Allo

Videoconference WebRTC example with an Elm frontend. Requires https. More info in the post on Elm discourse.

Setup and Run

# Install node packages
npm install

# Start the server
npm start

Heroku setup

git clone https://github.com/mpizenberg/elm-allo.git
cd elm-allo
heroku login
heroku create
git push heroku master

Nginx Reverse Proxy Configuration

http {
	server { ... }
	server { ... }
	server {
		server_name subdomain.domain.com;
		location / {
			# Special treatment to handle WebSocket hop-by-hop headers
			proxy_http_version 1.1;
			proxy_set_header Upgrade $http_upgrade;
			proxy_set_header Connection "upgrade";

			# Standard proxy
			proxy_pass http://localhost:8443;
			proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
			proxy_set_header X-Forwarded-Proto $scheme;
		}
		# ... stuff added by Certbot for SSL
	}
}

WebRTC Negotiation

Establishing a connection between two peers requires first a negotiation between each client. The server has the broker's role by relaying all messages between those peers.

All the WebRTC-specific code, including negotiation, is located in the public/WebRTCClient.js file. A high-level API is provided with the WebRTCCLient() function. Intermediate-level APIs are also provided with the SignalingSocket() and PeerConnection() functions. The core of the negotiation logic lives inside the Peerconnection() function. Two negotiation algorithms are implemented, but only one is activated.

The first negotiation algorithm follows a simple caller/callee pattern. It corresponds to the simpleNegotiation() function.

The second negotiation algorithm is called perfect negotiation. Both peers are considered equally and it tries to handle peer changes of states without glare (signaling collisions). A very useful blog post by Jan-Ivar Bruaroey introduces the perfect negotiation pattern. Unfortunately, browsers still have some issues preventing the usage of this pattern so it has been deactivated in our code. This corresponds to the perfectNegotiation() function.