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155 lines
3.2 KiB
155 lines
3.2 KiB
// RTP Session Transport Layer.
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package rtp
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import (
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"github.com/jart/gosip/dsp"
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"github.com/jart/gosip/sdp"
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"log"
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"math/rand"
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"net"
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"strconv"
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"strings"
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)
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const (
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rtpBindMaxAttempts = 10
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rtpBindPortMin = 16384
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rtpBindPortMax = 32768
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)
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type Frame [160]int16
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// Session allows sending and receiving slinear frames for a single SIP media
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// session. These frames are encoded as µLaw and transmitted over UDP. No
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// support for RTCP is provided.
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type Session struct {
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// Channel to which received RTP frames and errors are published.
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C <-chan *Frame
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R chan<- *Frame
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E <-chan error
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// Underlying UDP socket.
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Sock *net.UDPConn
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// Address of remote endpoint. This might change mid-session. If it's nil,
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// then egress packets are dropped.
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Peer *net.UDPAddr
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// Header is the current header that gets mutated with each transmit.
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Header Header
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obuf []byte
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}
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// Creates a new RTP µLaw 20ptime session listening on host with a random port
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// selected from the range [16384,32768].
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func NewSession(host string) (rs *Session, err error) {
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conn, err := listenRTP(host)
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if err != nil {
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return nil, err
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}
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sock := conn.(*net.UDPConn)
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c := make(chan *Frame)
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r := make(chan *Frame)
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e := make(chan error)
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go receiver(sock, c, e, r)
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return &Session{
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C: c,
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E: e,
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R: r,
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Sock: sock,
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Header: Header{
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PT: sdp.ULAWCodec.PT,
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Seq: 666,
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TS: 0,
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Ssrc: rand.Uint32(),
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},
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obuf: make([]byte, HeaderSize+160),
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}, nil
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}
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func (rs *Session) Send(frame *Frame) (err error) {
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if rs == nil || rs.Sock == nil || rs.Peer == nil {
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return nil
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}
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rs.Header.Write(rs.obuf)
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rs.Header.TS += 160
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rs.Header.Seq++
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for n := 0; n < 160; n++ {
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rs.obuf[HeaderSize+n] = byte(dsp.LinearToUlaw(int64(frame[n])))
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}
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_, err = rs.Sock.WriteTo(rs.obuf, rs.Peer)
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return
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}
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func (rs *Session) Close() {
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if rs == nil || rs.Sock == nil {
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return
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}
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rs.Sock.Close()
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if frame, ok := <-rs.C; ok {
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rs.R <- frame
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}
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<-rs.E
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rs.Sock = nil
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close(rs.R)
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}
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func (rs *Session) CloseAfterError() {
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if rs == nil || rs.Sock == nil {
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return
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}
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rs.Sock.Close()
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rs.Sock = nil
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close(rs.R)
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<-rs.E
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}
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func receiver(sock *net.UDPConn, c chan<- *Frame, e chan<- error, r <-chan *Frame) {
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buf := make([]byte, 2048)
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frame := new(Frame)
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for {
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amt, _, err := sock.ReadFrom(buf)
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if err != nil {
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close(c)
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e <- err
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break
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}
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// TODO(jart): Verify source address?
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// TODO(jart): Packet reordering? Drop duplicate packets?
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// TODO(jart): DTMF?
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var phdr Header
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err = phdr.Read(buf)
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if err != nil {
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// TODO(jart): Best logging strategy?
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continue
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}
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if phdr.PT != sdp.ULAWCodec.PT {
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continue
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}
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if amt != HeaderSize+160 {
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continue
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}
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for n := 0; n < 160; n++ {
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frame[n] = int16(dsp.UlawToLinear(int64(buf[HeaderSize+n])))
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}
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c <- frame
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frame = <-r
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}
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close(e)
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}
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func listenRTP(host string) (sock net.PacketConn, err error) {
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for i := 0; i < rtpBindMaxAttempts; i++ {
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port := rtpBindPortMin + rand.Int63()%(rtpBindPortMax-rtpBindPortMin+1)
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saddr := net.JoinHostPort(host, strconv.FormatInt(port, 10))
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sock, err = net.ListenPacket("udp", saddr)
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if err == nil || !strings.Contains(err.Error(), "address already in use") {
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break
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}
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log.Println("RTP listen congestion:", saddr)
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}
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return
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}
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