315 lines
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315 lines
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HTML
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<meta name="author" content="Arvid Norberg, arvid@rasterbar.com" />
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<div class="document">
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<div id="headerNav">
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<ul>
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<li class="first"><a href="/">Home</a></li>
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<li><a href="../../products.html">Products</a></li>
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<li><a href="../../contact.html">Contact</a></li>
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</ul>
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</div>
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<div id="header">
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<h1><span>Rasterbar Software</span></h1>
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<h2><span>Software developement and consulting</span></h2>
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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="libtorrent-plugins">
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<h1>libtorrent plugins</h1>
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<div class="contents topic" id="contents">
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<p class="topic-title first">Contents</p>
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<ul class="simple">
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<li><a class="reference internal" href="#libtorrent-plugins" id="id1">libtorrent plugins</a><ul>
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<li><a class="reference internal" href="#a-word-of-caution" id="id2">a word of caution</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#plugin-interface" id="id3">plugin interface</a></li>
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<li><a class="reference internal" href="#plugin" id="id4">plugin</a></li>
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<li><a class="reference internal" href="#torrent-plugin" id="id5">torrent_plugin</a><ul>
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<li><a class="reference internal" href="#new-connection" id="id6">new_connection()</a></li>
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<li><a class="reference internal" href="#on-piece-pass-on-piece-fail" id="id7">on_piece_pass() on_piece_fail()</a></li>
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<li><a class="reference internal" href="#tick" id="id8">tick()</a></li>
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<li><a class="reference internal" href="#on-pause-on-resume" id="id9">on_pause() on_resume()</a></li>
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<li><a class="reference internal" href="#on-files-checked" id="id10">on_files_checked()</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#peer-plugin" id="id11">peer_plugin</a></li>
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<li><a class="reference internal" href="#disk-buffer-holder" id="id12">disk_buffer_holder</a></li>
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</ul>
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</div>
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<p>libtorrent has a plugin interface for implementing extensions to the protocol.
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These can be general extensions for transferring metadata or peer exchange
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extensions, or it could be used to provide a way to customize the protocol
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to fit a particular (closed) network.</p>
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<p>In short, the plugin interface makes it possible to:</p>
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<ul class="simple">
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<li>register extension messages (sent in the extension handshake), see
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<a class="reference external" href="extension_protocol.html">extensions</a>.</li>
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<li>add data and parse data from the extension handshake.</li>
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<li>send extension messages and standard bittorrent messages.</li>
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<li>override or block the handling of standard bittorrent messages.</li>
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<li>save and restore state via the session state</li>
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<li>see all alerts that are posted</li>
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</ul>
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<div class="section" id="a-word-of-caution">
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<h2>a word of caution</h2>
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<p>Writing your own plugin is a very easy way to introduce serious bugs such as
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dead locks and race conditions. Since a plugin has access to internal
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structures it is also quite easy to sabotage libtorrent's operation.</p>
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<p>All the callbacks in this interface are called with the main libtorrent thread
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mutex locked. And they are always called from the libtorrent network thread. In
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case portions of your plugin are called from other threads, typically the main
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thread, you cannot use any of the member functions on the internal structures
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in libtorrent, since those require the mutex to be locked. Futhermore, you would
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also need to have a mutex on your own shared data within the plugin, to make
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sure it is not accessed at the same time from the libtorrent thread (through a
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callback). See <a class="reference external" href="http://www.boost.org/doc/html/mutex.html">boost thread's mutex</a>. If you need to send out a message from
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another thread, it is advised to use an internal queue, and do the actual
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sending in <tt class="docutils literal"><span class="pre">tick()</span></tt>.</p>
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<p>Since the plugin interface gives you easy access to internal structures, it
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is not supported as a stable API. Plugins should be considered spcific to a
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specific version of libtorrent. Although, in practice the internals mostly
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don't change that dramatically.</p>
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</div>
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</div>
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<div class="section" id="plugin-interface">
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<h1>plugin interface</h1>
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<p>The plugin interface consists of three base classes that the plugin may
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implement. These are called <tt class="docutils literal"><span class="pre">plugin</span></tt>, <tt class="docutils literal"><span class="pre">torrent_plugin</span></tt> and <tt class="docutils literal"><span class="pre">peer_plugin</span></tt>.
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They are found in the <tt class="docutils literal"><span class="pre"><libtorrent/extensions.hpp></span></tt> header.</p>
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<p>These plugins are instantiated for each session, torrent and possibly each peer,
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respectively.</p>
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<p>For plugins that only need per torrent state, it is enough to only implement
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<tt class="docutils literal"><span class="pre">torrent_plugin</span></tt> and pass a constructor function or function object to
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<tt class="docutils literal"><span class="pre">session::add_extension()</span></tt> or <tt class="docutils literal"><span class="pre">torrent_handle::add_extension()</span></tt> (if the
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torrent has already been started and you want to hook in the extension at
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run-time).</p>
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<p>The signature of the function is:</p>
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<pre class="literal-block">
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boost::shared_ptr<torrent_plugin> (*)(torrent*, void*);
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</pre>
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<p>The first argument is the internal torrent object, the second argument
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is the userdata passed to <tt class="docutils literal"><span class="pre">session::add_torrent()</span></tt> or
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<tt class="docutils literal"><span class="pre">torrent_handle::add_extension()</span></tt>.</p>
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<p>The function should return a <tt class="docutils literal"><span class="pre">boost::shared_ptr<torrent_plugin></span></tt> which
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may or may not be 0. If it is a null pointer, the extension is simply ignored
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for this torrent. If it is a valid pointer (to a class inheriting
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<tt class="docutils literal"><span class="pre">torrent_plugin</span></tt>), it will be associated with this torrent and callbacks
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will be made on torrent events.</p>
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<p>For more elaborate plugins which require session wide state, you would
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implement <tt class="docutils literal"><span class="pre">plugin</span></tt>, construct an object (in a <tt class="docutils literal"><span class="pre">boost::shared_ptr</span></tt>) and pass
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it in to <tt class="docutils literal"><span class="pre">session::add_extension()</span></tt>.</p>
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</div>
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<div class="section" id="plugin">
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<h1>plugin</h1>
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<pre class="literal-block">
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struct plugin
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{
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virtual ~plugin();
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virtual boost::shared_ptr<torrent_plugin> new_torrent(torrent* t, void* user);
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virtual void added(boost::weak_ptr<aux::session_impl> s);
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virtual void on_alert(alert const* a);
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virtual void on_tick();
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virtual void save_state(entry& ent) const;
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virtual void load_state(lazy_entry const& ent);
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};
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</pre>
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</div>
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<div class="section" id="torrent-plugin">
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<h1>torrent_plugin</h1>
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<p>The synopsis for <tt class="docutils literal"><span class="pre">torrent_plugin</span></tt> follows:</p>
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<pre class="literal-block">
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struct torrent_plugin
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{
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virtual ~torrent_plugin();
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virtual boost::shared_ptr<peer_plugin> new_connection(peer_connection*);
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virtual void on_piece_pass(int index);
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virtual void on_piece_failed(int index);
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virtual void tick();
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virtual bool on_pause();
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virtual bool on_resume();
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virtual void on_files_checked();
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};
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</pre>
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<p>This is the base class for a torrent_plugin. Your derived class is (if added
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as an extension) instantiated for each torrent in the session. The callback
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hook functions are defined as follows.</p>
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<div class="section" id="new-connection">
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<h2>new_connection()</h2>
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<pre class="literal-block">
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boost::shared_ptr<peer_plugin> new_connection(peer_connection*);
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</pre>
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<p>This function is called each time a new peer is connected to the torrent. You
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may choose to ignore this by just returning a default constructed
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<tt class="docutils literal"><span class="pre">shared_ptr</span></tt> (in which case you don't need to override this member
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function).</p>
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<p>If you need an extension to the peer connection (which most plugins do) you
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are supposed to return an instance of your <tt class="docutils literal"><span class="pre">peer_plugin</span></tt> class. Which in
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turn will have its hook functions called on event specific to that peer.</p>
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<p>The <tt class="docutils literal"><span class="pre">peer_connection</span></tt> will be valid as long as the <tt class="docutils literal"><span class="pre">shared_ptr</span></tt> is being
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held by the torrent object. So, it is generally a good idea to not keep a
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<tt class="docutils literal"><span class="pre">shared_ptr</span></tt> to your own peer_plugin. If you want to keep references to it,
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use <tt class="docutils literal"><span class="pre">weak_ptr</span></tt>.</p>
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<p>If this function throws an exception, the connection will be closed.</p>
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</div>
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<div class="section" id="on-piece-pass-on-piece-fail">
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<h2>on_piece_pass() on_piece_fail()</h2>
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<pre class="literal-block">
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void on_piece_pass(int index);
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void on_piece_failed(int index);
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</pre>
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<p>These hooks are called when a piece passes the hash check or fails the hash
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check, respectively. The <tt class="docutils literal"><span class="pre">index</span></tt> is the piece index that was downloaded.
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It is possible to access the list of peers that participated in sending the
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piece through the <tt class="docutils literal"><span class="pre">torrent</span></tt> and the <tt class="docutils literal"><span class="pre">piece_picker</span></tt>.</p>
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</div>
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<div class="section" id="tick">
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<h2>tick()</h2>
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<pre class="literal-block">
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void tick();
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</pre>
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<p>This hook is called approximately once per second. It is a way of making it
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easy for plugins to do timed events, for sending messages or whatever.</p>
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</div>
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<div class="section" id="on-pause-on-resume">
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<h2>on_pause() on_resume()</h2>
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<pre class="literal-block">
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bool on_pause();
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bool on_resume();
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</pre>
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<p>These hooks are called when the torrent is paused and unpaused respectively.
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The return value indicates if the event was handled. A return value of
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<tt class="docutils literal"><span class="pre">true</span></tt> indicates that it was handled, and no other plugin after this one
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will have this hook function called, and the standard handler will also not be
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invoked. So, returning true effectively overrides the standard behavior of
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pause or unpause.</p>
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<p>Note that if you call <tt class="docutils literal"><span class="pre">pause()</span></tt> or <tt class="docutils literal"><span class="pre">resume()</span></tt> on the torrent from your
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handler it will recurse back into your handler, so in order to invoke the
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standard handler, you have to keep your own state on whether you want standard
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behavior or overridden behavior.</p>
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</div>
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<div class="section" id="on-files-checked">
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<h2>on_files_checked()</h2>
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<pre class="literal-block">
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void on_files_checked();
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</pre>
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<p>This function is called when the initial files of the torrent have been
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checked. If there are no files to check, this function is called immediately.</p>
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<p>i.e. This function is always called when the torrent is in a state where it
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can start downloading.</p>
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</div>
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</div>
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<div class="section" id="peer-plugin">
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<h1>peer_plugin</h1>
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<pre class="literal-block">
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struct peer_plugin
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{
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virtual ~peer_plugin();
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virtual void add_handshake(entry&);
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virtual bool on_handshake(char const* reserved_bits);
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virtual bool on_extension_handshake(lazy_entry const& h);
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virtual bool on_choke();
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virtual bool on_unchoke();
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virtual bool on_interested();
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virtual bool on_not_interested();
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virtual bool on_have(int index);
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virtual bool on_bitfield(bitfield const& bits);
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virtual bool on_have_all();
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virtual bool on_have_none();
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virtual bool on_allowed_fast(int index);
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virtual bool on_request(peer_request const& req);
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virtual bool on_piece(peer_request const& piece, disk_buffer_holder& buffer);
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virtual bool on_cancel(peer_request const& req);
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virtual bool on_reject(peer_request const& req);
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virtual bool on_suggest(int index);
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virtual bool on_extended(int length
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, int msg, buffer::const_interval body);
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virtual bool on_unknown_message(int length, int msg
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, buffer::const_interval body);
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virtual void on_piece_pass(int index);
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virtual void on_piece_failed(int index);
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virtual void tick();
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virtual bool write_request(peer_request const& r);
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};
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</pre>
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</div>
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<div class="section" id="disk-buffer-holder">
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<h1>disk_buffer_holder</h1>
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<pre class="literal-block">
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struct disk_buffer_holder
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{
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disk_buffer_holder(aux::session_impl& s, char* b);
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~disk_buffer_holder();
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char* release();
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char* buffer();
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};
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</pre>
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<p>The disk buffer holder acts like a <tt class="docutils literal"><span class="pre">scoped_ptr</span></tt> that frees a disk buffer
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when it's destructed, unless it's released. <tt class="docutils literal"><span class="pre">release</span></tt> returns the disk
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buffer and transferres ownership and responsibility to free it to the caller.</p>
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<p>A disk buffer is freed by passing it to <tt class="docutils literal"><span class="pre">session_impl::free_disk_buffer()</span></tt>.</p>
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<p><tt class="docutils literal"><span class="pre">buffer()</span></tt> returns the pointer without transferring responsibility. If
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this buffer has been released, <tt class="docutils literal"><span class="pre">buffer()</span></tt> will return 0.</p>
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</div>
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</div>
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<div id="footer">
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<span>Copyright © 2005 Rasterbar Software.</span>
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