114 lines
4.7 KiB
HTML
114 lines
4.7 KiB
HTML
<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.11: http://docutils.sourceforge.net/" />
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<title></title>
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<meta name="author" content="Arvid Norberg, arvid@rasterbar.com" />
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<link rel="stylesheet" type="text/css" href="base.css" />
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<link rel="stylesheet" type="text/css" href="rst.css" />
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<script type="text/javascript">
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/* <![CDATA[ */
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(function() {
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var s = document.createElement('script'), t = document.getElementsByTagName('script')[0];
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s.type = 'text/javascript';
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s.async = true;
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s.src = 'http://api.flattr.com/js/0.6/load.js?mode=auto';
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t.parentNode.insertBefore(s, t);
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})();
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/* ]]> */
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</script>
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<link rel="stylesheet" href="style.css" type="text/css" />
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<style type="text/css">
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/* Hides from IE-mac \*/
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* html pre { height: 1%; }
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/* End hide from IE-mac */
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</style>
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</head>
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<body>
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<div class="document">
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<div id="container">
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<div id="header">
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<div id="orange"></div>
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<div id="logo"></div>
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</div>
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<div id="main">
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<table class="docinfo" frame="void" rules="none">
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<col class="docinfo-name" />
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<col class="docinfo-content" />
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<tbody valign="top">
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<tr><th class="docinfo-name">Author:</th>
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<td>Arvid Norberg, <a class="last reference external" href="mailto:arvid@rasterbar.com">arvid@rasterbar.com</a></td></tr>
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</tbody>
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</table>
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<div class="section" id="mainline-dht-extensions">
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<h1>Mainline DHT extensions</h1>
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<p>libtorrent implements a few extensions to the Mainline DHT protocol.</p>
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<div class="section" id="get-peers-response">
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<h2>get_peers response</h2>
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<p>libtorrent always responds with <tt class="docutils literal">nodes</tt> to a get_peers request. If it has
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peers for the specified info-hash, it will return <tt class="docutils literal">values</tt> as well. This is
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because just because some peer announced to us, doesn't mean that we are
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among the 8 closest nodes of the info hash. libtorrent also keeps traversing
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nodes using get_peers until it has found the 8 closest ones, and then announces
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to those nodes.</p>
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</div>
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<div class="section" id="forward-compatibility">
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<h2>forward compatibility</h2>
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<p>In order to support future DHT messages, any message which is not recognized
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but has either an <tt class="docutils literal">info_hash</tt> or <tt class="docutils literal">target</tt> argument is interpreted as
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find node for that target. i.e. it returns nodes. This allows future messages
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to be properly forwarded by clients that don't understand them instead of
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being blocked.</p>
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</div>
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<div class="section" id="client-identification">
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<h2>client identification</h2>
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<p>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.</p>
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<p>Currently known clients:</p>
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<table border="1" class="docutils">
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<colgroup>
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<col width="65%" />
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<col width="35%" />
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</colgroup>
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<tbody valign="top">
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<tr><td>uTorrent</td>
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<td><tt class="docutils literal">UT</tt></td>
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</tr>
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<tr><td>libtorrent</td>
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<td><tt class="docutils literal">LT</tt></td>
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</tr>
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<tr><td>MooPolice</td>
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<td><tt class="docutils literal">MP</tt></td>
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</tr>
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<tr><td>GetRight</td>
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<td><tt class="docutils literal">GR</tt></td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="ipv6-support">
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<h2>IPv6 support</h2>
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<p><strong>This extension is superseeded by</strong> <a class="reference external" href="http://bittorrent.org/beps/bep_0032.html">BEP 32</a>.</p>
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<p>The DHT messages that don't support IPv6 are the <tt class="docutils literal">nodes</tt> 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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<tt class="docutils literal">nodes2</tt>.</p>
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<p><tt class="docutils literal">nodes2</tt> may be present in replies that contains a <tt class="docutils literal">nodes</tt> 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).</p>
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<p>As an optimization, libtorrent does not include the extra key in case there are
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only IPv4 nodes present.</p>
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</div>
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</div>
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</div>
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</body>
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</html>
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