Foundations of Python Network Programming 978-1-4302-3004-5

CHAPTER 4 ■ SOCKET NAMES AND DNS
Using getsockaddr() in Your Own Code
To put everything together, I have assembled a quick example of how getaddrinfo() looks in actual
code. Take a look at Listing 4–1.
Listing 4–1. Using getaddrinfo()to Create and Connect a Socket
#!/usr/bin/env python
# Foundations of Python Network Programming - Chapter 4 - www_ping.py
# Find the WWW service of an arbitrary host using getaddrinfo().
import socket, sys
if len(sys.argv) != 2:
» print >>sys.stderr, 'usage: www_ping.py '
» sys.exit(2)
hostname_or_ip = sys.argv[1]
try:
» infolist = socket.getaddrinfo(
» » hostname_or_ip, 'www', 0, socket.SOCK_STREAM, 0,
» » socket.AI_ADDRCONFIG | socket.AI_V4MAPPED | socket.AI_CANONNAME,
» » )
except socket.gaierror, e:
» print 'Name service failure:', e.args[1]
» sys.exit(1)
info = infolist[0] # per standard recommendation, try the first one
socket_args = info[0:3]
address = info[4]
s = socket.socket(*socket_args)
try:
» s.connect(address)
except socket.error, e:
» print 'Network failure:', e.args[1]
else:
» print 'Success: host', info[3], 'is listening on port 80'
It performs a simple are-you-there test of whatever web server you name on the command line by
attempting a quick connection to port 80 with a streaming socket. Using the script would look
something like this:
$ python www_ping.py mit.edu
Success: host WEB.MIT.EDU is listening on port 80
$ python www_ping.py smtp.google.com
Network failure: Connection timed out
$ python www_ping.py no-such-host.com
Name service failure: No address associated with hostname
Note three things about the source code.
First, it is completely general, and contains no mention either of IP as a protocol nor of TCP as a
transport. If the user happened to type a hostname that the system recognized as a host to which it was
connected through AppleTalk (if you can imagine that sort of thing in this day and age), then
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