Homework - Python Proxy

Question

For programming exercises ( from the computer network: top-down approach (6th edition) from Kurose and Ross ) we are trying to develop a simple proxy server in python.

We were provided with the following code, wherever it says #Fill in start. ... #Fill in end. #Fill in start. ... #Fill in end. where we have to write code. My specific question and attempts will be below this original fragment.

We need to start the python server using python proxyserver.py [server_ip] , then go to localhost:8888/google.com and it should work when we are done.

 from socket import * import sys if len(sys.argv) <= 1: print 'Usage : "python ProxyServer.py server_ip"\n[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\r\n") tcpCliSock.send("Content-Type:text/html\r\n") # 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\n\n") # 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. 

Where does he say:

 # Create a socket on the proxyserver c = # Fill in start. # Fill in end. 

I tried:

 c = socket(AF_INET, SOCK_STREAM) 

It seems that you are creating a socket, and then to connect to port 80 of the host, I have:

 c.connect((hostn, 80)) 

Here hostn correct google.com according to some local print statements that I have. The next section that I have to fill out is #Read response into buffer , but I really don't understand what that means. I guess it has something to fileobj with fileobj being created just above.

Thanks in advance, please let me know if I missed everything that I should add.

UPDATE

My current code can be found here to see what I tried:

https://github.com/ardavis/Computer-Networks/blob/master/Lab%203/ProxyServer.py

Answer 1

This seems to be my potential solution. The pdf from homework mentions that I need to do something at the end, not sure what it is. But cache and proxies seem to work with this. Hope this helps someone else.

 from socket import * import sys if len(sys.argv) <= 1: print 'Usage: "python ProxyServer.py server_ip"\n[server_ip : It is the IP Address of the Proxy Server' sys.exit(2) # Create a server socket, bind it to a port and start listening tcpSerPort = 8888 tcpSerSock = socket(AF_INET, SOCK_STREAM) # Prepare a server socket tcpSerSock.bind(('', tcpSerPort)) tcpSerSock.listen(5) while True: # Start receiving data from the client print 'Ready to serve...' tcpCliSock, addr = tcpSerSock.accept() print 'Received a connection from: ', addr message = tcpCliSock.recv(1024) # Extract the filename from the given message print message.split()[1] filename = message.split()[1].partition("/")[2] fileExist = "false" filetouse = "/" + filename try: # Check whether the file exists in the cache f = open(filetouse[1:], "r") outputdata = f.readlines() fileExist = "true" print 'File Exists!' # ProxyServer finds a cache hit and generates a response message tcpCliSock.send("HTTP/1.0 200 OK\r\n") tcpCliSock.send("Content-Type:text/html\r\n") # Send the content of the requested file to the client for i in range(0, len(outputdata)): tcpCliSock.send(outputdata[i]) print 'Read from cache' # Error handling for file not found in cache except IOError: print 'File Exist: ', fileExist if fileExist == "false": # Create a socket on the proxyserver print 'Creating socket on proxyserver' c = socket(AF_INET, SOCK_STREAM) hostn = filename.replace("www.", "", 1) print 'Host Name: ', hostn try: # Connect to the socket to port 80 c.connect((hostn, 80)) print 'Socket connected to port 80 of the host' # 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\n\n") # Read the response into buffer buff = fileobj.readlines() # 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") for i in range(0, len(buff)): tmpFile.write(buff[i]) tcpCliSock.send(buff[i]) except: print 'Illegal request' else: # HTTP response message for file not found # Do stuff here print 'File Not Found...Stupid Andy' a = 2 # Close the socket and the server sockets tcpCliSock.close() # Do stuff here