As far as I know, one of the early proposals was about allowing web applications almost complete control over sockets, including the ability to create raw sockets and to listen for incoming connections exactly like a typical network daemon/server, but this proposal was later scraped because of security implications.

Fast forward to today and the Web Sockets API, even if still under development, are starting to get a stable shape and they will probably be implemented soon by the most forward-looking browser vendors.

The problem is, though, that the original proposal got crampled along the way and therefore there won’t be any means to create peer-to-peer connections between users, something that could enable all kinds of cool distributed systems.

That is, unless someone does something: what I’m thinking about right now is a kind of wrapper/extension around the Web Sockets API that does simply a few things:

1. allows a web application to register for incoming connections
2. opens up the required ports on the firewall/NAT
3. when a connection arrives, perform the handshaking required by the ws:// protocol and forwards a WebSocket object representing the connection to the application

Talking IDL, that would mean (the WebSocket interface is the current WHATWG proposal, while WebSocketListener is my addition):

[Constructor(in DOMString url, optional in DOMString protocol)]
interface WebSocket {
  readonly attribute DOMString URL;

  // ready state
  const unsigned short CONNECTING = 0;
  const unsigned short OPEN = 1;
  const unsigned short CLOSED = 2;
  readonly attribute unsigned short readyState;
  readonly attribute unsigned long bufferedAmount;

  // networking
           attribute Function onopen;
           attribute Function onmessage;
           attribute Function onclose;
  boolean send(in DOMString data);
  void close();
};

[Constructor(optional in short port, optional in DOMString protocol)]
interface WebSocketListener {
  readonly attribute short port;

  // ready state
  const unsigned short OPENING = 0;
  const unsigned short LISTENING = 1;
  const unsigned short CLOSED = 2;
  readonly attribute unsigned short readyState;

  // networking
           attribute Function onconnection;
  void close();
};

Talking about the Mozilla platform, points 1 and 3 are straightforward (once the Web Sockets API has been implemented), whereas point 2 will be platform-dependent and, therefore, trickier. Nevertheless, I think that all of this can be handled (with some work) by a Firefox extension.

Once Firefox will gain Web Sockets support I’ll definitely try to see if it is possible to add it.