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Initial commit of 'new' libtorrent. The Jamfile is broken and will hopefully be fixed soon.
2003-10-23 01:00:57 +02:00
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<title>libtorrent</title>
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<h1>libtorrent</h1>
*** empty log message ***
2003-10-23 18:55:52 +02:00
<table style="margin-left:auto;margin-right:auto" cellpadding="10">
<tr>
<td>
<a href="http://www.sourceforge.net/projects/libtorrent">sourceforge page</a>
</td>
<td>
<a href="http://lists.sourceforge.net/lists/listinfo/libtorrent-discuss">mailing list</a>
</td>
</tr>
</table>
Initial commit of 'new' libtorrent. The Jamfile is broken and will hopefully be fixed soon.
2003-10-23 01:00:57 +02:00
<p>
libtorrent is a C++ library that aims to be a good alternative to all the
<a href="links.html">other bittorrent implementations</a> around. It is a
library and not a full featured client, although it comes with a working
example client.
</p>
<p>
The main goals of libtorrent are:
</p>
<ul>
<li>to be cpu efficient
<li>to be memory efficient
<li>to be very easy to use
</ul>
<p>
libtorrent is not finished. It is an ongoing project (including this documentation).
The current state includes the following features:
</p>
<ul>
<li>multitracker extension support
(as <a href="http://home.elp.rr.com/tur/multitracker-spec.txt">described by TheShadow</a>)
<li>serves multiple torrents on a single port and a single thread
<li>supports http proxies and proxy authentication
<li>gzipped tracker-responses
<li>piece picking on block-level (as opposed to piece-level) like in
<a href="http://azureus.sourceforge.net/">Azureus</a>
</ul>
<p>
libtorrent is portable at least among windows, macosx, and UNIX-systems. It uses boost.thread,
boost.filesystem and various other boost libraries and zlib.
</p>
<h1>building</h1>
<p>
To build libtorrent you need <a href="http://www.boost.org">boost</a> and bjam installed.
Then you can use <tt>bjam</tt> to build libtorrent.
</p>
<p>
To make bjam work, you need to set the environment variable <tt>BOOST_ROOT</tt> to the
path where boost is installed (e.g. c:\boost_1_30_2 on windows). Then you can just run
<tt>bjam</tt> in the libtorrent directory.
</p>
<p>
TODO: more detailed build instructions.
</p>
<h1>using</h1>
<p>
The interface of libtorrent consists of a few classes. The main class is
the <tt>session</tt>, it contains the main loop that serves all torrents.
</p>
<h2>session</h2>
<p>
The <tt>session</tt> class has the following synopsis:
</p>
<pre>
class session: public boost::noncopyable
{
session(int listen_port);
torrent_handle add_torrent(const torrent_info&amp; t, const std::string&amp; save_path);
void set_http_settings(const http_settings&amp; settings);
};
</pre>
<p>
Once it's created, it will spawn the main thread that will do all the work.
The main thread will be idle as long it doesn't have any torrents to participate in.
You add torrents through the <tt>add_torrent()</tt>-function where you give an
object representing the information found in the torrent file and the path where you
want to save the files. The <tt>save_path</tt> will be prepended to the directory-
structure in the torrent-file.
</p>
<p>
How to parse a torrent file and create a <tt>torrent_info</tt> object is described below.
</p>
<p>
The <a href="#torrent_handle"><tt>torrent_handle</tt></a> returned by <tt>add_torrent</tt>
can be used to retrieve information about the torrent's progress, its peers etc. It
is also used to abort a torrent.
</p>
<p>
The constructor takes a listen port as argument, if the given port is busy it will
increase the port number by one and try again. If it still fails it will continue
increasing the port number until it succeeds or has failed 9 ports. <i>This will
change in the future to give more control of the listen-port.</i>
</p>
<h2>parsing torrent files</h2>
<p>
The torrent files are <a href="http://bitconjurer.org/BitTorrent/protocol.html">
bencoded</a>. There are two functions in libtorrent that can encode and decode
bencoded data. They are:
</p>
<h3>
template&lt;class InIt&gt;
entry bdecode(InIt start, InIt end);<br>
template&lt;class OutIt&gt;
void bencode(OutIt out, const entry&amp; e);
</h3>
<p>
The <tt>entry</tt> class is the internal representation of the bencoded data
and it can be used to retreive information, an entry can also be build by
the program and given to <tt>bencode()</tt> to encode it into the <tt>OutIt</tt>
iterator.
</p>
<p>
The <tt>OutIt</tt> and <tt>InIt</tt> are iterators
(<a href="http://www.sgi.com/tech/stl/InputIterator.html"><tt>InputIterator</tt></a>
and <a href="http://www.sgi.com/tech/stl/OutputIterator.html"><tt>OutputIterator</tt></a>
respectively). They are templates and are usually instantiated as
<a href="http://www.sgi.com/tech/stl/ostream_iterator.html">
<tt>std::ostream_iterator</tt></a>,
<a href="http://www.sgi.com/tech/stl/back_insert_iterator.html">
<tt>std::back_insert_iterator</tt></a> or
<a href="http://www.sgi.com/tech/stl/istream_iterator.html">
<tt>std::istream_iterator</tt></a>. These functions will assume that the iterator
refers to a character (<tt>char</tt>). So, if you want to encode entry <tt>e</tt>
into a buffer in memory, you can do it like this:
</p>
<code>
std::vector&lt;char&gt; buffer;
bencode(std::back_insert_iterator&lt;std::vector&lt;char&gt; &gt;(buf), e);
</code>
<p>
If you want to decode a torrent file from a buffer in memory, you can do it like this:
</p>
<code>
std::vector&lt;char&gt; buffer;
// ...
entry e = bdecode(buf.begin(), buf.end());
</code>
<p>
Or, if you have a raw char buffer:
</p>
<code>
const char* buf;
// ...
entry e = bdecode(buf, buf + data_size);
</code>
<p>
Now we just need to know how to retrieve information from the <tt>entry</tt>.
</p>
<h2>entry</h2>
<p>
The <tt>entry</tt> class represents one node in a bencoded hierarchy. It works as a
variant type, it can be either a list, a dictionary (<tt>std::map</tt>), an integer
or a string. This is its synopsis:
</p>
<pre>
class entry
{
public:
typedef std::map&lt;std::string, entry&gt; dictionary_type;
typedef std::string string_type;
typedef std::vector&lt;entry&gt; list_type;
typedef <i>implementation-defined</i> integer_type;
enum data_type
{
int_t,
string_t,
list_t,
dictionary_t,
undefined_t
};
data_type type() const;
entry();
entry(data_type t);
entry(const entry&amp; e);
void operator=(const entry&amp; e);
integer_type&amp; integer()
const integer_type&amp; integer() const;
string_type&amp; string();
const string_type&amp; string() const;
list_type&amp; list();
const list_type&amp; list() const;
dictionary_type&amp; dict();
const dictionary_type&amp; dict() const;
void print(std::ostream&amp; os, int indent) const;
};
</pre>
<p>
The <tt>integer()</tt>, <tt>string()</tt>, <tt>list()</tt> and <tt>dict()</tt> functions
are accessorts that return the respecive type. If the <tt>entry</tt> object isn't of the
type you request, the accessor will throw <tt>type_error</tt> (which derives from
<tt>std::runtime_error</tt>). You can ask an <tt>entry</tt> for its type through the
<tt>type()</tt> function.
</p>
<p>
The <tt>print()</tt> function is there for debug purposes only.
</p>
<p>
If you want to create an <tt>entry</tt> you give it the type you want it to have in its
constructor, and then use one of the non-const accessors to get a reference which you then
can assign the value you want it to have.
</p>
<p>
The typical code to get info from a torrent file will then look like this:
</p>
<code>
entry torrent_file;
// ...
const entry::dictionary_type&amp; dict = torrent_file.dict();
entry::dictionary_type::const_iterator i;
i = dict.find("announce");
if (i != dict.end())
{
std::string tracker_url= i-&gt;second.string();
std::cout &lt;&lt; tracker_url &lt;&lt; "\n";
}
</code>
<p>
To make it easier to extract information from a torren file, the class <tt>torrent_info</tt>
exists.
</p>
<h2>torrent_info</h2>
<p>
The <tt>torrent_info</tt> has the following synopsis:
</p>
<pre>
class torrent_info
{
public:
torrent_info(const entry&amp; torrent_file)
typedef std::vector&lt;file&gt;::const_iterator file_iterator;
typedef std::vector&lt;file&gt;::const_reverse_iterator reverse_file_iterator;
file_iterator begin_files() const;
file_iterator end_files() const;
reverse_file_iterator rbegin_files() const;
reverse_file_iterator rend_files() const;
std::size_t num_files() const;
const file&amp; file_at(int index) const;
const std::vector&lt;announce_entry&gt;&amp; trackers() const;
int prioritize_tracker(int index);
entry::integer_type total_size() const;
entry::integer_type piece_length() const;
std::size_t num_pieces() const;
const sha1_hash&amp; info_hash() const;
void print(std::ostream&amp; os) const;
entry::integer_type piece_size(unsigned int index) const;
const sha1_hash&amp; hash_for_piece(unsigned int index) const;
};
</pre>
<p>
This class will need some explanation. First of all, to get a list of all files
in the torrent, you can use <tt>begin_files()</tt>, <tt>end_files()</tt>,
<tt>rbegin_files()</tt> and <tt>rend_files()</tt>. These will give you standard vector
iterators with the type <tt>file</tt>.
</p>
<pre>
struct file
{
std::string path;
std::string filename;
entry::integer_type size;
};
</pre>
<p>
If you need index-access to files you can use the <tt>num_files()</tt> and <tt>file_at()
</tt> to access files using indices.
</p>
<p>
The <tt>print()</tt> function is there for debug purposes only. It will print the info from
the torrent file to the given outstream.
</p>
<p>
The <tt>trackers()</tt> function will return a sorted vector of <tt>announce_entry</tt>.
Each announce entry contains a string, which is the tracker url, and a tier index. The
tier index is the high-level priority. No matter which trackers that works or not, the
ones with lower tier will always be tried before the one with higher tier number.
</p>
<pre>
struct announce_entry
{
std::string url;
int tier;
};
</pre>
<p>
The <tt>prioritize_tracker()</tt> is used internally to move a tracker to the front
of its tier group. i.e. It will never be moved pass a tracker with a different tier
number. For more information about how multiple trackers are dealt with, see the
<a href="http://home.elp.rr.com/tur/multitracker-spec.txt">specification</a>.
</p>
<p>
<tt>total_size()</tt>, <tt>piece_length()</tt> and <tt>num_pieces()</tt> returns the total
number of bytes the torrent-file represents (all the files in it), the number of byte for
each piece and the total number of pieces, respectively. The difference between
<tt>piece_size()</tt> and <tt>piece_length()</tt> is that <tt>piece_size()</tt> takes
the piece index as argument and gives you the exact size of that piece. It will always
be the same as <tt>piece_length()</tt> except in the case of the last piece, which may
be smaller.
</p>
<p>
<tt>hash_for_piece()</tt> takes a piece-index and returns the 20-bytes sha1-hash for that
piece and <tt>info_hash()</tt> returns the 20-bytes sha1-hash for the info-section of the
torrent file. For more information on the <tt>sha1_hash</tt>, see the <a href="#big_number">big_number</a> class.
</p>
<h2><a name="torrent_handle"></a>torrent_hande</h2>
<p>
You will usually have to store your <tt>torrent_handle</tt>s somewhere, since it's the
object thought which you retrieve infromation about the torrent and aborts the torrent.
Its declaration looks like this:
</p>
<pre>
struct torrent_handle
{
torrent_handle();
float progress() const;
void get_peer_info(std::vector&lt;peer_info&gt;&amp; v);
void abort();
enum state_t
{
checking_files,
connecting_to_tracker,
downloading,
seeding
};
state_t state() const;
};
</pre>
<!-- TODO: temporary comment -->
<p><tt>progress()</tt> and <tt>state()</tt>is not implemented yet</tt>.</p>
<p>
<tt>progress()</tt> will return a value in the range [0, 1], that represents the progress
of the torrent's current task. It may be checking files, connecting to tracker, or downloading
etc. You can get the torrent's current task bu calling <tt>state()</tt>, it will return one of
the following:
</p>
<table>
<tr>
<td>
<tt>checking_files</tt>
</td>
<td>
The torrent has not started its download yet, and is currently checking existing
files or is queued for having its files checked.
</td>
</tr>
<tr>
<td>
<tt>connecting_to_tracker</tt>
</td>
<td>
The torrent is waiting for tracker reply or waiting to retry a tracker connection.
If it's waiting to retry the progress meter will hint about when it will retry.
</td>
</tr>
<tr>
<td>
<tt>downloading</tt>
</td>
<td>
The torrent is being downloaded. This is the state most torrents will be in most
of the time. The progress meter will tell how much of the files that has been
downloaded.
</td>
</tr>
<tr>
<td>
<tt>seeding</tt>
</td>
<td>
In this state the torrent has finished downloading and is a pure seeder.
</td>
</tr>
</table>
<p>
<tt>abort()</tt> will close all peer connections associated with this torrent and tell
the tracker that we've stopped participating in the swarm. This handle will become invalid
shortly after this call has been made.
</p>
<p>
<tt>get_peer_info()</tt> takes a reference to a vector that will be cleared and filled
with one entry for each peer connected to this torrent. Each entry contains information about
that particular peer. It contains the following information:
</p>
<pre>
struct peer_info
{
enum
{
interesting = 0x1,
choked = 0x2,
remote_interested = 0x4,
remote_choked = 0x8
};
unsigned int flags;
address ip;
float up_speed;
float down_speed;
peer_id id;
std::vector&lt;bool&gt; pieces;
};
</pre>
<p>
The <tt>flags</tt> attribute tells you in which state the peer is. It is set to
any combination of the four enums above. Where <tt>interesting</tt> means that we
are interested in pieces from this peer. <tt>choked</tt> means that <u>we</u> has
choked this peer. <tt>remote_interested</tt> and <tt>remote_choked</tt> means the
same thing but that the peer is interested in pieces from us and the peer has choked
<u>us</u>.
</p>
<p>
The <tt>ip</tt> field is the IP-address to this peer. Its type is a wrapper around the
actual address and the port number. See <a href"#address">address</a> class.
</p>
<p>
<tt>up_speed</tt> and <tt>down_speed</tt> is the current upload and download speed
we have to and from this peer. These figures are updated aproximately once every second.
</p>
<p>
<tt>id</tt> is the peer's id as used in the bit torrent protocol. This id can be used to
extract 'fingerprints' from the peer. Sometimes it can tell you which client the peer
is using.
</p>
<p>
<tt>pieces</tt> is a vector of booleans that has as many entries as there are pieces
in the torrent. Each boolean tells you if the peer has that piece (if it's set to true)
or if the peer miss that piece (set to false).
</p>
<h2>http_settings</h2>
<p>
You have some control over tracker requests through the <tt>http_settings</tt> object. You
create it and fill it with your settings and the use <tt>session::set_http_settings()</tt>
to apply them. You have control over proxy and authorization settings and also the user-agent
that will be sent to the tracker. The user-agent is a good way to identify your client.
</p>
<pre>
struct http_settings
{
http_settings();
std::string proxy_ip;
int proxy_port;
std::string proxy_login;
std::string proxy_password;
std::string user_agent;
};
</pre>
<p>
TODO: address
</p>
<h2><a name="big_number"></a>big_number</h2>
<p>
Both the <tt>peer_id</tt> and <tt>sha1_hash</tt> types are typedefs of the class
<tt>big_number</tt>. It represents 20 bytes of data. Its synopsis follows:
</p>
<pre>
class big_number
{
public:
bool operator==(const big_number&amp; n) const;
bool operator!=(const big_number&amp; n) const;
bool operator&lt;(const big_number&amp; n) const;
const unsigned char* begin() const;
const unsigned char* end() const;
unsigned char* begin();
unsigned char* end();
};
</pre>
<p>
The iterators gives you access to individual bytes.
</p>
<h1>Credits</h1>
<p>
Copyright &copy; 2003 Arvid Norberg
</p>
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