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LICENSE: Copy this header in case you want to use parts of the code from this
project.
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Authors: 
Rahul Bahal
Kevin Abraham
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README
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Approach:
We implemented the TCP and IP for this project. For this, we first had to get
the initial TCP handshake right. Next, we formed the GET request for the 
requested URL and sent it by encapsulating it in our packet.
Next, we created a method to receive the response from the server and 
acknowledged the packets accordingly. The retransmisisons are also handled in 
the code where we request again for a lost packet. We have also implemented a 
basic congestion window, checksum verification and an application timeout where
we assume the connection to be failed after 3 mins and let the user know about 
this. Finally, we end the connection by sending a FIN at the end.
We verified the downloaded file by comparing it with the original and matching
their checksums(we used md5sum to validate the checksums).
We also validate the response code and we are notifying the user in case of a 
non 200 response.


How to execute:
Note: Since this project deals with Raw socket connections, the user needs to be a 
ROOT user.

sudo ./rawhttpget [URL] OR ./rawhttpget [URL]

E.g: sudo ./rawhttpget http://david.choffnes.com/classes/cs4700sp16/project4.php

This will download a file "project4.php" or in case of hitting the root of the 
host(e.g: http://david.coffnes.com/), it will download a file "index.html".

Challenges:
The core of the application depended upon getting the concept of TCP/IP transfer
right and surprizingly seeing some behaviours that were slightly different from
our initial understanding after class, which were interesting.
1. Biggest challenge was to test the application as a large portion of code 
change/update was to be done before a new feature could be tested properly.
2. Second challenge was to correctly compute the field sizes for the headers.
3. Third challenge was to implement the congestion window size, checksum
verification and timeout after the code as a small change implemented incorrectly
would cause a crash.
4. Fourth challenge was to analyze the packet flow in wireshark. It seems easy
to use after a few tries but we required sometime to get used to the new tool.

Files:
The following are the files in our project directory:
http.py
tcp.py
ip.py
utils.py
README
rawhttpget
Makefile

Known Issue:
- Need a eth0 port for sending/receiving ethernet frames (Future Scope)
- Stress Tests may take sometime to execute. We tested the application with the 
2 MB file, and the time to download the file under 30 secs and ~5-7 mins for
10 MB file at our home network. We can imporove it's efficiency and have clear
plans and timeline to do the same.

References:
http://www.binarytides.com/raw-socket-programming-in-python-linux/
http://www.binarytides.com/python-packet-sniffer-code-linux/
http://www.networksorcery.com/enp/protocol/tcp.htm
http://stackoverflow.com/questions/24728088/python-parse-http-response-string 
http://stackoverflow.com/questions/366682/how-to-limit-execution-time-of-a-function-call-in-python
http://www.programcreek.com/python/example/50987/socket.AF_PACKET