72 lines
3.1 KiB
HTML
72 lines
3.1 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 0.5: 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" href="style.css" type="text/css" />
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</head>
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<body>
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<div class="document">
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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" 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">
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<h1><a id="mainline-dht-extensions" name="mainline-dht-extensions">Mainline DHT extensions</a></h1>
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<p>libtorrent implements a few extensions to the Mainline DHT protocol.</p>
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<div class="section">
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<h2><a id="client-identification" name="client-identification">client identification</a></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"><span class="pre">UT</span></tt></td>
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</tr>
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<tr><td>libtorrent</td>
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<td><tt class="docutils literal"><span class="pre">LT</span></tt></td>
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</tr>
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<tr><td>MooPolice</td>
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<td><tt class="docutils literal"><span class="pre">MP</span></tt></td>
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</tr>
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<tr><td>GetRight</td>
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<td><tt class="docutils literal"><span class="pre">GR</span></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">
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<h2><a id="ipv6-support" name="ipv6-support">IPv6 support</a></h2>
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<p>The DHT messages that don't support IPv6 are the <tt class="docutils literal"><span class="pre">nodes</span></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"><span class="pre">nodes2</span></tt>.</p>
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<p><tt class="docutils literal"><span class="pre">nodes2</span></tt> may be present in replies that contains a <tt class="docutils literal"><span class="pre">nodes</span></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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