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This is a directory of program listings from Chapter 7 of the book:
- Foundations of Python Network Programming
-
Third Edition, October 2014
by Brandon Rhodes and John Goerzen
You can learn more about the book by visiting the root of this GitHub source code repository.
Although the scripts in this chapter were written for Python 3, nearly
all of them can also be run successfully under Python 2. Simply use
3to2 to convert them to the older
syntax. The two that can run only under Python 3 are the two asyncio
scripts, because the asyncio framework depends upon the yield from
syntax that was not introduced until Python 3.
This chapter implements the same network service seven different ways. The seven different servers look pretty much the same when run from the command line, which is more or less the point. What is interesting about them is how differently they are written while yet providing exactly the same network service.
Any of the server scripts, when run at the command line, will let the
single client script — the appropriately named client.py — connect and
ask a series of questions to which the server replies with answers.
$ python3 srv_single.py '' &>server.log &
$ python3 client.py localhost
b'Simple is better than?' b'Complex.'
b'Beautiful is better than?' b'Ugly.'
b'Explicit is better than?' b'Implicit.'
$ cat server.log
Listening at ('', 1060)
Accepted connection from ('127.0.0.1', 41285)
Client socket to ('127.0.0.1', 41285) has closed
You can run the test.sh script if you want to verify that all seven
work correctly on your platform. The script will start each of the
servers in turn, and see whether the client can really connect or not.
Two final versions of the Zen-of-Python server require a bit of manual
configuration: the servers that are designed to run under the inetd
daemon. You can try them in the Playground
on the ftp.example.com host, where inetd happens to already be
running to provide a Telnet service for the scripts in Chapter 16. Once
you have the playground running, create a client host like h1:
$ ssh h1
Because each client host auto-mounts the py3 directory, you will have
access to the scripts and configuration file that need to be copied over
to ftp.example.com for the two services to run. You can perform the
copy using the following commands on host h1:
# cd /fopnp/py3/chapter07
# scp in_zen1.py in_zen2.py zen_utils.py ftp.example.com:/
# scp inetd.conf ftp.example.com:
# ssh ftp.example.com
Once the ssh command has offered you a prompt on the ftp machine,
you can run ps to verify that inetd is indeed running.
# ps axf
PID TTY STAT TIME COMMAND
...
36 ? Ss 0:00 /usr/sbin/inetd
...
Next, add the Zen-of-Python service to the existing list of inetd
services, and mark the Python scripts as publicly readable so that they
can be run as the brandon user:
# cat inetd.conf >> /etc/inetd.conf
# /etc/init.d/openbsd-inetd reload
# chmod a+r /*.py
You can now log back out of the ftp host and, from the h1 host,
connect to the inetd powered servers on both of the port numbers
mentioned in inet.conf:
# python3 client.py ftp.example.com -p 1060
b'Beautiful is better than?' b'Ugly.'
b'Explicit is better than?' b'Implicit.'
b'Simple is better than?' b'Complex.'
# python3 client.py ftp.example.com -p 1061
b'Beautiful is better than?' b'Ugly.'
b'Simple is better than?' b'Complex.'
b'Explicit is better than?' b'Implicit.'
If you later log back in to the ftp host, you can view the logs of
both servers.
# cat /tmp/zen.log
Accepted connection from ('10.25.1.65', 49327)
Client socket to ('10.25.1.65', 49327) has closed
Accepted connection from ('10.25.1.65', 49328)
Client socket to ('10.25.1.65', 49328) has closed