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https://github.com/bittorrent/libutp

uTorrent Transport Protocol library
https://github.com/bittorrent/libutp

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uTorrent Transport Protocol library

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# libutp - The uTorrent Transport Protocol library.

Copyright (c) 2010 BitTorrent, Inc.



uTP is a TCP-like implementation of [LEDBAT][ledbat] documented as a BitTorrent

extension in [BEP-29][bep29]. uTP provides reliable, ordered delivery

while maintaining minimum extra delay. It is implemented on top of UDP to be

cross-platform and functional today. As a result, uTP is the primary transport

for uTorrent peer-to-peer connections.



uTP is written in C++, but the external interface is strictly C (ANSI C89).



## The Interface



The uTP socket interface is a bit different from the Berkeley socket API to

avoid the need for our own select() implementation, and to make it easier to

write event-based code with minimal buffering.



When you create a uTP socket, you register a set of callbacks. Most notably, the

on_read callback is a reactive callback which occurs when bytes arrive off the

network. The write side of the socket is proactive, and you call UTP_Write to

indicate the number of bytes you wish to write. As packets are created, the

on_write callback is called for each packet, so you can fill the buffers with

data.



The libutp interface is not thread-safe. It was designed for use in a

single-threaded asyncronous context, although with proper synchronization

it may be used from a multi-threaded environment as well.



See utp.h for more details and other API documentation.



## Example



See ucat.c. Build with:

 

   make ucat



## Building



uTP has been known to build on Windows with MSVC and on linux and OS X with gcc.

On Windows, use the MSVC project files (utp.sln, and friends). On other platforms,

building the shared library is as simple as:



    make



To build one of the examples, which will statically link in everything it needs

from libutp:



    cd utp_test && make



## Packaging and API



The libutp API is considered unstable, and probably always will be. We encourage

you to test with the version of libutp you have, and be mindful when upgrading.

For this reason, it is probably also a good idea to bundle libutp with your

application.



## License



libutp is released under the [MIT][lic] license.



## Related Work



Research and analysis of congestion control mechanisms can be found [here.][survey]



[ledbat]: http://datatracker.ietf.org/wg/ledbat/charter/

[bep29]: http://www.bittorrent.org/beps/bep_0029.html

[lic]: http://www.opensource.org/licenses/mit-license.php

[survey]: http://datatracker.ietf.org/doc/draft-ietf-ledbat-survey/