Showing posts with label python. Show all posts
Showing posts with label python. Show all posts

Writing a Python xinetd Server

Yesterday I discovered the xinetd; an internet services daemon. I immediately liked the idea of writing simple services that work on stdin and stdout but that can be accessed over the internet via sockets. So, I set out to write a simple Python server that can be integrated with xinetd. Here is the server:
#!/usr/bin/python
import sys

request = ''
while True:
  data = sys.stdin.readline().strip()
  request = request + data + '<br>'
  if data == "":
    print 'HTTP/1.0 200 OK'
    print ''
    print '<html><body><p>'+request+'</p></body></html>'
    sys.stdout.flush()
    break;
I am assuming that a web browser will connect to my server, the server will then 'echo' the request back to the browser allowing the  browser to display the request. As you can see the input is received via stdin and output is returned via stdout.

If xinetd is not already installed then you will obviously have to install it first. Since I am doing this on Ubuntu the following works for me:
sudo apt-get install xinetd
After installing xinetd you need to create a config file for the service. I called my service http_echo and my config file (located in /etc/xinetd.d) is named similarly; http_echo. My configuration file looks like this:

service http_echo
{
    protocol       = tcp
    disable        = no
    port           = 9991
    flags          = REUSE
    socket_type    = stream
    wait           = no
    user           = johan
    server         = /home/johan/code/http_echo/http_echo
    log_on_failure += USERID
}
Most of this file is quite self explanatory. Please refer to the xinetd documentation for more information.The port property should make the service run on the specified port without having to add an entry in the services file (/etc/services) . I have had to add an entry in my services file to make this setup work:
http_echo    9991/tcp
Then simply restart the xinetd service:
sudo /etc/init.d/xinetd restart
Pointing a browser to the server on the specified port (9991), will yield the pleasing results below:
GET / HTTP/1.1
Host: localhost:9991
Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US) AppleWebKit/532.0 (KHTML, like Gecko) Chrome/3.0.195.33 Safari/532.0
Cache-Control: max-age=0
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
And that is how simple it is to write a service in Python that runs under xinetd.
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Convenient Python Command Runner

Here is a little piece of code which I tend to reuse quite often. It basically runs a command and return True if the command executed successfully or False if it did not. The second item in the return tuple is the stdout output of the command if any or the error if there was an error executing the command.

import subprocess

def runcmd(cmd):
  try:
    f = subprocess.Popen(cmd,shell=False,stdout=subprocess.PIPE,stderr=subprocess.PIPE)
    stdout = f.stdout.read();
    stderr = f.stderr.read();
   
    if f.stdout.close() == None and  f.stderr.close() == None:
      return True,stdout,stderr
    else:
      return False,stdout,stderr
  except OSError,x:
    return False,x
As usual the source code can be found here.
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Python SMTP Mail Sink

I've been using this little bit of python code quite extensively. It is basically a SMTP server built by extending the SMTPServer from the smtpd package (all standard with python). I then added a HTTP server frontend to this. This allows me to quickly start up a new SMTP server with a HTTP front end, which allows me to test mail functionality without having to log into a mail client etc. Initially when I wrote it it was because I was disconnected from the web and could not be bothered to install a full blown SMTP server on my laptop. This little application has probably seen more use than what I intended for it initially.

Have a look here for the script. Enjoy and have fun.
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