Emit message to all sockets except specifc one

[sebamarynissen]

In web processes we have the option of sending a message to all sockets except a specific one by using broadcasting. It would be nice to have this functionality when sending messages from non-web processes as well.

In order to make the emitter interchangeable with namespaces on web processes (see socketio/socket.io#3629), I propose to add a method .except() which can be used as

io.to('room').except('id').emit('hi', 'all');

I'd be happy to file a PR for this if the feature would be accepted. An implementation could look like this:

function Emitter(redis, prefix, nsp){
  this.redis = redis;
  this.prefix = prefix;
  this.nsp = nsp;
  this.channel = this.prefix + '#' + nsp + '#';

  this._rooms = [];
  this._flags = {};
  this._except = [];
}

Emitter.prototype.except = function(id){
  this._except.push(id);
  return this;
};

Emitter.prototype.emit = function(){
  // packet
  var args = Array.prototype.slice.call(arguments);
  var packet = { type: parser.EVENT, data: args, nsp: this.nsp };

  var opts = {
    rooms: this._rooms,
    flags: this._flags,
    except: this._except,
  };

  var msg = msgpack.encode([uid, packet, opts]);
  var channel = this.channel;
  if (opts.rooms && opts.rooms.length === 1) {
    channel += opts.rooms[0] + '#';
  }
  debug('publishing message to channel %s', channel);
  this.redis.publish(channel, msg);

  // reset state
  this._rooms = [];
  this._flags = {};
  this._except = {};

  return this;
};

This should work with socket.io-redis out of the box.