CS 453 - Assignment Set 1 (Spring 2005)

Given: February 1, 2005

Due: March 4 (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 a text file 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 in addition to the name of the file to read in. 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 [30 points total]: Write a basic web retrieval client that can parse a given URL, connect to a web server, and retrieve the object and save it to a file. 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 [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.
- B [10 points]: Construct a routine that uses the routine or object above 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.
- C [10 points]: Take the routines or objects constructed in the parts above and construct an application that takes a given URL string and retrieves the object and saves it to a file (including headers and status line). Errors must be printed for HTTP status codes other than 200 and for malformed URLs.
Part 4 [30 points total]: Write a basic web server that can handle the GET request method. You may not rely on any intrinsic language objects that do any of this for you. This part requires multiple pieces to be done so I suggest working on each part separately and verify that each part works by itself. These parts are:
- A [5 points]: Construct a routine or object that can read an HTTP/1.0 request from a socket and parse it into request method, request-URI, HTTP version, headers, etc.
- B [5 points]: Construct a routine or object to construct a HTTP/1.0 response given a status code, phrase, headers, and a body and send that response back on a socket.
- C [10 points]: Take the routines or objects constructed above and construct an application that listens on a port for connections. Connections that are accepted should then be treated like HTTP requests and use the routines or objects above. I.e. retrieve an HTTP request on a socket, parse it, open the file indicated by the URI and send the contents back as an HTTP response. Files that can not be opened should generate a 404 status code. Requests that are not "GET" should generate a 501 status code. Malformed requests should generate a 400 status code and response.
- D [3 points]: Modify the above so that it sends back the "Date" header with the time of day in it.
- E [3 points]: Modify the above so that it sends back the "Content-Length" header with the correct object size.
- F [4 points]: Modify the above so that it sends back the "Last-Modified" header with the correct object modification date.
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 01.31.2005)