Move tokio_kcp to local files

Cargo.lock

@@ -100,14 +100,16 @@ dependencies = [
 name = "fourth"
 version = "0.1.2"
 dependencies = [
+ "byte_string",
+ "bytes 1.1.0",
  "futures",
+ "kcp",
  "log 0.4.14",
  "pretty_env_logger",
  "serde",
  "serde_yaml",
  "tls-parser",
  "tokio",
- "tokio_kcp",
 ]
 
 [[package]]
@@ -764,19 +766,6 @@ dependencies = [
  "syn",
 ]
 
-[[package]]
-name = "tokio_kcp"
-version = "0.8.0"
-source = "git+https://github.com/Matrix-Zhang/tokio_kcp?rev=d93a2f2#d93a2f2ad2cba731dce8490f0960246d2a655033"
-dependencies = [
- "byte_string",
- "bytes 1.1.0",
- "futures",
- "kcp",
- "log 0.4.14",
- "tokio",
-]
-
 [[package]]
 name = "unicode-xid"
 version = "0.2.2"

Cargo.toml

@@ -24,4 +24,7 @@ futures = "0.3"
 tls-parser = "0.11"
 
 tokio = { version = "1.0", features = ["full"] }
-tokio_kcp = { git = "https://github.com/Matrix-Zhang/tokio_kcp", rev="d93a2f2" }
+
+bytes = "1.1"
+kcp = "0.4"
+byte_string = "1"

README-EN.md

@@ -10,7 +10,7 @@ Fourth is a layer 4 proxy implemented by Rust to listen on specific ports and tr
 
 - Listen on specific port and proxy to local or remote port
 - SNI-based rule without terminating TLS connection
-- Allow TCP inbound
+- Allow KCP inbound(warning: untested)
 
 ## Installation
 
@@ -60,6 +60,10 @@ upstream:
 
 Built-in two upstreams: ban(terminate connection immediately), echo
 
+## Thanks
+
+- [tokio_kcp](https://github.com/Matrix-Zhang/tokio_kcp)
+
 ## License
 
 Fourth is available under terms of Apache-2.0.

README.md

@@ -12,7 +12,7 @@ Fourth是一个Rust实现的Layer 4代理，用于监听指定端口TCP/KCP流
 
 - 监听指定端口代理到本地或远端指定端口
 - 监听指定端口，通过TLS ClientHello消息中的SNI进行分流
-- 支持KCP入站
+- 支持KCP入站（警告：未测试）
 
 ## 安装方法
 
@@ -73,6 +73,10 @@ upstream:
 
 可能以后会为Linux高内核版本的用户提供可选的io_uring加速。
 
+## 感谢
+
+- [tokio_kcp](https://github.com/Matrix-Zhang/tokio_kcp)
+
 ## 协议
 
 Fourth以Apache-2.0协议开源。

src/main.rs

@@ -1,4 +1,5 @@
 mod config;
+mod plugins;
 mod servers;
 
 use crate::config::Config;

src/plugins/kcp/config.rs

@@ -0,0 +1,110 @@
+use std::{io::Write, time::Duration};
+
+use kcp::Kcp;
+
+/// Kcp Delay Config
+#[derive(Debug, Clone, Copy)]
+pub struct KcpNoDelayConfig {
+    /// Enable nodelay
+    pub nodelay: bool,
+    /// Internal update interval (ms)
+    pub interval: i32,
+    /// ACK number to enable fast resend
+    pub resend: i32,
+    /// Disable congetion control
+    pub nc: bool,
+}
+
+impl Default for KcpNoDelayConfig {
+    fn default() -> KcpNoDelayConfig {
+        KcpNoDelayConfig {
+            nodelay: false,
+            interval: 100,
+            resend: 0,
+            nc: false,
+        }
+    }
+}
+
+#[allow(unused)]
+impl KcpNoDelayConfig {
+    /// Get a fastest configuration
+    ///
+    /// 1. Enable NoDelay
+    /// 2. Set ticking interval to be 10ms
+    /// 3. Set fast resend to be 2
+    /// 4. Disable congestion control
+    pub fn fastest() -> KcpNoDelayConfig {
+        KcpNoDelayConfig {
+            nodelay: true,
+            interval: 10,
+            resend: 2,
+            nc: true,
+        }
+    }
+
+    /// Get a normal configuration
+    ///
+    /// 1. Disable NoDelay
+    /// 2. Set ticking interval to be 40ms
+    /// 3. Disable fast resend
+    /// 4. Enable congestion control
+    pub fn normal() -> KcpNoDelayConfig {
+        KcpNoDelayConfig {
+            nodelay: false,
+            interval: 40,
+            resend: 0,
+            nc: false,
+        }
+    }
+}
+
+/// Kcp Config
+#[derive(Debug, Clone, Copy)]
+pub struct KcpConfig {
+    /// Max Transmission Unit
+    pub mtu: usize,
+    /// nodelay
+    pub nodelay: KcpNoDelayConfig,
+    /// Send window size
+    pub wnd_size: (u16, u16),
+    /// Session expire duration, default is 90 seconds
+    pub session_expire: Duration,
+    /// Flush KCP state immediately after write
+    pub flush_write: bool,
+    /// Flush ACKs immediately after input
+    pub flush_acks_input: bool,
+    /// Stream mode
+    pub stream: bool,
+}
+
+impl Default for KcpConfig {
+    fn default() -> KcpConfig {
+        KcpConfig {
+            mtu: 1400,
+            nodelay: KcpNoDelayConfig::normal(),
+            wnd_size: (256, 256),
+            session_expire: Duration::from_secs(90),
+            flush_write: false,
+            flush_acks_input: false,
+            stream: true,
+        }
+    }
+}
+
+impl KcpConfig {
+    /// Applies config onto `Kcp`
+    #[doc(hidden)]
+    pub fn apply_config<W: Write>(&self, k: &mut Kcp<W>) {
+        k.set_mtu(self.mtu).expect("invalid MTU");
+
+        k.set_nodelay(
+            self.nodelay.nodelay,
+            self.nodelay.interval,
+            self.nodelay.resend,
+            self.nodelay.nc,
+        );
+
+        k.set_wndsize(self.wnd_size.0, self.wnd_size.1);
+    }
+}

src/plugins/kcp/listener.rs

@@ -0,0 +1,128 @@
+use std::{
+    io::{self, ErrorKind},
+    net::SocketAddr,
+    sync::Arc,
+    time::Duration,
+};
+
+use byte_string::ByteStr;
+use kcp::{Error as KcpError, KcpResult};
+use log::{debug, error, trace};
+use tokio::{
+    net::{ToSocketAddrs, UdpSocket},
+    sync::mpsc,
+    task::JoinHandle,
+    time,
+};
+
+use crate::plugins::kcp::{config::KcpConfig, session::KcpSessionManager, stream::KcpStream};
+
+#[allow(unused)]
+pub struct KcpListener {
+    udp: Arc<UdpSocket>,
+    accept_rx: mpsc::Receiver<(KcpStream, SocketAddr)>,
+    task_watcher: JoinHandle<()>,
+}
+
+impl Drop for KcpListener {
+    fn drop(&mut self) {
+        self.task_watcher.abort();
+    }
+}
+
+impl KcpListener {
+    pub async fn bind<A: ToSocketAddrs>(config: KcpConfig, addr: A) -> KcpResult<KcpListener> {
+        let udp = UdpSocket::bind(addr).await?;
+        let udp = Arc::new(udp);
+        let server_udp = udp.clone();
+
+        let (accept_tx, accept_rx) = mpsc::channel(1024 /* backlogs */);
+        let task_watcher = tokio::spawn(async move {
+            let (close_tx, mut close_rx) = mpsc::channel(64);
+
+            let mut sessions = KcpSessionManager::new();
+            let mut packet_buffer = [0u8; 65536];
+            loop {
+                tokio::select! {
+                    conv = close_rx.recv() => {
+                        let conv = conv.expect("close_tx closed unexpectly");
+                        sessions.close_conv(conv);
+                        trace!("session conv: {} removed", conv);
+                    }
+
+                    recv_res = udp.recv_from(&mut packet_buffer) => {
+                        match recv_res {
+                            Err(err) => {
+                                error!("udp.recv_from failed, error: {}", err);
+                                time::sleep(Duration::from_secs(1)).await;
+                            }
+                            Ok((n, peer_addr)) => {
+                                let packet = &mut packet_buffer[..n];
+
+                                log::trace!("received peer: {}, {:?}", peer_addr, ByteStr::new(packet));
+
+                                let mut conv = kcp::get_conv(packet);
+                                if conv == 0 {
+                                    // Allocate a conv for client.
+                                    conv = sessions.alloc_conv();
+                                    debug!("allocate {} conv for peer: {}", conv, peer_addr);
+
+                                    kcp::set_conv(packet, conv);
+                                }
+
+                                let session = match sessions.get_or_create(&config, conv, &udp, peer_addr, &close_tx) {
+                                    Ok((s, created)) => {
+                                        if created {
+                                            // Created a new session, constructed a new accepted client
+                                            let stream = KcpStream::with_session(s.clone());
+                                            if let Err(..) = accept_tx.try_send((stream, peer_addr)) {
+                                                debug!("failed to create accepted stream due to channel failure");
+
+                                                // remove it from session
+                                                sessions.close_conv(conv);
+                                                continue;
+                                            }
+                                        }
+
+                                        s
+                                    },
+                                    Err(err) => {
+                                        error!("failed to create session, error: {}, peer: {}, conv: {}", err, peer_addr, conv);
+                                        continue;
+                                    }
+                                };
+
+                                // let mut kcp = session.kcp_socket().lock().await;
+                                // if let Err(err) = kcp.input(packet) {
+                                //     error!("kcp.input failed, peer: {}, conv: {}, error: {}, packet: {:?}", peer_addr, conv, err, ByteStr::new(packet));
+                                // }
+                                session.input(packet).await;
+                            }
+                        }
+                    }
+                }
+            }
+        });
+
+        Ok(KcpListener {
+            udp: server_udp,
+            accept_rx,
+            task_watcher,
+        })
+    }
+
+    pub async fn accept(&mut self) -> KcpResult<(KcpStream, SocketAddr)> {
+        match self.accept_rx.recv().await {
+            Some(s) => Ok(s),
+            None => Err(KcpError::IoError(io::Error::new(
+                ErrorKind::Other,
+                "accept channel closed unexpectly",
+            ))),
+        }
+    }
+
+    #[allow(unused)]
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.udp.local_addr()
+    }
+}

src/plugins/kcp/mod.rs

@@ -0,0 +1,14 @@
+//! Library of KCP on Tokio
+
+pub use self::{
+    config::{KcpConfig, KcpNoDelayConfig},
+    listener::KcpListener,
+    stream::KcpStream,
+};
+
+mod config;
+mod listener;
+mod session;
+mod skcp;
+mod stream;
+mod utils;

src/plugins/kcp/session.rs

@@ -0,0 +1,256 @@
+use std::{
+    collections::{hash_map::Entry, HashMap},
+    net::SocketAddr,
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        Arc,
+    },
+    time::Duration,
+};
+
+use byte_string::ByteStr;
+use kcp::KcpResult;
+use log::{error, trace};
+use tokio::{
+    net::UdpSocket,
+    sync::{mpsc, Mutex},
+    time::{self, Instant},
+};
+
+use crate::plugins::kcp::{skcp::KcpSocket, KcpConfig};
+
+pub struct KcpSession {
+    socket: Mutex<KcpSocket>,
+    closed: AtomicBool,
+    session_expire: Duration,
+    session_close_notifier: Option<mpsc::Sender<u32>>,
+    input_tx: mpsc::Sender<Vec<u8>>,
+}
+
+impl KcpSession {
+    fn new(
+        socket: KcpSocket,
+        session_expire: Duration,
+        session_close_notifier: Option<mpsc::Sender<u32>>,
+        input_tx: mpsc::Sender<Vec<u8>>,
+    ) -> KcpSession {
+        KcpSession {
+            socket: Mutex::new(socket),
+            closed: AtomicBool::new(false),
+            session_expire,
+            session_close_notifier,
+            input_tx,
+        }
+    }
+
+    pub fn new_shared(
+        socket: KcpSocket,
+        session_expire: Duration,
+        session_close_notifier: Option<mpsc::Sender<u32>>,
+    ) -> Arc<KcpSession> {
+        let is_client = session_close_notifier.is_none();
+
+        let (input_tx, mut input_rx) = mpsc::channel(64);
+
+        let udp_socket = socket.udp_socket().clone();
+
+        let session = Arc::new(KcpSession::new(
+            socket,
+            session_expire,
+            session_close_notifier,
+            input_tx,
+        ));
+
+        {
+            let session = session.clone();
+            tokio::spawn(async move {
+                let mut input_buffer = [0u8; 65536];
+                let update_timer = time::sleep(Duration::from_millis(10));
+                tokio::pin!(update_timer);
+
+                loop {
+                    tokio::select! {
+                        // recv() then input()
+                        // Drives the KCP machine forward
+                        recv_result = udp_socket.recv(&mut input_buffer), if is_client => {
+                            match recv_result {
+                                Err(err) => {
+                                    error!("[SESSION] UDP recv failed, error: {}", err);
+                                }
+                                Ok(n) => {
+                                    let input_buffer = &input_buffer[..n];
+                                    trace!("[SESSION] UDP recv {} bytes, going to input {:?}", n, ByteStr::new(input_buffer));
+
+                                    let mut socket = session.socket.lock().await;
+
+                                    match socket.input(input_buffer) {
+                                        Ok(true) => {
+                                            trace!("[SESSION] UDP input {} bytes and waked sender/receiver", n);
+                                        }
+                                        Ok(false) => {}
+                                        Err(err) => {
+                                            error!("[SESSION] UDP input {} bytes error: {}, input buffer {:?}", n, err, ByteStr::new(input_buffer));
+                                        }
+                                    }
+                                }
+                            }
+                        }
+
+                        // bytes received from listener socket
+                        input_opt = input_rx.recv() => {
+                            if let Some(input_buffer) = input_opt {
+                                let mut socket = session.socket.lock().await;
+                                match socket.input(&input_buffer) {
+                                    Ok(..) => {
+                                        trace!("[SESSION] UDP input {} bytes from channel {:?}", input_buffer.len(), ByteStr::new(&input_buffer));
+                                    }
+                                    Err(err) => {
+                                        error!("[SESSION] UDP input {} bytes from channel failed, error: {}, input buffer {:?}",
+                                               input_buffer.len(), err, ByteStr::new(&input_buffer));
+                                    }
+                                }
+                            }
+                        }
+
+                        // Call update() in period
+                        _ = &mut update_timer => {
+                            let mut socket = session.socket.lock().await;
+
+                            let is_closed = session.closed.load(Ordering::Acquire);
+                            if is_closed && socket.can_close() {
+                                trace!("[SESSION] KCP session closed");
+                                break;
+                            }
+
+                            // server socket expires
+                            if !is_client {
+                                // If this is a server stream, close it automatically after a period of time
+                                let last_update_time = socket.last_update_time();
+                                let elapsed = last_update_time.elapsed();
+
+                                if elapsed > session.session_expire {
+                                    if elapsed > session.session_expire * 2 {
+                                        // Force close. Client may have already gone.
+                                        trace!(
+                                            "[SESSION] force close inactive session, conv: {}, last_update: {}s ago",
+                                            socket.conv(),
+                                            elapsed.as_secs()
+                                        );
+                                        break;
+                                    }
+
+                                    if !is_closed {
+                                        trace!(
+                                            "[SESSION] closing inactive session, conv: {}, last_update: {}s ago",
+                                            socket.conv(),
+                                            elapsed.as_secs()
+                                        );
+                                        session.closed.store(true, Ordering::Release);
+                                    }
+                                }
+                            }
+
+                            match socket.update() {
+                                Ok(next_next) => {
+                                    update_timer.as_mut().reset(Instant::from_std(next_next));
+                                }
+                                Err(err) => {
+                                    error!("[SESSION] KCP update failed, error: {}", err);
+                                    update_timer.as_mut().reset(Instant::now() + Duration::from_millis(10));
+                                }
+                            }
+                        }
+                    }
+                }
+
+                {
+                    // Close the socket.
+                    // Wake all pending tasks and let all send/recv return EOF
+
+                    let mut socket = session.socket.lock().await;
+                    socket.close();
+                }
+
+                if let Some(ref notifier) = session.session_close_notifier {
+                    let socket = session.socket.lock().await;
+                    let _ = notifier.send(socket.conv()).await;
+                }
+            });
+        }
+
+        session
+    }
+
+    pub fn kcp_socket(&self) -> &Mutex<KcpSocket> {
+        &self.socket
+    }
+
+    pub fn close(&self) {
+        self.closed.store(true, Ordering::Release);
+    }
+
+    pub async fn input(&self, buf: &[u8]) {
+        self.input_tx
+            .send(buf.to_owned())
+            .await
+            .expect("input channel closed")
+    }
+}
+
+pub struct KcpSessionManager {
+    sessions: HashMap<u32, Arc<KcpSession>>,
+    next_free_conv: u32,
+}
+
+impl KcpSessionManager {
+    pub fn new() -> KcpSessionManager {
+        KcpSessionManager {
+            sessions: HashMap::new(),
+            next_free_conv: 0,
+        }
+    }
+
+    pub fn close_conv(&mut self, conv: u32) {
+        self.sessions.remove(&conv);
+    }
+
+    pub fn alloc_conv(&mut self) -> u32 {
+        loop {
+            let (mut c, _) = self.next_free_conv.overflowing_add(1);
+            if c == 0 {
+                let (nc, _) = c.overflowing_add(1);
+                c = nc;
+            }
+            self.next_free_conv = c;
+
+            if self.sessions.get(&self.next_free_conv).is_none() {
+                let conv = self.next_free_conv;
+                return conv;
+            }
+        }
+    }
+
+    pub fn get_or_create(
+        &mut self,
+        config: &KcpConfig,
+        conv: u32,
+        udp: &Arc<UdpSocket>,
+        peer_addr: SocketAddr,
+        session_close_notifier: &mpsc::Sender<u32>,
+    ) -> KcpResult<(Arc<KcpSession>, bool)> {
+        match self.sessions.entry(conv) {
+            Entry::Occupied(occ) => Ok((occ.get().clone(), false)),
+            Entry::Vacant(vac) => {
+                let socket = KcpSocket::new(config, conv, udp.clone(), peer_addr, config.stream)?;
+                let session = KcpSession::new_shared(
+                    socket,
+                    config.session_expire,
+                    Some(session_close_notifier.clone()),
+                );
+                trace!("created session for conv: {}, peer: {}", conv, peer_addr);
+                vac.insert(session.clone());
+                Ok((session, true))
+            }
+        }
+    }
+}

src/plugins/kcp/skcp.rs

@@ -0,0 +1,288 @@
+use std::{
+    io::{self, ErrorKind, Write},
+    net::SocketAddr,
+    sync::Arc,
+    task::{Context, Poll, Waker},
+    time::{Duration, Instant},
+};
+
+use futures::future;
+use kcp::{Error as KcpError, Kcp, KcpResult};
+use log::{error, trace};
+use tokio::{net::UdpSocket, sync::mpsc};
+
+use crate::plugins::kcp::{utils::now_millis, KcpConfig};
+
+/// Writer for sending packets to the underlying UdpSocket
+struct UdpOutput {
+    socket: Arc<UdpSocket>,
+    target_addr: SocketAddr,
+    delay_tx: mpsc::UnboundedSender<Vec<u8>>,
+}
+
+impl UdpOutput {
+    /// Create a new Writer for writing packets to UdpSocket
+    pub fn new(socket: Arc<UdpSocket>, target_addr: SocketAddr) -> UdpOutput {
+        let (delay_tx, mut delay_rx) = mpsc::unbounded_channel::<Vec<u8>>();
+
+        {
+            let socket = socket.clone();
+            tokio::spawn(async move {
+                while let Some(buf) = delay_rx.recv().await {
+                    if let Err(err) = socket.send_to(&buf, target_addr).await {
+                        error!("[SEND] UDP delayed send failed, error: {}", err);
+                    }
+                }
+            });
+        }
+
+        UdpOutput {
+            socket,
+            target_addr,
+            delay_tx,
+        }
+    }
+}
+
+impl Write for UdpOutput {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        match self.socket.try_send_to(buf, self.target_addr) {
+            Ok(n) => Ok(n),
+            Err(ref err) if err.kind() == ErrorKind::WouldBlock => {
+                // send return EAGAIN
+                // ignored as packet was lost in transmission
+                trace!(
+                    "[SEND] UDP send EAGAIN, packet.size: {} bytes, delayed send",
+                    buf.len()
+                );
+
+                self.delay_tx
+                    .send(buf.to_owned())
+                    .expect("channel closed unexpectly");
+
+                Ok(buf.len())
+            }
+            Err(err) => Err(err),
+        }
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+pub struct KcpSocket {
+    kcp: Kcp<UdpOutput>,
+    last_update: Instant,
+    socket: Arc<UdpSocket>,
+    flush_write: bool,
+    flush_ack_input: bool,
+    sent_first: bool,
+    pending_sender: Option<Waker>,
+    pending_receiver: Option<Waker>,
+    closed: bool,
+}
+
+impl KcpSocket {
+    pub fn new(
+        c: &KcpConfig,
+        conv: u32,
+        socket: Arc<UdpSocket>,
+        target_addr: SocketAddr,
+        stream: bool,
+    ) -> KcpResult<KcpSocket> {
+        let output = UdpOutput::new(socket.clone(), target_addr);
+        let mut kcp = if stream {
+            Kcp::new_stream(conv, output)
+        } else {
+            Kcp::new(conv, output)
+        };
+        c.apply_config(&mut kcp);
+
+        // Ask server to allocate one
+        if conv == 0 {
+            kcp.input_conv();
+        }
+
+        kcp.update(now_millis())?;
+
+        Ok(KcpSocket {
+            kcp,
+            last_update: Instant::now(),
+            socket,
+            flush_write: c.flush_write,
+            flush_ack_input: c.flush_acks_input,
+            sent_first: false,
+            pending_sender: None,
+            pending_receiver: None,
+            closed: false,
+        })
+    }
+
+    /// Call every time you got data from transmission
+    pub fn input(&mut self, buf: &[u8]) -> KcpResult<bool> {
+        match self.kcp.input(buf) {
+            Ok(..) => {}
+            Err(KcpError::ConvInconsistent(expected, actual)) => {
+                trace!(
+                    "[INPUT] Conv expected={} actual={} ignored",
+                    expected,
+                    actual
+                );
+                return Ok(false);
+            }
+            Err(err) => return Err(err),
+        }
+        self.last_update = Instant::now();
+
+        if self.flush_ack_input {
+            self.kcp.flush_ack()?;
+        }
+
+        Ok(self.try_wake_pending_waker())
+    }
+
+    /// Call if you want to send some data
+    pub fn poll_send(&mut self, cx: &mut Context<'_>, mut buf: &[u8]) -> Poll<KcpResult<usize>> {
+        if self.closed {
+            return Ok(0).into();
+        }
+
+        // If:
+        //     1. Have sent the first packet (asking for conv)
+        //     2. Too many pending packets
+        if self.sent_first
+            && (self.kcp.wait_snd() >= self.kcp.snd_wnd() as usize || self.kcp.waiting_conv())
+        {
+            trace!(
+                "[SEND] waitsnd={} sndwnd={} excceeded or waiting conv={}",
+                self.kcp.wait_snd(),
+                self.kcp.snd_wnd(),
+                self.kcp.waiting_conv()
+            );
+            self.pending_sender = Some(cx.waker().clone());
+            return Poll::Pending;
+        }
+
+        if !self.sent_first && self.kcp.waiting_conv() && buf.len() > self.kcp.mss() as usize {
+            buf = &buf[..self.kcp.mss() as usize];
+        }
+
+        let n = self.kcp.send(buf)?;
+        self.sent_first = true;
+        self.last_update = Instant::now();
+
+        if self.flush_write {
+            self.kcp.flush()?;
+        }
+
+        Ok(n).into()
+    }
+
+    /// Call if you want to send some data
+    #[allow(dead_code)]
+    pub async fn send(&mut self, buf: &[u8]) -> KcpResult<usize> {
+        future::poll_fn(|cx| self.poll_send(cx, buf)).await
+    }
+
+    #[allow(dead_code)]
+    pub fn try_recv(&mut self, buf: &mut [u8]) -> KcpResult<usize> {
+        if self.closed {
+            return Ok(0);
+        }
+        self.kcp.recv(buf)
+    }
+
+    pub fn poll_recv(&mut self, cx: &mut Context<'_>, buf: &mut [u8]) -> Poll<KcpResult<usize>> {
+        if self.closed {
+            return Ok(0).into();
+        }
+
+        match self.kcp.recv(buf) {
+            Ok(n) => Ok(n).into(),
+            Err(KcpError::RecvQueueEmpty) => {
+                self.pending_receiver = Some(cx.waker().clone());
+                Poll::Pending
+            }
+            Err(err) => Err(err).into(),
+        }
+    }
+
+    #[allow(dead_code)]
+    pub async fn recv(&mut self, buf: &mut [u8]) -> KcpResult<usize> {
+        future::poll_fn(|cx| self.poll_recv(cx, buf)).await
+    }
+
+    pub fn flush(&mut self) -> KcpResult<()> {
+        self.kcp.flush()?;
+        self.last_update = Instant::now();
+        Ok(())
+    }
+
+    fn try_wake_pending_waker(&mut self) -> bool {
+        let mut waked = false;
+
+        if self.pending_sender.is_some()
+            && self.kcp.wait_snd() < self.kcp.snd_wnd() as usize
+            && !self.kcp.waiting_conv()
+        {
+            let waker = self.pending_sender.take().unwrap();
+            waker.wake();
+
+            waked = true;
+        }
+
+        if self.pending_receiver.is_some() {
+            if let Ok(peek) = self.kcp.peeksize() {
+                if peek > 0 {
+                    let waker = self.pending_receiver.take().unwrap();
+                    waker.wake();
+
+                    waked = true;
+                }
+            }
+        }
+
+        waked
+    }
+
+    pub fn update(&mut self) -> KcpResult<Instant> {
+        let now = now_millis();
+        self.kcp.update(now)?;
+        let next = self.kcp.check(now);
+
+        self.try_wake_pending_waker();
+
+        Ok(Instant::now() + Duration::from_millis(next as u64))
+    }
+
+    pub fn close(&mut self) {
+        self.closed = true;
+        if let Some(w) = self.pending_sender.take() {
+            w.wake();
+        }
+        if let Some(w) = self.pending_receiver.take() {
+            w.wake();
+        }
+    }
+
+    pub fn udp_socket(&self) -> &Arc<UdpSocket> {
+        &self.socket
+    }
+
+    pub fn can_close(&self) -> bool {
+        self.kcp.wait_snd() == 0
+    }
+
+    pub fn conv(&self) -> u32 {
+        self.kcp.conv()
+    }
+
+    pub fn peek_size(&self) -> KcpResult<usize> {
+        self.kcp.peeksize()
+    }
+
+    pub fn last_update_time(&self) -> Instant {
+        self.last_update
+    }
+}

src/plugins/kcp/stream.rs

@@ -0,0 +1,183 @@
+use std::{
+    io::{self, ErrorKind},
+    net::{IpAddr, SocketAddr},
+    pin::Pin,
+    sync::Arc,
+    task::{Context, Poll},
+};
+
+use futures::{future, ready};
+use kcp::{Error as KcpError, KcpResult};
+use log::trace;
+use tokio::{
+    io::{AsyncRead, AsyncWrite, ReadBuf},
+    net::UdpSocket,
+};
+
+use crate::plugins::kcp::{config::KcpConfig, session::KcpSession, skcp::KcpSocket};
+
+pub struct KcpStream {
+    session: Arc<KcpSession>,
+    recv_buffer: Vec<u8>,
+    recv_buffer_pos: usize,
+    recv_buffer_cap: usize,
+}
+
+impl Drop for KcpStream {
+    fn drop(&mut self) {
+        self.session.close();
+    }
+}
+
+#[allow(unused)]
+impl KcpStream {
+    pub async fn connect(config: &KcpConfig, addr: SocketAddr) -> KcpResult<KcpStream> {
+        let udp = match addr.ip() {
+            IpAddr::V4(..) => UdpSocket::bind("0.0.0.0:0").await?,
+            IpAddr::V6(..) => UdpSocket::bind("[::]:0").await?,
+        };
+
+        let udp = Arc::new(udp);
+        let socket = KcpSocket::new(config, 0, udp, addr, config.stream)?;
+
+        let session = KcpSession::new_shared(socket, config.session_expire, None);
+
+        Ok(KcpStream::with_session(session))
+    }
+
+    pub(crate) fn with_session(session: Arc<KcpSession>) -> KcpStream {
+        KcpStream {
+            session,
+            recv_buffer: Vec::new(),
+            recv_buffer_pos: 0,
+            recv_buffer_cap: 0,
+        }
+    }
+
+    pub fn poll_send(&mut self, cx: &mut Context<'_>, buf: &[u8]) -> Poll<KcpResult<usize>> {
+        // Mutex doesn't have poll_lock, spinning on it.
+        let socket = self.session.kcp_socket();
+        let mut kcp = match socket.try_lock() {
+            Ok(guard) => guard,
+            Err(..) => {
+                cx.waker().wake_by_ref();
+                return Poll::Pending;
+            }
+        };
+
+        kcp.poll_send(cx, buf)
+    }
+
+    pub async fn send(&mut self, buf: &[u8]) -> KcpResult<usize> {
+        future::poll_fn(|cx| self.poll_send(cx, buf)).await
+    }
+
+    pub fn poll_recv(&mut self, cx: &mut Context<'_>, buf: &mut [u8]) -> Poll<KcpResult<usize>> {
+        loop {
+            // Consumes all data in buffer
+            if self.recv_buffer_pos < self.recv_buffer_cap {
+                let remaining = self.recv_buffer_cap - self.recv_buffer_pos;
+                let copy_length = remaining.min(buf.len());
+
+                buf.copy_from_slice(
+                    &self.recv_buffer[self.recv_buffer_pos..self.recv_buffer_pos + copy_length],
+                );
+                self.recv_buffer_pos += copy_length;
+                return Ok(copy_length).into();
+            }
+
+            // Mutex doesn't have poll_lock, spinning on it.
+            let socket = self.session.kcp_socket();
+            let mut kcp = match socket.try_lock() {
+                Ok(guard) => guard,
+                Err(..) => {
+                    cx.waker().wake_by_ref();
+                    return Poll::Pending;
+                }
+            };
+
+            // Try to read from KCP
+            // 1. Read directly with user provided `buf`
+            match ready!(kcp.poll_recv(cx, buf)) {
+                Ok(n) => {
+                    trace!("[CLIENT] recv directly {} bytes", n);
+                    return Ok(n).into();
+                }
+                Err(KcpError::UserBufTooSmall) => {}
+                Err(err) => return Err(err).into(),
+            }
+
+            // 2. User `buf` too small, read to recv_buffer
+            let required_size = kcp.peek_size()?;
+            if self.recv_buffer.len() < required_size {
+                self.recv_buffer.resize(required_size, 0);
+            }
+
+            match ready!(kcp.poll_recv(cx, &mut self.recv_buffer)) {
+                Ok(n) => {
+                    trace!("[CLIENT] recv buffered {} bytes", n);
+                    self.recv_buffer_pos = 0;
+                    self.recv_buffer_cap = n;
+                }
+                Err(err) => return Err(err).into(),
+            }
+        }
+    }
+
+    pub async fn recv(&mut self, buf: &mut [u8]) -> KcpResult<usize> {
+        future::poll_fn(|cx| self.poll_recv(cx, buf)).await
+    }
+}
+
+impl AsyncRead for KcpStream {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        match ready!(self.poll_recv(cx, buf.initialize_unfilled())) {
+            Ok(n) => {
+                buf.advance(n);
+                Ok(()).into()
+            }
+            Err(KcpError::IoError(err)) => Err(err).into(),
+            Err(err) => Err(io::Error::new(ErrorKind::Other, err)).into(),
+        }
+    }
+}
+
+impl AsyncWrite for KcpStream {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        match ready!(self.poll_send(cx, buf)) {
+            Ok(n) => Ok(n).into(),
+            Err(KcpError::IoError(err)) => Err(err).into(),
+            Err(err) => Err(io::Error::new(ErrorKind::Other, err)).into(),
+        }
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        // Mutex doesn't have poll_lock, spinning on it.
+        let socket = self.session.kcp_socket();
+        let mut kcp = match socket.try_lock() {
+            Ok(guard) => guard,
+            Err(..) => {
+                cx.waker().wake_by_ref();
+                return Poll::Pending;
+            }
+        };
+
+        match kcp.flush() {
+            Ok(..) => Ok(()).into(),
+            Err(KcpError::IoError(err)) => Err(err).into(),
+            Err(err) => Err(io::Error::new(ErrorKind::Other, err)).into(),
+        }
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Ok(()).into()
+    }
+}

src/plugins/kcp/utils.rs

@@ -0,0 +1,10 @@
+use std::time::{SystemTime, UNIX_EPOCH};
+
+#[inline]
+pub fn now_millis() -> u32 {
+    let start = SystemTime::now();
+    let since_the_epoch = start
+        .duration_since(UNIX_EPOCH)
+        .expect("time went afterwards");
+    (since_the_epoch.as_secs() * 1000 + since_the_epoch.subsec_millis() as u64 / 1_000_000) as u32
+}

src/plugins/mod.rs

@@ -0,0 +1 @@
+pub mod kcp;

src/servers/mod.rs

@@ -104,12 +104,12 @@ impl Server {
 
 #[cfg(test)]
 mod test {
+    use crate::plugins::kcp::{KcpConfig, KcpStream};
     use std::net::SocketAddr;
     use std::thread::{self, sleep};
     use std::time::Duration;
     use tokio::io::{AsyncReadExt, AsyncWriteExt};
     use tokio::net::{TcpListener, TcpStream};
-    use tokio_kcp::{KcpConfig, KcpStream};
 
     use super::*;
 

src/servers/protocol/kcp.rs

@@ -1,3 +1,4 @@
+use crate::plugins::kcp::{KcpConfig, KcpListener, KcpStream};
 use crate::servers::Proxy;
 use futures::future::try_join;
 use log::{debug, error, warn};
@@ -6,7 +7,6 @@ use std::sync::Arc;
 use tokio::io;
 use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt};
 use tokio::net::TcpStream;
-use tokio_kcp::{KcpConfig, KcpListener, KcpStream};
 
 pub async fn proxy(config: Arc<Proxy>) -> Result<(), Box<dyn std::error::Error>> {
     let kcp_config = KcpConfig::default();