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.
2 Task I: Multi-threaded HTTP Proxy
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, establising 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. Also note that the proxy should use Content-Length to determine how much response content to read from the server and forward to the client.
• The proxy closes the connection socket to the client.
To maintain a high level of throughput even under multiple simultaneous client requests, different requests should be handled in different threads, with a new thread created for each client request. In this project, you are required to use the pthreads (POSIX threads) library for the multi-threaded proxy implementation. You cannot use the select() call you used in Project 1 for handling multiple client connections.
To help you get started with your pthread implementation, I have provided code for a multi-threaded version of Project 1’s confserver. Note that this implementation only lets the server connect with multiple clients and display messages sent from these clients. The message forwarding necessary for conferencing operation is not implemented.
I have provided a file, project2.tgz. After downloading the file, run tar xzvf project2.tgz to extract the compressed files. The resulting directory should contain the following files:
multi-threaded-server.c contains source code of multi-threaded server confutils.c contains routines used by the server Makefile a make file used to build the multi-threaded-server executable.
2.1 How to test your implementation
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 remote02.cs.binghamton.edu port 47590. You can run the following Bash shell command in an EMPTY directory on a remote.cs computer to download web resource via your proxy.
export http_proxy=http://remote02.cs.binghamton.edu: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 browsercachewithout goingthroughtheproxy. Therefore, youarerecommendedto usewgetfordebugging and testing.
3 Task II: Caching
Your HTTP proxy must also implement the caching feature. With caching, the proxy stores the responses of past requests in its local storage. If an incoming request matches an entry in the cache, the proxy returns its cached data in its local storage to the client directly. This can greatly reduce the response time and reduce the network bandwidth.
For simplicity, you can assume that the cache size is infinite, i.e., the cache is big enough to store responses to all requests locally. This project requires that you implement the cache in-memory. That is, you cannot write any content to the persistent storage. When your proxy starts, the cache is empty.
Upon successfully serving a request, your proxy must write to standard output (stdout) the following items: client IP client’s IP address in dotted decimal representation requested URL cache status can only be one of the two values: CACHE_HIT or CACHE_MISS content length is the size of the entity body in bytes request time is request processing time in milliseconds resolution from when the connection from the client is accepted to when the connection to the client is closed (i.e., the last bytes were sent to the client).

These five items of a same request should be printed to a same line and seperated by the “|” character. Below is an example:
128.226.118.20|http://www.foo.com/bar.html|CACHE_MISS|2693|300
128.226.118.26|http://www.foo.com/bar.html|CACHE_HIT|2693|2
The first request for http://www.foo.com/bar.html was not found in the cache. So the resource was fetched from the remote server. Total request time was 300 ms. When a different client with a different IP address requested the same URL, it was a cache hit, and the request time was much smaller, only 2 ms.
4 How to submit
To submit the project, you should first create a directory whose name is identical to your BU email ID. For example, if your email ID is [email protected], you should create a directory called jdoe-project2.
You should put the following files into this directory:
1. All of your source code that implements the HTTP proxy. Note that your proxy executable should not take any command line arguments and must output the host name and port number it is running on.
2. A Makefile to compile your source code into one executable, which should be named proxy.
3. A Readme file describing the your implementation details and sample input/output.
Compress the directory (e.g., tar czvf jdoe-project2.tgz jdoe-project2) and submit the tarball (in tar.gz or tgz format) to myCourses. Again, if your email ID is [email protected], you should name your submission: jdoe-project2.tar.gz or jdoe-project2.tgz. Failure to use the right file name will result in a 5% point deduction.
Your project will be graded on the CS Department computers remote.cs.binghamton.edu. If your code does not compile on or cannot correctly run on the CS computers, you will receive zero points.
Your project must be your original work. We will use MOSS 1 to detect plagiarism in the projects.
Appendix
Below is a list of URLs you can use for testing your proxy and caching implementation.
http://www.cs.binghamton.edu/~yaoliu/courses/cs528/cs528.html
http://www.cs.binghamton.edu/~yaoliu/courses/cs528/course.css
http://www.cs.binghamton.edu/~yaoliu/courses/cs528/syllabus.pdf
http://www.cs.binghamton.edu/~yaoliu/courses/cs528/lena_std.tif
http://www.cs.binghamton.edu/~yaoliu/courses/cs528/skype-ubuntu-precise_4.3.0.37-1_i386.deb

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1 https://theory.stanford.edu/~aiken/moss/

The list below includes URLs from servers located outside the computer science department. Please do not test your proxy on these URLs unless you have successfully tested on the URLs above. You should also limit the number of requests you send to these websites. If the volume is too high, the external server may consider you are performing a denial-of-service (DoS) attack and may block your IP.
http://www.binghamton.edu:8080/asf-logo.png
http://www.binghamton.edu:8080/docs/setup.html
http://portquiz.net:10000/portquizm.png
http://httpbin.org/html
http://httpbin.org/image/png
http://httpbin.org/image/jpeg