The goal of this project is to build a functional HTTP/1.0 server. This assignment will teach you the basics of distributed programming, client/server structures, and issues in building high performance servers. While the course lectures will focus on the concepts that enable network communication, it is also important to understand the structure of systems that make use of the global Internet.
This project should be done in teams of two.
Due Date: February 3, 2015, before start of class
At a high level, a web server listens for connections on a socket (bound to a specific port on a host machine). Clients connect to this socket and use a simple text-based protocol to retrieve files from the server. For example, you might try the following command from a UNIX machine:
$ telnet www.cs.ucsd.edu 80 GET /index.php HTTP/1.0\n \n
(type two carriage returns after the "GET" command). This will return to you (on the command line) the html representing the "front page" of the UCSD computer science web page.
One of the key things to keep in mind in building your web server is that
the server is translating relative filenames (such as index.html) to absolute
filenames in a local filesystem. For example, you might decide to keep all the
files for your server in
~student/cse124/server/files/, which we
call the document root. When your server gets a request for index.html , it
will prepend the document root to the specified file and determine if the file
exists, and if the proper permissions are set on the file (typically the file
has to be world readable). If the file does not exist, a file not found error
is returned. If a file is present but the proper permissions are not set, a
permission denied error is returned. Otherwise, an HTTP OK message is returned
along with the contents of a file.
You should also note that web servers typically translate "
/" to "
GET /index.html". That is, index.html is assumed to
be the filename if no explicit filename is present. That is why the two URL's
http://www.cs.ucsd.edu/index.html" return equivalent results.
When you type a URL into a web browser, it will retrieve the contents of the
file. If the file is of type
text/html, it will parse the html
for embedded links (such as images) and then make separate connections to the
web server to retrieve the embedded files. If a web page contains 4 images, a
total of five separate connections will be made to the web server to retrieve
the html and the four image files.
For this assignment, you will need to support enough of the HTTP protocol to allow an existing web browser (Firefox, Chrome, or Safari) to connect to your web server and retrieve the contents of a web page with HTML code, as well as with in-line images, including jpg and png formats. One example you can use is the UCSD CS front page. Of course, this will require that you copy the appropriate files to your server's document directory. You will not need to have any support for the php aspects of the page.
At a high level, your web server will be structured something like the following:
Forever loop: Listen for connections Accept new connection from incoming client Parse HTTP/1.0 request Ensure well-formed request (return error otherwise) Determine if target file exists and if permissions are set properly (return error otherwise) Transmit contents of file to connect (by performing reads on the file and writes on the socket) Close the connection
You will have three main choices in how you structure your web server in the context of the above simple structure:
You may choose from C or C++ to build your web server but you must do it in
a Unix-like environment. You will want to become familiar with the
interactions of the following system calls to build your system:
connect(). We outline a number of
resources below with additional information on these system calls. A good book is
also available on this topic.
Note that the previous discussion assumes the HTTP/1.0 protocol. Next, add simple HTTP/1.1 support to your web server, consisting of persistent connections and pipelining of client requests to your web browser. You will also need to add some heuristic to your web server to determine when it will close a "persistent" connection. That is, after the results of a single request are returned (e.g., index.html), the server should by default leave the connection open for some period of time, allowing the client to reuse that connection to make subsequent requests. This timeout needs to be configured in the server.
You will be submitting a compressed tar archive named webserver.tar.gz containing your source code and a Makefile. Please do not submit any binary files. Instructions for how to submit your code will be posted on Piazza soon.
Your Makefile should build a binary named
should take two command line arguments: a port (an integer) and a path to the
document root (a string). Please verify that the following commands build and
your start your webserver:
tar -xzvf httpd.tar.gz make ./httpd <port> <path/to/document/root>
Provide simple server support for
".htaccess" files on a per-directory basis to limit the domains that are
allowed access to a given directory. You only need to implement the
allow/deny from 000.000.000.000/xx" syntax and rules should be
applied in descending order. You should be able to allow/deny from both ip
addresses as well as domain names. .htaccess rules do not have to be applied
recursively. An example of a .htaccess file includes:
The above file allows from any host in the 172.22.16.0/24 subnet, except for host 172.22.16.18. Any 'local' addresses in the 192.168 subnet are allowed, as is 'mymachine.ucsd.edu'. Any other hosts are denied (the default rule on the last line).
deny from 172.22.16.18/32 allow from 172.22.16.0/24 allow from 192.168.0.0/16 allow from mymachine.ucsd.edu deny from 0.0.0.0/0