46 lines
1.5 KiB
ReStructuredText
46 lines
1.5 KiB
ReStructuredText
:Author: Arvid Norberg, arvid@rasterbar.com
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Mainline DHT extensions
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=======================
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libtorrent implements a few extensions to the Mainline DHT protocol.
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client identification
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---------------------
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In each DHT packet, an extra key is inserted named "v". This is a string
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describing the client and version used. This can help alot when debugging
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and finding errors in client implementations. The string is encoded as four
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characters, two characters describing the client and two characters interpreted
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as a binary number describing the client version.
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Currently known clients:
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+---------------+--------+
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| uTorrent | ``UT`` |
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+---------------+--------+
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| libtorrent | ``LT`` |
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+---------------+--------+
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| MooPolice | ``MP`` |
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+---------------+--------+
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| GetRight | ``GR`` |
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+---------------+--------+
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IPv6 support
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------------
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The DHT messages that don't support IPv6 are the ``nodes`` replies.
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They encode all the contacts as 6 bytes packed together in sequence in a
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string. The problem is that IPv6 endpoints cannot be encoded as 6 bytes, but
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needs 18 bytes. The extension libtorrent applies is to add another key, called
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``nodes2``.
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``nodes2`` may be present in replies that contains a ``nodes`` key. It is encoded
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as a list of strings. Each string represents one contact and is encoded as 20
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bytes node-id and then a variable length encoded IP address (6 bytes in IPv4 case
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and 18 bytes in IPv6 case).
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As an optimization, libtorrent does not include the extra key in case there are
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only IPv4 nodes present.
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