libutp - The uTorrent Transport Protocol library.
Copyright (c) 2010 BitTorrent, Inc.
uTP is a TCP-like implementation of LEDBAT documented as a BitTorrent extension in BEP-29. uTP provides 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 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.
See utp.h for more details and other API documentation.
See the utp_test and utp_file directories for examples.
uTP has been known to build on Windows with MSVC and on linux and OS X with gcc. We don't have a makefile yet to build static or shared libraries. Here's how you can build one of the examples, which will link in everything it needs from libutp:
cd utp_test && make
libutp is released under the MIT license.
Research and analysis of congestion control mechanisms can be found here.