#Erlfaye

Erlfaye is an implementation in Erlang of the Faye server, a publish/subscribe server implemented using comet. The implementation is just a modified version of Erlycomet with some extensions. Mochiweb is the underlying HTTP server.

Currently Erlfaye supports the following transport mechanisms:

• Long polling
• Callback long polling
• Websockets

Installation

The erlfaye directory contains the code of the library. Compile it using the provided Makefile and install it in your Erlang home directory The erlfaye_demo folder contains a demo application. It can be built using Sinan. Once the application is built it can be started using the start.sh script.

Dependencies

• Mochiweb
• Mnesia

Usage

In order to use Erlfaye, the erlfaye_cluster process must be initiated. This is a description for a supervisor:

ErlfayeComet = {erlfaye_cluster,
                {erlfaye_cluster, start, []},
                permanent,
                1000,
                worker,
                [erlfaye_cluster]},

Once it is initiated, requests to Erlfaye must be bound to a URL in the Mochiweb service loop:

loop(Req, _, "/cometd", _) ->
    erlfaye_request:handle(Req);

Erlang processes can deliver messages to channels using the deliver_to_channel function:

tick() ->
    receive
        stop ->
            ok
    after 10000 ->
            {_,Secs,_} = now(),
            Channel = <<"/test/time">>,
            Data = Secs rem 1000,
            erlfaye_api:deliver_to_channel(Channel, Data),
            tick()
    end.

Erlang processes can also subscribe/unsubscribe to channels using the subscribe_process, unsubscribe_process functions:

start_local_handler() ->
    spawn(fun() ->
                  erlfaye_api:subscribe_process(self(),<<"/rpc/test">>),
                  erlfaye_api:subscribe_process(self(),<<"/test/time">>),                                    
                  local_handler_loop()
          end).
 
local_handler_loop() ->
    receive
        Data ->
            error_logger:warning_msg("Got an event: ~p ~n",[Data]),        
            local_handler_loop()
    end.

Browser JS applications can use the Faye browser client to send and receive notifications:

var client = new Faye.Client('http://myserver/cometd');

client.subscribe("/location", function(msg) {
   alert("Got an event");
});

client.publish("/location", {'latitude':40, 'longitude':-23});