343 lines
9.9 KiB
ReStructuredText
343 lines
9.9 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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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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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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and for the wpath version::
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bool Pred(boost::filesystem::wpath 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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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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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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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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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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add_file()
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----------
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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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Adds a file to the file storage. The ``flags`` 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::
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pad_file
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attribute_hidden
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attribute_executable
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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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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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create_torrent()
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----------------
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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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The ``piece_size`` 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 becalculated such that the torrent file is roughly 40 kB.
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If a ``pad_size_limit`` 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 od a piece. The pad_file_limit is ignored unless the
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``optimize`` flag is passed.
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The overload that takes a ``torrent_info`` 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 ``generate()``. 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 ``set_hash()``), will
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have any affect.
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The ``flags`` arguments specifies options for the torrent creation. It can
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be any combination of the following flags:
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optimize
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This will insert pad files to align the files to piece boundaries, for
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optimized disk-I/O.
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merkle
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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 16 kiB piece size.
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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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set_comment()
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-------------
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::
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void set_comment(char const* str);
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Sets the comment for the torrent. The string ``str`` should be utf-8 encoded.
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The comment in a torrent file is optional.
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set_creator()
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-------------
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::
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void set_creator(char const* str);
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Sets the creator of the torrent. The string ``str`` should be utf-8 encoded.
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This is optional.
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set_hash()
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----------
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::
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void set_hash(int index, sha1_hash const& h);
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This sets the SHA-1 hash for the specified piece (``index``). 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 `set_piece_hashes()`_.
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add_url_seed()
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--------------
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::
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void add_url_seed(std::string const& url);
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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.
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add_node()
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----------
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::
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void add_node(std::pair<std::string, int> const& node);
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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.
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add_tracker()
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-------------
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::
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void add_tracker(std::string const& url, int tier = 0);
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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 http:// 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.
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set_priv() priv()
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-----------------
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::
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void set_priv(bool p);
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bool priv() const;
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Sets and queries the private flag of the torrent.
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