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History

Juliusz Chroboczek 74c0721a2c Protect against monotonic time being non-monotonic. Within utp.cpp, there's a bunch of assertions that will cause us to crash if monotonic time isn't. While I have no idea about Windows, under Unix we use real time instead of monotonic time if POSIX clocks are not available, and real time can be stepped backwards. Since the protection is cheap, we perform it on all platforms.		2011-03-29 23:15:38 +00:00
..
LICENSE	import libutp into third-party/ and plug it in to autoconf, automake	2011-02-18 00:31:49 +00:00
Makefile.am	import libutp into third-party/ and plug it in to autoconf, automake	2011-02-18 00:31:49 +00:00
README.md	import libutp into third-party/ and plug it in to autoconf, automake	2011-02-18 00:31:49 +00:00
StdAfx.h	import libutp into third-party/ and plug it in to autoconf, automake	2011-02-18 00:31:49 +00:00
templates.h	import libutp into third-party/ and plug it in to autoconf, automake	2011-02-18 00:31:49 +00:00
utp.cpp	Revert "Protect against broken implementations of monotonic time."	2011-03-12 22:45:14 +00:00
utp.h	import libutp into third-party/ and plug it in to autoconf, automake	2011-02-18 00:31:49 +00:00
utp_config.h	make a note that we need to implement UTP_GetGlobalUTPBytesSent in libtransmission	2011-02-18 00:33:54 +00:00
utp_config_example.h	import libutp into third-party/ and plug it in to autoconf, automake	2011-02-18 00:31:49 +00:00
utp_utils.cpp	Protect against monotonic time being non-monotonic.	2011-03-29 23:15:38 +00:00
utp_utils.h	import libutp into third-party/ and plug it in to autoconf, automake	2011-02-18 00:31:49 +00:00
utypes.h	(trunk) #4138 "use stdbool.h instead of tr_bool" -- done.	2011-03-22 15:19:54 +00:00

README.md

libutp - The uTorrent Transport Protocol library.

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 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.

Examples

See the utp_test and utp_file directories for examples.

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

License

libutp is released under the MIT license.

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