CS 453 - Assignment Set 1 (Fall 2005)

Given: September 13, 2005

Due: October 14 (Friday), 2005

Language Options: C, C++, Java, or another approved language

OS Options: Must run on CSEE shell servers

Part 1 [20 points total]: Modify one of the echo client applications given in class. The new echo client you create should read lines from standard input and send each line to the echo server in a loop. It should compare the input data that it reads in with the data received from the server and alert the user if the data differs. The application should take the IP address and port to connect to from the command line. The application should disconnect from the server and exit gracefully upon receiving an end of file from standard input. It should be able to understand both hostnames and IP addresses in dotted decimal notation.
Part 2 [20 points total]: Modify one of the echo server applications given in class. The new echo server should have a few additions:
- A [3 points]: This new echo server should conform to the RFC document for the echo protocol given in class. This includes modifying the server to process each connection until the client disconnects. In other words, the server should loop around the recv/send part until the recv returns a value of 0 bytes received.
- B [2 points]: It should have the ability to take the port number to bind to from the command line.
- C [15 points]: It should handle multiple connections concurrently. For C/C++, this means adding usage of fork() and reaping all child processes or using POSIX threads. For Java, the use of the Thread class will be necessary. Follow a process per connection or thread per connection model as appropriate.
Part 3 [60 points total]: Write a web proxy server. This part requires multiple pieces to be done so I suggest working on each part separately and verifying that each part works by itself. These parts are:
- A [5 points]: Construct a routine or object to parse an HTTP 1.0 request to break it down into request method and URL. You may not rely on any intrinsic language objects that do HTTP parsing for you.
- B [10 points]: Construct a routine or object to parse a given URL string in the form http://hostname[:portnum]/pathname, where the part in [] is optional, into (1) host IP address, (2) port, and (3) URI. You may not rely on any intrinsic language objects that do URL parsing for you.
- C [15 points]: Construct a routine that uses the routine or object in part B to take a URL, connect to the correct web server, send a HTTP/1.0 GET request, and retrieve the response. You may not rely on any intrinsic language objects that do HTTP retrieval for you.
- D [15 points]: Take the routines or objects constructed in the parts above and construct an application that listens on a TCP port given on the command line, accepts client connections, receives client HTTP requests, parses HTTP requests, connects to and retrieves the object for the client, and returns the object to the client as a HTTP proxy would. Errors must be handled for hostnames that can not be looked up, for failed connection to web servers, and for request methods other than GET (i.e. returning 501 Not Implemented).
- E [10 points]: Expand upon part D by caching the response from the web server in a file. When another web client sends a request for the same object, return the cached copy instead of going back to the original server.
- F [5 points]: Expand upon part E by checking if the web server has an updated copy by sending an "If-Modified-Since" header with the date of the cached copy and handling the HTTP response from the web server appropriately.
Notes: Your submissions must at least compile before any credit will be given. Submissions that do not compile will not be graded. Submissions submitted after the due date will not be graded. All work must be your own original work. To get partial credit for parts of the assignment, you must demonstrate that those pieces work by themselves. If you share code with others, you will be given a 0 for the assignment. This assignment set is worth 25% of your total grade.

HTTP 1.0 Specification at http://www.w3.org/pub/WWW/Protocols/HTTP/1.0/spec.html

Todd L. Montgomery (revised 09.13.2005)