C#: Question about socket programming (sync or async)

Question

I'm writing an instant messaging server in C# for learning purposes. My question is whether I should use synchronous or asynchronous sockets to handle the IM clients. The goal is to handle as many clients as possible.

I'm not quite sure but as far as I know with async sockets the packets don't arrive in order which means when you send 2 chat messages and there is a delay/lag it's possible that the second one arrive before the first one. Is this right and if so, is there a way to solve this issue?

About sync sockets: Is synchronous sockets a good solution for many clients? Do I have to check every socket/connection in a loop if there are new packets? If so, isn't this quite slow?

Last question: Assume I want to implement a way to send files (e.g. images) through the protocol (which is a non-standard binary protocol btw), can I still send messages while uploading?

Answer 1

The goal is to handle as many clients as possible.

Async then. It scales a lot better.

I'm not quite sure but as far as I know with async sockets the packets don't arrive in order which means when you send 2 chat messages and there is a delay/lag it's possible that the second one arrive before the first one.

TCP guarantees that everything arrives in order.

Assume I want to implement a way to send files (e.g. images) through the protocol (which is a non-standard binary protocol btw), can I still send messages while uploading

I recommend that you use a separate connection for file transfers. Use the first connection to do a handshake (determine which port to use and specify file name etc). Then use Socket.SendFile on the new socket to transfer the file.