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121 lines
2.6 KiB
121 lines
2.6 KiB
// RTP Session Transport Layer.
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package rtp
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import (
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"errors"
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"fmt"
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"github.com/jart/gosip/dsp"
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"github.com/jart/gosip/sdp"
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"github.com/jart/gosip/util"
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"math/rand"
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"net"
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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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// 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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ibuf []byte
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obuf []byte
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phdr Header
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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) (s *Session, err error) {
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sock, 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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return &Session{
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Sock: sock.(*net.UDPConn),
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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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}, err
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}
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func (s *Session) Send(frame Frame) (err error) {
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if s.Peer == nil {
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return nil
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}
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if s.obuf == nil {
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s.obuf = make([]byte, HeaderSize+160)
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}
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s.Header.Write(s.obuf)
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s.Header.TS += 160
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s.Header.Seq++
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for n := 0; n < 160; n++ {
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s.obuf[HeaderSize+n] = byte(dsp.LinearToUlaw(int64(frame[n])))
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}
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_, err = s.Sock.WriteTo(s.obuf, s.Peer)
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return
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}
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func (s *Session) Recv(frame Frame) (err error) {
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if s.ibuf == nil {
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s.ibuf = make([]byte, 2048)
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}
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for {
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amt, _, err := s.Sock.ReadFrom(s.ibuf)
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if err != nil {
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return err
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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(s.ibuf)
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if err != nil {
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return err
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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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return errors.New(fmt.Sprintf("Unexpected RTP packet size: %d", amt))
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}
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for n := 0; n < 160; n++ {
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frame[n] = int16(dsp.UlawToLinear(int64(s.ibuf[HeaderSize+n])))
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}
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return nil
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}
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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.Int()%(rtpBindPortMax-rtpBindPortMin+1)
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saddr := util.HostPortToString(host, uint16(port))
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sock, err = net.ListenPacket("udp", saddr)
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if err != nil {
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if !strings.Contains(err.Error(), "address already in use") {
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break
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}
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}
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}
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return
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}
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