feat(tcp): add getter methods for TCP socket metrics (#3)

- Add remote_mss, remote_win_len, remote_win_scale getters
- Add rtt, rtt_var, rto, retransmits getters
- Add cwnd, ssthresh getters via congestion controller trait
- Add local_seq_no, remote_last_ack getters
- Implement cwnd and ssthresh for Cubic, Reno, and NoControl controllers

Signed-off-by: longjin <longjin@dragonos.org>

Author: fslongjin

src/socket/tcp.rs

@@ -683,6 +683,50 @@ impl<'a> Socket<'a> {
         self.nagle
     }
 
+    pub fn remote_mss(&self) -> usize {
+        self.remote_mss
+    }
+
+    pub fn remote_win_len(&self) -> usize {
+        self.remote_win_len
+    }
+
+    pub fn remote_win_scale(&self) -> Option<u8> {
+        self.remote_win_scale
+    }
+
+    pub fn rtt(&self) -> u32 {
+        self.rtte.rtt
+    }
+
+    pub fn rtt_var(&self) -> u32 {
+        self.rtte.deviation
+    }
+
+    pub fn rto(&self) -> Duration {
+        self.rtte.retransmission_timeout()
+    }
+
+    pub fn retransmits(&self) -> u8 {
+        self.rtte.rto_count
+    }
+
+    pub fn cwnd(&self) -> usize {
+        self.congestion_controller.cwnd()
+    }
+
+    pub fn ssthresh(&self) -> usize {
+        self.congestion_controller.ssthresh()
+    }
+
+    pub fn local_seq_no(&self) -> TcpSeqNumber {
+        self.local_seq_no
+    }
+
+    pub fn remote_last_ack(&self) -> Option<TcpSeqNumber> {
+        self.remote_last_ack
+    }
+
     /// Return the current window field value, including scaling according to RFC 1323.
     ///
     /// Used in internal calculations as well as packet generation.

src/socket/tcp/congestion.rs

@@ -30,6 +30,12 @@ pub(super) trait Controller {
 
     /// Set the maximum segment size.
     fn set_mss(&mut self, mss: usize) {}
+
+    /// Returns the current congestion window size.
+    fn cwnd(&self) -> usize;
+
+    /// Returns the current slow start threshold.
+    fn ssthresh(&self) -> usize;
 }
 
 #[derive(Debug)]
@@ -73,6 +79,16 @@ impl AnyController {
         AnyController::None(no_control::NoControl)
     }
 
+    #[inline]
+    pub fn cwnd(&self) -> usize {
+        self.inner().cwnd()
+    }
+
+    #[inline]
+    pub fn ssthresh(&self) -> usize {
+        self.inner().ssthresh()
+    }
+
     #[inline]
     pub fn inner_mut(&mut self) -> &mut dyn Controller {
         match self {

src/socket/tcp/congestion/cubic.rs

@@ -38,6 +38,14 @@ impl Controller for Cubic {
         self.cwnd
     }
 
+    fn cwnd(&self) -> usize {
+        self.cwnd
+    }
+
+    fn ssthresh(&self) -> usize {
+        self.ssthresh
+    }
+
     fn on_retransmit(&mut self, now: Instant) {
         self.w_max = self.cwnd;
         self.ssthresh = self.cwnd >> 1;

src/socket/tcp/congestion/no_control.rs

@@ -8,4 +8,12 @@ impl Controller for NoControl {
     fn window(&self) -> usize {
         usize::MAX
     }
+
+    fn cwnd(&self) -> usize {
+        0
+    }
+
+    fn ssthresh(&self) -> usize {
+        usize::MAX
+    }
 }

src/socket/tcp/congestion/reno.rs

@@ -47,6 +47,14 @@ impl Controller for Reno {
         self.ssthresh = (self.cwnd >> 1).max(self.min_cwnd);
     }
 
+    fn cwnd(&self) -> usize {
+        self.cwnd
+    }
+
+    fn ssthresh(&self) -> usize {
+        self.ssthresh
+    }
+
     fn on_retransmit(&mut self, _now: Instant) {
         self.cwnd = (self.cwnd >> 1).max(self.min_cwnd);
     }