ComunicRTCProxy/relay.go

/// RTC Relay
///
/// @author Pierre Hubert

package main

import (
	"encoding/json"
	"log"
	"time"

	"github.com/pion/webrtc/v2"
)

const (
	// SDP This is a SDP signal
	SDP = iota

	// CANDIDATE This is a candidate
	CANDIDATE = iota
)

type receivedSignal struct {
	peerID    string
	callHash  string
	sigType   uint
	offer     webrtc.SessionDescription
	candidate webrtc.ICECandidateInit
}

/// We keep for each connection its channel
var closeChan = make(chan string)
var connections = make(map[string]chan receivedSignal)

/// Process incoming messages
func onSignal(callHash, peerID string, data map[string]interface{}) {

	// Close all the channels that requested so
	processCloseRequests()

	// Decode received signal
	newSignal := receivedSignal{
		peerID:   peerID,
		callHash: callHash,
	}

	if data["type"] == "SDP" {
		newSignal.sigType = SDP
		newSignal.offer.Type = webrtc.SDPTypeOffer
		newSignal.offer.SDP = data["data"].(map[string]interface{})["sdp"].(string)

	} else if data["type"] == "CANDIDATE" {
		newSignal.sigType = CANDIDATE

		// I have to re-encode data to initialize ICECandidate
		var enc []byte
		enc, err := json.Marshal(data["data"])
		if err != nil {
			log.Printf("Could not re-encode candidate ! %s", err)
			return
		}

		err = json.Unmarshal(enc, &newSignal.candidate)
		if err != nil {
			log.Printf("Discarding invalid candidate: %s", err)
			return
		}

	} else {
		log.Fatalf("Invalid signal type: %s !", data["type"])
	}

	// Check if we are attempting to connect as viewer to a non existing channel
	if _, ok := connections[callHash]; !ok {
		if peerID != "0" || newSignal.sigType != SDP {
			println("Attempting to connect as viewer | send candidate to a non-ready broadcast!")
			return
		}
	}

	// Handle new offers
	if newSignal.sigType == SDP && peerID == "0" {

		// Check if we are overwriting another connection
		if _, ok := connections[callHash]; ok {
			closeConnection(callHash)
		}

		connections[callHash] = make(chan receivedSignal, 10)
		go newCall(newSignal, connections[callHash])

	} else {
		// Forward the message to the channel
		connections[callHash] <- newSignal
	}
}

/// Close a connection
func closeConnection(callHash string) {
	log.Printf("Closing call %s", callHash)
	if val, ok := connections[callHash]; ok {
		close(val)
		delete(connections, callHash)
	}
}

// Ask for a channel to be closed
func askForClose(callHash string) {
	closeChan <- callHash
}

// Process channel close requests (in thread safe way)
func processCloseRequests() {
	for {
		select {
		case id := <-closeChan:
			closeConnection(id)
		case <-time.After(time.Millisecond * 10):
			return
		}
	}
}

/// Start new call
func newCall(mainOffer receivedSignal, ch chan receivedSignal) {

	// Since we are answering use PayloadTypes declared by offerer
	mediaEngine := webrtc.MediaEngine{}
	err := mediaEngine.PopulateFromSDP(mainOffer.offer)
	if err != nil {
		log.Println("Error: invalid data in offer!", err)
		askForClose(mainOffer.callHash)
		return
	}

}