(&self) -> (u64, mpsc::Receiver<MeResponse>) {
         let id = self.next_id.fetch_add(1, Ordering::Relaxed);
-        let (tx, rx) = mpsc::channel(1024);
+        let (tx, rx) = mpsc::channel(ROUTE_CHANNEL_CAPACITY);
         self.inner.write().await.map.insert(id, tx);
         (id, rx)
     }
@@ -83,12 +93,16 @@ impl ConnRegistry {
         None
     }
 
-    pub async fn route(&self, id: u64, resp: MeResponse) -> bool {
+    pub async fn route(&self, id: u64, resp: MeResponse) -> RouteResult {
         let inner = self.inner.read().await;
         if let Some(tx) = inner.map.get(&id) {
-            tx.try_send(resp).is_ok()
+            match tx.try_send(resp) {
+                Ok(()) => RouteResult::Routed,
+                Err(TrySendError::Closed(_)) => RouteResult::ChannelClosed,
+                Err(TrySendError::Full(_)) => RouteResult::QueueFull,
+            }
         } else {
-            false
+            RouteResult::NoConn
         }
     }