A Reusable Windows Socket Server Class With C++ - Chunking the byte stream (Contd.) (Page 5 of 6 )
Since we're a simple server we have a fairly important limitation, all our messages must fit into the IO buffer size that our server is using. Often this is a practical limitation, maximum message sizes can be known in advance and by setting our IO buffer size to be at least our maximum message size we avoid having to copy data around. If this isn't a viable limitation for your server then you'll need to have an alternative strategy here, copying data out of IO buffers and into something big enough to hold your whole message, or, processing the message in pieces...
In our simple server if the message is too big then we simply shutdown the socket connection, throw away the garbage data, and wait for the client to go away...
So how do we implement GetMinimumMessageSize() and GetMessageSize(), well, obviously it's protocol dependant, but for our packet echo server we do it like this:
You may have noticed that in the case where we had a message and some extra data we called SplitBuffer() to break the complete message out into its own buffer, and then, once we'd dealt with it, we called Release(). This is a little of the implementation of the socket server's buffer allocator poking through. The buffers are reference counted. The only time we need to worry about this is if we create a new buffer using SplitBuffer, or if we decide to call AddRef() on the buffer because we wish to pass it off to another thread for processing. We'll cover this in more detail in the next article, but the gist of it is that every time we post a read or a write the buffer's reference count goes up and every time a read or write completes the count goes down, when there are no outstanding references the buffer goes back into the pool for reuse.
A packet echo server A packet based echo server is available for download in SocketServer2.zip. The server expects to receive packets of up to 256 bytes which have a 1 byte header. The header byte contains the total length of the packet (including the header). The server reads complete packets and echos them back to the client. You can test the echo server by using telnet, if you're feeling clever ;) Simply telnet to localhost on port 5001 (the port that the sample uses by default) and type stuff and watch it get typed back at you. (Hint, CTRL B is 2 which is the smallest packet that contains data).
A real internet RFC protocol Some of the common internet protocols, such as RFC 1939 (POP3), use a crlf terminated ASCII text stream command structure. An example of how such a server might be implemented using the CSocketServer classes presented here can be found in SocketServer3.zip.