Notes and Thoughts

QuickChat and WebRTC

November 12, 2013

I’ve been working on a personal project called QuickChat for the past several weeks. A large part of the project uses WebRTC. It’s been a lot of fun and I’ve learned a lot during this process.

Starting QuickChat

I built QuickChat to scratch my own itch. Part of my responsibility as a programmer is to screen new programmers before inviting them for an on-site interview. Usually, this screening process involves a conversation using one of the following tools: Skype, Google Hangouts, or plain old telephone.

Over time using these tools became increasingly frustrating for the following reasons:

Skype and Hangouts have no builtin scheduling feature and require a separate tool to setup a future call.

What I really wanted is a tool through which I can send someone a URL and when they clicked on that URL, they are taken to a web page where I can start talking to them right away. After reading a bit about WebRTC, it seemed like the perfect technology to use to build the purpose-built tool I had in mind.

About WebRTC

WebRTC is a current W3C draft allowing web browsers to create peer-to-peer connections. With WebRTC’s high-level APIs, developers have access to:

These APIs allow developers to create low-friction, secure and high-quality communication tools. If you are building tools for the web, WebRTC is worth your attention.

The QuickChat Stack

To jumpstart the building of QuickChat, I started with static the HTML chat pages and WebRTC media APIs. This enabled me to focus on:

After a couple of days, I had a simple and reasonably functional video chat interface. Next, I worked on building a web app to provide:

One interesting bit about building the direct file transfer feature. Until Chrome v31, only unreliable data channels were available; so, you could lose data when sending files. So, I added transfer reliability at the application level. This took some effort to get working and the overhead resulted in a significant performance hit. I removed this bit of code once Chrome v31 shipped. Currently, WebRTC data channel connections between Firefox and Chrome do not work. But, I expect this to change in the near future.

The rest of the work was straightforward. I used Django to build the web app and Gevent-Socketio to build the Websocket chat server. The Websocket chat server is also used for WebRTC signaling.

WebRTC Signaling

WebRTC signaling defines how peers establish a direct connection to each other. WebRTC does not define the signaling transport itself, so anything can be used to pass session descriptions (ex. email.) But for Web apps, using Websockets is the fastest and most convenient way to do this. So, the chat servers act as a "signaling server" allowing users to identify and pass opaque bits of data, called session descriptions, to each other. Session descriptions contain media capabilities (microphone presence, video camera resolution, supported codecs, etc.) and information about how to connect directly to a remote peer.

In some cases, because of network topology, peers may be unable to establish a direct network connection to each other. So, a relay server (called a TURN server) must be used. This is not as fast as a direct connection, but all WebRTC capabilities are supported.

Signaling was the most complicated bit of getting a WebRTC connection working. It requires strict coordination of both the local and remote clients and the tooling to trace signaling state during this process is immature. I created a simple wrapper similar to AndYet’s simplewebrtc library.

Here’s a simplified view of the WebRTC signaling workflow:

signaling workflow

Final Thoughts and Useful Resources

Overall, I am pretty happy how QuickChat turned out. I hope to continue hacking on it and add other useful features. If you try it out and have any feedback, let me know here or via the website.

I am also happy with how well WebRTC worked. It’s not perfect, though. Once in a while a video chat will freeze and there’s not enough information provided to the app developer to figure what has has happened. Reconnecting the peers and restarting the video usually clears it up.

WebRTC is one of the most exciting things to happen to the web in a long time. I am really looking forward to see what creative developers build with it.

Here are some useful resources if you are planning on building something built on WebRTC:

Tags: web, realtime, video, audio, file, sharing, messaging, learning, webrtc, javascript, python, quickchat

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