A Simple C++/SDL_Net Chat Server & Client

Update – Nov 2011: I’ve refactored this code into something significantly easier to work with, modify and extend – so you should probably try this instead: http://r3dux.org/2011/11/a-simple-csdl_net-chat-server-client-rewritten/.


I was due to be teaching some network programming in the new term, so I thought I’d try to find the simplest library for cross-platform socket programming and knock up some examples that I could teach from. The trouble is, there are lots of different socket libraries… Lots and lots. So I did a bit of investigating and came up with the following:

Library Good Points Bad Points
Boost ASIO
  • The real deal – a world-class, well documented socket library
  • Comprehensive – you can do absolutely anything with it
  • More complicated than I’d like for the level I’m teaching at – I’m not convinced they’ll get it
  • You need to include the boost library in each project, which makes each project big (like 60MB+ big)
C++ Sockets Library
  • Lots of documentation
  • Appears to be very solid from all accounts
  • I couldn’t get it to play ball!
SDL_net
  • Pretty small
  • Works without you having to jump through too many hoops
  • Decent level of abstraction without the need to mess about with too much C (as opposed to C++) stuff
  • Does not require SDL – SDL_net can be happily used standalone
  • Good documentation available at:
    http://www.libsdl.org/projects/SDL_net/docs/index.html
  • You do still need to transfer strings to char array pointers
  • Resolving hosts and IPs puts the details in Network Byte Order (i.e. Big Endian) numbers, which you then have to jump through hoops to retrieve as human-readable values, so you end up doing stuff like hacking a unsigned 32-bit number into an array of four 8-bit numbers to get the dot-quad IP address etc.
NetLink Socket Library
  • Small!
  • No documentation at all (that I could find), which could be because…
  • …netlink is already the name of a *nix socket mechanism which transfers data between kernel-space and user-space – why the hell would you name your C++ socket library with a name which is already used for a different type of socket communication? Fail.
SimpleSockets (now defunct)
  • ?!?
  • Surprisingly for a library called SimpleSockets, not that simple – lots of memset and memcpy stuff needed

In the end I chose SDL_net as teh winnah, as I’d already done some SDL stuff with the class previously (before switching to GLFW to minimise code-bloat), and I managed to get SDL_net up and communicating pretty easily. So, for the next couple of days I put together some simple client/server examples, culminating in the code you’ll find below, which is a (very) simple IRC-esque chat server.

Have a look – you can tell what it’s doing from the output in the windows:

SDL_net Client-Server Example
The server is in the middle, the clients connect in, and chat commences (click for larger, more legible version)

Although I’ve written this code in Linux, as SDL_net is cross-platform, this code should be cross platform – only there are two tweaks you’ll need to make for it to work in Windows: I’ve used some custom kbhit and getch functions to check for a keypress and read what key was pressed, if one was. These functions come natively with Windows, so you should use the native versions and strip the custom ones out.

With those small changes made this should work fine in Windows – but if it doesn’t please feel free to fix it yourself and send me the changes you made :)

As the code for all this is a couple of hundred lines for each for the client and server I’ve put all the source after the jump. Part of the reason it’s so large is that I’ve commented it to the hilt (no really, I’ve gone to town on it – even by my exceptionally verbose standards) as it was originally meant to be a teaching aid. Also, I’ve also left a lot of commented-out debug code in there, so you can uncomment it if you’d like to see exactly what’s going on behind the scenes.

Anyways, I hope this is of use to someone starting off socket programming with SDL_net – and if you have any issues or such please feel free to sling a comment in the article and I’ll do my best to help out.

Cheers!

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