package kcp import ( "crypto/rand" "encoding/binary" "hash/crc32" "io" "net" "sync" "sync/atomic" "time" "github.com/pkg/errors" "golang.org/x/net/ipv4" ) 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 magic number for each packet nonceSize = 16 // 4-bytes packet checksum crcSize = 4 // overall crypto header size cryptHeaderSize = nonceSize + crcSize // maximum packet size mtuLimit = 1500 // FEC keeps rxFECMulti* (dataShard+parityShard) ordered packets in memory rxFECMulti = 3 // accept backlog acceptBacklog = 128 // prerouting(to session) queue qlen = 128 ) const ( errBrokenPipe = "broken pipe" errInvalidOperation = "invalid operation" ) var ( // global packet buffer // shared among sending/receiving/FEC xmitBuf sync.Pool ) func init() { xmitBuf.New = func() interface{} { return make([]byte, mtuLimit) } } type ( // UDPSession defines a KCP session implemented by UDP UDPSession struct { updaterIdx int // record slice index in updater conn net.PacketConn // the underlying packet connection kcp *KCP // KCP ARQ protocol l *Listener // point to the Listener if it's accepted by Listener block BlockCrypt // block encryption // kcp receiving is based on packets // recvbuf turns packets into stream recvbuf []byte bufptr []byte // extended output buffer(with header) ext []byte // FEC fecDecoder *fecDecoder fecEncoder *fecEncoder // settings remote net.Addr // remote peer address rd time.Time // read deadline wd time.Time // write deadline headerSize int // the overall header size added before KCP frame ackNoDelay bool // send ack immediately for each incoming packet writeDelay bool // delay kcp.flush() for Write() for bulk transfer dup int // duplicate udp packets // notifications die chan struct{} // notify session has Closed chReadEvent chan struct{} // notify Read() can be called without blocking chWriteEvent chan struct{} // notify Write() can be called without blocking chErrorEvent chan error // notify Read() have an error isClosed bool // flag the session has Closed mu sync.Mutex } setReadBuffer interface { SetReadBuffer(bytes int) error } setWriteBuffer interface { SetWriteBuffer(bytes int) error } ) // newUDPSession create a new udp session for client or server func newUDPSession(conv uint32, dataShards, parityShards int, l *Listener, conn net.PacketConn, remote net.Addr, block BlockCrypt) *UDPSession { sess := new(UDPSession) sess.die = make(chan struct{}) sess.chReadEvent = make(chan struct{}, 1) sess.chWriteEvent = make(chan struct{}, 1) sess.chErrorEvent = make(chan error, 1) sess.remote = remote sess.conn = conn sess.l = l sess.block = block sess.recvbuf = make([]byte, mtuLimit) // FEC initialization sess.fecDecoder = newFECDecoder(rxFECMulti*(dataShards+parityShards), dataShards, parityShards) if sess.block != nil { sess.fecEncoder = newFECEncoder(dataShards, parityShards, cryptHeaderSize) } else { sess.fecEncoder = newFECEncoder(dataShards, parityShards, 0) } // calculate header size if sess.block != nil { sess.headerSize += cryptHeaderSize } if sess.fecEncoder != nil { sess.headerSize += fecHeaderSizePlus2 } // only allocate extended packet buffer // when the extra header is required if sess.headerSize > 0 { sess.ext = make([]byte, mtuLimit) } sess.kcp = NewKCP(conv, func(buf []byte, size int) { if size >= IKCP_OVERHEAD { sess.output(buf[:size]) } }) sess.kcp.SetMtu(IKCP_MTU_DEF - sess.headerSize) // add current session to the global updater, // which periodically calls sess.update() updater.addSession(sess) if sess.l == nil { // it's a client connection go sess.readLoop() atomic.AddUint64(&DefaultSnmp.ActiveOpens, 1) } else { atomic.AddUint64(&DefaultSnmp.PassiveOpens, 1) } currestab := atomic.AddUint64(&DefaultSnmp.CurrEstab, 1) maxconn := atomic.LoadUint64(&DefaultSnmp.MaxConn) if currestab > maxconn { atomic.CompareAndSwapUint64(&DefaultSnmp.MaxConn, maxconn, currestab) } return sess } // Read implements net.Conn func (s *UDPSession) Read(b []byte) (n int, err error) { for { s.mu.Lock() if len(s.bufptr) > 0 { // copy from buffer into b n = copy(b, s.bufptr) s.bufptr = s.bufptr[n:] s.mu.Unlock() 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 atomic.AddUint64(&DefaultSnmp.BytesReceived, uint64(size)) if len(b) >= size { // direct write to b s.kcp.Recv(b) s.mu.Unlock() return size, nil } // resize kcp receive buffer // to make sure recvbuf has enough capacity if cap(s.recvbuf) < size { s.recvbuf = make([]byte, size) } // resize recvbuf slice length s.recvbuf = s.recvbuf[:size] s.kcp.Recv(s.recvbuf) n = copy(b, s.recvbuf) // copy to b s.bufptr = s.recvbuf[n:] // update pointer s.mu.Unlock() return n, nil } // read deadline var timeout *time.Timer var c <-chan time.Time if !s.rd.IsZero() { if time.Now().After(s.rd) { s.mu.Unlock() return 0, errTimeout{} } delay := s.rd.Sub(time.Now()) timeout = time.NewTimer(delay) c = timeout.C } s.mu.Unlock() // wait for read event or timeout select { case <-s.chReadEvent: case <-c: case <-s.die: case err = <-s.chErrorEvent: if timeout != nil { timeout.Stop() } return n, err } if timeout != nil { timeout.Stop() } } } // Write implements net.Conn func (s *UDPSession) Write(b []byte) (n int, err error) { for { s.mu.Lock() if s.isClosed { s.mu.Unlock() return 0, errors.New(errBrokenPipe) } // api flow control 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:] } } if !s.writeDelay { s.kcp.flush(false) } s.mu.Unlock() atomic.AddUint64(&DefaultSnmp.BytesSent, uint64(n)) return n, nil } // write deadline 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{} } delay := s.wd.Sub(time.Now()) timeout = time.NewTimer(delay) c = timeout.C } s.mu.Unlock() // wait for write event or timeout select { case <-s.chWriteEvent: case <-c: case <-s.die: } if timeout != nil { timeout.Stop() } } } // Close closes the connection. func (s *UDPSession) Close() error { // remove this session from updater & listener(if necessary) updater.removeSession(s) if s.l != nil { // notify listener s.l.closeSession(sessionKey{ addr: s.remote.String(), convID: s.kcp.conv, }) } s.mu.Lock() defer s.mu.Unlock() if s.isClosed { return errors.New(errBrokenPipe) } 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. func (s *UDPSession) LocalAddr() net.Addr { return s.conn.LocalAddr() } // RemoteAddr returns the remote network address. The Addr returned is shared by all invocations of RemoteAddr, so do not modify it. func (s *UDPSession) RemoteAddr() net.Addr { return s.remote } // SetDeadline sets the deadline associated with the listener. A zero time value disables the deadline. func (s *UDPSession) SetDeadline(t time.Time) error { s.mu.Lock() defer s.mu.Unlock() s.rd = t s.wd = t return nil } // SetReadDeadline implements the Conn SetReadDeadline method. func (s *UDPSession) SetReadDeadline(t time.Time) error { s.mu.Lock() defer s.mu.Unlock() s.rd = t return nil } // SetWriteDeadline implements the Conn SetWriteDeadline method. func (s *UDPSession) SetWriteDeadline(t time.Time) error { s.mu.Lock() defer s.mu.Unlock() s.wd = t return nil } // SetWriteDelay delays write for bulk transfer until the next update interval func (s *UDPSession) SetWriteDelay(delay bool) { s.mu.Lock() defer s.mu.Unlock() s.writeDelay = delay } // SetWindowSize set maximum window size func (s *UDPSession) SetWindowSize(sndwnd, rcvwnd int) { s.mu.Lock() defer s.mu.Unlock() s.kcp.WndSize(sndwnd, rcvwnd) } // SetMtu sets the maximum transmission unit(not including UDP header) func (s *UDPSession) SetMtu(mtu int) bool { if mtu > mtuLimit { return false } s.mu.Lock() defer s.mu.Unlock() s.kcp.SetMtu(mtu - s.headerSize) return true } // SetStreamMode toggles the stream mode on/off func (s *UDPSession) SetStreamMode(enable bool) { s.mu.Lock() defer s.mu.Unlock() if enable { s.kcp.stream = 1 } else { s.kcp.stream = 0 } } // SetACKNoDelay changes ack flush option, set true to flush ack immediately, func (s *UDPSession) SetACKNoDelay(nodelay bool) { s.mu.Lock() defer s.mu.Unlock() s.ackNoDelay = nodelay } // SetDUP duplicates udp packets for kcp output, for testing purpose only func (s *UDPSession) SetDUP(dup int) { s.mu.Lock() defer s.mu.Unlock() s.dup = dup } // SetNoDelay calls nodelay() of kcp // https://github.com/skywind3000/kcp/blob/master/README.en.md#protocol-configuration func (s *UDPSession) SetNoDelay(nodelay, interval, resend, nc int) { s.mu.Lock() defer s.mu.Unlock() s.kcp.NoDelay(nodelay, interval, resend, nc) } // SetDSCP sets the 6bit DSCP field of IP header, 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.(*connectedUDPConn); ok { return ipv4.NewConn(nc.UDPConn).SetTOS(dscp << 2) } else if nc, ok := s.conn.(net.Conn); ok { return ipv4.NewConn(nc).SetTOS(dscp << 2) } } return errors.New(errInvalidOperation) } // SetReadBuffer sets the socket read buffer, no effect if it's accepted from Listener func (s *UDPSession) SetReadBuffer(bytes int) error { s.mu.Lock() defer s.mu.Unlock() if s.l == nil { if nc, ok := s.conn.(setReadBuffer); ok { return nc.SetReadBuffer(bytes) } } return errors.New(errInvalidOperation) } // SetWriteBuffer sets the socket write buffer, no effect if it's accepted from Listener func (s *UDPSession) SetWriteBuffer(bytes int) error { s.mu.Lock() defer s.mu.Unlock() if s.l == nil { if nc, ok := s.conn.(setWriteBuffer); ok { return nc.SetWriteBuffer(bytes) } } return errors.New(errInvalidOperation) } // output pipeline entry // steps for output data processing: // 0. Header extends // 1. FEC // 2. CRC32 // 3. Encryption // 4. WriteTo kernel 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) } // 2&3. crc32 & encryption if s.block != nil { io.ReadFull(rand.Reader, ext[:nonceSize]) checksum := crc32.ChecksumIEEE(ext[cryptHeaderSize:]) binary.LittleEndian.PutUint32(ext[nonceSize:], checksum) s.block.Encrypt(ext, ext) for k := range ecc { io.ReadFull(rand.Reader, ecc[k][:nonceSize]) checksum := crc32.ChecksumIEEE(ecc[k][cryptHeaderSize:]) binary.LittleEndian.PutUint32(ecc[k][nonceSize:], checksum) s.block.Encrypt(ecc[k], ecc[k]) } } // 4. WriteTo kernel nbytes := 0 npkts := 0 for i := 0; i < s.dup+1; i++ { if n, err := s.conn.WriteTo(ext, s.remote); err == nil { nbytes += n npkts++ } } for k := range ecc { if n, err := s.conn.WriteTo(ecc[k], s.remote); err == nil { nbytes += n npkts++ } } atomic.AddUint64(&DefaultSnmp.OutPkts, uint64(npkts)) atomic.AddUint64(&DefaultSnmp.OutBytes, uint64(nbytes)) } // kcp update, returns interval for next calling func (s *UDPSession) update() (interval time.Duration) { s.mu.Lock() s.kcp.flush(false) if s.kcp.WaitSnd() < int(s.kcp.snd_wnd) { s.notifyWriteEvent() } interval = time.Duration(s.kcp.interval) * time.Millisecond s.mu.Unlock() return } // GetConv gets conversation id of a session func (s *UDPSession) GetConv() uint32 { return s.kcp.conv } func (s *UDPSession) notifyReadEvent() { select { case s.chReadEvent <- struct{}{}: default: } } func (s *UDPSession) notifyWriteEvent() { select { case s.chWriteEvent <- struct{}{}: default: } } func (s *UDPSession) kcpInput(data []byte) { var kcpInErrors, fecErrs, fecRecovered, fecParityShards uint64 if s.fecDecoder != nil { f := s.fecDecoder.decodeBytes(data) s.mu.Lock() if f.flag == typeData { if ret := s.kcp.Input(data[fecHeaderSizePlus2:], true, s.ackNoDelay); ret != 0 { kcpInErrors++ } } if f.flag == typeData || f.flag == typeFEC { if f.flag == typeFEC { fecParityShards++ } recovers := s.fecDecoder.decode(f) for _, r := range recovers { if len(r) >= 2 { // must be larger than 2bytes sz := binary.LittleEndian.Uint16(r) if int(sz) <= len(r) && sz >= 2 { if ret := s.kcp.Input(r[2:sz], false, s.ackNoDelay); ret == 0 { fecRecovered++ } else { kcpInErrors++ } } else { fecErrs++ } } else { fecErrs++ } } } // notify reader if n := s.kcp.PeekSize(); n > 0 { s.notifyReadEvent() } s.mu.Unlock() } else { s.mu.Lock() if ret := s.kcp.Input(data, true, s.ackNoDelay); ret != 0 { kcpInErrors++ } // notify reader if n := s.kcp.PeekSize(); n > 0 { s.notifyReadEvent() } s.mu.Unlock() } atomic.AddUint64(&DefaultSnmp.InPkts, 1) atomic.AddUint64(&DefaultSnmp.InBytes, uint64(len(data))) if fecParityShards > 0 { atomic.AddUint64(&DefaultSnmp.FECParityShards, fecParityShards) } if kcpInErrors > 0 { atomic.AddUint64(&DefaultSnmp.KCPInErrors, kcpInErrors) } if fecErrs > 0 { atomic.AddUint64(&DefaultSnmp.FECErrs, fecErrs) } if fecRecovered > 0 { atomic.AddUint64(&DefaultSnmp.FECRecovered, fecRecovered) } } func (s *UDPSession) receiver(ch chan<- []byte) { for { data := xmitBuf.Get().([]byte)[:mtuLimit] if n, _, err := s.conn.ReadFrom(data); err == nil && n >= s.headerSize+IKCP_OVERHEAD { select { case ch <- data[:n]: case <-s.die: return } } else if err != nil { s.chErrorEvent <- err return } else { atomic.AddUint64(&DefaultSnmp.InErrs, 1) } } } // read loop for client session func (s *UDPSession) readLoop() { chPacket := make(chan []byte, qlen) go s.receiver(chPacket) for { select { case data := <-chPacket: raw := data 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) } xmitBuf.Put(raw) case <-s.die: return } } } type ( sessionKey struct { addr string convID uint32 } // Listener defines a server listening for connections Listener struct { block BlockCrypt // block encryption dataShards int // FEC data shard parityShards int // FEC parity shard fecDecoder *fecDecoder // FEC mock initialization conn net.PacketConn // the underlying packet connection sessions map[sessionKey]*UDPSession // all sessions accepted by this Listener chAccepts chan *UDPSession // Listen() backlog chSessionClosed chan sessionKey // session close queue headerSize int // the overall header size added before KCP frame die chan struct{} // notify the listener has closed rd atomic.Value // read deadline for Accept() wd atomic.Value } // incoming packet inPacket struct { from net.Addr data []byte } ) // monitor incoming data for all connections of server func (l *Listener) monitor() { // cache last session var lastKey sessionKey var lastSession *UDPSession chPacket := make(chan inPacket, qlen) go l.receiver(chPacket) for { select { case p := <-chPacket: raw := p.data data := p.data from := p.from 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 { 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 { key := sessionKey{ addr: from.String(), convID: conv, } var s *UDPSession var ok bool // packets received from an address always come in batch. // cache the session for next packet, without querying map. if key == lastKey { s, ok = lastSession, true } else if s, ok = l.sessions[key]; ok { lastSession = s lastKey = key } if !ok { // new session if len(l.chAccepts) < cap(l.chAccepts) && len(l.sessions) < 4096 { // do not let new session overwhelm accept queue and connection count s := newUDPSession(conv, l.dataShards, l.parityShards, l, l.conn, from, l.block) s.kcpInput(data) l.sessions[key] = s l.chAccepts <- s } } else { s.kcpInput(data) } } } xmitBuf.Put(raw) case key := <-l.chSessionClosed: if key == lastKey { lastKey = sessionKey{} } delete(l.sessions, key) case <-l.die: return } } } func (l *Listener) receiver(ch chan<- inPacket) { for { data := xmitBuf.Get().([]byte)[:mtuLimit] if n, from, err := l.conn.ReadFrom(data); err == nil && n >= l.headerSize+IKCP_OVERHEAD { select { case ch <- inPacket{from, data[:n]}: case <-l.die: return } } else if err != nil { return } else { atomic.AddUint64(&DefaultSnmp.InErrs, 1) } } } // 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) } // SetWriteBuffer sets the socket write buffer for the Listener func (l *Listener) SetWriteBuffer(bytes int) error { if nc, ok := l.conn.(setWriteBuffer); ok { return nc.SetWriteBuffer(bytes) } return errors.New(errInvalidOperation) } // SetDSCP sets the 6bit DSCP field of IP header func (l *Listener) SetDSCP(dscp int) error { if nc, ok := l.conn.(net.Conn); ok { return ipv4.NewConn(nc).SetTOS(dscp << 2) } return errors.New(errInvalidOperation) } // Accept implements the Accept method in the Listener interface; it waits for the next call and returns a generic Conn. func (l *Listener) Accept() (net.Conn, error) { return l.AcceptKCP() } // AcceptKCP accepts a KCP connection func (l *Listener) AcceptKCP() (*UDPSession, error) { var timeout <-chan time.Time if tdeadline, ok := l.rd.Load().(time.Time); ok && !tdeadline.IsZero() { timeout = time.After(tdeadline.Sub(time.Now())) } select { case <-timeout: return nil, &errTimeout{} case c := <-l.chAccepts: return c, nil case <-l.die: return nil, errors.New(errBrokenPipe) } } // SetDeadline sets the deadline associated with the listener. A zero time value disables the deadline. func (l *Listener) SetDeadline(t time.Time) error { l.SetReadDeadline(t) l.SetWriteDeadline(t) return nil } // SetReadDeadline implements the Conn SetReadDeadline method. func (l *Listener) SetReadDeadline(t time.Time) error { l.rd.Store(t) return nil } // SetWriteDeadline implements the Conn SetWriteDeadline method. func (l *Listener) SetWriteDeadline(t time.Time) error { l.wd.Store(t) return nil } // Close stops listening on the UDP address. Already Accepted connections are not closed. func (l *Listener) Close() error { close(l.die) return l.conn.Close() } // closeSession notify the listener that a session has closed func (l *Listener) closeSession(key sessionKey) bool { select { case l.chSessionClosed <- key: return true case <-l.die: return false } } // Addr returns the listener's network address, The Addr returned is shared by all invocations of Addr, so do not modify it. 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 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") } conn, err := net.ListenUDP("udp", udpaddr) if err != nil { return nil, errors.Wrap(err, "net.ListenUDP") } return ServeConn(block, dataShards, parityShards, conn) } // ServeConn serves KCP protocol for a single packet connection. func ServeConn(block BlockCrypt, dataShards, parityShards int, conn net.PacketConn) (*Listener, error) { l := new(Listener) l.conn = conn l.sessions = make(map[sessionKey]*UDPSession) l.chAccepts = make(chan *UDPSession, acceptBacklog) l.chSessionClosed = make(chan sessionKey) l.die = make(chan struct{}) l.dataShards = dataShards l.parityShards = parityShards l.block = block l.fecDecoder = newFECDecoder(rxFECMulti*(dataShards+parityShards), dataShards, parityShards) // calculate header size if l.block != nil { l.headerSize += cryptHeaderSize } if l.fecDecoder != nil { l.headerSize += fecHeaderSizePlus2 } go l.monitor() return l, nil } // Dial connects to the remote address "raddr" on the network "udp" 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 func DialWithOptions(raddr string, block BlockCrypt, dataShards, parityShards int) (*UDPSession, error) { udpaddr, err := net.ResolveUDPAddr("udp", raddr) if err != nil { return nil, errors.Wrap(err, "net.ResolveUDPAddr") } udpconn, err := net.DialUDP("udp", nil, udpaddr) if err != nil { return nil, errors.Wrap(err, "net.DialUDP") } return NewConn(raddr, block, dataShards, parityShards, &connectedUDPConn{udpconn}) } // 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") } var convid uint32 binary.Read(rand.Reader, binary.LittleEndian, &convid) return newUDPSession(convid, dataShards, parityShards, nil, conn, udpaddr, block), nil } 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 { return nil, errors.Wrap(err, "net.ResolveUDPAddr") } var pConn net.PacketConn = conn if connected { pConn = &connectedUDPConn{conn} } return newUDPSession(convid, dataShards, parityShards, nil, pConn, udpaddr, block), nil } // returns current time in milliseconds func currentMs() uint32 { return uint32(time.Now().UnixNano() / int64(time.Millisecond)) } // connectedUDPConn is a wrapper for net.UDPConn which converts WriteTo syscalls // to Write syscalls that are 4 times faster on some OS'es. This should only be // used for connections that were produced by a net.Dial* call. type connectedUDPConn struct{ *net.UDPConn } // WriteTo redirects all writes to the Write syscall, which is 4 times faster. func (c *connectedUDPConn) WriteTo(b []byte, addr net.Addr) (int, error) { return c.Write(b) }