Socket.readBytes does not move the pointer

I got confused by a weird problem trying to use ByteArrays to send an object and unsigned int on top of Socket. I am trying to handle the case where I can receive data in multiple packets.

Here is my socket data handler:

protected function handleSocketData(e:ProgressEvent):void{
        var s:Socket = e.target as Socket;

        trace("pre if " + len + " " + s.bytesAvailable);
        if (len == 0 && s.bytesAvailable >= 4) {
            len = s.readUnsignedInt();

        }

        trace(len + " " + s.bytesAvailable);
        if (len > 0 && s.bytesAvailable >= len){
            var ba:ByteArray = new ByteArray();
            //s.readBytes(ba, 0, len);
            s.readBytes(ba, 0, s.bytesAvailable); //should be len

            //trace("handle socket before inflate " + ba.length);
            ba.inflate();
            //trace("handle socket after inflate " + ba.length);
            var o:Object = ba.readObject();
            Overlord.updatePlayers(o);
            trace(o.player);
            len = 0;


        }
}

The problem is s.readBytes(ba, 0, len);

I use len (defined in the class scope) to handle the case where I can get multiple packages. Now this seems to work first when I receive data through a socket.

pre if 0 44 - trace I'm getting before the first if statement
38 40 - trace I'm getting after
frank - Everything comes in fine, working!

Now, if I send the data over the socket again:

**first send:**
pre if 0 44
38 40
frank - working, yay!
**things start to fail every send after:**
pre if 0 46
218759168 42
pre if 218759168 84
218759168 84
pre if 218759168 127
218759168 127

Now it seems that readBytes leaves data in the buffer.

The strange part, when I change s.readBytes(ba, 0, len);to s.readBytes(ba, 0, s.bytesAvailable);, everything works:

With s.readBytes (ba, 0, s.bytesAvailable);

**first send**
pre if 0 44
38 40
frank
**everything seems to work after, no old data in the buffer?**
pre if 0 44
38 40
frank
pre if 0 43
37 39
frank

bytesAvailable , .

pre if 2214 2218
2214 2218
RangeError: Error #2006: The supplied index is out of bounds.
at flash.utils::ByteArray/readObject()

, , , , socket.bytesAvailable. - ?

. ByteArray , .

        public function sendData(socketData:*):void{
        if(_connected){
            //trace("sending");
            var ba:ByteArray = new ByteArray();
            ba.writeObject(socketData);
            ba.position = 0;
            //trace("byteArray len before send and defalte: " + ba.length)
            ba.deflate();
            //trace("byteArray len before send and after defalte: " + ba.length)
            socket.writeUnsignedInt(ba.length);
            socket.writeBytes(ba, 0, ba.length);
            socket.flush();
        } else {
            throw new Error("Socket not open");
        }
    }