415 lines
18 KiB
HTML
415 lines
18 KiB
HTML
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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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<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
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<title>creating torrents</title>
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<meta name="author" content="Arvid Norberg, arvid@rasterbar.com" />
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<body>
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<div class="document" id="creating-torrents">
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<div id="container">
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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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<h1 class="title">creating torrents</h1>
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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="contents topic" id="table-of-contents">
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<p class="topic-title first">Table of contents</p>
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<ul class="simple">
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<li><a class="reference internal" href="#overview" id="id2">overview</a></li>
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<li><a class="reference internal" href="#high-level-example" id="id3">high level example</a></li>
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<li><a class="reference internal" href="#add-files" id="id4">add_files</a></li>
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<li><a class="reference internal" href="#set-piece-hashes" id="id5">set_piece_hashes()</a></li>
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<li><a class="reference internal" href="#file-storage" id="id6">file_storage</a><ul>
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<li><a class="reference internal" href="#add-file" id="id7">add_file()</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#create-torrent" id="id8">create_torrent</a><ul>
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<li><a class="reference internal" href="#id1" id="id9">create_torrent()</a></li>
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<li><a class="reference internal" href="#generate" id="id10">generate()</a></li>
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<li><a class="reference internal" href="#set-comment" id="id11">set_comment()</a></li>
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<li><a class="reference internal" href="#set-creator" id="id12">set_creator()</a></li>
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<li><a class="reference internal" href="#set-hash" id="id13">set_hash()</a></li>
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<li><a class="reference internal" href="#add-url-seed" id="id14">add_url_seed()</a></li>
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<li><a class="reference internal" href="#add-node" id="id15">add_node()</a></li>
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<li><a class="reference internal" href="#add-tracker" id="id16">add_tracker()</a></li>
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<li><a class="reference internal" href="#set-priv-priv" id="id17">set_priv() priv()</a></li>
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</ul>
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</li>
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</ul>
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</div>
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<div class="section" id="overview">
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<h1>overview</h1>
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<p>This section describes the functions and classes that are used
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to create torrent files. It is a layered API with low level classes
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and higher level convenience functions. A torrent is created in 4
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steps:</p>
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<ol class="arabic simple">
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<li>first the files that will be part of the torrent are determined.</li>
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<li>the torrent properties are set, such as tracker url, web seeds,
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DHT nodes etc.</li>
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<li>Read through all the files in the torrent, SHA-1 all the data
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and set the piece hashes.</li>
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<li>The torrent is bencoded into a file or buffer.</li>
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</ol>
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<p>If there are a lot of files and or deep directoy hierarchies to
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traverse, step one can be time consuming.</p>
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<p>Typically step 3 is by far the most time consuming step, since it
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requires to read all the bytes from all the files in the torrent.</p>
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<p>All of these classes and functions are declared by including
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<tt class="docutils literal"><span class="pre">libtorrent/create_torrent.hpp</span></tt>.</p>
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</div>
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<div class="section" id="high-level-example">
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<h1>high level example</h1>
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<pre class="literal-block">
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file_storage fs;
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// recursively adds files in directories
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add_files(fs, "./my_torrent");
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create_torrent t(fs);
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t.add_tracker("http://my.tracker.com/announce");
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t.set_creator("libtorrent example");
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// reads the files and calculates the hashes
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set_piece_hashes(t, ".");
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ofstream out("my_torrent.torrent", std::ios_base::binary);
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bencode(std::ostream_iterator<char>(out), t.generate());
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</pre>
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</div>
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<div class="section" id="add-files">
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<h1>add_files</h1>
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<blockquote>
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<pre class="literal-block">
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template <class Pred>
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void add_files(file_storage& fs, boost::filesystem::path const& path, Pred p);
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template <class Pred>
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void add_files(file_storage& fs, boost::filesystem::wpath const& path, Pred p);
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void add_files(file_storage& fs, boost::filesystem::path const& path);
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void add_files(file_storage& fs, boost::filesystem::wpath const& path);
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</pre>
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</blockquote>
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<p>Adds the file specified by <tt class="docutils literal"><span class="pre">path</span></tt> to the <tt class="docutils literal"><span class="pre">file_storage</span></tt> object. In case <tt class="docutils literal"><span class="pre">path</span></tt>
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refers to a diretory, files will be added recursively from the directory.</p>
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<p>If specified, the predicate <tt class="docutils literal"><span class="pre">p</span></tt> is called once for every file and directory that
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is encountered. files for which <tt class="docutils literal"><span class="pre">p</span></tt> returns true are added, and directories for
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which <tt class="docutils literal"><span class="pre">p</span></tt> returns true are traversed. <tt class="docutils literal"><span class="pre">p</span></tt> must have the following signature:</p>
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<pre class="literal-block">
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bool Pred(boost::filesystem::path const& p);
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</pre>
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<p>and for the wpath version:</p>
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<pre class="literal-block">
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bool Pred(boost::filesystem::wpath const& p);
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</pre>
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<p>The path that is passed in to the predicate is the full path of the file or
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directory. If no predicate is specified, all files are added, and all directories
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are traveresed.</p>
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<p>The ".." directory is never traversed.</p>
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</div>
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<div class="section" id="set-piece-hashes">
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<h1>set_piece_hashes()</h1>
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<blockquote>
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<pre class="literal-block">
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template <class Fun>
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void set_piece_hashes(create_torrent& t, boost::filesystem::path const& p, Fun f);
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template <class Fun>
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void set_piece_hashes(create_torrent& t, boost::filesystem::wpath const& p, Fun f);
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template <class Fun>
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void set_piece_hashes(create_torrent& t, boost::filesystem::path const& p, Fun f
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, error_code& ec);
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template <class Fun>
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void set_piece_hashes(create_torrent& t, boost::filesystem::wpath const& p, Fun f
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, error_code& ec);
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void set_piece_hashes(create_torrent& t, boost::filesystem::path const& p);
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void set_piece_hashes(create_torrent& t, boost::filesystem::wpath const& p);
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void set_piece_hashes(create_torrent& t, boost::filesystem::path const& p
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, error_code& ec);
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void set_piece_hashes(create_torrent& t, boost::filesystem::wpath const& p
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, error_code& ec);
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</pre>
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</blockquote>
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<p>This function will assume that the files added to the torrent file exists at path
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<tt class="docutils literal"><span class="pre">p</span></tt>, read those files and hash the content and set the hashes in the <tt class="docutils literal"><span class="pre">create_torrent</span></tt>
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object. The optional function <tt class="docutils literal"><span class="pre">f</span></tt> is called in between every hash that is set. <tt class="docutils literal"><span class="pre">f</span></tt>
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must have the following signature:</p>
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<pre class="literal-block">
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void Fun(int);
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</pre>
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<p>The overloads that don't take an <tt class="docutils literal"><span class="pre">error_code&</span></tt> may throw an exception in case of a
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file error, the other overloads sets the error code to reflect the error, if any.</p>
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</div>
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<div class="section" id="file-storage">
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<h1>file_storage</h1>
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<p>The <tt class="docutils literal"><span class="pre">file_storage</span></tt> class represents a file list and the piece
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size. Everything necessary to interpret a regular bittorrent storage
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file structure. Its synopsis:</p>
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<pre class="literal-block">
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class file_storage
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{
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public:
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bool is_valid() const;
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enum flags_t
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{
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pad_file = 1,
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attribute_hidden = 2,
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attribute_executable = 4
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};
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void add_file(file_entry const& e);
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void add_file(fs::path const& p, size_type size, int flags = 0);
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void add_file(fs::wpath const& p, size_type size, int flags = 0);
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void rename_file(int index, std::string const& new_filename);
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void rename_file(int index, std::wstring const& new_filename);
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std::vector<file_slice> map_block(int piece, size_type offset
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, int size) const;
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peer_request map_file(int file, size_type offset, int size) const;
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typedef std::vector<file_entry>::const_iterator iterator;
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typedef std::vector<file_entry>::const_reverse_iterator reverse_iterator;
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iterator begin() const;
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iterator end() const;
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reverse_iterator rbegin();
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reverse_iterator rend() const;
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int num_files() const;
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file_entry const& at(int index) const;
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size_type total_size() const;
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void set_num_pieces(int n);
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int num_pieces() const;
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void set_piece_length(int l);
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int piece_length() const;
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int piece_size(int index) const;
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void set_name(std::string const& n);
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void set_name(std::wstring const& n);
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const std::string& name() const;
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void swap(file_storage& ti);
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}
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</pre>
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<div class="section" id="add-file">
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<h2>add_file()</h2>
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<blockquote>
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<pre class="literal-block">
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void add_file(file_entry const& e);
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void add_file(fs::path const& p, size_type size, int flags = 0);
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void add_file(fs::wpath const& p, size_type size, int flags = 0);
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</pre>
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</blockquote>
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<p>Adds a file to the file storage. The <tt class="docutils literal"><span class="pre">flags</span></tt> argument sets attributes on the file.
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The file attributes is an extension and may not work in all bittorrent clients.
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The possible arreibutes are:</p>
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<pre class="literal-block">
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pad_file
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attribute_hidden
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attribute_executable
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</pre>
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</div>
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</div>
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<div class="section" id="create-torrent">
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<h1>create_torrent</h1>
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<p>The <tt class="docutils literal"><span class="pre">create_torrent</span></tt> class has the following synopsis:</p>
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<pre class="literal-block">
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struct create_torrent
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{
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enum { optimize = 1, merkle = 2 };
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create_torrent(file_storage& fs, int piece_size = 0, int pad_size_limit = -1, int flags = optimize);
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create_torrent(torrent_info const& ti);
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entry generate() const;
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file_storage const& files() const;
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void set_comment(char const* str);
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void set_creator(char const* str);
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void set_hash(int index, sha1_hash const& h);
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void add_url_seed(std::string const& url);
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void add_node(std::pair<std::string, int> const& node);
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void add_tracker(std::string const& url, int tier = 0);
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void set_priv(bool p);
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int num_pieces() const;
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int piece_length() const;
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int piece_size(int i) const;
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bool priv() const;
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};
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</pre>
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<div class="section" id="id1">
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<h2>create_torrent()</h2>
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<blockquote>
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<pre class="literal-block">
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enum { optimize = 1, merkle = 2 };
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create_torrent(file_storage& fs, int piece_size = 0, int pad_size_limit = -1, int flags = optimize);
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create_torrent(torrent_info const& ti);
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</pre>
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</blockquote>
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<p>The <tt class="docutils literal"><span class="pre">piece_size</span></tt> is the size of each piece in bytes. It must
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be a multiple of 16 kiB. If a piece size of 0 is specified, a
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piece_size will be calculated such that the torrent file is roughly 40 kB.</p>
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<p>If a <tt class="docutils literal"><span class="pre">pad_size_limit</span></tt> is specified (other than -1), any file larger than
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the specified number of bytes will be preceeded by a pad file to align it
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with the start of a piece. The pad_file_limit is ignored unless the
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<tt class="docutils literal"><span class="pre">optimize</span></tt> flag is passed.</p>
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<p>The overload that takes a <tt class="docutils literal"><span class="pre">torrent_info</span></tt> object will make a verbatim
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copy of its info dictionary (to preserve the info-hash). The copy of
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the info dictionary will be used by <tt class="docutils literal"><span class="pre">generate()</span></tt>. This means
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that none of the member functions of create_torrent that affects
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the content of the info dictionary (such as <tt class="docutils literal"><span class="pre">set_hash()</span></tt>), will
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have any affect.</p>
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<p>The <tt class="docutils literal"><span class="pre">flags</span></tt> arguments specifies options for the torrent creation. It can
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be any combination of the following flags:</p>
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<dl class="docutils">
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<dt>optimize</dt>
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<dd>This will insert pad files to align the files to piece boundaries, for
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optimized disk-I/O.</dd>
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<dt>merkle</dt>
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<dd>This will create a merkle hash tree torrent. A merkle torrent cannot
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be opened in clients that don't specifically support merkle torrents.
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The benefit is that the resulting torrent file will be much smaller and
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not grow with more pieces. When this option is specified, it is
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recommended to have a fairly small piece size, say 64 kiB.</dd>
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</dl>
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</div>
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<div class="section" id="generate">
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<h2>generate()</h2>
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<blockquote>
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<pre class="literal-block">
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entry generate() const;
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</pre>
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</blockquote>
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<p>This function will generate the .torrent file as a bencode tree. In order to
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generate the flat file, use the bencode() function.</p>
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<p>It may be useful to add custom entries to the torrent file before bencoding it
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and saving it to disk.</p>
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</div>
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<div class="section" id="set-comment">
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<h2>set_comment()</h2>
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<blockquote>
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<pre class="literal-block">
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void set_comment(char const* str);
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</pre>
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</blockquote>
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<p>Sets the comment for the torrent. The string <tt class="docutils literal"><span class="pre">str</span></tt> should be utf-8 encoded.
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The comment in a torrent file is optional.</p>
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</div>
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<div class="section" id="set-creator">
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<h2>set_creator()</h2>
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<blockquote>
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<pre class="literal-block">
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void set_creator(char const* str);
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</pre>
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</blockquote>
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<p>Sets the creator of the torrent. The string <tt class="docutils literal"><span class="pre">str</span></tt> should be utf-8 encoded.
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This is optional.</p>
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</div>
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<div class="section" id="set-hash">
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<h2>set_hash()</h2>
|
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<blockquote>
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<pre class="literal-block">
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void set_hash(int index, sha1_hash const& h);
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</pre>
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</blockquote>
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<p>This sets the SHA-1 hash for the specified piece (<tt class="docutils literal"><span class="pre">index</span></tt>). You are required
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to set the hash for every piece in the torrent before generating it. If you have
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the files on disk, you can use the high level convenience function to do this.
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See <a class="reference internal" href="#set-piece-hashes">set_piece_hashes()</a>.</p>
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</div>
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<div class="section" id="add-url-seed">
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<h2>add_url_seed()</h2>
|
|
<blockquote>
|
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<pre class="literal-block">
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|
void add_url_seed(std::string const& url);
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</pre>
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</blockquote>
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<p>This adds a url seed to the torrent. You can have any number of url seeds. For a
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single file torrent, this should be an HTTP url, pointing to a file with identical
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content as the file of the torrent. For a multi-file torrent, it should point to
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a directory containing a directory with the same name as this torrent, and all the
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files of the torrent in it.</p>
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</div>
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<div class="section" id="add-node">
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<h2>add_node()</h2>
|
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<blockquote>
|
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<pre class="literal-block">
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|
void add_node(std::pair<std::string, int> const& node);
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</pre>
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</blockquote>
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<p>This adds a DHT node to the torrent. This especially useful if you're creating a
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tracker less torrent. It can be used by clients to bootstrap their DHT node from.
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The node is a hostname and a port number where there is a DHT node running.
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You can have any number of DHT nodes in a torrent.</p>
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</div>
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<div class="section" id="add-tracker">
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<h2>add_tracker()</h2>
|
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<blockquote>
|
|
<pre class="literal-block">
|
|
void add_tracker(std::string const& url, int tier = 0);
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</pre>
|
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</blockquote>
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<p>Adds a tracker to the torrent. This is not strictly required, but most torrents
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use a tracker as their main source of peers. The url should be an <a class="reference external" href="http://">http://</a> or udp://
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url to a machine running a bittorrent tracker that accepts announces for this torrent's
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info-hash. The tier is the fallback priority of the tracker. All trackers with tier 0 are
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tried first (in any order). If all fail, trackers with tier 1 are tried. If all of those
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fail, trackers with tier 2 are tried, and so on.</p>
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</div>
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<div class="section" id="set-priv-priv">
|
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<h2>set_priv() priv()</h2>
|
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<blockquote>
|
|
<pre class="literal-block">
|
|
void set_priv(bool p);
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bool priv() const;
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</pre>
|
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</blockquote>
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<p>Sets and queries the private flag of the torrent.</p>
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</div>
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</div>
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