Description
In this homework, we’ll look at the HTTP protocol as a Web server. After creating your
personal repository, you will find that the hw5 directory contains:
homework5.c: Skeleton code for the server side of a TCP application. This will be the
primary file for this assignment, but feel free to modularize and create other files if you
prefer to do so.
WWW/: A directory containing example files for your Web server to distribute.
thread_example.c: Example code that illustrates a very simple threaded programming
scenario. You are not required to use or make any changes to this file, but you should
understand what it does.
A Makefile. If you modularize your code into different files, make sure those changes
are reflected in the Makefile (and don’t forget to git add those files to your personal git
repo!).
Your server program will receive two arguments: 1) the port number it should listen on for
incoming connections, and 2) the directory out of which it will serve files (often called the
document root in production Web servers) For example:
CS 361 Summer 2020 Home Schedule Homeworks
6/15/2020 CS 361 Summer 2020 – HW5
https://sites.google.com/uic.edu/cs361summer2020/homeworks/hw5?authuser=1 2/4
document root in production Web servers). For example:
$ ./homework5 8080 WWW
This command will tell your Web server to listen for connections on port 8080 and serve
files out of the WWW directory. That is, the WWW directory is considered ‘/’ when
responding to requests. For example, if you’re asked for /index.html, you should respond
with the file that resides in WWW/index.html. If you’re asked for /dir1/dir2/file.ext, you
should respond with the file WWW/dir1/dir2/file.ext.
Requirements
In addition to serving requested files, your server should handle at least the following cases:
1. HTML, text, and image files should all display properly. You’ll need to return the proper
HTTP Content-Type header in your response, based on the file ending. Also, other binary
file types like PDFs should be handled correctly. You don’t need to handle everything on
that list, but you should at least be able to handle files with html, txt, jpeg, jpg, gif, png,
and pdf extensions.
2. If asked for a file that does not exist, you should respond with a 404 error code with a
readable error page, just like a Web server would. It doesn’t need to be fancy, but it
should contain some basic HTML so that the browser renders something and makes the
error clear.
3. Some clients may be slow to complete a connection or send a request. Your server
should be able to serve multiple clients concurrently, not just back-to-back. For this
homework, use multithreading with pthreads to handle concurrent connections. We’ll
try event-based concurrency in a future homework assignment.
4. If the path requested by the client is a directory, you should handle the request as if it
was for the file index.html inside that directory. Hint: use the stat() system call to
determine if a path is a directory or a file. The st_mode field in the stat struct has what
you need.
5. The Web server should respond with a list of files when the user requests a directory that
does not contain an index.html file. You can read the contents of a directory using the
opendir() and readdir() calls. Together they behave like an iterator, that is, you can
open a (DIR *) with opendir and then continue calling readdir(), which returns info for
one file, on that (DIR *) until it returns NULL. In lab8, you will be provided with and
example code on how to read in contents of a directory and print them to stdout. Note
that there should be no additional files created on the server’s disk to respond to the
request. The response should mimic result of running python -m SimpleHTTPServer
Wh t ti h ld b bl t t i b t f b t i f fil f
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When testing, you should be able to retrieve byte-for-byte copies of files from your server.
Use wget or curl to fetch files and md5sum or diff to compare the fetched file with the
original. We will do this when grading. For full credit, the files need to be exact replicas of the
original.
Tips
Please read the skeleton code to get a feel for what is available and what you should be
doing.
As of the release of this assignment, we have not covered the concepts related to
networking in class; to start on this homework, take a look at chapter 11 (especially 11.5
and 11.6) from the textbook to learn more about the network programming in C.
The labs on 3/30 and 4/6 will help you get started on the assignment as well.
Take compiler warnings seriously. Unless it’s an unused variable, you should address the
warning as soon as you see it. Dealing with a pile of warnings just makes things more
difficult later.
Test your code in small increments. It’s much easier to localize a bug when you’ve only
changed a few lines.
If you need to copy a specific number of bytes from one buffer to another, and you’re not
100% sure that the data will be entirely text, use memcpy() rather than strncpy(). The
latter terminates early if it finds a null terminator (‘\0’).
If you’re trying to do some sort of specific string or memory manipulation, feel free to ask
if there’s a better/recommended way to do it rather than brute force. Often there may be
a standard library function that will make things easier.
Roughly, your server should follow this sequence:
1. Read the arguments, bind to the specified port, and find your document root (you might
find the chdir() system call helpful).
2. Accept a connection, and hand it off to a new thread for concurrent processing.
3. Receive and parse a request from the client.
4. Look for the path that was requested, starting from your document root (the second
argument to your program). One of four things should happen:
1. If the path exists and it’s a file, formulate a response (with the Content-Type header
set) and send it back to the client.
2. If the path exists and it’s a directory that contains an index.html file, respond with that
file.
3. If the path exists and it’s a directory that does NOT contain an index.html file, respond
CS 361 Summer 2020 Home Schedule Homeworks
6/15/2020 CS 361 Summer 2020 – HW5
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p y , p
with a directory listing.
4. If the path does not exist, respond with a 404 code with a basic error page.
5. Close the connection, and continue serving other clients.
Turn-in instructions and Grading
You need to submit homework5.c to Gradescope. Grading will be done automatically using
a script. We will publish this script after grading has completed; you are responsible for
writing your own test cases. If you wish, you can share test cases you have written with the
class.
Reminders
Always, always, always check the return value of any system calls you make! This is
especially important for send, recv, read, and write calls that tell you how many bytes
were read or written.
If you have any questions about the homework requirements or specification, please post
on Piazza.
CS 361 Summer 2020 Home Schedule Homeworks
