Basic Client-Server Design for persistent connections?

Question

Here's as far as I understand it:

1. Client & Server make connection

2. Client sends server data

3. Server interprets data, sends client data

4. So on, and so forth, until client sends disconnect signal.

I'm just wondering about implementation. Step 2 and 3 are confusing to me, maybe I'm over-complicating it. Is there anymore to interpreting the data than a giant switch statement?

Any good books on client/server design? Specifically talking about multithreaded servers, scalability, and message design (byte 1 = header info, byte 2 = blah blah, etc)? Specifically geared towards C++.

Answer 1

I woould think about packets, packet types, packets identifiers and storages of packet types handlers.

An idea is to only send a data in form of packets. Each packet holds its identifier(optional) and type at the beginning (length would be useful too) you have a bunch of packet handlers on each side of connection each handlers manages packets of corresponding type (reads and interprets). If you send a packet length you can even skip usupported types of packets allowing differrent client and server versions.