| NetProg 2002 HW2 |
| Project Description | Deliverables | Grading | Submission | Notes & Hints |
Your assignment is to write a Proxy HTTP Server. Your server must be able to handle GET, HEAD and POST requests (it can ignore any request that specifies any other HTTP request method) sent by a client speaking HTTP version 1.0 or 1.1. Your proxy should work with any HTTP client (browser), we will be testing it with a custom HTTP client written just to torture your server.
Your server must use a port number specified as the first command line parameter (from argv[1]). Your program will be run by an automated system that requires that your server understand that it should use the port number specified on the command line!
Your server must handle GET, HEAD and POST request methods.
Your server can ignore any other HTTP request method (treat the request as an invalid request).
Your server must forward HTTP request headers to the server and response headers back to the client.
Your server does not need to be concurrent (although it's not hard and will make your proxy much more usable).
We must not be able to kill your server simply by sending an invalid request.
We must not be able to kill your server by stopping or killing the client (this includes pressing the STOP button in Netscape or IE).
Your server does not need to support all the fancy features of HTTP version 1.1, we are looking for basic functionality (by fancy, I mean things like persistent connections...).
To keep track of all requests, your server should print one line (to standard output) for each request serviced. The line should include the host name or IP address of the client, and the original request-line sent by the client (not any of headers that accompanied the request). For example, the following might be the output generated by your server if it received some requests from a client running on monica.cs.rpi.edu:
> hw2 1234 monica.cs.rpi.edu: GET http://www.cs.rpi.edu/ monica.cs.rpi.edu: GET http://www.cs.rpi.edu/gfx/backg5.jpg monica.cs.rpi.edu: GET http://www.cs.rpi.edu/gfx/logo.jpg monica.cs.rpi.edu: GET http://www.yahoo.com/images/annakornikova.jpg monica.cs.rpi.edu: GET http://fred.com/purchase.asp?prod=17&qty=102 monica.cs.rpi.edu: HEAD http://www.slashdot.org/ monica.cs.rpi.edu: POST http://www.fbi.gov/insecuresubmission.cgi |
Note that it is not necessary to include the HTTP version number in the output (but feel free to do so if you want).
You should submit all source code files necessary to build your server. If you use a Makefile please include it, if not you need to include instructions on how to build your server. Your submission must also include a file named README that includes the following:
Your Name
A list of files and a 1-line description of the contents of each file.
References to any borrowed code (the source code must also include this information).
A description of any known problems. If you think you know how to solve the problem(s) and simply didn't have time to do so - let us know how!
Anything else you think might be useful to us, such as what you learned, what you had trouble with, if the project was too hard or too easy, etc.
Your server will be tested to make sure it works properly. We will use a test client that will do it's best to mess up your server by sending nonsense, incredibly long request lines, and invalid web addresses (yes, it will also send many valid requests). It is acceptable that your proxy respond to any nonsense request by sending back an HTTP response code that indicates an error and closing the connection. It's not hard to send back an HTML document as well (that describes the error), but this is not required.
Your testing should include using a real browser (you can tell
Netscape or IE to use your server as a proxy), Dave will demonstrate
this in class. Although using a real browser through your proxy is
a great test, you need to remember that our client will send nonsense
requests to your server (and it may be hard to get a real browser to
do this). You can use telnet to connect to your proxy and
send nonsense, or write your own test client. IMPORTANT: Make
sure your proxy can handle images, don't rely soley on simple HTML
documents for all your testing!
Points will be awarded as follows (partial credit is available for each item):
| GET and HEAD requests work properly with polite clients | 30% |
|---|---|
| POST works properly with polite clients | 20% |
| bad requests are handled without problems | 25% |
| Style/readability | 25% |
IMPORTANT NOTES ON GRADING:
We will check for memory leaks and deduct points (up to 5 points) if we detect a problem. Your server should not get larger (should not require an endless supply of memory) as it handles each request. Make sure you clean up any dynamically allocated memory that is no longer needed!
We will also look through your source code to make sure that you
handle all possible errors (not just those that our test client can
produce). You can lose up to 10 points for not handling errors. You
decide what to do when an error occurs, the important thing to
remember is that the server should continue running if possible.
Feel free to print out error messages (but it's not required).
In many cases an error returned by a system call can be dealt with by
terminating the connection to the client and moving on to the next
client. Other cases are clearly fatal - for example if
bind won't
give you the port requested, then the server can't get started...
Submission of your homework is via email, the general idea is to send an email message with all your files as attachments. There is an automated email submission system that will respond to your submission right away, so you will have a record that we got your files.
All projects must be submitted via email to netprog-submit@cs.rpi.edu. The subject line of the submission message should contain a single number indicating the project number (2 for HW2). You must include your files as attachments, feel free to send a zip-file or a tar file.
Don't send compiled code!
You can expect a return email indicating receipt of your project submission immediately. This receipt will include a list of all the files that were successfully extracted by the submission script - please look over the receipt carefully to make sure your submission worked.
Multiple Submissions: You can resubmit up to 10 times for each project, we will always grade the last submission received unless you tell us otherwise.
You need to have a basic understanding of HTTP! The best places to look for information are RFC 1945 HTTP 1.0 and RFC 2616 HTTP 1.1.
You may want to start with this document: Basic HTTP (1992) from w3.org. This document is an incomplete description of HTTP 1.0 (from an early proposal, I think), but it has most of the information you need for this project and is a much easier read than the RFC.
We are not worried about whether your server can support every nitty-gritty detail of HTTP 1.1, but rather that you can write a proxy server that is usable (from a browser), robust (can deal with nonsense requests and rude clients), and the code is something that could be extended to support all the nitty-gritty details of HTTP 1.1 (We expect code that has no memory leaks, handles all errors, etc).
If a client closes a connection prematurely, your server can
receive a SIGPIPE (this happens when you call write()
on a socket that has been closed by the other end). By default,
a SIGPIPE will kill your process - so you need to handle this
situation. Check out section 5.13 in the text for a description
of how to handle this.
If you decide to make your server concurrent (via
fork()), you can't leave zombie processes around - they
must be handled by your server. If you don't know what a zombie
process is, either look it up (the book describes how to avoid
zombies) or don't use fork(). (You might also consider
reviewing your notes from OpSys!).