go2rtc/pkg/webrtc/conn.go

package webrtc

import (
	"github.com/AlexxIT/go2rtc/pkg/core"
	"github.com/pion/rtcp"
	"github.com/pion/rtp"
	"github.com/pion/webrtc/v3"
	"time"
)

type Conn struct {
	core.Listener

	UserAgent string
	Desc      string
	Mode      core.Mode

	pc *webrtc.PeerConnection

	medias    []*core.Media
	receivers []*core.Receiver
	senders   []*core.Sender

	recv int
	send int

	offer  string
	remote string
	closed core.Waiter
}

func NewConn(pc *webrtc.PeerConnection) *Conn {
	c := &Conn{pc: pc}

	pc.OnICECandidate(func(candidate *webrtc.ICECandidate) {
		// last candidate will be empty
		if candidate != nil {
			c.Fire(candidate)
		}
	})

	pc.OnDataChannel(func(channel *webrtc.DataChannel) {
		c.Fire(channel)
	})

	pc.OnICEConnectionStateChange(func(state webrtc.ICEConnectionState) {
		if state != webrtc.ICEConnectionStateChecking {
			return
		}
		pc.SCTP().Transport().ICETransport().OnSelectedCandidatePairChange(
			func(pair *webrtc.ICECandidatePair) {
				c.remote = pair.Remote.String()
			},
		)
	})

	pc.OnTrack(func(remote *webrtc.TrackRemote, receiver *webrtc.RTPReceiver) {
		media, codec := c.getMediaCodec(remote)
		if media == nil {
			return
		}

		track, err := c.GetTrack(media, codec)
		if err != nil {
			return
		}

		switch c.Mode {
		case core.ModePassiveProducer, core.ModeActiveProducer:
			// replace the theoretical list of codecs with the actual list of codecs
			if len(media.Codecs) > 1 {
				media.Codecs = []*core.Codec{codec}
			}
		}

		if c.Mode == core.ModePassiveProducer && remote.Kind() == webrtc.RTPCodecTypeVideo {
			go func() {
				pkts := []rtcp.Packet{&rtcp.PictureLossIndication{MediaSSRC: uint32(remote.SSRC())}}
				for range time.NewTicker(time.Second * 2).C {
					if err := pc.WriteRTCP(pkts); err != nil {
						return
					}
				}
			}()
		}

		for {
			b := make([]byte, ReceiveMTU)
			n, _, err := remote.Read(b)
			if err != nil {
				return
			}

			c.recv += n

			packet := &rtp.Packet{}
			if err := packet.Unmarshal(b[:n]); err != nil {
				return
			}

			track.WriteRTP(packet)
		}
	})

	// OK connection:
	// 15:01:46 ICE connection state changed: checking
	// 15:01:46 peer connection state changed: connected
	// 15:01:54 peer connection state changed: disconnected
	// 15:02:20 peer connection state changed: failed
	//
	// Fail connection:
	// 14:53:08 ICE connection state changed: checking
	// 14:53:39 peer connection state changed: failed
	pc.OnConnectionStateChange(func(state webrtc.PeerConnectionState) {
		c.Fire(state)

		switch state {
		case webrtc.PeerConnectionStateDisconnected, webrtc.PeerConnectionStateFailed, webrtc.PeerConnectionStateClosed:
			// disconnect event comes earlier, than failed
			// but it comes only for success connections
			_ = c.Close()
		}
	})

	return c
}

func (c *Conn) Close() error {
	c.closed.Done()
	return c.pc.Close()
}

func (c *Conn) AddCandidate(candidate string) error {
	// pion uses only candidate value from json/object candidate struct
	return c.pc.AddICECandidate(webrtc.ICECandidateInit{Candidate: candidate})
}

func (c *Conn) getTranseiver(mid string) *webrtc.RTPTransceiver {
	for _, tr := range c.pc.GetTransceivers() {
		if tr.Mid() == mid {
			return tr
		}
	}
	return nil
}

func (c *Conn) getMediaCodec(remote *webrtc.TrackRemote) (*core.Media, *core.Codec) {
	for _, tr := range c.pc.GetTransceivers() {
		// search Transeiver for this TrackRemote
		if tr.Receiver() == nil || tr.Receiver().Track() != remote {
			continue
		}

		// search Media for this MID
		for _, media := range c.medias {
			if media.ID != tr.Mid() || media.Direction != core.DirectionRecvonly {
				continue
			}

			// search codec for this PayloadType
			for _, codec := range media.Codecs {
				if codec.PayloadType != uint8(remote.PayloadType()) {
					continue
				}
				return media, codec
			}
		}
	}

	// fix moment when core.ModePassiveProducer or core.ModeActiveProducer
	// sends new codec with new payload type to same media
	// check GetTrack
	panic(core.Caller())

	return nil, nil
}