195 lines
5.1 KiB
ReStructuredText
195 lines
5.1 KiB
ReStructuredText
=================
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creating torrents
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=================
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:Author: Arvid Norberg, arvid@rasterbar.com
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.. contents:: Table of contents
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:depth: 2
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:backlinks: none
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overview
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========
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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:
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1. first the files that will be part of the torrent are determined.
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2. the torrent properties are set, such as tracker url, web seeds,
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DHT nodes etc.
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3. Read through all the files in the torrent, SHA-1 all the data
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and set the piece hashes.
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4. The torrent is bencoded into a file or buffer.
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If there are a lot of files and or deep directoy hierarchies to
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traverse, step one can be time consuming.
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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.
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All of these classes and functions are declared by including
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``libtorrent/create_torrent.hpp``.
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high level example
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==================
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::
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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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add_files
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=========
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::
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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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Adds the file specified by ``path`` to the ``file_storage`` object. In case ``path``
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refers to a diretory, files will be added recursively from the directory.
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If specified, the predicate ``p`` is called once for every file and directory that
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is encountered. files for which ``p`` returns true are added, and directories for
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which ``p`` returns true are traversed. ``p`` must have the following signature::
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bool Pred(boost::filesystem::path const& p);
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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.
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The ".." directory is never traversed.
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set_piece_hashes()
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==================
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::
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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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This function will assume that the files added to the torrent file exists at path
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``p``, read those files and hash the content and set the hashes in the ``create_torrent``
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object. The optional function ``f`` is called in between every hash that is set. ``f``
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must have the following signature::
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void Fun(int);
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file_storage
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============
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The ``file_storage`` 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::
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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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create_torrent
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==============
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The ``create_torrent`` class has the following synopsis::
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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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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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create_torrent()
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----------------
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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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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.
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generate()
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----------
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::
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entry generate() const;
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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.
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It may be useful to add custom entries to the torrent file before bencoding it
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and saving it to disk.
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