wc

wc

This library was used to build dropinchat.com for YC Hacks.

A Go web server compatible with closure-library's goog.net.WebChannel. A WebChannel represents a logical bi-directional communication channel between client and server. By exposing a generic communication interface which can be implemented over a variety of transports (eg: BrowserChannel, WebSockets, WebRTC, etc) WebChannel provides additional flexibility over programming directly on top of WebSockets.

The client-side portion of WebChannel is open sourced (APLv2) as part of closure-library. Unfortunately, Google has not released the server-side portion of the code required to use WebChannel meaningfully. The wc package provides an open source (BSD) licensed golang server-side library to fill this missing gap.

See the wcchat package for an example application.

WebChannel

From goog.net.WebChannel:

Similar to HTML5 WebSocket and Closure BrowserChannel, WebChannel offers an abstraction for point-to-point socket-like communication between a browser client and a remote origin.

WebChannels are created via WebChannel. Multiple WebChannels may be multiplexed over the same WebChannelTransport, which represents the underlying physical connectivity over standard wire protocols such as HTTP and SPDY.

A WebChannels in turn represents a logical communication channel between the client and server end point. A WebChannel remains open for as long as the client or server end-point allows.

Messages may be delivered in-order or out-of-order, reliably or unreliably over the same WebChannel. Message delivery guarantees of a WebChannel is to be specified by the application code; and the choice of the underlying wire protocols is completely transparent to the API users.

Client-to-client messaging via WebRTC based transport may also be support via the same WebChannel API in future.

At the time of this writing (5/2014) the only WebChannel transport included in closure-library is BrowserChannel. As additional transports are added wc intends to add support for them as well.

BrowserChannel

From goog.net.BrowserChannel:

A BrowserChannel simulates a bidirectional socket over HTTP. It is the basis of the Gmail Chat IM connections to the server.

BrowserChannel works on all major browsers (including IE5.5+) using a variety of technologies including forever iframes (IE < 10) and XHR Streaming (IE10+ and non-IE).

Client Usage (JavaScript)

To connect from the client:

• goog.net.WebChannel.Options
• Implement a BrowserChannel.Handler subclass
• Instantiate a BrowserChannel and connect()
• call channel.sendMap() to send data

goog.require('goog.net.createWebChannelTransport');
goog.require('goog.net.WebChannel');

/**
 * @type {!goog.net.WebChannelTransport}
 */
var channelTransport = goog.net.createWebChannelTransport();

/**
 * @type {!goog.net.WebChannel.Options}
 */
var options = { supportsCrossDomainXhr: true };

/**
 * @type {!goog.net.WebChannel}
 */
var channel = channelTransport.createWebChannel('/channel', options);


/**
 * Browser channel handler.
 * @constructor
 * @extends {goog.net.BrowserChannel.Handler}
 */
demo.ChannelHandler = function() {};
goog.inherits(demo.ChannelHandler, goog.net.BrowserChannel.Handler);

/** @inheritDoc */
demo.ChannelHandler.prototype.channelHandleArray = function(browserChannel, array) {
  ...
};

var handler = new demo.ChannelHandler();
var channelDebug = new goog.net.ChannelDebug();
var channel = new goog.net.BrowserChannel('8', ['<host prefix>', '<blocked prefix>']);
channel.setSupportsCrossDomainXhrs(true);
channel.setHandler(handler);
channel.setChannelDebug(channelDebug);
channel.connect('channel/test', 'channel/bind', {});

channel.sendMap(...);

channel.disconnect();

Server Usage (Go)

TODO(ahochhaus): Document

go get github.com/samegoal/wc

Docs

Demo Chat Application

Alternate Implementations

• C++: libevent-browserchannel-server; protocol documentation
• Node.JS: node-browserchannel
• Go (golang): go-browserchannel
• Clojure clj-browserchannel

Thanks

• mdavids, upstream author of BrowserChannel, for all of the help he provided.