Extend bufferedAmount property

[alexions]

The bufferedAmount property is good for your application to control how much messages you can send (to avoid memory overhead), but it works only if you disable perMessageDeflate.

I propose to extend the property by calculating _sender.queue size as well.

Example:

get bufferedAmount () {
    var amount = 0;
    var senderQueueSize = 0;
    
    if (this._socket) amount = this._socket.bufferSize || 0;
    
    if (this._sender && this._sender.queue) {
      for (i = 0; i < this._sender.queue.length; i += 1) {
        senderQueueSize += this._sender.queue[i].data.length;
      }
    }
    return amount + senderQueueSize;
}

The best solution is to avoid cycle at all by adding queueSize variable to _sender and add/subtract length when adding a new element to queue.

get bufferedAmount () {
    var amount = 0;
    var senderQueueSize = 0;
    
    if (this._socket) amount = this._socket.bufferSize || 0;
    return amount + this._sender.queueSize;
}

[lpinca]

It makes sense but it's slightly harder as, in some cases, the data to send is converted to a buffer only before writing to the socket. This can probably be fixed though by converting the data to a buffer before it is added to the queue.

Are you up for creating a PR?