r3dux.org

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:

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:

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!

Read the rest of this entry »

Update: The method below for getting a virtualbox IP from your DHCP works (in linux) – but it turns out there’s an easier way (kindly pointed out by Mike in the comments below). You can just change your VirtualBox network settings from NAT to Bridged Adapter and point it at eth0/wlan0 or whichever connection is being used for networking. Then, optionally, you can configure the MAC address of the bridged adapter and set your router to assign a specific IP to a specific bridged adapter. Also, the built-in Bridged Adapter method works to deploy solutions from XNA Game Studio to my Xbox 360, so I’m rapt! Thanks, Mike!

Note: The below bit is for linux only, the above method should work on any host OS!

VirtualBox is an awesome bit of kit and I <3 it long time ten-dorrah.

But by default when your virtual copy of Windows/Linux/Solaris/Whatever grabs an IP address, it does so through NAT, and at version 3.0.4, this means it gives us a default Category A network address (i.e. 10.x.y.z).

It’s a working cat-A address, as in it’s fully functional and can talk to the Internet and all that, but sometimes life is a lot easier if you have an IP in the same range as the DHCP pool your router is dishing out. For example, my lappy is 192.168.1.101 internally, my Wii might be 192.168.1.102, the NAS .103 etc, so I want my virtualboxen to take addresses like .104, .105 and such.

I’m doing this to bridge my wireless connection on wlan0, if you’re bridging an ethernet connection substitute eth0 or whatever connection as necessary.

Also, to perform the bridging using this method, you’ll need some tools (feel free to sudo apt-get install NAME-OF-TOOL as necessary):
- 1.) uml-utilities
- 2.) parprouted
- 3.) bcrelay

Now, with that lot installed, run the following commands (provided here in bash script form):

#!/bin/bash
 
# To use this script you will need the following utilities installed:
# 1.) uml-utilities 2.) parprouted  3.) bcrelay
# sudo apt-get install 'em
 
# Enable IP forwarding
sudo sysctl net.ipv4.ip_forward=1
 
# Create a TAP as your current logged in user (replace with -u YOUR-USER-NAME if you want...)
sudo tunctl -u $USER
 
# Tell tap0 to respond to ARP (Address Resolution Protocal) packets 
sudo sysctl net.ipv4.conf.tap0.proxy_arp=1
 
# Give your TAP (tap0) an IP address and enable it (make sure the IP address is OUTSIDE the DHCP range on your router)
sudo ip addr add 192.168.1.150/32 dev tap0
sudo ip link set tap0 up
 
# Run parprouted and make it add routes automatically for wlan0 and tap0 as needed
# Make the command "parprouted -d wlan0 tap0" to display routes added and additional info. No sudo necc. for this one.
parprouted wlan0 tap0
 
# Use bcrelay on your net connection and TAP to "rewrite the layer-2 header and forward broadcast messages between network interfaces"
# The "-d" in this instance MAKES bcrelay work as a daemon. Need to sudo this or it doesn't work.
sudo bcrelay -d -i tap0 -o wlan0

Now, fire up VirtualBox and for your machine of choice change the network selection from NAT to tap0 as shown:

Then boot up your virtual machine and check the IP:

Great. Super. Smashing. =D

Note: The entire reason I wanted to grab an IP from the router was so my virtual copy of XP could be on the same network as my XBox 360, so I could deploy games to it through XNA Studio 3.1, however XNA Studio is very fussy about timing when it comes to registering the 360, and although it can see the 360 using the bridge, and it tries to connect, it times out before it can fully establish a connection. I guess I’ll have to go with an IP routes method of bridging if I want it to work for that purpose, but as yet I haven’t quite figured it all out. Will keep trying when I have time, or if you know a way, feel free to call me technically incompetent and sling a solution in the comments! Cheers!