Description
In this project, you are going to build a simple web server that implements a subset of the
HTTP/1.1 protocol specification called TritonHTTP (located in Canvas).
TritonHTTP Specification
The TritonHTTP spec is located in Canvas.
Project overview
Basic web server functionality
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 the TritonHTTP protocol to retrieve files
from the server. Your server will read data from the client, using the framing and parsing
techniques discussed in class to interpret one or more requests (if the client is using pipelined
requests). Every time your server reads in a full request, you will service that request and send
back a response back to the client. After sending back one (or more) responses, your server
will either close the connection (if instructed to do so by the client via the “Connection: close”
header, described below, or after an appropriate timeout occurs (also described below). Your
web server will then continue waiting for future client connections. Your client should be
implemented in a concurrent manner, so that it can process multiple client requests overlapping
in time.
Project details
Below are some of the details on implementing your project.
Mapping relative URLs to absolute file paths
Clients make requests to files using a Uniform Resource Locator, such as
/images/cyrpto/enigma.jpg. One of the key things to keep in mind in building your web server is
that the server must translate that relative URL into an absolute filename on the local filesystem.
For example, you might decide to keep all the files for your server in
~aturing/cse101/server/www-files/, which we call the document root. When your server gets a
request for the above-mentioned enigma.jpg file, it will prepend the document root to the
specified file to get an absolute file name of
~aturing/cse101/server/www-files/images/crypto/enigma.jpg. You need to ensure that
malformed or malicious URLs cannot “escape” your document root to access other files. For
example, if a client submits the URL /images/../../../.ssh/id_dsa, they should not be able to
download the ~aturing/.ssh/id_dsa file. If a client uses one or more .. directories in such a way
that the server would “escape” the document root, you should return a 404 Not Found error
back to the client. However, it is valid if the client requests a URL like
~aturing/cse101/server/www-files/../../../cse101/server/www-files/images/crypto/enigma.jpg,
where the URL does not escape from the document root.
Supporting MIME types
Most applications interpret the contents of files based on their extensions (e.g. homework.txt
represents an ASCII text file, whereas icon.jpg represents a JPEG image). Historically, file
extensions have not played much of a role with the HTTP protocol, in part because sometimes
web servers will dynamically generate content on demand. So, for example, a request line of the
form
GET /cgi-bin/genhaiku.pl HTTP/1.1
….
Might invoke an external helper program (in this case, written in Perl), to generate a haiku poem
on demand. But how to interpret the data that is returned? Is it ASCII text? A Word file? An
image with the poem written in the center?
Web servers explicitly indicate the type of file via the “Content-Type” header. Examples include:
Content-Type: image/jpeg
Content-Type: application/msword
Content-Type: text/plain
When serving files out of the document root, your web server will need to convert the file’s
extension to one of these “MIME types”. There is a mapping file called mime.types included in
your starter code that you should use to determine the mime type for local files so you can
properly set the Content-Type response header. If a file is requested with a file extension not
included in the mime.types file, you should return “application/octet-stream”.
Executable
Your server binary should be called with ./run-server.sh script and should take one argument
which references the configuration file (which may be stored anywhere on the filesystem, so do
not assume it is in the current directory). For example:
$ ./run-server.sh /home/aturing/myconfig.ini
$ ./run-server.sh ~aturing/myconfig.ini
$ ./run-server.sh ../configs/myconfig.ini
Experimentation
We have provided you with starter code that relies on Go’s own internal http web server. You
can use this to experiment and explore with what a “real” webserver does under a variety of
conditions. Note that the full HTTP specification is several thousand pages long, and we
certainly do not expect you to implement all of that! We’re only focusing on a relatively small
subset of the overall protocol. As a result, you may see Go’s implementation of the web server
doing things we didn’t ask you to (for example, Go’s web server appends a character set
specifier to the Content-Type header and returns a header called “X-Content-Type-Options”
which we don’t cover in our class. You can just ignore those differences and focus on the subset
of HTTP described in the TritonHTTP specification, linked above.
If an aspect of what we’re expecting from you is unclear, please ask. We do encourage you to
experiment with Go’s in-built webserver first before asking about whether your web server
“should” act in a certain way or not.
Testing strategies
We have written up a separate document to guide you in developing a testing strategy for your
project. This document is located in Canvas.
Grading
Correctness/functionality: 75%
Basic functionality for 200 error code responses (30%)
● This category represents error-free, valid requests that result in a 200 status code.
○ The response headers should be set correctly
○ The response body should match the content
● You should support directories and subdirectories
● “http://server:port/” should be mapped to “http://server:port/index.html”
● You should correctly support the MIME types specified in mime.types
Basic functionality for non-200 error code responses (22.5%):
● Handles 404 for files that aren’t found
● Handles 404 for URLs that escape the doc root
● Correctly handles malformed HTTP requests by issuing a 400 error and closing the
connection
Concurrency (7.5%):
● Your server should be able to handle concurrent clients using goroutines
Pipelining (15%):
● Your server should be able to handle two or more requests that are pipelined together in
the same TCP connection
● Your server should handle the Connection: close header correctly
● Your server should implement a 5-second timeout (refreshed after a successful read)
correctly for requests that are not explicitly closed via the Connection: close header
Testing strategy and completeness: 25%
One quarter of your grade will be determined by the completeness of your testing strategy. For
each of the rubric items above, you are to create one or more test cases that you use to
determine whether your web server is working correctly for that particular rubric item. The
specific form your tests take can vary. On one extreme is developing a complete unit test
framework that is fully automated. While that would be the most complete, it is certainly not
necessary for this class project. Other examples of testing strategies include shell scripts or
other scripts (written in Go, Python, or other languages), or even a text file write up of the
command-line tests that you ran along with the output that you saw so that you knew it was
correct. Note that it is possible to get full points on the testing strategy even if your actual code
doesn’t work, as long as it is complete and fully tests the above rubric items. Likewise, it is
possible to submit a fully working project and yet not receive full points on the testing strategy if
the testing strategy is incomplete.
You should document your testing strategy using a file or files in the testing subdirectory. If you
used command line tools (e.g. printf and nc), list each of your tests and the output you found
and expected in a clearly marked file (e.g. TESTING.md or TESTING.txt, etc). If you have
scripts or other code to test your server, put it there and make sure you clearly mark which
rubric items are associated with the different tests.
Submitting your work
Log into gradescope.com and upload your code. This assignment is to be done in groups of 1
(solo) or 2. Make sure to log into gradescope by clicking the link in Canvas! This will ensure
that your grade “syncs” correctly.
Submission guidelines:
You’ll be turning in your project on Gradescope. If you have worked in groups, please add your
group members by clicking on “Group Members” option. There are two options to submit your
code on Gradescope:
● GitHub:
Choose your GitHub repository and upload the right branch.
● Upload:
Your submission should be a single ZIP file named module2.zip which should have files
with the following structure:
|– module2.zip
|– README.md
|– src
|– testing
|– sample_htdocs
Make sure that the directory structure remains the same as provided in the starter code.
Do not include large files(video, audio files) in your submission.
Due date/time
Listed on the course calendar/schedule on the Canvas site
Starter code
● Link to the starter code github invitation
