Advanced Programmings AT3

Net code

Here are some things that you should probably need to know when writing net code (networking code), so that when you go to view mine, you won't be overwhelmed.

File Descriptors

• A file descriptor is a number that points to a file.
• If you find the process id for the code that is created when you build and execute this code, you can actually find the file in /proc//<id returned from bind(2) or equivalent net functions>.
• This file is a random, unique number that is created by Linux or whatever OS that links said number to a file.
• In this case, we are creating a file which will store the retrieved request into /proc, that is why it returns an integer inside the socket() call.
• If you understand this, I recomend you read the man pages for socket(2), bind(2), listen(2), accept(2), and close(). This is relevant to Server::Serve(1) in Server.cpp

TCP Linger / Time-Wait

• When you open a server, it opens up a port as you know
• When the application closes, and thus the socket is closed too, the socket "can go into a TIME-WAIT state on the end that initiated the close" - Lewis Van Winkle
• When you use SO_REUSEADDR (socket, reuse address), you can pretty much override the old one
• Example in Server::Serve(1):

int res = 1;
if (setsockopt(serverFileDescriptor, SOL_SOCKET, SO_REUSEADDR,
               (void*)&res, sizeof(res)) < 0) { }