Your task is to develop a small web proxy server which is able to cache web pages. It is a very simple proxy server which only understands simple GET-requests, but is able to handle all kinds of objects - not just HTML pages, but also images.

Code

Below you will find the skeleton code for the client. You are to complete the skeleton code. The places where you need to fill in code are marked with #Fill in start and #Fill in end. Each place may require one or more lines of code.

Running the Proxy Server

Run the proxy server program using your command prompt and then request a web page from your browser. Direct the requests to the proxy server using your IP address and port number.

For e.g. http://localhost:8888/www.google.com

To use the proxy server with browser and proxy on separate computers, you will need the IP address on which your proxy server is running. In this case, while running the proxy, you will have to replace the localhost with the IP address of the computer where the proxy server is running. Also note the port number used. You will replace the port number used here 8888 with the port number you have used in your server code at which your proxy server is listening.

Configuring your Browser

You can also directly configure your web browser to use your proxy. This depends on your browser. In Internet Explorer, you can set the proxy in Tools > Internet Options > Connections tab > LAN Settings. In Netscape (and derived browsers such as Mozilla), you can set the proxy in Tools > Options > Advanced tab > Network tab > Connection Settings. In both cases you need to give the address of the proxy and the port number that you gave when you ran the proxy server. You should be able to run the proxy and the browser on the same computer without any problem. With this approach, to get a web page using the proxy server, you simply provide the URL of the page you want.

For e.g. http://www.google.com

What to Hand in

You will hand in the complete proxy server code and screenshots at the client side verifying that you indeed get the web page via the proxy server.

Skeleton Python Code for the Proxy Server

from socket import *

import sys

if len(sys.argv) <= 1:

print('Usage : "python ProxyServer.py server_ip" [server_ip : It is the IP Address Of Proxy Server')

sys.exit(2)

# Create a server socket, bind it to a port and start listening

tcpSerSock = socket(AF_INET, SOCK_STREAM)

# Fill in start.

# Fill in end.

while 1:

# Strat receiving data from the client

print('Ready to serve...')

tcpCliSock, addr = tcpSerSock.accept()

print('Received a connection from:', addr)

message = # Fill in start. # Fill in end.

print(message)

# Extract the filename from the given message

print(message.split()[1])

filename = message.split()[1].partition("/")[2]

print(filename)

fileExist = "false"

filetouse = "/" + filename

print(filetouse)

try:

# Check wether the file exist in the cache

f = open(filetouse[1:], "r")

outputdata = f.readlines()

fileExist = "true"

# ProxyServer finds a cache hit and generates a response message

tcpCliSock.send("HTTP/1.0 200 OK ")

tcpCliSock.send("Content-Type:text/html ")

# Fill in start.

# Fill in end.

print('Read from cache')

# Error handling for file not found in cache

except IOError:

if fileExist == "false":

# Create a socket on the proxyserver

c = # Fill in start. # Fill in end.

hostn = filename.replace("www.","",1)

print(hostn)

try:

# Connect to the socket to port 80

# Fill in start.

# Fill in end.

# Create a temporary file on this socket and ask port 80 for the file requested by the client

fileobj = c.makefile('r', 0)

fileobj.write("GET "+"http://" + filename + " HTTP/1.0 ")

# Read the response into buffer

# Fill in start.

# Fill in end.

# Create a new file in the cache for the requested file.

# Also send the response in the buffer to client socket and the corresponding file in the cache

tmpFile = open("./" + filename,"wb")

# Fill in start.

# Fill in end.

except:

print("Illegal request")

else:

# HTTP response message for file not found

# Fill in start.

# Fill in end.

# Close the client and the server sockets

tcpCliSock.close()

# Fill in start.

# Fill in end.