bittorrent-python

This repository contains the implementation of a bittorrent-like P2P network written in python in collabration with @arman-aminian and was the course project of the Fall 2020 Computer Networks course.

Each node in the network first contacts the tracker to transfer the essential information and then acts based on that.

General Explanation

As said before, nodes need to communicate with the tracker to send or receive the information required for their action, which is either uploading a file or downloading one. Note that sending/receiving multiple files do not create an issue since every action is done via a corresponding thread. Each node's files are placed in a separate folder to simulate the real world.

Possible actions are:

• Upload: The node first tells the tracker it wants to upload a file and the tracker adds that node to a list holding the owners of a file. Then, it waits for download requests from other nodes.
• Download: After telling the tracker, the node receives the list of owners of that requested file. Then, asks the file size from one of the owners and divides that size by the owners length. After that, each uploader sends its portion of the file and the whole process is done via a thread for each part. After all threads are done, the file is glued together.
• Exit: Exits the network while de-allocating the previously held socket. The tracker then removes this node from the owners list.

Communication Messages

There are four distinct types of message that is transferred between objects in the network:

1. NodeToTracker: Tells the tracker whether it has a file and wants to upload it (mode have), wants to receive (download) a file (mode need), or wants to exit the network (mode exit).
2. TrackerToNode: Responds to a node who wants to download a file and transfers the owner list of that file to them.
3. SizeInformation: Sent when a node starts downloading a file and wants to know the size of that. size = -1 when the downloader asks the size.
4. FileCommunication: The most crucial message type which contains the actual parts of data sent by different nodes.

We tried to make the code self-explanatory, so everything else should be easy to understand by just looking at the code.

Usage

First, you need to run the tracker; To do that, simply run python3 tracker.py. Then you need to run some nodes using the following line:

python3 node.py -n <node name> -p <input port> <output port>

Now the node.py waits for your command to be entered. Possible commands are:

• torrent -setMode upload <filename> to upload a file and wait for requests.
• torrent -setMode download <filename> to start downloading a file.
• torrent exit to exit the network.

More

project_files/ contains two files: the project explanation and the project report which is a complete guide of how this program works. Both written in persian.

These are some improvements that might be done in the future:

• Adding Documentation.
• Not every node has the full file, so we need to assign the uploaders their portion of the file based on some other formula to balance everything.
• The downloader may not receive the whole file, so we need to request the missing parts again.

Contributions

Any form of feedback (issues, pull requests, discussion) would be a huge help to us so thank you in advance!