/Web-Server

A simple web server written in python

Primary LanguagePython

A Simple Web Server

This is a sample code for buiding a simple web server. The tutorial is from Ruslan's blog.

The basic mode of how web server works

  1. Run webserver1.py. The web server creates a socket to accept connections.
  2. Run client1.py. The client sends http request to the server.(You can also just visit http://localhost:8888/helloin the browser.)
  3. The client will receive http response content.

WSGI(Python Web Server Gateway Interface)

There are various web frameworks in Python, such as Django, Flask and Pyramid etc. How could we run web server with multiple web frameworks without changing any modifying server's code? The answer is WSGI.

  1. Run wsgiserver.py. This is a simple WSGI server impletation.
  2. You can use any Python web framework to write the application and run with it.
  3. There is a test for Django in helloworld. It's just a simple Django test project.
  4. Run djangoapp.py. It will run Django application with your Web server.
python webserver2.py djangoapp:app

Try to visit http://localhost:8888/hello.

You can also try other frameworks, it will also work well.

Concurrent Server

  1. Run iterativeserver.py. This is a basic web server to handle one request at a time.

  2. Run sleepserver.py. This server handles one request and then blocks for 60 secondes.

  3. Now run concurrentserver.py. This is a concurrent server by using fork() system call. The parent process accepts a connection and child process handles it.

  4. You should not forget close duplicate file descriptors in parent and child process. Because parent and child share the same file descriptors after the call to fork. You can examine what will happen if we do not close duplicate descriptors in concurrentserver2.py.

    • The server no longer sleeps for 60s, but the curl doesn't terminate. It will eventually run out of available file descriptors;Run client2.py to test.
    • Your server creates zombie processes. Even if you try to kill zombies with $ kill -9 , they will survive. (A zombie is a process that has terminated, but its parent has not waited for it and has not received its termination status yet. )

  5. You need to modify your server code to wait for zombies to get their termination status.It was modified in concurrentserver3.py.

  6. But if your child processes send too many SIGCHLD signals, the server process will miss serverl signals, which left several zombies still running background.It was modified in concurrentserver_final.py.

Now, we have built a simple web server.

##References:

  1. Ruslan's blog
  2. python socket docs
  3. socket programming