2006-04-25 23:04:48 +02:00
|
|
|
<?xml version="1.0" encoding="utf-8" ?>
|
|
|
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
|
|
|
|
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
|
|
|
|
|
<head>
|
2012-01-14 17:04:25 +01:00
|
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
|
|
|
<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
|
|
|
|
|
<title></title>
|
|
|
|
|
<meta name="author" content="Arvid Norberg, arvid@rasterbar.com Ludvig Strigeus, ludde@utorrent.com" />
|
|
|
|
|
<link rel="stylesheet" type="text/css" href="../../css/base.css" />
|
|
|
|
|
<link rel="stylesheet" type="text/css" href="../../css/rst.css" />
|
2010-12-08 05:44:20 +01:00
|
|
|
<script type="text/javascript">
|
|
|
|
|
/* <![CDATA[ */
|
|
|
|
|
(function() {
|
|
|
|
|
var s = document.createElement('script'), t = document.getElementsByTagName('script')[0];
|
|
|
|
|
s.type = 'text/javascript';
|
|
|
|
|
s.async = true;
|
|
|
|
|
s.src = 'http://api.flattr.com/js/0.6/load.js?mode=auto';
|
|
|
|
|
t.parentNode.insertBefore(s, t);
|
|
|
|
|
})();
|
|
|
|
|
/* ]]> */
|
|
|
|
|
</script>
|
2006-06-20 01:26:38 +02:00
|
|
|
<link rel="stylesheet" href="style.css" type="text/css" />
|
2008-10-17 05:23:30 +02:00
|
|
|
<style type="text/css">
|
|
|
|
|
/* Hides from IE-mac \*/
|
|
|
|
|
* html pre { height: 1%; }
|
|
|
|
|
/* End hide from IE-mac */
|
|
|
|
|
</style>
|
2006-04-25 23:04:48 +02:00
|
|
|
</head>
|
|
|
|
|
<body>
|
|
|
|
|
<div class="document">
|
2008-10-17 05:23:30 +02:00
|
|
|
<div id="container">
|
|
|
|
|
<div id="headerNav">
|
|
|
|
|
<ul>
|
|
|
|
|
<li class="first"><a href="/">Home</a></li>
|
|
|
|
|
<li><a href="../../products.html">Products</a></li>
|
|
|
|
|
<li><a href="../../contact.html">Contact</a></li>
|
|
|
|
|
</ul>
|
|
|
|
|
</div>
|
|
|
|
|
<div id="header">
|
|
|
|
|
<h1><span>Rasterbar Software</span></h1>
|
|
|
|
|
<h2><span>Software developement and consulting</span></h2>
|
|
|
|
|
</div>
|
|
|
|
|
<div id="main">
|
2006-11-28 19:18:37 +01:00
|
|
|
|
2006-04-25 23:04:48 +02:00
|
|
|
<table class="docinfo" frame="void" rules="none">
|
|
|
|
|
<col class="docinfo-name" />
|
|
|
|
|
<col class="docinfo-content" />
|
|
|
|
|
<tbody valign="top">
|
|
|
|
|
<tr><th class="docinfo-name">Author:</th>
|
2009-03-21 05:36:46 +01:00
|
|
|
<td>Arvid Norberg, <a class="reference external" href="mailto:arvid@rasterbar.com">arvid@rasterbar.com</a>
|
|
|
|
|
Ludvig Strigeus, <a class="last reference external" href="mailto:ludde@utorrent.com">ludde@utorrent.com</a></td></tr>
|
2006-04-25 23:04:48 +02:00
|
|
|
</tbody>
|
|
|
|
|
</table>
|
2008-10-17 05:23:30 +02:00
|
|
|
<div class="section" id="extension-protocol-for-bittorrent">
|
|
|
|
|
<h1>extension protocol for bittorrent</h1>
|
2006-04-25 23:04:48 +02:00
|
|
|
<p>The intention of this protocol is to provide a simple and thin transport
|
|
|
|
|
for extensions to the bittorrent protocol. Supporting this protocol makes
|
|
|
|
|
it easy to add new extensions without interfering with the standard
|
|
|
|
|
bittorrent protocol or clients that don't support this extension or the
|
|
|
|
|
one you want to add.</p>
|
|
|
|
|
<p>To advertise to other clients that you support, one bit from the reserved
|
|
|
|
|
bytes is used.</p>
|
|
|
|
|
<p>The bit selected for the extension protocol is bit 20 from the right (counting
|
|
|
|
|
starts at 0). So (reserved_byte[5] & 0x10) is the expression to use for checking
|
|
|
|
|
if the client supports extended messaging.</p>
|
|
|
|
|
<p>Once support for the protocol is established, the client is supposed to
|
|
|
|
|
support 1 new message:</p>
|
|
|
|
|
<table border="1" class="docutils">
|
|
|
|
|
<colgroup>
|
|
|
|
|
<col width="86%" />
|
|
|
|
|
<col width="14%" />
|
|
|
|
|
</colgroup>
|
|
|
|
|
<thead valign="bottom">
|
|
|
|
|
<tr><th class="head">name</th>
|
|
|
|
|
<th class="head">id</th>
|
|
|
|
|
</tr>
|
|
|
|
|
</thead>
|
|
|
|
|
<tbody valign="top">
|
|
|
|
|
<tr><td><tt class="docutils literal"><span class="pre">extended</span></tt></td>
|
|
|
|
|
<td>20</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</tbody>
|
|
|
|
|
</table>
|
|
|
|
|
<p>This message is sent as any other bittorrent message, with a 4 byte length
|
|
|
|
|
prefix and a single byte identifying the message (the single byte being 20
|
|
|
|
|
in this case). At the start of the payload of the message, is a single byte
|
|
|
|
|
message identifier. This identifier can refer to different extension messages
|
|
|
|
|
and only one ID is specified, 0. If the ID is 0, the message is a handshake
|
|
|
|
|
message which is described below. The layout of a general <tt class="docutils literal"><span class="pre">extended</span></tt> message
|
|
|
|
|
follows (including the message headers used by the bittorrent protocol):</p>
|
|
|
|
|
<table border="1" class="docutils">
|
|
|
|
|
<colgroup>
|
|
|
|
|
<col width="15%" />
|
|
|
|
|
<col width="85%" />
|
|
|
|
|
</colgroup>
|
|
|
|
|
<thead valign="bottom">
|
|
|
|
|
<tr><th class="head">size</th>
|
|
|
|
|
<th class="head">description</th>
|
|
|
|
|
</tr>
|
|
|
|
|
</thead>
|
|
|
|
|
<tbody valign="top">
|
|
|
|
|
<tr><td>uint32_t</td>
|
|
|
|
|
<td>length prefix. Specifies the number of bytes for the
|
|
|
|
|
entire message. (Big endian)</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr><td>uint8_t</td>
|
|
|
|
|
<td>bittorrent message ID, = 20</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr><td>uint8_t</td>
|
|
|
|
|
<td>extended message ID. 0 = handshake, >0 = extended
|
|
|
|
|
message as specified by the handshake.</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</tbody>
|
|
|
|
|
</table>
|
2008-10-17 05:23:30 +02:00
|
|
|
<div class="section" id="handshake-message">
|
|
|
|
|
<h2>handshake message</h2>
|
2006-04-25 23:04:48 +02:00
|
|
|
<p>The payload of the handshake message is a bencoded dictionary. All items
|
|
|
|
|
in the dictionary are optional. Any unknown names should be ignored
|
|
|
|
|
by the client. All parts of the dictionary are case sensitive.
|
|
|
|
|
This is the defined item in the dictionary:</p>
|
|
|
|
|
<table border="1" class="docutils">
|
|
|
|
|
<colgroup>
|
|
|
|
|
<col width="11%" />
|
|
|
|
|
<col width="89%" />
|
|
|
|
|
</colgroup>
|
|
|
|
|
<thead valign="bottom">
|
|
|
|
|
<tr><th class="head">name</th>
|
|
|
|
|
<th class="head">description</th>
|
|
|
|
|
</tr>
|
|
|
|
|
</thead>
|
|
|
|
|
<tbody valign="top">
|
|
|
|
|
<tr><td>m</td>
|
2006-11-27 01:04:20 +01:00
|
|
|
<td><p class="first">Dictionary of supported extension messages which maps
|
|
|
|
|
names of extensions to an extended message ID for each
|
|
|
|
|
extension message. The only requirement on these IDs
|
|
|
|
|
is that no extension message share the same one. Setting
|
2006-04-25 23:04:48 +02:00
|
|
|
an extension number to zero means that the extension is
|
|
|
|
|
not supported/disabled. The client should ignore any
|
2006-11-27 01:04:20 +01:00
|
|
|
extension names it doesn't recognize.</p>
|
|
|
|
|
<p class="last">The extension message IDs are the IDs used to send the
|
|
|
|
|
extension messages to the peer sending this handshake.
|
|
|
|
|
i.e. The IDs are local to this particular peer.</p>
|
|
|
|
|
</td>
|
2006-04-25 23:04:48 +02:00
|
|
|
</tr>
|
|
|
|
|
</tbody>
|
|
|
|
|
</table>
|
2006-11-27 01:04:20 +01:00
|
|
|
<p>Here are some other items that an implementation may choose to support:</p>
|
2006-04-25 23:04:48 +02:00
|
|
|
<table border="1" class="docutils">
|
|
|
|
|
<colgroup>
|
2007-08-22 07:31:42 +02:00
|
|
|
<col width="12%" />
|
|
|
|
|
<col width="88%" />
|
2006-04-25 23:04:48 +02:00
|
|
|
</colgroup>
|
|
|
|
|
<thead valign="bottom">
|
|
|
|
|
<tr><th class="head">name</th>
|
|
|
|
|
<th class="head">description</th>
|
|
|
|
|
</tr>
|
|
|
|
|
</thead>
|
|
|
|
|
<tbody valign="top">
|
|
|
|
|
<tr><td>p</td>
|
|
|
|
|
<td>Local TCP listen port. Allows each side to learn about
|
|
|
|
|
the TCP port number of the other side. Note that there is
|
|
|
|
|
no need for the receiving side of the connection to send
|
|
|
|
|
this extension message, since its port number is already
|
|
|
|
|
known.</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr><td>v</td>
|
2007-08-22 07:31:42 +02:00
|
|
|
<td>Client name and version (as a utf-8 string).
|
2006-04-25 23:04:48 +02:00
|
|
|
This is a much more reliable way of identifying the
|
|
|
|
|
client than relying on the peer id encoding.</td>
|
|
|
|
|
</tr>
|
2007-08-22 07:31:42 +02:00
|
|
|
<tr><td>yourip</td>
|
|
|
|
|
<td>A string containing the compact representation of the ip
|
|
|
|
|
address this peer sees you as. i.e. this is the
|
|
|
|
|
receiver's external ip address (no port is included).
|
2007-09-10 03:57:40 +02:00
|
|
|
This may be either an IPv4 (4 bytes) or an IPv6
|
|
|
|
|
(16 bytes) address.</td>
|
2007-08-22 07:31:42 +02:00
|
|
|
</tr>
|
2007-10-01 04:47:57 +02:00
|
|
|
<tr><td>ipv6</td>
|
|
|
|
|
<td>If this peer has an IPv6 interface, this is the compact
|
|
|
|
|
representation of that address (16 bytes). The client may
|
|
|
|
|
prefer to connect back via the IPv6 address.</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr><td>ipv4</td>
|
|
|
|
|
<td>If this peer has an IPv4 interface, this is the compact
|
|
|
|
|
representation of that address (4 bytes). The client may
|
|
|
|
|
prefer to connect back via this interface.</td>
|
|
|
|
|
</tr>
|
2006-05-15 00:30:05 +02:00
|
|
|
<tr><td>reqq</td>
|
|
|
|
|
<td>An integer, the number of outstanding request messages
|
|
|
|
|
this client supports without dropping any. The default in
|
|
|
|
|
in libtorrent is 250.</td>
|
|
|
|
|
</tr>
|
2006-04-25 23:04:48 +02:00
|
|
|
</tbody>
|
|
|
|
|
</table>
|
|
|
|
|
<p>The handshake dictionary could also include extended handshake
|
|
|
|
|
information, such as support for encrypted headers or anything
|
|
|
|
|
imaginable.</p>
|
|
|
|
|
<p>An example of what the payload of a handshake message could look like:</p>
|
|
|
|
|
<table border="1" class="docutils">
|
|
|
|
|
<colgroup>
|
|
|
|
|
<col width="36%" />
|
|
|
|
|
<col width="64%" />
|
|
|
|
|
</colgroup>
|
|
|
|
|
<thead valign="bottom">
|
|
|
|
|
<tr><th class="head" colspan="2">Dictionary</th>
|
|
|
|
|
</tr>
|
|
|
|
|
</thead>
|
|
|
|
|
<tbody valign="top">
|
|
|
|
|
<tr><td><tt class="docutils literal"><span class="pre">m</span></tt></td>
|
|
|
|
|
<td><table border="1" class="first last docutils">
|
|
|
|
|
<colgroup>
|
|
|
|
|
<col width="88%" />
|
|
|
|
|
<col width="12%" />
|
|
|
|
|
</colgroup>
|
|
|
|
|
<thead valign="bottom">
|
|
|
|
|
<tr><th class="head" colspan="2">Dictionary</th>
|
|
|
|
|
</tr>
|
|
|
|
|
</thead>
|
|
|
|
|
<tbody valign="top">
|
|
|
|
|
<tr><td><tt class="docutils literal"><span class="pre">LT_metadata</span></tt></td>
|
|
|
|
|
<td>1</td>
|
|
|
|
|
</tr>
|
2006-11-27 01:04:20 +01:00
|
|
|
<tr><td><tt class="docutils literal"><span class="pre">ut_pex</span></tt></td>
|
2006-04-25 23:04:48 +02:00
|
|
|
<td>2</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</tbody>
|
|
|
|
|
</table>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr><td><tt class="docutils literal"><span class="pre">p</span></tt></td>
|
|
|
|
|
<td>6881</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr><td><tt class="docutils literal"><span class="pre">v</span></tt></td>
|
|
|
|
|
<td>"µTorrent 1.2"</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</tbody>
|
|
|
|
|
</table>
|
|
|
|
|
<p>and in the encoded form:</p>
|
|
|
|
|
<p><tt class="docutils literal"><span class="pre">d1:md11:LT_metadatai1e6:µT_PEXi2ee1:pi6881e1:v13:\xc2\xb5Torrent</span> <span class="pre">1.2e</span></tt></p>
|
|
|
|
|
<p>To make sure the extension names do not collide by mistake, they should be
|
|
|
|
|
prefixed with the two (or one) character code that is used to identify the
|
|
|
|
|
client that introduced the extension. This applies for both the names of
|
|
|
|
|
extension messages, and for any additional information put inside the
|
|
|
|
|
top-level dictionary. All one and two byte identifiers are invalid to use
|
|
|
|
|
unless defined by this specification.</p>
|
|
|
|
|
<p>This message should be sent immediately after the standard bittorrent handshake
|
|
|
|
|
to any peer that supports this extension protocol. It is valid to send the
|
|
|
|
|
handshake message more than once during the lifetime of a connection,
|
|
|
|
|
the sending client should not be disconnected. An implementation may choose
|
|
|
|
|
to ignore the subsequent handshake messages (or parts of them).</p>
|
|
|
|
|
<p>Subsequent handshake messages can be used to enable/disable extensions
|
|
|
|
|
without restarting the connection. If a peer supports changing extensions
|
|
|
|
|
at run time, it should note that the <tt class="docutils literal"><span class="pre">m</span></tt> dictionary is additive.
|
|
|
|
|
It's enough that it contains the actual <em>CHANGES</em> to the extension list.
|
|
|
|
|
To disable the support for <tt class="docutils literal"><span class="pre">LT_metadata</span></tt> at run-time, without affecting
|
|
|
|
|
any other extensions, this message should be sent:
|
|
|
|
|
<tt class="docutils literal"><span class="pre">d11:LT_metadatai0ee</span></tt>.
|
|
|
|
|
As specified above, the value 0 is used to turn off an extension.</p>
|
|
|
|
|
<p>The extension IDs must be stored for every peer, becuase every peer may have
|
|
|
|
|
different IDs for the same extension.</p>
|
|
|
|
|
<p>This specification, deliberately, does not specify any extensions such as
|
|
|
|
|
peer-exchange or metadata exchange. This protocol is merely a transport
|
|
|
|
|
for the actual extensions to the bittorrent protocol and the extensions
|
|
|
|
|
named in the example above (such as <tt class="docutils literal"><span class="pre">p</span></tt>) are just examples of possible
|
|
|
|
|
extensions.</p>
|
|
|
|
|
</div>
|
2008-10-17 05:23:30 +02:00
|
|
|
<div class="section" id="rationale">
|
|
|
|
|
<h2>rationale</h2>
|
2006-04-25 23:04:48 +02:00
|
|
|
<p>The reason why the extension messages' IDs would be defined in the handshake
|
2006-11-27 01:04:20 +01:00
|
|
|
is to avoid having a global registry of message IDs. Instead the names of the
|
|
|
|
|
extension messages requires unique names, which is much easier to do without
|
|
|
|
|
a global registry. The convention is to use a two letter prefix on the
|
|
|
|
|
extension message names, the prefix would identify the client first
|
|
|
|
|
implementing the extension message. e.g. <tt class="docutils literal"><span class="pre">LT_metadata</span></tt> is implemented by
|
|
|
|
|
libtorrent, and hence it has the <tt class="docutils literal"><span class="pre">LT</span></tt> prefix.</p>
|
2006-04-25 23:04:48 +02:00
|
|
|
<p>If the client supporting the extensions can decide which numbers the messages
|
|
|
|
|
it receives will have, it means they are constants within that client. i.e.
|
|
|
|
|
they can be used in <tt class="docutils literal"><span class="pre">switch</span></tt> statements. It's easy for the other end to
|
|
|
|
|
store an array with the ID's we expect for each message and use that for
|
|
|
|
|
lookups each time it sends an extension message.</p>
|
|
|
|
|
<p>The reason for having a dictionary instead of having an array (using
|
|
|
|
|
implicitly assigned index numbers to the extensions) is that if a client
|
|
|
|
|
want to disable some extensions, the ID numbers would change, and it wouldn't
|
|
|
|
|
be able to use constants (and hence, not use them in a <tt class="docutils literal"><span class="pre">switch</span></tt>). If the
|
|
|
|
|
messages IDs would map directly to bittorrent message IDs, It would also make
|
|
|
|
|
it possible to map extensions in the handshake to existing extensions with
|
|
|
|
|
fixed message IDs.</p>
|
|
|
|
|
<p>The reasoning behind having a single byte as extended message identifier is
|
|
|
|
|
to follow the the bittorrent spec. with its single byte message identifiers.
|
|
|
|
|
It is also considered to be enough. It won't limit the total number of
|
|
|
|
|
extensions, only the number of extensions used simultaneously.</p>
|
|
|
|
|
<p>The reason for using single byte identifiers for the standardized handshake
|
|
|
|
|
identifiers is 1) The mainline DHT uses single byte identifiers. 2) Saves
|
|
|
|
|
bandwidth. The only advantage of longer messages is that it makes the
|
|
|
|
|
protocol more readable for a human, but the BT protocol wasn't designed to
|
|
|
|
|
be a human readable protocol, so why bother.</p>
|
|
|
|
|
</div>
|
|
|
|
|
</div>
|
2008-10-17 05:23:30 +02:00
|
|
|
</div>
|
|
|
|
|
<div id="footer">
|
|
|
|
|
<span>Copyright © 2005 Rasterbar Software.</span>
|
|
|
|
|
</div>
|
|
|
|
|
</div>
|
|
|
|
|
<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
|
|
|
|
|
</script>
|
|
|
|
|
<script type="text/javascript">
|
|
|
|
|
_uacct = "UA-1599045-1";
|
|
|
|
|
urchinTracker();
|
|
|
|
|
</script>
|
2006-04-25 23:04:48 +02:00
|
|
|
</div>
|
|
|
|
|
</body>
|
|
|
|
|
</html>
|
