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10 KiB
HTML
254 lines
10 KiB
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<?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>creating torrents</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="../../css/base.css" />
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<link rel="stylesheet" type="text/css" href="../../css/rst.css" />
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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" 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></li>
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<li><a class="reference internal" href="#create-torrent" id="id7">create_torrent</a><ul>
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<li><a class="reference internal" href="#id1" id="id8">create_torrent()</a></li>
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<li><a class="reference internal" href="#generate" id="id9">generate()</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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void add_files(file_storage& fs, boost::filesystem::path 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>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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void set_piece_hashes(create_torrent& t, boost::filesystem::path const& p);
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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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</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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void add_file(file_entry const& e);
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void add_file(fs::path const& p, size_type size);
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void rename_file(int index, std::string 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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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>
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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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create_torrent(file_storage& fs, int piece_size);
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create_torrent(file_storage& fs);
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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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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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};
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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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create_torrent(file_storage& fs, int piece_size);
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create_torrent(file_storage& fs);
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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 contrstructor that does not take a piece_size will calculate
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a piece size such that the torrent file is roughly 40 kB.</p>
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<p>The overlad 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 not
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have any affect.</p>
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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>
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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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</div>
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</div>
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<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
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</script>
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<script type="text/javascript">
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_uacct = "UA-1599045-1";
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urchinTracker();
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</script>
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</body>
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</html>
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