forked from premiere/premiere-libtorrent
69 lines
2.4 KiB
ReStructuredText
69 lines
2.4 KiB
ReStructuredText
:Author: Arvid Norberg, arvid@libtorrent.org
|
|
|
|
Mainline DHT extensions
|
|
=======================
|
|
|
|
libtorrent implements a few extensions to the Mainline DHT protocol.
|
|
|
|
get_peers response
|
|
------------------
|
|
|
|
libtorrent always responds with ``nodes`` to a get_peers request. If it has
|
|
peers for the specified info-hash, it will return ``values`` as well. This is
|
|
because just because some peer announced to us, doesn't mean that we are
|
|
among the 8 closest nodes of the info hash. libtorrent also keeps traversing
|
|
nodes using get_peers until it has found the 8 closest ones, and then announces
|
|
to those nodes.
|
|
|
|
forward compatibility
|
|
---------------------
|
|
|
|
In order to support future DHT messages, any message which is not recognized
|
|
but has either an ``info_hash`` or ``target`` argument is interpreted as
|
|
find node for that target. i.e. it returns nodes. This allows future messages
|
|
to be properly forwarded by clients that don't understand them instead of
|
|
being blocked.
|
|
|
|
client identification
|
|
---------------------
|
|
|
|
In each DHT packet, an extra key is inserted named "v". This is a string
|
|
describing the client and version used. This can help alot when debugging
|
|
and finding errors in client implementations. The string is encoded as four
|
|
characters, two characters describing the client and two characters interpreted
|
|
as a binary number describing the client version.
|
|
|
|
Currently known clients:
|
|
|
|
+---------------+--------+
|
|
| uTorrent | ``UT`` |
|
|
+---------------+--------+
|
|
| libtorrent | ``LT`` |
|
|
+---------------+--------+
|
|
| MooPolice | ``MP`` |
|
|
+---------------+--------+
|
|
| GetRight | ``GR`` |
|
|
+---------------+--------+
|
|
|
|
IPv6 support
|
|
------------
|
|
|
|
**This extension is superseeded by** `BEP 32`_.
|
|
|
|
.. _`BEP 32`: https://bittorrent.org/beps/bep_0032.html
|
|
|
|
The DHT messages that don't support IPv6 are the ``nodes`` replies.
|
|
They encode all the contacts as 6 bytes packed together in sequence in a
|
|
string. The problem is that IPv6 endpoints cannot be encoded as 6 bytes, but
|
|
needs 18 bytes. The extension libtorrent applies is to add another key, called
|
|
``nodes2``.
|
|
|
|
``nodes2`` may be present in replies that contains a ``nodes`` key. It is encoded
|
|
as a list of strings. Each string represents one contact and is encoded as 20
|
|
bytes node-id and then a variable length encoded IP address (6 bytes in IPv4 case
|
|
and 18 bytes in IPv6 case).
|
|
|
|
As an optimization, libtorrent does not include the extra key in case there are
|
|
only IPv4 nodes present.
|
|
|