update vendors

vendor/github.com/fatedier/kcp-go/sess.go

@@ -1,9 +1,17 @@
+// Package kcp-go is a Reliable-UDP library for golang.
+//
+// This library intents to provide a smooth, resilient, ordered,
+// error-checked and anonymous delivery of streams over UDP packets.
+//
+// The interfaces of this package aims to be compatible with
+// net.Conn in standard library, but offers powerful features for advanced users.
 package kcp
 
 import (
 	"crypto/rand"
 	"encoding/binary"
 	"hash/crc32"
+	"io"
 	"net"
 	"sync"
 	"sync/atomic"
@@ -14,14 +22,6 @@ import (
 	"golang.org/x/net/ipv6"
 )
 
-type errTimeout struct {
-	error
-}
-
-func (errTimeout) Timeout() bool   { return true }
-func (errTimeout) Temporary() bool { return true }
-func (errTimeout) Error() string   { return "i/o timeout" }
-
 const (
 	// 16-bytes nonce for each packet
 	nonceSize = 16
@@ -42,9 +42,9 @@ const (
 	acceptBacklog = 128
 )
 
-const (
-	errBrokenPipe       = "broken pipe"
-	errInvalidOperation = "invalid operation"
+var (
+	errInvalidOperation = errors.New("invalid operation")
+	errTimeout          = errors.New("timeout")
 )
 
 var (
@@ -72,8 +72,6 @@ type (
 		// recvbuf turns packets into stream
 		recvbuf []byte
 		bufptr  []byte
-		// header extended output buffer, if has header
-		ext []byte
 
 		// FEC codec
 		fecDecoder *fecDecoder
@@ -90,16 +88,27 @@ type (
 
 		// notifications
 		die          chan struct{} // notify current session has Closed
+		dieOnce      sync.Once
 		chReadEvent  chan struct{} // notify Read() can be called without blocking
 		chWriteEvent chan struct{} // notify Write() can be called without blocking
-		chReadError  chan error    // notify PacketConn.Read() have an error
-		chWriteError chan error    // notify PacketConn.Write() have an error
+
+		// socket error handling
+		socketReadError      atomic.Value
+		socketWriteError     atomic.Value
+		chSocketReadError    chan struct{}
+		chSocketWriteError   chan struct{}
+		socketReadErrorOnce  sync.Once
+		socketWriteErrorOnce sync.Once
 
 		// nonce generator
 		nonce Entropy
 
-		isClosed bool // flag the session has Closed
-		mu       sync.Mutex
+		// packets waiting to be sent on wire
+		txqueue         []ipv4.Message
+		xconn           batchConn // for x/net
+		xconnWriteError error
+
+		mu sync.Mutex
 	}
 
 	setReadBuffer interface {
@@ -119,14 +128,26 @@ func newUDPSession(conv uint32, dataShards, parityShards int, l *Listener, conn
 	sess.nonce.Init()
 	sess.chReadEvent = make(chan struct{}, 1)
 	sess.chWriteEvent = make(chan struct{}, 1)
-	sess.chReadError = make(chan error, 1)
-	sess.chWriteError = make(chan error, 1)
+	sess.chSocketReadError = make(chan struct{})
+	sess.chSocketWriteError = make(chan struct{})
 	sess.remote = remote
 	sess.conn = conn
 	sess.l = l
 	sess.block = block
 	sess.recvbuf = make([]byte, mtuLimit)
 
+	// cast to writebatch conn
+	if _, ok := conn.(*net.UDPConn); ok {
+		addr, err := net.ResolveUDPAddr("udp", conn.LocalAddr().String())
+		if err == nil {
+			if addr.IP.To4() != nil {
+				sess.xconn = ipv4.NewPacketConn(conn)
+			} else {
+				sess.xconn = ipv6.NewPacketConn(conn)
+			}
+		}
+	}
+
 	// FEC codec initialization
 	sess.fecDecoder = newFECDecoder(rxFECMulti*(dataShards+parityShards), dataShards, parityShards)
 	if sess.block != nil {
@@ -143,17 +164,12 @@ func newUDPSession(conv uint32, dataShards, parityShards int, l *Listener, conn
 		sess.headerSize += fecHeaderSizePlus2
 	}
 
-	// we only need to allocate extended packet buffer if we have the additional header
-	if sess.headerSize > 0 {
-		sess.ext = make([]byte, mtuLimit)
-	}
-
 	sess.kcp = NewKCP(conv, func(buf []byte, size int) {
-		if size >= IKCP_OVERHEAD {
+		if size >= IKCP_OVERHEAD+sess.headerSize {
 			sess.output(buf[:size])
 		}
 	})
-	sess.kcp.SetMtu(IKCP_MTU_DEF - sess.headerSize)
+	sess.kcp.ReserveBytes(sess.headerSize)
 
 	// register current session to the global updater,
 	// which call sess.update() periodically.
@@ -165,6 +181,7 @@ func newUDPSession(conv uint32, dataShards, parityShards int, l *Listener, conn
 	} else {
 		atomic.AddUint64(&DefaultSnmp.PassiveOpens, 1)
 	}
+
 	currestab := atomic.AddUint64(&DefaultSnmp.CurrEstab, 1)
 	maxconn := atomic.LoadUint64(&DefaultSnmp.MaxConn)
 	if currestab > maxconn {
@@ -186,11 +203,6 @@ func (s *UDPSession) Read(b []byte) (n int, err error) {
 			return n, nil
 		}
 
-		if s.isClosed {
-			s.mu.Unlock()
-			return 0, errors.New(errBrokenPipe)
-		}
-
 		if size := s.kcp.PeekSize(); size > 0 { // peek data size from kcp
 			if len(b) >= size { // receive data into 'b' directly
 				s.kcp.Recv(b)
@@ -220,7 +232,7 @@ func (s *UDPSession) Read(b []byte) (n int, err error) {
 		if !s.rd.IsZero() {
 			if time.Now().After(s.rd) {
 				s.mu.Unlock()
-				return 0, errTimeout{}
+				return 0, errors.WithStack(errTimeout)
 			}
 
 			delay := s.rd.Sub(time.Now())
@@ -229,63 +241,66 @@ func (s *UDPSession) Read(b []byte) (n int, err error) {
 		}
 		s.mu.Unlock()
 
-		// wait for read event or timeout
+		// wait for read event or timeout or error
 		select {
 		case <-s.chReadEvent:
-		case <-c:
-		case <-s.die:
-		case err = <-s.chReadError:
 			if timeout != nil {
 				timeout.Stop()
 			}
-			return n, err
-		}
-
-		if timeout != nil {
-			timeout.Stop()
+		case <-c:
+			return 0, errors.WithStack(errTimeout)
+		case <-s.chSocketReadError:
+			return 0, s.socketReadError.Load().(error)
+		case <-s.die:
+			return 0, errors.WithStack(io.ErrClosedPipe)
 		}
 	}
 }
 
 // Write implements net.Conn
-func (s *UDPSession) Write(b []byte) (n int, err error) {
+func (s *UDPSession) Write(b []byte) (n int, err error) { return s.WriteBuffers([][]byte{b}) }
+
+// WriteBuffers write a vector of byte slices to the underlying connection
+func (s *UDPSession) WriteBuffers(v [][]byte) (n int, err error) {
 	for {
-		s.mu.Lock()
-		if s.isClosed {
-			s.mu.Unlock()
-			return 0, errors.New(errBrokenPipe)
+		select {
+		case <-s.chSocketWriteError:
+			return 0, s.socketWriteError.Load().(error)
+		case <-s.die:
+			return 0, errors.WithStack(io.ErrClosedPipe)
+		default:
 		}
 
-		// controls how much data will be sent to kcp core
-		// to prevent the memory from exhuasting
+		s.mu.Lock()
 		if s.kcp.WaitSnd() < int(s.kcp.snd_wnd) {
-			n = len(b)
-			for {
-				if len(b) <= int(s.kcp.mss) {
-					s.kcp.Send(b)
-					break
-				} else {
-					s.kcp.Send(b[:s.kcp.mss])
-					b = b[s.kcp.mss:]
+			for _, b := range v {
+				n += len(b)
+				for {
+					if len(b) <= int(s.kcp.mss) {
+						s.kcp.Send(b)
+						break
+					} else {
+						s.kcp.Send(b[:s.kcp.mss])
+						b = b[s.kcp.mss:]
+					}
 				}
 			}
 
-			// flush immediately if the queue is full
 			if s.kcp.WaitSnd() >= int(s.kcp.snd_wnd) || !s.writeDelay {
 				s.kcp.flush(false)
+				s.uncork()
 			}
 			s.mu.Unlock()
 			atomic.AddUint64(&DefaultSnmp.BytesSent, uint64(n))
 			return n, nil
 		}
 
-		// deadline for current writing operation
 		var timeout *time.Timer
 		var c <-chan time.Time
 		if !s.wd.IsZero() {
 			if time.Now().After(s.wd) {
 				s.mu.Unlock()
-				return 0, errTimeout{}
+				return 0, errors.WithStack(errTimeout)
 			}
 			delay := s.wd.Sub(time.Now())
 			timeout = time.NewTimer(delay)
@@ -293,44 +308,52 @@ func (s *UDPSession) Write(b []byte) (n int, err error) {
 		}
 		s.mu.Unlock()
 
-		// wait for write event or timeout
 		select {
 		case <-s.chWriteEvent:
-		case <-c:
-		case <-s.die:
-		case err = <-s.chWriteError:
 			if timeout != nil {
 				timeout.Stop()
 			}
-			return n, err
-		}
-
-		if timeout != nil {
-			timeout.Stop()
+		case <-c:
+			return 0, errors.WithStack(errTimeout)
+		case <-s.chSocketWriteError:
+			return 0, s.socketWriteError.Load().(error)
+		case <-s.die:
+			return 0, errors.WithStack(io.ErrClosedPipe)
 		}
 	}
 }
 
+// uncork sends data in txqueue if there is any
+func (s *UDPSession) uncork() {
+	if len(s.txqueue) > 0 {
+		s.tx(s.txqueue)
+		s.txqueue = s.txqueue[:0]
+	}
+	return
+}
+
 // Close closes the connection.
 func (s *UDPSession) Close() error {
-	// remove current session from updater & listener(if necessary)
-	updater.removeSession(s)
-	if s.l != nil { // notify listener
-		s.l.closeSession(s.remote)
-	}
+	var once bool
+	s.dieOnce.Do(func() {
+		close(s.die)
+		once = true
+	})
 
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	if s.isClosed {
-		return errors.New(errBrokenPipe)
+	if once {
+		// remove from updater
+		updater.removeSession(s)
+		atomic.AddUint64(&DefaultSnmp.CurrEstab, ^uint64(0))
+
+		if s.l != nil { // belongs to listener
+			s.l.closeSession(s.remote)
+			return nil
+		} else { // client socket close
+			return s.conn.Close()
+		}
+	} else {
+		return errors.WithStack(io.ErrClosedPipe)
 	}
-	close(s.die)
-	s.isClosed = true
-	atomic.AddUint64(&DefaultSnmp.CurrEstab, ^uint64(0))
-	if s.l == nil { // client socket close
-		return s.conn.Close()
-	}
-	return nil
 }
 
 // LocalAddr returns the local network address. The Addr returned is shared by all invocations of LocalAddr, so do not modify it.
@@ -390,7 +413,7 @@ func (s *UDPSession) SetMtu(mtu int) bool {
 
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	s.kcp.SetMtu(mtu - s.headerSize)
+	s.kcp.SetMtu(mtu)
 	return true
 }
 
@@ -412,7 +435,9 @@ func (s *UDPSession) SetACKNoDelay(nodelay bool) {
 	s.ackNoDelay = nodelay
 }
 
-// SetDUP duplicates udp packets for kcp output, for testing purpose only
+// (deprecated)
+//
+// SetDUP duplicates udp packets for kcp output.
 func (s *UDPSession) SetDUP(dup int) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -427,19 +452,29 @@ func (s *UDPSession) SetNoDelay(nodelay, interval, resend, nc int) {
 	s.kcp.NoDelay(nodelay, interval, resend, nc)
 }
 
-// SetDSCP sets the 6bit DSCP field of IP header, no effect if it's accepted from Listener
+// SetDSCP sets the 6bit DSCP field in IPv4 header, or 8bit Traffic Class in IPv6 header.
+//
+// It has no effect if it's accepted from Listener.
 func (s *UDPSession) SetDSCP(dscp int) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	if s.l == nil {
-		if nc, ok := s.conn.(net.Conn); ok {
-			if err := ipv4.NewConn(nc).SetTOS(dscp << 2); err != nil {
-				return ipv6.NewConn(nc).SetTrafficClass(dscp)
-			}
+	if s.l != nil {
+		return errInvalidOperation
+	}
+	if nc, ok := s.conn.(net.Conn); ok {
+		var succeed bool
+		if err := ipv4.NewConn(nc).SetTOS(dscp << 2); err == nil {
+			succeed = true
+		}
+		if err := ipv6.NewConn(nc).SetTrafficClass(dscp); err == nil {
+			succeed = true
+		}
+
+		if succeed {
 			return nil
 		}
 	}
-	return errors.New(errInvalidOperation)
+	return errInvalidOperation
 }
 
 // SetReadBuffer sets the socket read buffer, no effect if it's accepted from Listener
@@ -451,7 +486,7 @@ func (s *UDPSession) SetReadBuffer(bytes int) error {
 			return nc.SetReadBuffer(bytes)
 		}
 	}
-	return errors.New(errInvalidOperation)
+	return errInvalidOperation
 }
 
 // SetWriteBuffer sets the socket write buffer, no effect if it's accepted from Listener
@@ -463,37 +498,29 @@ func (s *UDPSession) SetWriteBuffer(bytes int) error {
 			return nc.SetWriteBuffer(bytes)
 		}
 	}
-	return errors.New(errInvalidOperation)
+	return errInvalidOperation
 }
 
 // post-processing for sending a packet from kcp core
 // steps:
-// 0. Header extending
 // 1. FEC packet generation
 // 2. CRC32 integrity
 // 3. Encryption
-// 4. WriteTo kernel
+// 4. TxQueue
 func (s *UDPSession) output(buf []byte) {
 	var ecc [][]byte
 
-	// 0. extend buf's header space(if necessary)
-	ext := buf
-	if s.headerSize > 0 {
-		ext = s.ext[:s.headerSize+len(buf)]
-		copy(ext[s.headerSize:], buf)
-	}
-
 	// 1. FEC encoding
 	if s.fecEncoder != nil {
-		ecc = s.fecEncoder.encode(ext)
+		ecc = s.fecEncoder.encode(buf)
 	}
 
 	// 2&3. crc32 & encryption
 	if s.block != nil {
-		s.nonce.Fill(ext[:nonceSize])
-		checksum := crc32.ChecksumIEEE(ext[cryptHeaderSize:])
-		binary.LittleEndian.PutUint32(ext[nonceSize:], checksum)
-		s.block.Encrypt(ext, ext)
+		s.nonce.Fill(buf[:nonceSize])
+		checksum := crc32.ChecksumIEEE(buf[cryptHeaderSize:])
+		binary.LittleEndian.PutUint32(buf[nonceSize:], checksum)
+		s.block.Encrypt(buf, buf)
 
 		for k := range ecc {
 			s.nonce.Fill(ecc[k][:nonceSize])
@@ -503,28 +530,23 @@ func (s *UDPSession) output(buf []byte) {
 		}
 	}
 
-	// 4. WriteTo kernel
-	nbytes := 0
-	npkts := 0
+	// 4. TxQueue
+	var msg ipv4.Message
 	for i := 0; i < s.dup+1; i++ {
-		if n, err := s.conn.WriteTo(ext, s.remote); err == nil {
-			nbytes += n
-			npkts++
-		} else {
-			s.notifyWriteError(err)
-		}
+		bts := xmitBuf.Get().([]byte)[:len(buf)]
+		copy(bts, buf)
+		msg.Buffers = [][]byte{bts}
+		msg.Addr = s.remote
+		s.txqueue = append(s.txqueue, msg)
 	}
 
 	for k := range ecc {
-		if n, err := s.conn.WriteTo(ecc[k], s.remote); err == nil {
-			nbytes += n
-			npkts++
-		} else {
-			s.notifyWriteError(err)
-		}
+		bts := xmitBuf.Get().([]byte)[:len(ecc[k])]
+		copy(bts, ecc[k])
+		msg.Buffers = [][]byte{bts}
+		msg.Addr = s.remote
+		s.txqueue = append(s.txqueue, msg)
 	}
-	atomic.AddUint64(&DefaultSnmp.OutPkts, uint64(npkts))
-	atomic.AddUint64(&DefaultSnmp.OutBytes, uint64(nbytes))
 }
 
 // kcp update, returns interval for next calling
@@ -535,6 +557,7 @@ func (s *UDPSession) update() (interval time.Duration) {
 	if s.kcp.WaitSnd() < waitsnd {
 		s.notifyWriteEvent()
 	}
+	s.uncork()
 	s.mu.Unlock()
 	return
 }
@@ -556,10 +579,39 @@ func (s *UDPSession) notifyWriteEvent() {
 	}
 }
 
+func (s *UDPSession) notifyReadError(err error) {
+	s.socketReadErrorOnce.Do(func() {
+		s.socketReadError.Store(err)
+		close(s.chSocketReadError)
+	})
+}
+
 func (s *UDPSession) notifyWriteError(err error) {
-	select {
-	case s.chWriteError <- err:
-	default:
+	s.socketWriteErrorOnce.Do(func() {
+		s.socketWriteError.Store(err)
+		close(s.chSocketWriteError)
+	})
+}
+
+// packet input stage
+func (s *UDPSession) packetInput(data []byte) {
+	dataValid := false
+	if s.block != nil {
+		s.block.Decrypt(data, data)
+		data = data[nonceSize:]
+		checksum := crc32.ChecksumIEEE(data[crcSize:])
+		if checksum == binary.LittleEndian.Uint32(data) {
+			data = data[crcSize:]
+			dataValid = true
+		} else {
+			atomic.AddUint64(&DefaultSnmp.InCsumErrors, 1)
+		}
+	} else if s.block == nil {
+		dataValid = true
+	}
+
+	if dataValid {
+		s.kcpInput(data)
 	}
 }
 
@@ -568,16 +620,16 @@ func (s *UDPSession) kcpInput(data []byte) {
 
 	if s.fecDecoder != nil {
 		if len(data) > fecHeaderSize { // must be larger than fec header size
-			f := s.fecDecoder.decodeBytes(data)
-			if f.flag == typeData || f.flag == typeFEC { // header check
-				if f.flag == typeFEC {
+			f := fecPacket(data)
+			if f.flag() == typeData || f.flag() == typeParity { // header check
+				if f.flag() == typeParity {
 					fecParityShards++
 				}
 				recovers := s.fecDecoder.decode(f)
 
 				s.mu.Lock()
 				waitsnd := s.kcp.WaitSnd()
-				if f.flag == typeData {
+				if f.flag() == typeData {
 					if ret := s.kcp.Input(data[fecHeaderSizePlus2:], true, s.ackNoDelay); ret != 0 {
 						kcpInErrors++
 					}
@@ -598,6 +650,8 @@ func (s *UDPSession) kcpInput(data []byte) {
 					} else {
 						fecErrs++
 					}
+					// recycle the recovers
+					xmitBuf.Put(r)
 				}
 
 				// to notify the readers to receive the data
@@ -608,6 +662,7 @@ func (s *UDPSession) kcpInput(data []byte) {
 				if s.kcp.WaitSnd() < waitsnd {
 					s.notifyWriteEvent()
 				}
+				s.uncork()
 				s.mu.Unlock()
 			} else {
 				atomic.AddUint64(&DefaultSnmp.InErrs, 1)
@@ -627,6 +682,7 @@ func (s *UDPSession) kcpInput(data []byte) {
 		if s.kcp.WaitSnd() < waitsnd {
 			s.notifyWriteEvent()
 		}
+		s.uncork()
 		s.mu.Unlock()
 	}
 
@@ -644,50 +700,7 @@ func (s *UDPSession) kcpInput(data []byte) {
 	if fecRecovered > 0 {
 		atomic.AddUint64(&DefaultSnmp.FECRecovered, fecRecovered)
 	}
-}
 
-// the read loop for a client session
-func (s *UDPSession) readLoop() {
-	buf := make([]byte, mtuLimit)
-	var src string
-	for {
-		if n, addr, err := s.conn.ReadFrom(buf); err == nil {
-			// make sure the packet is from the same source
-			if src == "" { // set source address
-				src = addr.String()
-			} else if addr.String() != src {
-				atomic.AddUint64(&DefaultSnmp.InErrs, 1)
-				continue
-			}
-
-			if n >= s.headerSize+IKCP_OVERHEAD {
-				data := buf[:n]
-				dataValid := false
-				if s.block != nil {
-					s.block.Decrypt(data, data)
-					data = data[nonceSize:]
-					checksum := crc32.ChecksumIEEE(data[crcSize:])
-					if checksum == binary.LittleEndian.Uint32(data) {
-						data = data[crcSize:]
-						dataValid = true
-					} else {
-						atomic.AddUint64(&DefaultSnmp.InCsumErrors, 1)
-					}
-				} else if s.block == nil {
-					dataValid = true
-				}
-
-				if dataValid {
-					s.kcpInput(data)
-				}
-			} else {
-				atomic.AddUint64(&DefaultSnmp.InErrs, 1)
-			}
-		} else {
-			s.chReadError <- err
-			return
-		}
-	}
 }
 
 type (
@@ -704,98 +717,91 @@ type (
 		chAccepts       chan *UDPSession // Listen() backlog
 		chSessionClosed chan net.Addr    // session close queue
 		headerSize      int              // the additional header to a KCP frame
-		die             chan struct{}    // notify the listener has closed
-		rd              atomic.Value     // read deadline for Accept()
-		wd              atomic.Value
+
+		die     chan struct{} // notify the listener has closed
+		dieOnce sync.Once
+
+		// socket error handling
+		socketReadError     atomic.Value
+		chSocketReadError   chan struct{}
+		socketReadErrorOnce sync.Once
+
+		rd atomic.Value // read deadline for Accept()
 	}
 )
 
-// monitor incoming data for all connections of server
-func (l *Listener) monitor() {
-	// a cache for session object last used
-	var lastAddr string
-	var lastSession *UDPSession
-	buf := make([]byte, mtuLimit)
-	for {
-		if n, from, err := l.conn.ReadFrom(buf); err == nil {
-			if n >= l.headerSize+IKCP_OVERHEAD {
-				data := buf[:n]
-				dataValid := false
-				if l.block != nil {
-					l.block.Decrypt(data, data)
-					data = data[nonceSize:]
-					checksum := crc32.ChecksumIEEE(data[crcSize:])
-					if checksum == binary.LittleEndian.Uint32(data) {
-						data = data[crcSize:]
-						dataValid = true
-					} else {
-						atomic.AddUint64(&DefaultSnmp.InCsumErrors, 1)
+// packet input stage
+func (l *Listener) packetInput(data []byte, addr net.Addr) {
+	dataValid := false
+	if l.block != nil {
+		l.block.Decrypt(data, data)
+		data = data[nonceSize:]
+		checksum := crc32.ChecksumIEEE(data[crcSize:])
+		if checksum == binary.LittleEndian.Uint32(data) {
+			data = data[crcSize:]
+			dataValid = true
+		} else {
+			atomic.AddUint64(&DefaultSnmp.InCsumErrors, 1)
+		}
+	} else if l.block == nil {
+		dataValid = true
+	}
+
+	if dataValid {
+		l.sessionLock.Lock()
+		s, ok := l.sessions[addr.String()]
+		l.sessionLock.Unlock()
+
+		if !ok { // new address:port
+			if len(l.chAccepts) < cap(l.chAccepts) { // do not let the new sessions overwhelm accept queue
+				var conv uint32
+				convValid := false
+				if l.fecDecoder != nil {
+					isfec := binary.LittleEndian.Uint16(data[4:])
+					if isfec == typeData {
+						conv = binary.LittleEndian.Uint32(data[fecHeaderSizePlus2:])
+						convValid = true
 					}
-				} else if l.block == nil {
-					dataValid = true
+				} else {
+					conv = binary.LittleEndian.Uint32(data)
+					convValid = true
 				}
 
-				if dataValid {
-					addr := from.String()
-					var s *UDPSession
-					var ok bool
-
-					// the packets received from an address always come in batch,
-					// cache the session for next packet, without querying map.
-					if addr == lastAddr {
-						s, ok = lastSession, true
-					} else {
-						l.sessionLock.Lock()
-						if s, ok = l.sessions[addr]; ok {
-							lastSession = s
-							lastAddr = addr
-						}
-						l.sessionLock.Unlock()
-					}
-
-					if !ok { // new session
-						if len(l.chAccepts) < cap(l.chAccepts) { // do not let the new sessions overwhelm accept queue
-							var conv uint32
-							convValid := false
-							if l.fecDecoder != nil {
-								isfec := binary.LittleEndian.Uint16(data[4:])
-								if isfec == typeData {
-									conv = binary.LittleEndian.Uint32(data[fecHeaderSizePlus2:])
-									convValid = true
-								}
-							} else {
-								conv = binary.LittleEndian.Uint32(data)
-								convValid = true
-							}
-
-							if convValid { // creates a new session only if the 'conv' field in kcp is accessible
-								s := newUDPSession(conv, l.dataShards, l.parityShards, l, l.conn, from, l.block)
-								s.kcpInput(data)
-								l.sessionLock.Lock()
-								l.sessions[addr] = s
-								l.sessionLock.Unlock()
-								l.chAccepts <- s
-							}
-						}
-					} else {
-						s.kcpInput(data)
-					}
+				if convValid { // creates a new session only if the 'conv' field in kcp is accessible
+					s := newUDPSession(conv, l.dataShards, l.parityShards, l, l.conn, addr, l.block)
+					s.kcpInput(data)
+					l.sessionLock.Lock()
+					l.sessions[addr.String()] = s
+					l.sessionLock.Unlock()
+					l.chAccepts <- s
 				}
-			} else {
-				atomic.AddUint64(&DefaultSnmp.InErrs, 1)
 			}
 		} else {
-			return
+			s.kcpInput(data)
 		}
 	}
 }
 
+func (l *Listener) notifyReadError(err error) {
+	l.socketReadErrorOnce.Do(func() {
+		l.socketReadError.Store(err)
+		close(l.chSocketReadError)
+
+		// propagate read error to all sessions
+		l.sessionLock.Lock()
+		for _, s := range l.sessions {
+			s.notifyReadError(err)
+		}
+		l.sessionLock.Unlock()
+	})
+}
+
 // SetReadBuffer sets the socket read buffer for the Listener
 func (l *Listener) SetReadBuffer(bytes int) error {
 	if nc, ok := l.conn.(setReadBuffer); ok {
 		return nc.SetReadBuffer(bytes)
 	}
-	return errors.New(errInvalidOperation)
+	return errInvalidOperation
 }
 
 // SetWriteBuffer sets the socket write buffer for the Listener
@@ -803,18 +809,25 @@ func (l *Listener) SetWriteBuffer(bytes int) error {
 	if nc, ok := l.conn.(setWriteBuffer); ok {
 		return nc.SetWriteBuffer(bytes)
 	}
-	return errors.New(errInvalidOperation)
+	return errInvalidOperation
 }
 
-// SetDSCP sets the 6bit DSCP field of IP header
+// SetDSCP sets the 6bit DSCP field in IPv4 header, or 8bit Traffic Class in IPv6 header.
 func (l *Listener) SetDSCP(dscp int) error {
 	if nc, ok := l.conn.(net.Conn); ok {
-		if err := ipv4.NewConn(nc).SetTOS(dscp << 2); err != nil {
-			return ipv6.NewConn(nc).SetTrafficClass(dscp)
+		var succeed bool
+		if err := ipv4.NewConn(nc).SetTOS(dscp << 2); err == nil {
+			succeed = true
+		}
+		if err := ipv6.NewConn(nc).SetTrafficClass(dscp); err == nil {
+			succeed = true
+		}
+
+		if succeed {
+			return nil
 		}
-		return nil
 	}
-	return errors.New(errInvalidOperation)
+	return errInvalidOperation
 }
 
 // Accept implements the Accept method in the Listener interface; it waits for the next call and returns a generic Conn.
@@ -831,11 +844,13 @@ func (l *Listener) AcceptKCP() (*UDPSession, error) {
 
 	select {
 	case <-timeout:
-		return nil, &errTimeout{}
+		return nil, errors.WithStack(errTimeout)
 	case c := <-l.chAccepts:
 		return c, nil
+	case <-l.chSocketReadError:
+		return nil, l.socketReadError.Load().(error)
 	case <-l.die:
-		return nil, errors.New(errBrokenPipe)
+		return nil, errors.WithStack(io.ErrClosedPipe)
 	}
 }
 
@@ -853,15 +868,21 @@ func (l *Listener) SetReadDeadline(t time.Time) error {
 }
 
 // SetWriteDeadline implements the Conn SetWriteDeadline method.
-func (l *Listener) SetWriteDeadline(t time.Time) error {
-	l.wd.Store(t)
-	return nil
-}
+func (l *Listener) SetWriteDeadline(t time.Time) error { return errInvalidOperation }
 
-// Close stops listening on the UDP address. Already Accepted connections are not closed.
+// Close stops listening on the UDP address, and closes the socket
 func (l *Listener) Close() error {
-	close(l.die)
-	return l.conn.Close()
+	var once bool
+	l.dieOnce.Do(func() {
+		close(l.die)
+		once = true
+	})
+
+	if once {
+		return l.conn.Close()
+	} else {
+		return errors.WithStack(io.ErrClosedPipe)
+	}
 }
 
 // closeSession notify the listener that a session has closed
@@ -881,16 +902,21 @@ func (l *Listener) Addr() net.Addr { return l.conn.LocalAddr() }
 // Listen listens for incoming KCP packets addressed to the local address laddr on the network "udp",
 func Listen(laddr string) (net.Listener, error) { return ListenWithOptions(laddr, nil, 0, 0) }
 
-// ListenWithOptions listens for incoming KCP packets addressed to the local address laddr on the network "udp" with packet encryption,
-// dataShards, parityShards defines Reed-Solomon Erasure Coding parameters
+// ListenWithOptions listens for incoming KCP packets addressed to the local address laddr on the network "udp" with packet encryption.
+//
+// 'block' is the block encryption algorithm to encrypt packets.
+//
+// 'dataShards', 'parityShards' specifiy how many parity packets will be generated following the data packets.
+//
+// Check https://github.com/klauspost/reedsolomon for details
 func ListenWithOptions(laddr string, block BlockCrypt, dataShards, parityShards int) (*Listener, error) {
 	udpaddr, err := net.ResolveUDPAddr("udp", laddr)
 	if err != nil {
-		return nil, errors.Wrap(err, "net.ResolveUDPAddr")
+		return nil, errors.WithStack(err)
 	}
 	conn, err := net.ListenUDP("udp", udpaddr)
 	if err != nil {
-		return nil, errors.Wrap(err, "net.ListenUDP")
+		return nil, errors.WithStack(err)
 	}
 
 	return ServeConn(block, dataShards, parityShards, conn)
@@ -908,6 +934,7 @@ func ServeConn(block BlockCrypt, dataShards, parityShards int, conn net.PacketCo
 	l.parityShards = parityShards
 	l.block = block
 	l.fecDecoder = newFECDecoder(rxFECMulti*(dataShards+parityShards), dataShards, parityShards)
+	l.chSocketReadError = make(chan struct{})
 
 	// calculate header size
 	if l.block != nil {
@@ -921,15 +948,21 @@ func ServeConn(block BlockCrypt, dataShards, parityShards int, conn net.PacketCo
 	return l, nil
 }
 
-// Dial connects to the remote address "raddr" on the network "udp"
+// Dial connects to the remote address "raddr" on the network "udp" without encryption and FEC
 func Dial(raddr string) (net.Conn, error) { return DialWithOptions(raddr, nil, 0, 0) }
 
 // DialWithOptions connects to the remote address "raddr" on the network "udp" with packet encryption
+//
+// 'block' is the block encryption algorithm to encrypt packets.
+//
+// 'dataShards', 'parityShards' specifiy how many parity packets will be generated following the data packets.
+//
+// Check https://github.com/klauspost/reedsolomon for details
 func DialWithOptions(raddr string, block BlockCrypt, dataShards, parityShards int) (*UDPSession, error) {
 	// network type detection
 	udpaddr, err := net.ResolveUDPAddr("udp", raddr)
 	if err != nil {
-		return nil, errors.Wrap(err, "net.ResolveUDPAddr")
+		return nil, errors.WithStack(err)
 	}
 	network := "udp4"
 	if udpaddr.IP.To4() == nil {
@@ -938,30 +971,33 @@ func DialWithOptions(raddr string, block BlockCrypt, dataShards, parityShards in
 
 	conn, err := net.ListenUDP(network, nil)
 	if err != nil {
-		return nil, errors.Wrap(err, "net.DialUDP")
+		return nil, errors.WithStack(err)
 	}
 
 	return NewConn(raddr, block, dataShards, parityShards, conn)
 }
 
+// NewConn3 establishes a session and talks KCP protocol over a packet connection.
+func NewConn3(convid uint32, raddr net.Addr, block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*UDPSession, error) {
+	return newUDPSession(convid, dataShards, parityShards, nil, conn, raddr, block), nil
+}
+
+// NewConn2 establishes a session and talks KCP protocol over a packet connection.
+func NewConn2(raddr net.Addr, block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*UDPSession, error) {
+	var convid uint32
+	binary.Read(rand.Reader, binary.LittleEndian, &convid)
+	return NewConn3(convid, raddr, block, dataShards, parityShards, conn)
+}
+
 // NewConn establishes a session and talks KCP protocol over a packet connection.
 func NewConn(raddr string, block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*UDPSession, error) {
 	udpaddr, err := net.ResolveUDPAddr("udp", raddr)
 	if err != nil {
-		return nil, errors.Wrap(err, "net.ResolveUDPAddr")
+		return nil, errors.WithStack(err)
 	}
-
-	var convid uint32
-	binary.Read(rand.Reader, binary.LittleEndian, &convid)
-	return newUDPSession(convid, dataShards, parityShards, nil, conn, udpaddr, block), nil
+	return NewConn2(udpaddr, block, dataShards, parityShards, conn)
 }
 
-// monotonic reference time point
-var refTime time.Time = time.Now()
-
-// currentMs returns current elasped monotonic milliseconds since program startup
-func currentMs() uint32 { return uint32(time.Now().Sub(refTime) / time.Millisecond) }
-
 func NewConnEx(convid uint32, connected bool, raddr string, block BlockCrypt, dataShards, parityShards int, conn *net.UDPConn) (*UDPSession, error) {
 	udpaddr, err := net.ResolveUDPAddr("udp", raddr)
 	if err != nil {