WebRTC Example

example.go

package main

import (
	"code.google.com/p/go.net/websocket"

	"net/http"
	"log"
)

// all code is in an init function to avoid any name collisions
func init() {
	type (
		Message struct {
			Topic string `json:"topic"`
			From uint32 `json:"from"`
			To uint32 `json:"to"`
			Type string `json:"type"`
			Data interface{} `json:"data"`
		}
	)

	var (
		topics = make(map[string]map[uint32]chan Message)
		in = make(chan Message)
	)

	send := func(out chan Message, msg Message) {
		// drop messages when we're full
		select {
			case out<-msg:
			default:
		}
	}
	subscribe := func(topicId string, userId uint32, out chan Message) {
		topic, ok := topics[topicId]
		// create a topic if it doesn't exist
		if !ok {
			topic = make(map[uint32]chan Message)
			topics[topicId] = topic
		}
		// add the user to the topic
		topic[userId] = out

		// let the other subscribers know the new user just subscribed
		for id, c := range topic {
			if id != userId {
				send(c, Message{
					Topic: topicId,
					From: userId,
					To: id,
					Type: "SUBSCRIBED",
				})
			}
		}
	}
	unsubscribe := func(topicId string, userId uint32) {
		topic, ok := topics[topicId]
		// just give up if the topic doesn't exist
		if !ok {
			return
		}
		_, ok = topic[userId]
		// also give up if the user isn't already subscribed to this topic
		if !ok {
			return
		}
		// delete the user from the topic
		delete(topic, userId)

		// let the other subscribers know the user unsubscribed
		for id, c := range topic {
			send(c, Message{
				Topic: topicId,
				From: userId,
				To: id,
				Type: "UNSUBSCRIBED",
			})
		}

		// delete the topic if it's empty
		if len(topic) == 0 {
			delete(topics, topicId)
		}
	}

	// all incoming messages are handled by this go routine (keeps us from needing
	// a lock)
	go func() {
		for msg := range in {
			switch msg.Type {
			// drop ID messages
			case "ID":
			case "SUBSCRIBE":
				subscribe(msg.Topic, msg.From, msg.Data.(chan Message))
			case "UNSUBSCRIBE":
				unsubscribe(msg.Topic, msg.From)
			// everything else we forward along
			default:
				topic, ok := topics[msg.Topic]
				if !ok {
					continue
				}
				c, ok := topic[msg.To]
				if ok {
					send(c, msg)
				}
			}
		}
	}()

	http.Handle("/channel", websocket.Server{
		// make it so we can connect from any domain
		Config: websocket.Config{
			Header: http.Header(map[string][]string{
				"Access-Control-Allow-Origin": []string{"*"},
			}),
		},
		Handler: func(ws *websocket.Conn) {
			// generate a new id (using a full cycle PRNG
			//   http://godoc.org/github.com/cznic/mathutil#NewFC32
			// )
			id := <-idGenerator

			log.Println(id, "connected")

			// keep track of our existing subscriptions so we can unsubcribe
			subscriptions := []string{}

			// this is our output channel which the main goroutine will send messages 
			//   to. We buffer up to 5 messages and start dropping if the client can't 
			//   keep up.
			out := make(chan Message, 5)

			// on disconnect we unsubscribe from any subscriptions
			defer func() {
				for _, topicId := range subscriptions {
					in <- Message{
						Topic: topicId,
						From: id,
						Type: "UNSUBSCRIBE",
					}
				}
				close(out)
				ws.Close()
				log.Println(id, "disconnected")
			}()

			// send the user the id (we want this to be first which is why we send it
			//   here)
			out <- Message{
				Type: "ID",
				To: id,
			}

			// fire up a goroutine which will send all the messages
			go func() {
				for msg := range out {
					websocket.JSON.Send(ws, msg)
				}
			}()

			// start reading messages from the client
			for {
				var msg Message
				err := websocket.JSON.Receive(ws, &msg)
				if err != nil {
					break
				}
				// overwrite the from id
				msg.From = id
				// for subscriptions we add it to our list of subscriptions and make the
				//   Data be the out channel
				if msg.Type == "SUBSCRIBE" {
					subscriptions = append(subscriptions, msg.Topic)
					msg.Data = out
				}
				// and send it along to the main goroutine
				in <- msg
			}
		},
	});
}

example.js

RTCPeerConnection = window.RTCPeerConnection || window.webkitRTCPeerConnection || window.mozRTCPeerConnection;
RTCIceCandidate = window.RTCIceCandidate || window.mozRTCIceCandidate;

var chatLog = document.getElementById("chat-log");
var chatForm = document.getElementById("chat-form");
var chatHistory = document.getElementById("chat-history");
var chatInput = document.getElementById("chat-input");

var topic, ws, pc, dc, from, to, candidates = [];

function trace(msg) {
  chatLog.textContent += msg + "\n";
}

// connect to the signaling server
function startWebSocket() {
  ws = new WebSocket("ws://api.badgerodon.com:9000/channel");
  ws.onopen = function() {
    trace("     web socket | opened");
    ws.send(JSON.stringify({
      topic: topic,
      type: "SUBSCRIBE"
    }));
  };
  ws.onclose = function() {
    trace("web socket | closed");
  };
  ws.onmessage = function(evt) {
    var msg = JSON.parse(evt.data);
    switch (msg.type) {
    // (1) the server tells us our id
    case "ID":
      trace("     web socket | your id: " + msg.to);
      from = msg.to;
      break;
    // (2a) the first user to show up will be told when the second user shows up
    case "SUBSCRIBED":
      trace("     web socket | joined: " + msg.from);
      to = msg.from;
      // start the connection
      startPeerConnection();
      // send an offer to the other user
      sendOffer();
      break;
    case "UNSUBSCRIBED":
      trace("     web socket | left: " + msg.from);
      break;
    // (2b) the second user receives the first user's offer
    case "OFFER":
      trace("     web socket | offer from: " + msg.from + ", " + JSON.stringify(msg.data));
      to = msg.from;
      // start the connection
      startPeerConnection();
      // accept the offer
      setRemoteDescription(msg.data);
      // send an answer to the first user
      sendAnswer();
      break;
    // (3a) the first user receives the answer from the second user
		case "ANSWER":
      trace("     web socket | answer from: " + msg.from + ", " + JSON.stringify(msg.data));
      setRemoteDescription(msg.data);
			break;
    // (4) both users receive ICE candidates from each other
		case "CANDIDATE":
      trace("     web socket | candidate from: " + msg.from + ", " + JSON.stringify(msg.data));
      addCandidates(msg.data);
			break;
    }
  };
}

// connect to a peer
function startPeerConnection() {
  if (dc) {
    dc.close();
    dc = null;
  }
  if (pc) {
    pc.close();
    pc = null;
  }

  pc = new RTCPeerConnection({
    iceServers: [{
      // stun allows NAT traversal
      url: "stun:stun.l.google.com:19302"
    }]
  }, {
    // we are going to communicate over a data channel
    optional: [{
      RtpDataChannels: true
    }]
  });
  // send all ice candidates to our peer
  pc.onicecandidate = function(evt) {
    if (evt.candidate) {
      ws.send(JSON.stringify({
        topic: topic,
        type: "CANDIDATE",
        to: to,
        data: evt.candidate
      }));
    }
  };
  // close on disconnect
  pc.oniceconnectionstatechange = function(evt) {
    trace("peer connection | ice connection state: " + (pc && pc.iceConnectionState));
    if (pc && pc.iceConnectionState === 'disconnected') {
      pc.close();
    }
  };

  // create the data channel, use TCP
  dc = pc.createDataChannel("RTCDataChannel", {
    reliable: true
  });
  dc.onopen = function(evt) {
    trace("   data channel | opened");
  };
  dc.onclose = function(evt) {
    trace("   data channel | closed");
  };
  dc.onerror = function(evt) {
    trace("   data channel | error: " + JSON.stringify(evt));
  }
  dc.onmessage = function(evt) {
    var msg = JSON.parse(evt.data);
    switch (msg.type) {
    case "MESSAGE":
      trace("   data channel | message from: " + msg.from + ", " + msg.data);
      onMessage(msg);
      break;
    }
  };
}

function sendOffer() {
  pc.createOffer(function(description) {
    pc.setLocalDescription(description);
    ws.send(JSON.stringify({
      topic: topic,
      type: "OFFER",
      to: to,
      data: description
    }));
  }, null, {
    optional: [],
    mandatory: {
      OfferToReceiveAudio: false,
      OfferToReceiveVideo: false
    }
  });
}

function sendAnswer() {
  pc.createAnswer(function(description) {
    pc.setLocalDescription(description);
    ws.send(JSON.stringify({
      topic: topic,
      type: "ANSWER",
      to: to,
      data: description
    }));
  });
}

function setRemoteDescription(description) {
  pc.setRemoteDescription(new RTCSessionDescription(description));
  addCandidates();
}

function addCandidates(/* 0 or more candidates */) {
  candidates.push.apply(candidates, arguments);

  // only actually add the candidates if the remote description has been set
  if (pc.remoteDescription) {
    for (var i=0; i<candidates.length; i++) {
      pc.addIceCandidate(new RTCIceCandidate(candidates[i]));
    }
    candidates = [];
  }
}

function onMessage(msg) {
  chatHistory.textContent += msg.from + ": " + msg.data + "\n";
}

function onSubmit(evt) {
  evt.preventDefault();

  var text = chatInput.value;
  chatInput.value = "";
  var msg = {
    type: "MESSAGE",
    data: text,
    from: from,
    to: to
  };
  onMessage(msg);
  dc.send(JSON.stringify(msg));
}

chatForm.addEventListener("submit", onSubmit);

function main() {
  while (!topic) {
    topic = prompt("Please Enter a Topic", "");
  }
  startWebSocket();
}

main();