Packet data structure?

Question

I'm designing a game server and I have never done anything like this before. I was just wondering what a good structure for a packet would be data-wise? I am using TCP if it matters. Here's an example, and what I was considering using as of now:

(each value in brackets is a byte)

[Packet length][Action ID][Number of Parameters]
[Parameter 1 data length as int][Parameter 1 data type][Parameter 1 data (multi byte)]
[Parameter 2 data length as int][Parameter 2 data type][Parameter 2 data (multi byte)]
[Parameter n data length as int][Parameter n data type][Parameter n data (multi byte)]

Like I said, I really have never done anything like this before so what I have above could be complete bull, which is why I'm asking ;). Also, is passing the total packet length even necessary?

Answer 1

Passing the total packet length is a good idea. It might cost two more bytes, but you can peek and wait for the socket to have a full packet ready to sip before receiving. That makes code easier.

Overall, I agree with brazzy, a language supplied serialization mechanism is preferrable over any self-made.

Other than that (I think you are using a C-ish language without serialization), I would put the packet ID as the first data on the packet data structure. IMHO that's some sort of convention because the first data member of a struct is always at position 0 and any struct can be downcast to that, identifying otherwise anonymous data.

Your compiler may or may not produce packed structures, but that way you can allocate a buffer, read the packet in and then either cast the structure depending on the first data member. If you are out of luck and it does not produce packed structures, be sure to have a serialization method for each struct that will construct from the (obviously non-destination) memory.

Endiannes is a factor, particularly on C-like languages. Be sure to make clear that packets are of the same endianness always or that you can identify a different endian based on a signature or something. An odd thing that's very cool: C# and .NET seems to always hold data in little-endian convention when you access them using like discussed in this post here. Found that out when porting such an application to Mono on a SUN. Cool, but if you have that setup you should use the serialization means of C# anyways.

Other than that, your setup looks very okay!