Sockets

Domains

AF_INET / AF_INET6#

IPv4 and IPv6, respectively. Though be careful lumping them together, they are separate implementations with different behaviors.

AF_UNIX - Unix domain socket (UDS)#

• TLPI Chapter 57
• unix(7)
• My own introductory post

Types

• SOCK_STREAM - reliable, non message boundary preserving.
• SOCK_DGRAM - unreliable, message boundary preserving.
• SOCK_SEQPACKET - reliable, message boundary preserving. Linux-specific. Mainly for AF_UNIX usage.

More details on these in this blog

Syscalls

A minimal sockets example will use these syscalls:

• accept/accept4
• socket
• bind
• connect
• getsockname
• getpeername
• listen
• recv/recvfrom
• send/sendto
• shutdown
  • Lots of examples (including mine) use close() on the socket FD but technically shutdown is better as it’s socket-specific and offers more control. See explanation here

Socket options (blog post forthcoming):

• getsockopt
• setsockopt

I use these primarily for passing sockets via SCM_RIGHTS (blog post forthcoming):

• recvmsg
• sendmsg
• socketpair

Others:

• shutdown

Relevant Cheatsheets

• lsof
• ss

Other Resources

• Beej’s Guide (pretty legendary, love the writing style)
• socket(7) manpage
• Python sockets guide
• Python low-level socket API