Description
Project Description
HTTP GET requests are used to request data from the specified source. For
example, if we want to access a webpage at
http://www.foo.com/bar.html, our browser will send something similar
to the following HTTP GET request.
GET /bar.html HTTP/1.1
Host: www.foo.com
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64;
rv:28.0) Gecko/20100101 Firefox/28.0
Accept:text/html,application/xhtml+xml,application/xml;
q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
In the above example, our browser is the client, and Host: www.foo.com is
the server host name. The client is requesting server resource located at
/bar.html. Usually, HTTP servers run on port 80. So, by default, the server port
number is 80. If, for example, the HTTP server runs on port 8080, then the URL
would be http://www.foo.com:8080/bar.html, and the Host field in
the HTTP request will also contain the port number: www.foo.com:8080.
The HTTP server responds with HTTP response. A valid HTTP response includes:
(1) the status line, (2) the response header, and (3) the entity body. For example,
the text below shows an example HTTP response. Notice that this response header
includes a field: Content-Length, which tells the client how much data to
expect.
HTTP/1.1 200 OK
Date: Thu, 02 Apr 2015 01:51:49 GMT
Server: Apache/2.2.16 (Debian)
Last-Modified: Tue, 10 Feb 2015 17:56:15 GMT
ETag: “56638402b-a85-50ebf9a5ecdc0”
Accept-Ranges: bytes
Content-Length: 2693
Content-Type: text/html; charset=ISO-8859-1
… …
An HTTP proxy is an application that resides between the HTTP client and
server. The HTTP proxy relays the client’s HTTP requests to the HTTP server, and
forwards the server’s response back to the client. Proxies are often used when the
client cannot directly connect with the HTTP server. If a client is configured to use
an HTTP proxy, the HTTP GET request it sends out will not only include path to
the resource at the server, but also the server host name. For example, the request
would look like:
GET http://www.foo.com/bar.html HTTP/1.1
Host: www.foo.com
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64;
rv:28.0) Gecko/20100101 Firefox/28.0
Accept:text/html,application/xhtml+xml,application/xml;
q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
To request the resource for the client, the HTTP proxy starts a new TCP
connection with the server host www.foo.com at port number 80 and ask for file
bar.html. When the HTTP proxy relays this request from the client, it will have
to remove the host name, http://www.foo.com from the request line of the
GET request, so that the request line specifies only the local resource path at the
destination server. When the HTTP response arrives at the proxy, the proxy will
forward it to the client. If the proxy is correctly implemented, a client web-browser
should be able to display the requested resource.
You need to write the proxy program. Your HTTP proxy should support a subset
of the HTTP standard. It only needs to forward HTTP GET requests and should
only support basic portions of the standard. That is, you do not need to support
persistent connections, request pipelining or other, advanced portions of the
standard. Your proxy must only correctly handle HTTP requests where a single
request/response pair is sent over a single TCP connection. Specifically, your
proxy should operate as follows:
• It should create a TCP server socket to listen for incoming TCP connections
on an unused port, and output the host name and port number the proxy is
running on.
• When a new connection request comes in, the proxy accepts the connection,
establishing a TCP connection with the client.
• The proxy reads HTTP request sent from the client and prepares an HTTP
request to send to the HTTP server.
• The proxy starts a new connection with the HTTP server, and sends its
prepared HTTP request to the server.
• The proxy reads the HTTP response and forwards the HTTP response (the
status line, the response header, and the entity body).
• The proxy closes the TCP connection with the server.
• The proxy sends the server’s response back to the client via its TCP
connection with the client. This TCP connection with the client should have
remained open during its communication with the server.
• The proxy closes the connection socket to the client.
FAQ
* What is in the folder?
utils.c functions used by the proxy server
proxy.c contains source code of the proxy
utils.h header file of utils.c
makefile make file to build proxy
proxy proxy executable
* What do we have to do?
You have to supply the missing code in the files ‘utils.c’ and
‘proxy.c’. The location of missing code is
marked with “TODO:”. Your task is to fill in the missing code.
* How do I test my programs?
You first download a resource located at a URL using the wget command without
the proxy. This is the correct resource. Then you download the same resource at
the same URL with your proxy. Use the diff command to check if the two
downloaded resources matches.
Suppose your HTTP proxy is started on eecs325-VirtualBox port 47590.
You can run the following Bash shell command
$> bash
$> export http_proxy=http://127.0.0.1:47590 && wget
http://www.foo.com/bar.html
To download without the HTTP proxy, use the following command:
$> export http_proxy=”” && wget
http://www.foo.com/bar.html
Note:
• You MUST replace http://www.foo.com/bar.html with a valid URL.
• Since this is only an HTTP proxy, not an HTTPS proxy, your URL MUST
use HTTP, not HTTPS.
• You may also run your HTTP proxy on your own machine and use
Wireshark for debugging.
• Your web browser also has a cache. A second request for the same URL
may be directly served by your browser cache without going through the
proxy. Therefore, you are recommended to use wget for debugging and
testing.
REMINDERS
o Submit your code to Canvas in a tarball file by running command in terminal:
zip -r [you-case-id]-proj-2.zip project-2
o If your code does not compile or could not run, you will not get credits.
o Document your code (by inserting comments in your code)
o DUE: 11:59 pm, Tuesday, May 7th
Appendix
Below is a list of URLs you can use for testing your proxy implementation.
http://engineering.case.edu/eecs
http://engineering.case.edu/eecs/about
http://engineering.case.edu/eecs/node/190
http://engineering.case.edu
http://engineering.case.edu/eecs/node/306
http://engineering.case.edu/eecs/research
http://engineering.case.edu/eecs/sites/engineering.case
.edu.eecs/files/images/header-research.jpg
https://engineering.case.edu/eecs/seminars
