Cameron Albert

Ramblings of software development, games and technology.

Data Format for Socket Server Packets

For my PBBG Engine I started off programming it all for the web and AJAX. Recently I added support for sockets by porting over my socket server code I wrote for a Flash server and incorporating the code into the PBBG Engine. In a previous post about my PBBG Engine Architecture I outlined my plans for how the socket and web pieces would work together. I spent some time today refining my command pipeline and server protocol for the socket side of the engine and will probably utilize that on the web side as well.

I decided on the following format for the data packets that will go to and from the server and client. Since it is just bytes going back and forth and I wanted to keep the data streams as small as possible I decided to abandon the string based command protocol and use this instead:

The first 2 bytes of the packet will be used to store an Int16 (short) value that indicates the command to execute. I have an event being raised from the game engine that allows the implementing libraries to set the game commands. This was a Dictionary<string, ICommand> but I am going to change it to a Dictionary<short, ICommand>. That will save me some bytes back and forth without passing the command names. I can have the clientsend the proper short value for the command typed into the console or just have the links and events in the client supply the proper short value.

The next 4 bytes will be the integer length value of the message. This will allow me to know when this message ends and the next one begins.

All the bytes following up to the length value will be the actual message sent to the client or sent to the server.

The server is already validating commands, I will just need to modify to validate these bytes and watch for buffer over runs. I still need to work out validating that a logged in user is sending the information but I will work out something, maybe have the client send the encrypted authentication key to the server after a connection is opened but before commands can be processed. 

 

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Written by Cameron

March 2, 2008 at 10:35 pm

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