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https://github.com/transmission/transmission
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66 lines
2.4 KiB
Markdown
66 lines
2.4 KiB
Markdown
# libutp - The uTorrent Transport Protocol library.
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Copyright (c) 2010 BitTorrent, Inc.
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uTP is a TCP-like implementation of [LEDBAT][ledbat] documented as a BitTorrent
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extension in [BEP-29][bep29]. uTP provides provides reliable, ordered delivery
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while maintaining minimum extra delay. It is implemented on top of UDP to be
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cross-platform and functional today. As a result, uTP is the primary transport
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for uTorrent peer-to-peer connections.
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uTP is written in C++, but the external interface is strictly C (ANSI C89).
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## The Interface
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The uTP socket interface is a bit different from the Berkeley socket API to
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avoid the need for our own select() implementation, and to make it easier to
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write event-based code with minimal buffering.
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When you create a uTP socket, you register a set of callbacks. Most notably, the
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on_read callback is a reactive callback which occurs when bytes arrive off the
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network. The write side of the socket is proactive, and you call UTP_Write to
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indicate the number of bytes you wish to write. As packets are created, the
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on_write callback is called for each packet, so you can fill the buffers with
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data.
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The libutp interface is not thread-safe. It was designed for use in a
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single-threaded asyncronous context, although with proper synchronization
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it may be used from a multi-threaded environment as well.
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See utp.h for more details and other API documentation.
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## Examples
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See the utp_test and utp_file directories for examples.
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## Building
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uTP has been known to build on Windows with MSVC and on linux and OS X with gcc.
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On Windows, use the MSVC project files (utp.sln, and friends). On other platforms,
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building the shared library is as simple as:
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make
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To build one of the examples, which will statically link in everything it needs
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from libutp:
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cd utp_test && make
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## Packaging and API
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The libutp API is considered unstable, and probably always will be. We encourage
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you to test with the version of libutp you have, and be mindful when upgrading.
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For this reason, it is probably also a good idea to bundle libutp with your
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application.
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## License
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libutp is released under the [MIT][lic] license.
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## Related Work
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Research and analysis of congestion control mechanisms can be found [here.][survey]
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[ledbat]: http://datatracker.ietf.org/wg/ledbat/charter/
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[bep29]: http://www.bittorrent.org/beps/bep_0029.html
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[lic]: http://www.opensource.org/licenses/mit-license.php
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[survey]: http://datatracker.ietf.org/doc/draft-ietf-ledbat-survey/
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