Agile Enterprise Application Development with Flex

Building a Custom Acknowledging Channel

In this section, we’ll build a custom acknowledging channel for the RTMP protocol, even though you can implement a similar class for AMF-based messaging. The principles of creating custom channels remain the same regardless of the selected protocol. We’ll discuss the differences of the communication protocols in Chapter 6.

As stated earlier, you need to overload the receive() method and, for each incoming instance of ReliableServerMessage, add the clientId concatenated with the message sequence number to the array called received:

override public function receive(
 msg:IMessage, ...rest:Array) : void {
 if (msg is ReliableServerMessage) {
   var seqNo : Number = Number(msg.headers["seqNo"]);
   received.push( msg.clientId + "|"+ seqNo);
 }
 super.receive( msg, rest);
}

Every time the new message arrives from the server, the method receive() will be called and a new reliable message will be added to the array received. As a reminder, adding a seqNo in the message header should be done in the Java code that sends the message. You’ll see the use of the message property clientId a little later, on the server’s QoSAdapter; it’s used to avoid collision between multiple clients, potentially confirming the same range of message sequences.

Figure 5-5. Classes involved in the No Server Message Left Behind solution

The code of the client’s custom RTMP channel is presented ...