Simpletorrent

Simpletorrent is a BitTorrent CLI client that downloads files. It is written in C.

It's a project I worked on to improve my understanding of C and networking. It's a very basic implementation of the Bittorrent protocol (version one).

Things I've Learnt

• The BitTorrent protocol
• Sockets programming
• Byte arrays
• Using a Debugger (LLDB)
• HTTP Protocol
• Endianess
• Open Addressing Hash Table
• Concurrency in C
• Bencode Parsing

What this can't do

Because this project is for my learning, I didn't implement the following:

• Distributed Hash Table
• Peer Exchange
• A network listener (this allows other peers to connect to you without you initiating)
• Rarest piece handler
• Reconnection to more peers at scheduled times

Compilation

This program was written and tested on a Mac OS X (Big Sur). I believe it should be easily compiled on other Unix-like OS with minimal changes. Before you compile, make sure you change the openssl location here and here to the correct one on your system. Once that is done, type the following in your terminal

    export LDFLAGS=-L/usr/local/opt/openssl/lib
    export CPPFLAGS=-I/usr/local/opt/openssl/include
    export PKG_CONFIG_PATH=/usr/local/opt/openssl/lib/pkgconfig
    LD_LIBRARY_PATH=/usr/local/opt/openssl/lib:"${LD_LIBRARY_PATH}"
    CPATH=/usr/local/opt/openssl/include:"${CPATH}"
    PKG_CONFIG_PATH=/usr/local/opt/openssl/lib/pkgconfig:"${PKG_CONFIG_PATH}"
    make

Running the program

All you just have to is run: ./simpletorrent {path_to_torrent_file}

This will download the file to the same location as your binary.

Sources

I'm so grateful to Gallexis (80% of this program design was inspired by this) and the BitTorrent Unofficial Spec. Thank you guys.

Contributions

Contributions are welcome, you can easily ask me questions here. Pull requests are also welcome. We are all here to learn!