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<title>libtorrent manual</title>
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<div class="document" id="libtorrent-manual">
<h1 class="title">libtorrent manual</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Author:</th>
<td>Arvid Norberg, <a class="last reference" href="mailto:c99ang&#64;cs.umu.se">c99ang&#64;cs.umu.se</a></td></tr>
</tbody>
</table>
<div class="contents topic" id="contents">
<p class="topic-title first"><a name="contents">Contents</a></p>
<ul class="simple">
<li><a class="reference" href="#introduction" id="id19" name="id19">introduction</a></li>
<li><a class="reference" href="#downloading-and-building" id="id20" name="id20">downloading and building</a><ul>
<li><a class="reference" href="#cygwin-and-msvc" id="id21" name="id21">cygwin and msvc</a></li>
<li><a class="reference" href="#release-and-debug-builds" id="id22" name="id22">release and debug builds</a></li>
</ul>
</li>
<li><a class="reference" href="#using" id="id23" name="id23">using</a></li>
<li><a class="reference" href="#session" id="id24" name="id24">session</a><ul>
<li><a class="reference" href="#id7" id="id25" name="id25">session()</a></li>
<li><a class="reference" href="#id8" id="id26" name="id26">~session()</a></li>
<li><a class="reference" href="#add-torrent" id="id27" name="id27">add_torrent()</a></li>
<li><a class="reference" href="#remove-torrent" id="id28" name="id28">remove_torrent()</a></li>
<li><a class="reference" href="#disable-extensions-enable-extension" id="id29" name="id29">disable_extensions() enable_extension()</a></li>
<li><a class="reference" href="#set-upload-rate-limit-set-download-rate-limit" id="id30" name="id30">set_upload_rate_limit() set_download_rate_limit()</a></li>
<li><a class="reference" href="#set-max-uploads-set-max-connections" id="id31" name="id31">set_max_uploads() set_max_connections()</a></li>
<li><a class="reference" href="#set-ip-filter" id="id32" name="id32">set_ip_filter()</a></li>
<li><a class="reference" href="#status" id="id33" name="id33">status()</a></li>
<li><a class="reference" href="#is-listening-listen-port-listen-on" id="id34" name="id34">is_listening() listen_port() listen_on()</a></li>
<li><a class="reference" href="#pop-alert-set-severity-level" id="id35" name="id35">pop_alert() set_severity_level()</a></li>
</ul>
</li>
<li><a class="reference" href="#entry" id="id36" name="id36">entry</a><ul>
<li><a class="reference" href="#integer-string-list-dict-type" id="id37" name="id37">integer() string() list() dict() type()</a></li>
</ul>
</li>
<li><a class="reference" href="#torrent-info" id="id38" name="id38">torrent_info</a><ul>
<li><a class="reference" href="#id9" id="id39" name="id39">torrent_info()</a></li>
<li><a class="reference" href="#set-comment-set-piece-size-set-creator-set-hash-add-tracker-add-file" id="id40" name="id40">set_comment() set_piece_size() set_creator() set_hash() add_tracker() add_file()</a></li>
<li><a class="reference" href="#create-torrent" id="id41" name="id41">create_torrent()</a></li>
<li><a class="reference" href="#begin-files-end-files-rbegin-files-rend-files" id="id42" name="id42">begin_files() end_files() rbegin_files() rend_files()</a></li>
<li><a class="reference" href="#num-files-file-at" id="id43" name="id43">num_files() file_at()</a></li>
<li><a class="reference" href="#print" id="id44" name="id44">print()</a></li>
<li><a class="reference" href="#trackers" id="id45" name="id45">trackers()</a></li>
<li><a class="reference" href="#total-size-piece-length-piece-size-num-pieces" id="id46" name="id46">total_size() piece_length() piece_size() num_pieces()</a></li>
<li><a class="reference" href="#hash-for-piece-info-hash" id="id47" name="id47">hash_for_piece() info_hash()</a></li>
<li><a class="reference" href="#name-comment-creation-date" id="id48" name="id48">name() comment() creation_date()</a></li>
</ul>
</li>
<li><a class="reference" href="#torrent-handle" id="id49" name="id49">torrent_handle</a><ul>
<li><a class="reference" href="#save-path" id="id50" name="id50">save_path()</a></li>
<li><a class="reference" href="#move-storage" id="id51" name="id51">move_storage()</a></li>
<li><a class="reference" href="#force-reannounce" id="id52" name="id52">force_reannounce()</a></li>
<li><a class="reference" href="#connect-peer" id="id53" name="id53">connect_peer()</a></li>
<li><a class="reference" href="#set-ratio" id="id54" name="id54">set_ratio()</a></li>
<li><a class="reference" href="#set-upload-limit-set-download-limit" id="id55" name="id55">set_upload_limit() set_download_limit()</a></li>
<li><a class="reference" href="#pause-resume-is-paused" id="id56" name="id56">pause() resume() is_paused()</a></li>
<li><a class="reference" href="#is-seed" id="id57" name="id57">is_seed()</a></li>
<li><a class="reference" href="#has-metadata" id="id58" name="id58">has_metadata()</a></li>
<li><a class="reference" href="#set-tracker-login" id="id59" name="id59">set_tracker_login()</a></li>
<li><a class="reference" href="#use-interface" id="id60" name="id60">use_interface()</a></li>
<li><a class="reference" href="#info-hash" id="id61" name="id61">info_hash()</a></li>
<li><a class="reference" href="#id11" id="id62" name="id62">set_max_uploads() set_max_connections()</a></li>
<li><a class="reference" href="#write-resume-data" id="id63" name="id63">write_resume_data()</a></li>
<li><a class="reference" href="#metadata" id="id64" name="id64">metadata()</a></li>
<li><a class="reference" href="#id12" id="id65" name="id65">status()</a></li>
<li><a class="reference" href="#get-download-queue" id="id66" name="id66">get_download_queue()</a></li>
<li><a class="reference" href="#get-peer-info" id="id67" name="id67">get_peer_info()</a></li>
<li><a class="reference" href="#get-torrent-info" id="id68" name="id68">get_torrent_info()</a></li>
<li><a class="reference" href="#is-valid" id="id69" name="id69">is_valid()</a></li>
</ul>
</li>
<li><a class="reference" href="#torrent-status" id="id70" name="id70">torrent_status</a></li>
<li><a class="reference" href="#peer-info" id="id71" name="id71">peer_info</a></li>
<li><a class="reference" href="#address" id="id72" name="id72">address</a></li>
<li><a class="reference" href="#http-settings" id="id73" name="id73">http_settings</a></li>
<li><a class="reference" href="#ip-filter" id="id74" name="id74">ip_filter</a><ul>
<li><a class="reference" href="#id14" id="id75" name="id75">ip_filter()</a></li>
<li><a class="reference" href="#add-rule" id="id76" name="id76">add_rule()</a></li>
<li><a class="reference" href="#access" id="id77" name="id77">access()</a></li>
<li><a class="reference" href="#export-filter" id="id78" name="id78">export_filter()</a></li>
</ul>
</li>
<li><a class="reference" href="#big-number" id="id79" name="id79">big_number</a></li>
<li><a class="reference" href="#hasher" id="id80" name="id80">hasher</a></li>
<li><a class="reference" href="#fingerprint" id="id81" name="id81">fingerprint</a></li>
<li><a class="reference" href="#free-functions" id="id82" name="id82">free functions</a><ul>
<li><a class="reference" href="#identify-client" id="id83" name="id83">identify_client()</a></li>
<li><a class="reference" href="#bdecode-bencode" id="id84" name="id84">bdecode() bencode()</a></li>
</ul>
</li>
<li><a class="reference" href="#alerts" id="id85" name="id85">alerts</a><ul>
<li><a class="reference" href="#listen-failed-alert" id="id86" name="id86">listen_failed_alert</a></li>
<li><a class="reference" href="#file-error-alert" id="id87" name="id87">file_error_alert</a></li>
<li><a class="reference" href="#tracker-announce-alert" id="id88" name="id88">tracker_announce_alert</a></li>
<li><a class="reference" href="#tracker-alert" id="id89" name="id89">tracker_alert</a></li>
<li><a class="reference" href="#tracker-reply-alert" id="id90" name="id90">tracker_reply_alert</a></li>
<li><a class="reference" href="#hash-failed-alert" id="id91" name="id91">hash_failed_alert</a></li>
<li><a class="reference" href="#peer-ban-alert" id="id92" name="id92">peer_ban_alert</a></li>
<li><a class="reference" href="#peer-error-alert" id="id93" name="id93">peer_error_alert</a></li>
<li><a class="reference" href="#invalid-request-alert" id="id94" name="id94">invalid_request_alert</a></li>
<li><a class="reference" href="#torrent-finished-alert" id="id95" name="id95">torrent_finished_alert</a></li>
<li><a class="reference" href="#metadata-received-alert" id="id96" name="id96">metadata_received_alert</a></li>
<li><a class="reference" href="#fastresume-rejected-alert" id="id97" name="id97">fastresume_rejected_alert</a></li>
<li><a class="reference" href="#dispatcher" id="id98" name="id98">dispatcher</a></li>
</ul>
</li>
<li><a class="reference" href="#exceptions" id="id99" name="id99">exceptions</a><ul>
<li><a class="reference" href="#invalid-handle" id="id100" name="id100">invalid_handle</a></li>
<li><a class="reference" href="#duplicate-torrent" id="id101" name="id101">duplicate_torrent</a></li>
<li><a class="reference" href="#invalid-encoding" id="id102" name="id102">invalid_encoding</a></li>
<li><a class="reference" href="#type-error" id="id103" name="id103">type_error</a></li>
<li><a class="reference" href="#invalid-torrent-file" id="id104" name="id104">invalid_torrent_file</a></li>
</ul>
</li>
<li><a class="reference" href="#examples" id="id105" name="id105">examples</a><ul>
<li><a class="reference" href="#dump-torrent" id="id106" name="id106">dump_torrent</a></li>
<li><a class="reference" href="#simple-client" id="id107" name="id107">simple client</a></li>
<li><a class="reference" href="#make-torrent" id="id108" name="id108">make_torrent</a></li>
</ul>
</li>
<li><a class="reference" href="#fast-resume" id="id109" name="id109">fast resume</a><ul>
<li><a class="reference" href="#file-format" id="id110" name="id110">file format</a></li>
</ul>
</li>
<li><a class="reference" href="#threads" id="id111" name="id111">threads</a></li>
<li><a class="reference" href="#storage-allocation" id="id112" name="id112">storage allocation</a><ul>
<li><a class="reference" href="#full-allocation" id="id113" name="id113">full allocation</a></li>
<li><a class="reference" href="#compact-allocation" id="id114" name="id114">compact allocation</a></li>
</ul>
</li>
<li><a class="reference" href="#extensions" id="id115" name="id115">extensions</a><ul>
<li><a class="reference" href="#chat-messages" id="id116" name="id116">chat messages</a></li>
<li><a class="reference" href="#metadata-from-peers" id="id117" name="id117">metadata from peers</a></li>
</ul>
</li>
<li><a class="reference" href="#filename-checks" id="id118" name="id118">filename checks</a></li>
<li><a class="reference" href="#acknowledgements" id="id119" name="id119">acknowledgements</a></li>
</ul>
</div>
<div class="section" id="introduction">
<h1><a name="introduction">introduction</a></h1>
<p>libtorrent is a C++ library that aims to be a good alternative to all the
other bittorrent implementations 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>
<blockquote>
<ul class="simple">
<li>to be cpu efficient</li>
<li>to be memory efficient</li>
<li>to be very easy to use</li>
</ul>
</blockquote>
<p>libtorrent is not finished. It is an ongoing project (including this documentation).
The current state includes the following features:</p>
<blockquote>
<ul class="simple">
<li>multitracker extension support (as <a class="reference" href="http://home.elp.rr.com/tur/multitracker-spec.txt">described by John Hoffman</a>)</li>
<li>serves multiple torrents on a single port and a single thread</li>
<li>supports http proxies and proxy authentication</li>
<li>gzipped tracker-responses</li>
<li>piece picking on block-level like in <a class="reference" href="http://azureus.sourceforge.net">Azureus</a> (as opposed to piece-level).</li>
<li>queues torrents for file check, instead of checking all of them in parallel.</li>
<li>uses separate threads for checking files and for main downloader, with a fool-proof
thread-safe library interface. (i.e. There's no way for the user to cause a deadlock).</li>
<li>can limit the upload and download bandwidth usage and the maximum number of unchoked peers</li>
<li>piece-wise, unordered, file allocation</li>
<li>implements fair trade. User settable trade-ratio, must at least be 1:1,
but one can choose to trade 1 for 2 or any other ratio that isn't unfair to the other
party. (i.e. real tit for tat)</li>
<li>fast resume support, a way to get rid of the costly piece check at the start
of a resumed torrent. Saves the storage state, piece_picker state as well as all local
peers in a separate fast-resume file.</li>
<li>supports the extension protocol <a class="reference" href="http://nolar.com/azureus/extended.htm">described by Nolar</a>. See <a class="reference" href="#extensions">extensions</a>.</li>
<li>supports files &gt; 2 gigabytes.</li>
<li>supports the <tt class="docutils literal"><span class="pre">no_peer_id=1</span></tt> extension that will ease the load off trackers.</li>
<li>supports the <a class="reference" href="udp_tracker_protocol.html">udp-tracker protocol</a> by Olaf van der Spek.</li>
<li>possibility to limit the number of connections.</li>
<li>delays have messages if there's no other outgoing traffic to the peer, and doesn't
send have messages to peers that already has the piece. This saves bandwidth.</li>
<li>does not have any requirements on the piece order in a torrent that it resumes. This
means it can resume a torrent downloaded by any client.</li>
<li>adjusts the length of the request queue depending on download rate.</li>
<li>supports the <tt class="docutils literal"><span class="pre">compact=1</span></tt> tracker parameter.</li>
<li>selective downloading. The ability to select which parts of a torrent you
want to download.</li>
<li>ip filter</li>
</ul>
</blockquote>
<p>libtorrent is portable at least among Windows, MacOSX and other UNIX-systems. It uses Boost.Thread,
Boost.Filesystem, Boost.Date_time and various other boost libraries as well as zlib.</p>
<p>libtorrent has been successfully compiled and tested on:</p>
<blockquote>
<ul class="simple">
<li>Windows 2000 vc7.1</li>
<li>Linux x86 GCC 3.0.4, GCC 3.2.3, GCC 3.4.2</li>
<li>MacOS X, (Apple's) GCC 3.3, (Apple's) GCC 4.0</li>
<li>SunOS 5.8 GCC 3.1</li>
<li>Cygwin GCC 3.3.3</li>
</ul>
</blockquote>
<p>Fails on:</p>
<blockquote>
<ul class="simple">
<li>GCC 2.95.4 (<tt class="docutils literal"><span class="pre">std::ios_base</span></tt> is missing)</li>
<li>msvc6 sp5</li>
</ul>
</blockquote>
<p>libtorrent is released under the <a class="reference" href="http://www.opensource.org/licenses/bsd-license.php">BSD-license</a>.</p>
</div>
<div class="section" id="downloading-and-building">
<h1><a name="downloading-and-building">downloading and building</a></h1>
<p>To acquire the latest version of libtorrent, you'll have to grab it from CVS. You'll find instructions
on how to do this <a class="reference" href="http://sourceforge.net/cvs/?group_id=79942">here</a> (see Anonymous CVS access).</p>
<p>The easiest way to build libtorrent is probably to use <a class="reference" href="http://sourceforge.net/project/showfiles.php?group_id=7586&amp;package_id=80982&amp;release_id=278763">boost-build</a>. Make sure you install it
correctly by setting the environment variable <tt class="docutils literal"><span class="pre">BOOST_BUILD_PATH</span></tt> to point to your boost build
installation. Also you have to modify the <tt class="docutils literal"><span class="pre">user_config.jam</span></tt> to reflect the toolsets you have installed.
(if you're building with gcc, uncomment the line &quot;using gcc ;&quot;)</p>
<p>You also need to install <a class="reference" href="http://sourceforge.net/project/showfiles.php?group_id=7586&amp;package_id=8041&amp;release_id=284047">boost</a> (at least version 1.32.0).</p>
<p>Before you invoke <tt class="docutils literal"><span class="pre">bjam</span></tt> you have to set the environment variable <tt class="docutils literal"><span class="pre">BOOST_ROOT</span></tt> to the
path where you installed boost. This will be used to build and link against the required
boost libraries as well as be used as include path for boost headers.</p>
<p>To build you just have to run:</p>
<pre class="literal-block">
bjam &lt;toolset&gt; link=static
</pre>
<p>in the libtorrent directory.</p>
<p>If you're building on a platform where dlls share the same heap, you can build libtorrent
as a dll too, by typing <tt class="docutils literal"><span class="pre">link=shared</span></tt> instead of <tt class="docutils literal"><span class="pre">link=static</span></tt>.</p>
<p>To build on MacOS X, you need the latest version of boost-build, from the <a class="reference" href="http://sourceforge.net/cvs/?group_id=7586">boost cvs</a>.</p>
<p>If you're making your own project file, note that there are two versions of the file
abstraction. There's one <tt class="docutils literal"><span class="pre">file_win.cpp</span></tt> which relies on windows file API that supports
files larger than 2 Gigabytes. This does not work in vc6 for some reason, possibly because
it may require windows NT and above. The other file, <tt class="docutils literal"><span class="pre">file.cpp</span></tt> is the default
implementation that simply relies on the standard low level io routines (read, write etc.),
this is the preferred implementation that should be used in all cases.</p>
<div class="section" id="cygwin-and-msvc">
<h2><a name="cygwin-and-msvc">cygwin and msvc</a></h2>
<p>Note that if you're building on windows using the <tt class="docutils literal"><span class="pre">msvc</span></tt> toolset, you cannot run it
from a cygwin terminal, you'll have to run it from a <tt class="docutils literal"><span class="pre">cmd</span></tt> terminal. The same goes for
cygwin, if you're building with gcc (mingw) you'll have to run it from a cygwin terminal.
Also, make sure the paths are correct in the different environments. In cygwin, the paths
(<tt class="docutils literal"><span class="pre">BOOST_BUILD_PATH</span></tt> and <tt class="docutils literal"><span class="pre">BOOST_ROOT</span></tt>) should be in the typical unix-format (e.g.
<tt class="docutils literal"><span class="pre">/cygdrive/c/boost_1_32_0</span></tt>). In the windows environment, they should have the typical
windows format (<tt class="docutils literal"><span class="pre">c:/boost_1_32_0</span></tt>).</p>
<p>If you're building in developer studio, you may have to set the compiler options
&quot;force conformance in for loop scope&quot;, &quot;treat wchar_t as built-in type&quot; and
&quot;Enable Run-Time Type Info&quot; to Yes.</p>
</div>
<div class="section" id="release-and-debug-builds">
<h2><a name="release-and-debug-builds">release and debug builds</a></h2>
<p>The <tt class="docutils literal"><span class="pre">Jamfile</span></tt> can build both a release and debug version of libtorrent. In debug mode,
libtorrent will have pretty expensive invariant checks and asserts built into it. If you
want to disable such checks (you want to do that in a release build) you can see the
table below for which defines you can use to control the build. The <tt class="docutils literal"><span class="pre">Jamfile</span></tt> will define
<tt class="docutils literal"><span class="pre">NDEBUG</span></tt> when it's building a release build. There are two other build variants available
in the <tt class="docutils literal"><span class="pre">Jamfile</span></tt>. debug_log and release_log, these two variants inherits from the
debug and release variants respectively, but adds extra logging (<tt class="docutils literal"><span class="pre">TORRENT_VERBOSE_LOGGIN</span></tt>).</p>
<table border="1" class="docutils">
<colgroup>
<col width="40%" />
<col width="60%" />
</colgroup>
<thead valign="bottom">
<tr><th>macro</th>
<th>description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">NDEBUG</span></tt></td>
<td>If you define this macro, all asserts,
invariant checks and general debug code will be
removed. This option takes precedence over
other debug settings.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">TORRENT_LOGGING</span></tt></td>
<td>This macro will enable logging of the session
events, such as tracker announces and incoming
connections (as well as blocked connections).</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">TORRENT_VERBOSE_LOGGING</span></tt></td>
<td>If you define this macro, every peer connection
will log its traffic to a log file as well as
the session log.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">TORRENT_STORAGE_DEBUG</span></tt></td>
<td>This will enable extra expensive invariant
checks in the storage, including logging of
piece sorting.</td>
</tr>
</tbody>
</table>
<p>If you experience that libtorrent uses unreasonable amounts of cpu, it will definately help to
define <tt class="docutils literal"><span class="pre">NDEBUG</span></tt>, since it will remove the invariant checks within the library.</p>
<p>The <tt class="docutils literal"><span class="pre">Jamfile</span></tt> has the following build variants:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">release</span></tt> - release version without any logging</li>
<li><tt class="docutils literal"><span class="pre">release_log</span></tt> - release version with standard logging</li>
<li><tt class="docutils literal"><span class="pre">release_vlog</span></tt> - release version with verbose logging (all peer connections are logged)</li>
<li><tt class="docutils literal"><span class="pre">debug</span></tt> - debug version without any logging</li>
<li><tt class="docutils literal"><span class="pre">debug_log</span></tt> - debug version with standard logging</li>
<li><tt class="docutils literal"><span class="pre">debug_vlog</span></tt> - debug version with verbose logging</li>
</ul>
</blockquote>
</div>
</div>
<div class="section" id="using">
<h1><a name="using">using</a></h1>
<p>The interface of libtorrent consists of a few classes. The main class is
the <tt class="docutils literal"><span class="pre">session</span></tt>, it contains the main loop that serves all torrents.</p>
<p>The basic usage is as follows:</p>
<ul>
<li><p class="first">conststruct a session</p>
</li>
<li><p class="first">parse .torrent-files and add them to the session (see <a class="reference" href="#bdecode-bencode">bdecode() bencode()</a>)</p>
</li>
<li><dl class="first docutils">
<dt>main loop (see <a class="reference" href="#session">session</a>)</dt>
<dd><ul class="first last simple">
<li>query the torrent_handles for progress (see <a class="reference" href="#torrent-handle">torrent_handle</a>)</li>
<li>query the session for information</li>
<li>add and remove torrents from the session at run-time</li>
</ul>
</dd>
</dl>
</li>
<li><p class="first">save resume data for all torrent_handles (optional)</p>
</li>
<li><p class="first">destruct session object</p>
</li>
</ul>
<p>Each class and function is described in this manual.</p>
</div>
<div class="section" id="session">
<h1><a name="session">session</a></h1>
<p>The <tt class="docutils literal"><span class="pre">session</span></tt> class has the following synopsis:</p>
<pre class="literal-block">
class session: public boost::noncopyable
{
session(const fingerprint&amp; print = libtorrent::fingerprint(&quot;LT&quot;, 0, 1, 0, 0));
session(
const fingerprint&amp; print
, std::pair&lt;int, int&gt; listen_port_range
, const char* listen_interface = 0);
torrent_handle add_torrent(
entry const&amp; e
, boost::filesystem::path const&amp; save_path
, entry const&amp; resume_data = entry()
, bool compact_mode = true
, int block_size = 16 * 1024);
torrent_handle add_torrent(
char const* tracker_url
, sha1_hash const&amp; info_hash
, boost::filesystem::path const&amp; save_path
, entry const&amp; resume_data = entry()
, bool compact_mode = true
, int block_size = 16 * 1024);
void remove_torrent(torrent_handle const&amp; h);
void disable_extensions();
void enable_extension(peer_connection::extension_index);
void set_http_settings(const http_settings&amp; settings);
void set_upload_rate_limit(int bytes_per_second);
void set_download_rate_limit(int bytes_per_second);
void set_max_uploads(int limit);
void set_max_connections(int limit);
void set_ip_filter(ip_filter const&amp; f);
session_status status() const;
bool is_listening() const;
unsigned short listen_port() const;
bool listen_on(
std::pair&lt;int, int&gt; const&amp; port_range
, char const* interface = 0);
std::auto_ptr&lt;alert&gt; pop_alert();
void set_severity_level(alert::severity_t s);
};
</pre>
<p>Once it's created, the session object 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.</p>
<div class="section" id="id7">
<h2><a name="id7">session()</a></h2>
<blockquote>
<pre class="literal-block">
session(fingerprint const&amp; print = libtorrent::fingerprint(&quot;LT&quot;, 0, 1, 0, 0));
session(fingerprint const&amp; print
, std::pair&lt;int, int&gt; listen_port_range
, char const* listen_interface = 0);
</pre>
</blockquote>
<p>If the fingerprint in the first overload is ommited, the client will get a default
fingerprint stating the version of libtorrent. The fingerprint is a short string that will be
used in the peer-id to identify the client and the client's version. For more details see the
<a class="reference" href="#fingerprint">fingerprint</a> class. The constructor that only takes a fingerprint will not open a
listen port for the session, to get it running you'll have to call <tt class="docutils literal"><span class="pre">session::listen_on()</span></tt>.
The other constructor, that takes a port range and an interface as well as the fingerprint
will automatically try to listen on a port on the given interface. For more information about
the parameters, see <tt class="docutils literal"><span class="pre">listen_on()</span></tt> function.</p>
</div>
<div class="section" id="id8">
<h2><a name="id8">~session()</a></h2>
<p>The destructor of session will notify all trackers that our torrents have been shut down.
If some trackers are down, they will time out. All this before the destructor of session
returns. So, it's adviced that any kind of interface (such as windows) are closed before
destructing the sessoin object. Because it can take a few second for it to finish. The
timeout can be set with <tt class="docutils literal"><span class="pre">set_http_settings()</span></tt>.</p>
</div>
<div class="section" id="add-torrent">
<h2><a name="add-torrent">add_torrent()</a></h2>
<blockquote>
<pre class="literal-block">
torrent_handle add_torrent(
entry const&amp; e
, boost::filesystem::path const&amp; save_path
, entry const&amp; resume_data = entry()
, bool compact_mode = true
, int block_size = 16 * 1024);
torrent_handle add_torrent(
char const* tracker_url
, sha1_hash const&amp; info_hash
, boost::filesystem::path const&amp; save_path
, entry const&amp; resume_data = entry()
, bool compact_mode = true
, int block_size = 16 * 1024);
</pre>
</blockquote>
<p>You add torrents through the <tt class="docutils literal"><span class="pre">add_torrent()</span></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 class="docutils literal"><span class="pre">save_path</span></tt> will be prepended to the directory
structure in the torrent-file.</p>
<p>If the torrent you are trying to add already exists in the session (is either queued
for checking, being checked or downloading) <tt class="docutils literal"><span class="pre">add_torrent()</span></tt> will throw
<a class="reference" href="#duplicate-torrent">duplicate_torrent</a> which derives from <tt class="docutils literal"><span class="pre">std::exception</span></tt>.</p>
<p>The optional parameter, <tt class="docutils literal"><span class="pre">resume_data</span></tt> can be given if up to date fast-resume data
is available. The fast-resume data can be acquired from a running torrent by calling
<tt class="docutils literal"><span class="pre">torrent_handle::write_resume_data()</span></tt>. See <a class="reference" href="#fast-resume">fast resume</a>.</p>
<p>The <tt class="docutils literal"><span class="pre">compact_mode</span></tt> paramater refers to the layout of the storage for this torrent. If
set to true (default), the storage will grow as more pieces are downloaded, and pieces
are rearranged to finally be in their correct places once the entire torrent has been
downloaded. If it is false, the entire storage is allocated before download begins. I.e.
the files contained in the torrent are filled with zeroes, and each downloaded piece
is put in its final place directly when downloaded. For more info, see <a class="reference" href="#storage-allocation">storage allocation</a>.</p>
<p><tt class="docutils literal"><span class="pre">block_size</span></tt> sets the preferred request size, i.e. the number of bytes to request from
a peer at a time. This block size must be a divisor of the piece size, and since the piece
size is an even power of 2, so must the block size be. If the block size given here turns
out to be greater than the piece size, it will simply be clamped to the piece size.</p>
<p>The <a class="reference" href="#torrent-handle">torrent_handle</a> returned by <tt class="docutils literal"><span class="pre">add_torrent()</span></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 second overload that takes a tracker url and an info-hash instead of metadata (<tt class="docutils literal"><span class="pre">entry</span></tt>)
can be used with torrents where (at least some) peers support the metadata extension. For
the overload to be available, libtorrent must be built with extensions enabled
(<tt class="docutils literal"><span class="pre">TORRENT_ENABLE_EXTENSIONS</span></tt> defined).</p>
</div>
<div class="section" id="remove-torrent">
<h2><a name="remove-torrent">remove_torrent()</a></h2>
<blockquote>
<pre class="literal-block">
void remove_torrent(torrent_handle const&amp; h);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">remove_torrent()</span></tt> will close all peer connections associated with the torrent and tell
the tracker that we've stopped participating in the swarm.</p>
</div>
<div class="section" id="disable-extensions-enable-extension">
<h2><a name="disable-extensions-enable-extension">disable_extensions() enable_extension()</a></h2>
<blockquote>
<pre class="literal-block">
void disable_extensions();
void enable_extension(peer_connection::extension_index);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">disable_extensions()</span></tt> will disable all extensions available in libtorrent.
<tt class="docutils literal"><span class="pre">enable_extension()</span></tt> will enable a single extension. The available extensions
are enumerated in the <tt class="docutils literal"><span class="pre">peer_connection</span></tt> class. These are the available extensions:</p>
<pre class="literal-block">
enum extension_index
{
extended_chat_message,
extended_metadata_message,
extended_peer_exchange_message,
extended_listen_port_message,
num_supported_extensions
};
</pre>
<p><em>peer_exchange is not implemented yet</em></p>
<p>By default, all extensions are enabled.
For more information about the extensions, see the <a class="reference" href="#extensions">extensions</a> section.</p>
</div>
<div class="section" id="set-upload-rate-limit-set-download-rate-limit">
<h2><a name="set-upload-rate-limit-set-download-rate-limit">set_upload_rate_limit() set_download_rate_limit()</a></h2>
<blockquote>
<pre class="literal-block">
void set_upload_rate_limit(int bytes_per_second);
void set_download_rate_limit(int bytes_per_second);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">set_upload_rate_limit()</span></tt> set the maximum number of bytes allowed to be
sent to peers per second. This bandwidth is distributed among all the peers. If
you don't want to limit upload rate, you can set this to -1 (the default).
<tt class="docutils literal"><span class="pre">set_download_rate_limit()</span></tt> works the same way but for download rate instead
of upload rate.</p>
</div>
<div class="section" id="set-max-uploads-set-max-connections">
<h2><a name="set-max-uploads-set-max-connections">set_max_uploads() set_max_connections()</a></h2>
<blockquote>
<pre class="literal-block">
void set_max_uploads(int limit);
void set_max_connections(int limit);
</pre>
</blockquote>
<p>These functions will set a global limit on the number of unchoked peers (uploads)
and the number of connections opened. The number of connections is set to a hard
minimum of at least two connections per torrent, so if you set a too low
connections limit, and open too many torrents, the limit will not be met. The
number of uploads is at least one per torrent.</p>
</div>
<div class="section" id="set-ip-filter">
<h2><a name="set-ip-filter">set_ip_filter()</a></h2>
<blockquote>
<pre class="literal-block">
void set_ip_filter(ip_filter const&amp; filter);
</pre>
</blockquote>
<p>Sets a filter that will be used to reject and accept incoming as well as outgoing
connections based on their originating ip address. The default filter will allow
connections to any ip address. To build a set of rules for which addresses are
accepted and not, see <a class="reference" href="#ip-filter">ip_filter</a>.</p>
</div>
<div class="section" id="status">
<h2><a name="status">status()</a></h2>
<blockquote>
<pre class="literal-block">
session_status status() const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">status()</span></tt> returns session wide-statistics and status. The <tt class="docutils literal"><span class="pre">session_status</span></tt>
struct has the following members:</p>
<pre class="literal-block">
struct session_status
{
bool has_incoming_connections;
float upload_rate;
float download_rate;
float payload_upload_rate;
float payload_download_rate;
size_type total_download;
size_type total_upload;
size_type total_payload_download;
size_type total_payload_upload;
int num_peers;
};
</pre>
<p><tt class="docutils literal"><span class="pre">has_incoming_connections</span></tt> is false as long as no incoming connections have been
established on the listening socket. Every time you change the listen port, this will
be reset to false.</p>
<p><tt class="docutils literal"><span class="pre">upload_rate</span></tt>, <tt class="docutils literal"><span class="pre">download_rate</span></tt>, <tt class="docutils literal"><span class="pre">payload_download_rate</span></tt> and <tt class="docutils literal"><span class="pre">payload_upload_rate</span></tt>
are the total download and upload rates accumulated from all torrents. The payload
versions is the payload download only.</p>
<p><tt class="docutils literal"><span class="pre">total_download</span></tt> and <tt class="docutils literal"><span class="pre">total_upload</span></tt> are the total number of bytes downloaded and
uploaded to and from all torrents. <tt class="docutils literal"><span class="pre">total_payload_download</span></tt> and <tt class="docutils literal"><span class="pre">total_payload_upload</span></tt>
are the same thing but where only the payload is considered.</p>
<p><tt class="docutils literal"><span class="pre">num_peers</span></tt> is the total number of peer connections this session have.</p>
</div>
<div class="section" id="is-listening-listen-port-listen-on">
<h2><a name="is-listening-listen-port-listen-on">is_listening() listen_port() listen_on()</a></h2>
<blockquote>
<pre class="literal-block">
bool is_listening() const;
unsigned short listen_port() const;
bool listen_on(
std::pair&lt;int, int&gt; const&amp; port_range
, char const* interface = 0);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">is_listening()</span></tt> will tell you wether or not the session has successfully
opened a listening port. If it hasn't, this function will return false, and
then you can use <tt class="docutils literal"><span class="pre">listen_on()</span></tt> to make another try.</p>
<p><tt class="docutils literal"><span class="pre">listen_port()</span></tt> returns the port we ended up listening on. Since you just pass
a port-range to the constructor and to <tt class="docutils literal"><span class="pre">listen_on()</span></tt>, to know which port it
ended up using, you have to ask the session using this function.</p>
<p><tt class="docutils literal"><span class="pre">listen_on()</span></tt> will change the listen port and/or the listen interface. If the
session is already listening on a port, this socket will be closed and a new socket
will be opened with these new settings. The port range is the ports it will try
to listen on, if the first port fails, it will continue trying the next port within
the range and so on. The interface parameter can be left as 0, in that case the
os will decide which interface to listen on, otherwise it should be the ip-address
of the interface you want the listener socket bound to. <tt class="docutils literal"><span class="pre">listen_on()</span></tt> returns true
if it managed to open the socket, and false if it failed. If it fails, it will also
generate an appropriate alert (<a class="reference" href="#listen-failed-alert">listen_failed_alert</a>).</p>
<p>The interface parameter can also be a hostname that will resolve to the device you
want to listen on.</p>
</div>
<div class="section" id="pop-alert-set-severity-level">
<h2><a name="pop-alert-set-severity-level">pop_alert() set_severity_level()</a></h2>
<blockquote>
<pre class="literal-block">
std::auto_ptr&lt;alert&gt; pop_alert();
void set_severity_level(alert::severity_t s);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">pop_alert()</span></tt> is used to ask the session if any errors or events has occured. With
<tt class="docutils literal"><span class="pre">set_severity_level()</span></tt> you can filter how serious the event has to be for you to
receive it through <tt class="docutils literal"><span class="pre">pop_alert()</span></tt>. For information, see <a class="reference" href="#alerts">alerts</a>.</p>
</div>
</div>
<div class="section" id="entry">
<h1><a name="entry">entry</a></h1>
<p>The <tt class="docutils literal"><span class="pre">entry</span></tt> class represents one node in a bencoded hierarchy. It works as a
variant type, it can be either a list, a dictionary (<tt class="docutils literal"><span class="pre">std::map</span></tt>), an integer
or a string. This is its synopsis:</p>
<pre class="literal-block">
class entry
{
public:
typedef std::list&lt;std::pair&lt;std::string, entry&gt; &gt; dictionary_type;
typedef std::string string_type;
typedef std::list&lt;entry&gt; list_type;
typedef size_type integer_type;
enum data_type
{
int_t,
string_t,
list_t,
dictionary_t,
undefined_t
};
data_type type() const;
entry(dictionary_type const&amp;);
entry(string_type const&amp;);
entry(list_type const&amp;);
entry(integer_type const&amp;);
entry();
entry(data_type t);
entry(entry const&amp; e);
~entry();
void operator=(entry const&amp; e);
void operator=(dictionary_type const&amp;);
void operator=(string_type const&amp;);
void operator=(list_type const&amp;);
void operator=(integer_type const&amp;);
integer_type&amp; integer();
integer_type const&amp; integer() const;
string_type&amp; string();
string_type const&amp; string() const;
list_type&amp; list();
list_type const&amp; list() const;
dictionary_type&amp; dict();
dictionary_type const&amp; dict() const;
// these functions requires that the entry
// is a dictionary, otherwise they will throw
entry&amp; operator[](char const* key);
entry&amp; operator[](std::string const&amp; key);
entry const&amp; operator[](char const* key) const;
entry const&amp; operator[](std::string const&amp; key) const;
entry* find_key(char const* key);
entry const* find_key(char const* key) const;
void print(std::ostream&amp; os, int indent = 0) const;
};
</pre>
<p><em>TODO: finish documentation of entry.</em></p>
<div class="section" id="integer-string-list-dict-type">
<h2><a name="integer-string-list-dict-type">integer() string() list() dict() type()</a></h2>
<blockquote>
<pre class="literal-block">
integer_type&amp; integer();
integer_type const&amp; integer() const;
string_type&amp; string();
string_type const&amp; string() const;
list_type&amp; list();
list_type const&amp; list() const;
dictionary_type&amp; dict();
dictionary_type const&amp; dict() const;
</pre>
</blockquote>
<p>The <tt class="docutils literal"><span class="pre">integer()</span></tt>, <tt class="docutils literal"><span class="pre">string()</span></tt>, <tt class="docutils literal"><span class="pre">list()</span></tt> and <tt class="docutils literal"><span class="pre">dict()</span></tt> functions
are accessors that return the respecive type. If the <tt class="docutils literal"><span class="pre">entry</span></tt> object isn't of the
type you request, the accessor will throw <a class="reference" href="#type-error">type_error</a> (which derives from
<tt class="docutils literal"><span class="pre">std::runtime_error</span></tt>). You can ask an <tt class="docutils literal"><span class="pre">entry</span></tt> for its type through the
<tt class="docutils literal"><span class="pre">type()</span></tt> function.</p>
<p>The <tt class="docutils literal"><span class="pre">print()</span></tt> function is there for debug purposes only.</p>
<p>If you want to create an <tt class="docutils literal"><span class="pre">entry</span></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>
<pre class="literal-block">
entry torrent_file;
// ...
entry::dictionary_type const&amp; dict = torrent_file.dict();
entry::dictionary_type::const_iterator i;
i = dict.find(&quot;announce&quot;);
if (i != dict.end())
{
std::string tracker_url= i-&gt;second.string();
std::cout &lt;&lt; tracker_url &lt;&lt; &quot;\n&quot;;
}
</pre>
<p>To make it easier to extract information from a torren file, the class <tt class="docutils literal"><span class="pre">torrent_info</span></tt>
exists.</p>
</div>
</div>
<div class="section" id="torrent-info">
<h1><a name="torrent-info">torrent_info</a></h1>
<p>The <tt class="docutils literal"><span class="pre">torrent_info</span></tt> has the following synopsis:</p>
<pre class="literal-block">
class torrent_info
{
public:
torrent_info();
torrent_info(sha1_hash const&amp; info_hash);
torrent_info(entry const&amp; torrent_file);
entry create_torrent() const;
void set_comment(char const* str);
void set_piece_size(int size);
void set_creator(char const* str);
void set_hash(int index, sha1_hash const&amp; h);
void add_tracker(std::string const&amp; url, int tier = 0);
void add_file(boost::filesystem::path file, size_type size);
typedef std::vector&lt;file_entry&gt;::const_iterator file_iterator;
typedef std::vector&lt;file_entry&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;
int num_files() const;
file_entry const&amp; file_at(int index) const;
std::vector&lt;announce_entry&gt; const&amp; trackers() const;
size_type total_size() const;
size_type piece_length() const;
int num_pieces() const;
sha1_hash const&amp; info_hash() const;
std::stirng const&amp; name() const;
std::string const&amp; comment() const;
boost::optional&lt;boost::posix_time::ptime&gt;
creation_date() const;
void print(std::ostream&amp; os) const;
size_type piece_size(unsigned int index) const;
sha1_hash const&amp; hash_for_piece(unsigned int index) const;
};
</pre>
<div class="section" id="id9">
<h2><a name="id9">torrent_info()</a></h2>
<blockquote>
<pre class="literal-block">
torrent_info();
torrent_info(sha1_hash const&amp; info_hash);
torrent_info(entry const&amp; torrent_file);
</pre>
</blockquote>
<p>The default constructor of <tt class="docutils literal"><span class="pre">torrent_info</span></tt> is used when creating torrent files. It will
initialize the object to an empty torrent, containing no files. The info hash will be set
to 0 when this constructor is used. To use the empty <tt class="docutils literal"><span class="pre">torrent_info</span></tt> object, add files
and piece hashes, announce URLs and optionally a creator tag and comment. To do this you
use the members <tt class="docutils literal"><span class="pre">set_comment()</span></tt>, <tt class="docutils literal"><span class="pre">set_piece_size()</span></tt>, <tt class="docutils literal"><span class="pre">set_creator()</span></tt>, <tt class="docutils literal"><span class="pre">set_hash()</span></tt>
etc.</p>
<p>The contructor that takes an info-hash is identical to the default constructor with the
exception that it will initialize the info-hash to the given value. This is used internally
when downloading torrents without the metadata. The metadata will be created by libtorrent
as soon as it has been downloaded from the swarm.</p>
<p>The last constructor is the one that is used in most cases. It will create a <tt class="docutils literal"><span class="pre">torrent_info</span></tt>
object from the information found in the given torrent_file. The <tt class="docutils literal"><span class="pre">entry</span></tt> represents a tree
node in an bencoded file. To load an ordinary .torrent file into an <tt class="docutils literal"><span class="pre">entry</span></tt>, use bdecode(),
see <a class="reference" href="#bdecode-bencode">bdecode() bencode()</a>.</p>
</div>
<div class="section" id="set-comment-set-piece-size-set-creator-set-hash-add-tracker-add-file">
<h2><a name="set-comment-set-piece-size-set-creator-set-hash-add-tracker-add-file">set_comment() set_piece_size() set_creator() set_hash() add_tracker() add_file()</a></h2>
<blockquote>
<pre class="literal-block">
void set_comment(char const* str);
void set_piece_size(int size);
void set_creator(char const* str);
void set_hash(int index, sha1_hash const&amp; h);
void add_tracker(std::string const&amp; url, int tier = 0);
void add_file(boost::filesystem::path file, size_type size);
</pre>
</blockquote>
<p>These files are used when creating a torrent file. <tt class="docutils literal"><span class="pre">set_comment()</span></tt> will simply set
the comment that belongs to this torrent. The comment can be retrieved with the
<tt class="docutils literal"><span class="pre">comment()</span></tt> member.</p>
<p><tt class="docutils literal"><span class="pre">set_piece_size()</span></tt> will set the size of each piece in this torrent. The piece size must
be an even multiple of 2. i.e. usually something like 256 kiB, 512 kiB, 1024 kiB etc. The
size is given in number of bytes.</p>
<p><tt class="docutils literal"><span class="pre">set_creator()</span></tt> is an optional attribute that can be used to identify your application
that was used to create the torrent file.</p>
<p><tt class="docutils literal"><span class="pre">set_hash()</span></tt> writes the hash for the piece with the given piece-index. You have to call
this function for every piece in the torrent. Usually the <a class="reference" href="#hasher">hasher</a> is used to calculate
the sha1-hash for a piece.</p>
<p><tt class="docutils literal"><span class="pre">add_tracker()</span></tt> adds a tracker to the announce-list. The <tt class="docutils literal"><span class="pre">tier</span></tt> determines the order in
which the trackers are to be tried. For more iformation see <a class="reference" href="#trackers">trackers()</a>.</p>
<p><tt class="docutils literal"><span class="pre">add_file()</span></tt> adds a file to the torrent. The order in which you add files will determine
the order in which they are placed in the torrent file. You have to add at least one file
to the torrent. The <tt class="docutils literal"><span class="pre">path</span></tt> you give has to be a relative path from the root directory
of the torrent. The <tt class="docutils literal"><span class="pre">size</span></tt> is given in bytes.</p>
<p>When you have added all the files and hashes to your torrent, you can generate an <tt class="docutils literal"><span class="pre">entry</span></tt>
which then can be encoded as a .torrent file. You do this by calling <a class="reference" href="#create-torrent">create_torrent()</a>.</p>
<p>For a complete example of how to create a torrent from a file structure, see <a class="reference" href="#make-torrent">make_torrent</a>.</p>
</div>
<div class="section" id="create-torrent">
<h2><a name="create-torrent">create_torrent()</a></h2>
<blockquote>
<pre class="literal-block">
entry create_torrent();
</pre>
</blockquote>
<p>Returns an <tt class="docutils literal"><span class="pre">entry</span></tt> representing the bencoded tree of data that makes up a .torrent file.
You can save this data as a torrent file with bencode() (see <a class="reference" href="#bdecode-bencode">bdecode() bencode()</a>), for a
complete example, see <a class="reference" href="#make-torrent">make_torrent</a>.</p>
<p>This function is not const because it will also set the info-hash of the <tt class="docutils literal"><span class="pre">torrent_info</span></tt>
object.</p>
</div>
<div class="section" id="begin-files-end-files-rbegin-files-rend-files">
<h2><a name="begin-files-end-files-rbegin-files-rend-files">begin_files() end_files() rbegin_files() rend_files()</a></h2>
<blockquote>
<pre class="literal-block">
file_iterator begin_files() const;
file_iterator end_files() const;
reverse_file_iterator rbegin_files() const;
reverse_file_iterator rend_files() const;
</pre>
</blockquote>
<p>This class will need some explanation. First of all, to get a list of all files
in the torrent, you can use <tt class="docutils literal"><span class="pre">begin_files()</span></tt>, <tt class="docutils literal"><span class="pre">end_files()</span></tt>,
<tt class="docutils literal"><span class="pre">rbegin_files()</span></tt> and <tt class="docutils literal"><span class="pre">rend_files()</span></tt>. These will give you standard vector
iterators with the type <tt class="docutils literal"><span class="pre">file_entry</span></tt>.</p>
<p>The <tt class="docutils literal"><span class="pre">path</span></tt> is the full (relative) path of each file. i.e. if it is a multi-file
torrent, all the files starts with a directory with the same name as <tt class="docutils literal"><span class="pre">torrent_info::name()</span></tt>.</p>
<pre class="literal-block">
struct file_entry
{
boost::filesystem::path path;
size_type size;
};
</pre>
</div>
<div class="section" id="num-files-file-at">
<h2><a name="num-files-file-at">num_files() file_at()</a></h2>
<blockquote>
<pre class="literal-block">
int num_files() const;
file_entry const&amp; file_at(int index) const;
</pre>
</blockquote>
<p>If you need index-access to files you can use the <tt class="docutils literal"><span class="pre">num_files()</span></tt> and <tt class="docutils literal"><span class="pre">file_at()</span></tt>
to access files using indices.</p>
</div>
<div class="section" id="print">
<h2><a name="print">print()</a></h2>
<blockquote>
<pre class="literal-block">
void print(std::ostream&amp; os) const;
</pre>
</blockquote>
<p>The <tt class="docutils literal"><span class="pre">print()</span></tt> function is there for debug purposes only. It will print the info from
the torrent file to the given outstream.</p>
</div>
<div class="section" id="trackers">
<h2><a name="trackers">trackers()</a></h2>
<blockquote>
<pre class="literal-block">
std::vector&lt;announce_entry&gt; const&amp; trackers() const;
</pre>
</blockquote>
<p>The <tt class="docutils literal"><span class="pre">trackers()</span></tt> function will return a sorted vector of <tt class="docutils literal"><span class="pre">announce_entry</span></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 class="literal-block">
struct announce_entry
{
announce_entry(std::string const&amp; url);
std::string url;
int tier;
};
</pre>
</div>
<div class="section" id="total-size-piece-length-piece-size-num-pieces">
<h2><a name="total-size-piece-length-piece-size-num-pieces">total_size() piece_length() piece_size() num_pieces()</a></h2>
<blockquote>
<pre class="literal-block">
size_type total_size() const;
size_type piece_length() const;
size_type piece_size(unsigned int index) const;
int num_pieces() const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">total_size()</span></tt>, <tt class="docutils literal"><span class="pre">piece_length()</span></tt> and <tt class="docutils literal"><span class="pre">num_pieces()</span></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 class="docutils literal"><span class="pre">piece_size()</span></tt> and <tt class="docutils literal"><span class="pre">piece_length()</span></tt> is that <tt class="docutils literal"><span class="pre">piece_size()</span></tt> takes
the piece index as argument and gives you the exact size of that piece. It will always
be the same as <tt class="docutils literal"><span class="pre">piece_length()</span></tt> except in the case of the last piece, which may
be smaller.</p>
</div>
<div class="section" id="hash-for-piece-info-hash">
<h2><a name="hash-for-piece-info-hash">hash_for_piece() info_hash()</a></h2>
<blockquote>
<pre class="literal-block">
size_type piece_size(unsigned int index) const;
sha1_hash const&amp; hash_for_piece(unsigned int index) const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">hash_for_piece()</span></tt> takes a piece-index and returns the 20-bytes sha1-hash for that
piece and <tt class="docutils literal"><span class="pre">info_hash()</span></tt> returns the 20-bytes sha1-hash for the info-section of the
torrent file. For more information on the <tt class="docutils literal"><span class="pre">sha1_hash</span></tt>, see the <a class="reference" href="#big-number">big_number</a> class.</p>
</div>
<div class="section" id="name-comment-creation-date">
<h2><a name="name-comment-creation-date">name() comment() creation_date()</a></h2>
<blockquote>
<pre class="literal-block">
std::string const&amp; name() const;
std::string const&amp; comment() const;
boost::optional&lt;boost::posix_time::ptime&gt; creation_date() const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">name()</span></tt> returns the name of the torrent.</p>
<p><tt class="docutils literal"><span class="pre">comment()</span></tt> returns the comment associated with the torrent. If there's no comment,
it will return an empty string. <tt class="docutils literal"><span class="pre">creation_date()</span></tt> returns a <a class="reference" href="http://www.boost.org/libs/date_time/doc/class_ptime.html">boost::posix_time::ptime</a>
object, representing the time when this torrent file was created. If there's no timestamp
in the torrent file, this will return a date of january 1:st 1970.</p>
</div>
</div>
<div class="section" id="torrent-handle">
<h1><a name="torrent-handle">torrent_handle</a></h1>
<p>You will usually have to store your torrent handles somewhere, since it's the
object through which you retrieve infromation about the torrent and aborts the torrent.
Its declaration looks like this:</p>
<pre class="literal-block">
struct torrent_handle
{
torrent_handle();
torrent_status status();
void get_download_queue(std::vector&lt;partial_piece_info&gt;&amp; queue);
void get_peer_info(std::vector&lt;peer_info&gt;&amp; v);
torrent_info const&amp; get_torrent_info();
bool is_valid();
entry write_resume_data();
std::vector&lt;char&gt; const&amp; metadata() const;
void force_reannounce();
void connect_peer(address const&amp; adr) const;
void set_tracker_login(std::string const&amp; username, std::string const&amp; password);
std::vector&lt;announce_entry&gt; const&amp; trackers() const;
void replace_trackers(std::vector&lt;announce_entry&gt; const&amp;);
void set_ratio(float ratio);
void set_max_uploads(int max_uploads);
void set_max_connections(int max_connections);
void set_upload_limit(int limit);
void set_download_limit(int limit);
void use_interface(char const* net_interface);
void pause();
void resume();
bool is_paused() const;
bool is_seed() const;
void filter_piece(int index, bool filter);
void filter_pieces(std::vector&lt;bool&gt; const&amp; bitmask);
bool is_piece_filtered(int index) const;
std::vector&lt;bool&gt; filtered_pieces() const;
void filter_files(std::vector&lt;bool&gt; const&amp; files);
bool has_metadata() const;
boost::filsystem::path save_path() const;
bool move_storage(boost::filesystem::path const&amp; save_path);
sha1_hash info_hash() const;
bool operator==(torrent_handle const&amp;) const;
bool operator!=(torrent_handle const&amp;) const;
bool operator&lt;(torrent_handle const&amp;) const;
};
</pre>
<p>The default constructor will initialize the handle to an invalid state. Which means you cannot
perform any operation on it, unless you first assign it a valid handle. If you try to perform
any operation on an uninitialized handle, it will throw <tt class="docutils literal"><span class="pre">invalid_handle</span></tt>.</p>
<p><strong>TODO: document trackers() and replace_trackers()</strong></p>
<p><strong>TODO: document filter_piece(), filter_pieces(), is_piece_filtered(), filtered_pieces() and filter_files()</strong></p>
<div class="section" id="save-path">
<h2><a name="save-path">save_path()</a></h2>
<blockquote>
<pre class="literal-block">
boost::filsystem::path save_path() const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">save_path()</span></tt> returns the path that was given to <a class="reference" href="#add-torrent">add_torrent()</a> when this torrent
was started.</p>
</div>
<div class="section" id="move-storage">
<h2><a name="move-storage">move_storage()</a></h2>
<blockquote>
<pre class="literal-block">
bool move_storage(boost::filsystem::path const&amp; save_path);
</pre>
</blockquote>
<p>Moves the file(s) that this torrent are currently seeding from or downloading to. This
operation will only have the desired effect if the given <tt class="docutils literal"><span class="pre">save_path</span></tt> is located on
the same drive as the original save path. If the move operation fails, this function
returns false, otherwise true. Post condition for successful operation is:
<tt class="docutils literal"><span class="pre">save_path()</span> <span class="pre">==</span> <span class="pre">save_path</span></tt>.</p>
</div>
<div class="section" id="force-reannounce">
<h2><a name="force-reannounce">force_reannounce()</a></h2>
<blockquote>
<pre class="literal-block">
void force_reannounce();
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">force_reannounce()</span></tt> will force this torrent to do another tracker request, to receive new
peers. If the torrent is invalid, queued or in checking mode, this functions will throw
<a class="reference" href="#invalid-handle">invalid_handle</a>.</p>
</div>
<div class="section" id="connect-peer">
<h2><a name="connect-peer">connect_peer()</a></h2>
<blockquote>
<pre class="literal-block">
void connect_peer(address const&amp; adr) const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">connect_peer()</span></tt> is a way to manually connect to peers that one believe is a part of the
torrent. If the peer does not respond, or is not a member of this torrent, it will simply
be disconnected. No harm can be done by using this other than an unnecessary connection
attempt is made. If the torrent is uninitialized or in queued or checking mode, this
will throw <a class="reference" href="#invalid-handle">invalid_handle</a>.</p>
</div>
<div class="section" id="set-ratio">
<h2><a name="set-ratio">set_ratio()</a></h2>
<blockquote>
<pre class="literal-block">
void set_ratio(float ratio);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">set_ratio()</span></tt> sets the desired download / upload ratio. If set to 0, it is considered being
infinite. i.e. the client will always upload as much as it can, no matter how much it gets back
in return. With this setting it will work much like the standard clients.</p>
<p>Besides 0, the ratio can be set to any number greater than or equal to 1. It means how much to
attempt to upload in return for each download. e.g. if set to 2, the client will try to upload
2 bytes for every byte received. The default setting for this is 0, which will make it work
as a standard client.</p>
</div>
<div class="section" id="set-upload-limit-set-download-limit">
<h2><a name="set-upload-limit-set-download-limit">set_upload_limit() set_download_limit()</a></h2>
<blockquote>
<pre class="literal-block">
void set_upload_limit(int limit);
void set_download_limit(int limit);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">set_upload_limit</span></tt> will limit the upload bandwidth used by this particular torrent to the
limit you set. It is given as the number of bytes per second the torrent is allowed to upload.
<tt class="docutils literal"><span class="pre">set_download_limit</span></tt> works the same way but for download bandwidth instead of upload bandwidth.
Note that setting a higher limit on a torrent then the global limit (<tt class="docutils literal"><span class="pre">session::set_upload_rate_limit</span></tt>)
will not override the global rate limit. The torrent can never upload more than the global rate
limit.</p>
</div>
<div class="section" id="pause-resume-is-paused">
<h2><a name="pause-resume-is-paused">pause() resume() is_paused()</a></h2>
<blockquote>
<pre class="literal-block">
void pause();
void resume();
bool is_paused() const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">pause()</span></tt>, and <tt class="docutils literal"><span class="pre">resume()</span></tt> will disconnect all peers and reconnect all peers respectively.
When a torrent is paused, it will however remember all share ratios to all peers and remember
all potential (not connected) peers. You can use <tt class="docutils literal"><span class="pre">is_paused()</span></tt> to determine if a torrent
is currently paused. Torrents may be paused automatically if there is a file error (eg. disk full)
or something similar. See <a class="reference" href="#file-error-alert">file_error_alert</a>.</p>
</div>
<div class="section" id="is-seed">
<h2><a name="is-seed">is_seed()</a></h2>
<blockquote>
<pre class="literal-block">
bool is_seed() const;
</pre>
</blockquote>
<p>Returns true if the torrent is in seed mode (i.e. if it has finished downloading).</p>
</div>
<div class="section" id="has-metadata">
<h2><a name="has-metadata">has_metadata()</a></h2>
<blockquote>
<pre class="literal-block">
bool has_metadata() const;
</pre>
</blockquote>
<p>Returns true if this torrent has metadata (either it was started from a .torrent file or the
metadata has been downloaded). The only scenario where this can return false is when the torrent
was started torrent-less (i.e. with just an info-hash and tracker ip). Note that if the torrent
doesn't have metadata, the member <a class="reference" href="#get-torrent-info">get_torrent_info()</a> will throw.</p>
</div>
<div class="section" id="set-tracker-login">
<h2><a name="set-tracker-login">set_tracker_login()</a></h2>
<blockquote>
<pre class="literal-block">
void set_tracker_login(std::string const&amp; username, std::string const&amp; password);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">set_tracker_login()</span></tt> sets a username and password that will be sent along in the HTTP-request
of the tracker announce. Set this if the tracker requires authorization.</p>
</div>
<div class="section" id="use-interface">
<h2><a name="use-interface">use_interface()</a></h2>
<blockquote>
<pre class="literal-block">
void use_interface(char const* net_interface);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">use_interface()</span></tt> sets the network interface this torrent will use when it opens outgoing
connections. By default, it uses the same interface as the <a class="reference" href="#session">session</a> uses to listen on. The
parameter can be a string containing an ip-address or a hostname.</p>
</div>
<div class="section" id="info-hash">
<h2><a name="info-hash">info_hash()</a></h2>
<blockquote>
<pre class="literal-block">
sha1_hash info_hash() const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">info_hash()</span></tt> returns the info-hash for the torrent.</p>
</div>
<div class="section" id="id11">
<h2><a name="id11">set_max_uploads() set_max_connections()</a></h2>
<blockquote>
<pre class="literal-block">
void set_max_uploads(int max_uploads);
void set_max_connections(int max_connections);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">set_max_uploads()</span></tt> sets the maximum number of peers that's unchoked at the same time on this
torrent. If you set this to -1, there will be no limit.</p>
<p><tt class="docutils literal"><span class="pre">set_max_connections()</span></tt> sets the maximum number of connection this torrent will open. If all
connections are used up, incoming connections may be refused or poor connections may be closed.
This must be at least 2. The default is unlimited number of connections. If -1 is given to the
function, it means unlimited.</p>
</div>
<div class="section" id="write-resume-data">
<h2><a name="write-resume-data">write_resume_data()</a></h2>
<blockquote>
<pre class="literal-block">
entry write_resume_data();
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">write_resume_data()</span></tt> generates fast-resume data and returns it as an <a class="reference" href="#entry">entry</a>. This <a class="reference" href="#entry">entry</a>
is suitable for being bencoded. For more information about how fast-resume works, see <a class="reference" href="#fast-resume">fast resume</a>.</p>
<p>There are three cases where this function will just return an empty <tt class="docutils literal"><span class="pre">entry</span></tt>:</p>
<blockquote>
<ol class="arabic simple">
<li>The torrent handle is invalid.</li>
<li>The torrent is checking (or is queued for checking) its storage, it will obviously
not be ready to write resume data.</li>
<li>The torrent hasn't received valid metadata and was started without metadata
(see libtorrent's <a class="reference" href="#metadata-from-peers">metadata from peers</a> extension)</li>
</ol>
</blockquote>
<p>Note that by the time this function returns, the resume data may already be invalid if the torrent
is still downloading! The recommended practice is to first pause the torrent, then generate the
fast resume data, and then close it down.</p>
</div>
<div class="section" id="metadata">
<h2><a name="metadata">metadata()</a></h2>
<blockquote>
<pre class="literal-block">
std::vector&lt;char&gt; const&amp; metadata() const;
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">metadata()</span></tt> will return a reference to a buffer containing the exact info part of the
.torrent file. This buffer will be valid as long as the torrent is still running. When hashed,
it will produce the same hash as the info-hash.</p>
</div>
<div class="section" id="id12">
<h2><a name="id12">status()</a></h2>
<blockquote>
<pre class="literal-block">
torrent_status status();
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">status()</span></tt> will return a structure with information about the status of this
torrent. If the <a class="reference" href="#torrent-handle">torrent_handle</a> is invalid, it will throw <a class="reference" href="#invalid-handle">invalid_handle</a> exception.
See <a class="reference" href="#torrent-status">torrent_status</a>.</p>
</div>
<div class="section" id="get-download-queue">
<h2><a name="get-download-queue">get_download_queue()</a></h2>
<blockquote>
<pre class="literal-block">
void get_download_queue(std::vector&lt;partial_piece_info&gt;&amp; queue);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">get_download_queue()</span></tt> takes a non-const reference to a vector which it will fill with
information about pieces that are partially downloaded or not downloaded at all but partially
requested. The entry in the vector (<tt class="docutils literal"><span class="pre">partial_piece_info</span></tt>) looks like this:</p>
<pre class="literal-block">
struct partial_piece_info
{
enum { max_blocks_per_piece };
int piece_index;
int blocks_in_piece;
std::bitset&lt;max_blocks_per_piece&gt; requested_blocks;
std::bitset&lt;max_blocks_per_piece&gt; finished_blocks;
peer_id peer[max_blocks_per_piece];
int num_downloads[max_blocks_per_piece];
};
</pre>
<p><tt class="docutils literal"><span class="pre">piece_index</span></tt> is the index of the piece in question. <tt class="docutils literal"><span class="pre">blocks_in_piece</span></tt> is the
number of blocks in this particular piece. This number will be the same for most pieces, but
the last piece may have fewer blocks than the standard pieces.</p>
<p><tt class="docutils literal"><span class="pre">requested_blocks</span></tt> is a bitset with one bit per block in the piece. If a bit is set, it
means that that block has been requested, but not necessarily fully downloaded yet. To know
from whom the block has been requested, have a look in the <tt class="docutils literal"><span class="pre">peer</span></tt> array. The bit-index
in the <tt class="docutils literal"><span class="pre">requested_blocks</span></tt> and <tt class="docutils literal"><span class="pre">finished_blocks</span></tt> correspons to the array-index into
<tt class="docutils literal"><span class="pre">peers</span></tt> and <tt class="docutils literal"><span class="pre">num_downloads</span></tt>. The array of peers is contains the id of the
peer the piece was requested from. If a piece hasn't been requested (the bit in
<tt class="docutils literal"><span class="pre">requested_blocks</span></tt> is not set) the peer array entry will be undefined.</p>
<p>The <tt class="docutils literal"><span class="pre">finished_blocks</span></tt> is a bitset where each bit says if the block is fully downloaded
or not. And the <tt class="docutils literal"><span class="pre">num_downloads</span></tt> array says how many times that block has been downloaded.
When a piece fails a hash verification, single blocks may be redownloaded to see if the hash teast
may pass then.</p>
</div>
<div class="section" id="get-peer-info">
<h2><a name="get-peer-info">get_peer_info()</a></h2>
<blockquote>
<pre class="literal-block">
void get_peer_info(std::vector&lt;peer_info&gt;&amp;);
</pre>
</blockquote>
<p><tt class="docutils literal"><span class="pre">get_peer_info()</span></tt> takes a reference to a vector that will be cleared and filled
with one entry for each peer connected to this torrent, given the handle is valid. If the
<a class="reference" href="#torrent-handle">torrent_handle</a> is invalid, it will throw <a class="reference" href="#invalid-handle">invalid_handle</a> exception. Each entry in
the vector contains information about that particular peer. See <a class="reference" href="#peer-info">peer_info</a>.</p>
</div>
<div class="section" id="get-torrent-info">
<h2><a name="get-torrent-info">get_torrent_info()</a></h2>
<blockquote>
<pre class="literal-block">
torrent_info const&amp; get_torrent_info();
</pre>
</blockquote>
<p>Returns a const reference to the <a class="reference" href="#torrent-info">torrent_info</a> object associated with this torrent.
This reference is valid as long as the <a class="reference" href="#torrent-handle">torrent_handle</a> is valid, no longer. If the
<a class="reference" href="#torrent-handle">torrent_handle</a> is invalid or if it doesn't have any metadata, <a class="reference" href="#invalid-handle">invalid_handle</a>
exception will be thrown. The torrent may be in a state without metadata only if
it was started without a .torrent file, i.e. by using the libtorrent extension of
just supplying a tracker and info-hash.</p>
</div>
<div class="section" id="is-valid">
<h2><a name="is-valid">is_valid()</a></h2>
<blockquote>
<pre class="literal-block">
bool is_valid() const;
</pre>
</blockquote>
<p>Returns true if this handle refers to a valid torrent and false if it hasn't been initialized
or if the torrent it refers to has been aborted. Note that a handle may become invalid after
it has been added to the session. Usually this is because the storage for the torrent is
somehow invalid or if the filenames are not allowed (and hence cannot be opened/created) on
your filesystem. If such an error occurs, a <a class="reference" href="#file-error-alert">file_error_alert</a> is generated and all handles
that refers to that torrent will become invalid.</p>
</div>
</div>
<div class="section" id="torrent-status">
<h1><a name="torrent-status">torrent_status</a></h1>
<p>It contains the following fields:</p>
<pre class="literal-block">
struct torrent_status
{
enum state_t
{
queued_for_checking,
checking_files,
connecting_to_tracker,
downloading,
finished,
seeding
};
state_t state;
bool paused;
float progress;
boost::posix_time::time_duration next_announce;
boost::posix_time::time_duration announce_interval;
std::string current_tracker;
size_type total_download;
size_type total_upload;
size_type total_payload_download;
size_type total_payload_upload;
size_type total_failed_bytes;
float download_rate;
float upload_rate;
float download_payload_rate;
float upload_payload_rate;
int num_peers;
int num_complete;
int num_incomplete;
const std::vector&lt;bool&gt;* pieces;
size_type total_done;
size_type total_wanted_done;
size_type total_wanted;
int num_seeds;
float distributed_copies;
int block_size;
};
</pre>
<p><tt class="docutils literal"><span class="pre">progress</span></tt> is a value in the range [0, 1], that represents the progress of the
torrent's current task. It may be checking files or downloading. The torrent's
current task is in the <tt class="docutils literal"><span class="pre">state</span></tt> member, it will be one of the following:</p>
<table border="1" class="docutils">
<colgroup>
<col width="31%" />
<col width="69%" />
</colgroup>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">queued_for_checking</span></tt></td>
<td>The torrent is in the queue for being checked. But there
currently is another torrent that are being checked.
This torrent will wait for its turn.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">checking_files</span></tt></td>
<td>The torrent has not started its download yet, and is
currently checking existing files.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">connecting_to_tracker</span></tt></td>
<td>The torrent has sent a request to the tracker and is
currently waiting for a response</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">downloading</span></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 class="docutils literal"><span class="pre">finished</span></tt></td>
<td>In this state the torrent has finished downloading but
still doesn't have the entire torrent. i.e. some pieces
are filtered and won't get downloaded.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">seeding</span></tt></td>
<td>In this state the torrent has finished downloading and
is a pure seeder.</td>
</tr>
</tbody>
</table>
<p>When downloading, the progress is <tt class="docutils literal"><span class="pre">total_wanted_done</span></tt> / <tt class="docutils literal"><span class="pre">total_wanted</span></tt>.</p>
<p><tt class="docutils literal"><span class="pre">paused</span></tt> is set to true if the torrent is paused and false otherwise.</p>
<p><tt class="docutils literal"><span class="pre">next_announce</span></tt> is the time until the torrent will announce itself to the tracker. And
<tt class="docutils literal"><span class="pre">announce_interval</span></tt> is the time the tracker want us to wait until we announce ourself
again the next time.</p>
<p><tt class="docutils literal"><span class="pre">current_tracker</span></tt> is the URL of the last working tracker. If no tracker request has
been successful yet, it's set to an empty string.</p>
<p><tt class="docutils literal"><span class="pre">total_download</span></tt> and <tt class="docutils literal"><span class="pre">total_upload</span></tt> is the number of bytes downloaded and
uploaded to all peers, accumulated, <em>this session</em> only.</p>
<p><tt class="docutils literal"><span class="pre">total_payload_download</span></tt> and <tt class="docutils literal"><span class="pre">total_payload_upload</span></tt> counts the amount of bytes
send and received this session, but only the actual oayload data (i.e the interesting
data), these counters ignore any protocol overhead.</p>
<p><tt class="docutils literal"><span class="pre">total_failed_bytes</span></tt> is the number of bytes that has been downloaded and that
has failed the piece hash test. In other words, this is just how much crap that
has been downloaded.</p>
<p><tt class="docutils literal"><span class="pre">pieces</span></tt> is the bitmask that represents which pieces we have (set to true) and
the pieces we don't have. It's a pointer and may be set to 0 if the torrent isn't
downloading or seeding.</p>
<p><tt class="docutils literal"><span class="pre">download_rate</span></tt> and <tt class="docutils literal"><span class="pre">upload_rate</span></tt> are the total rates for all peers for this
torrent. These will usually have better precision than summing the rates from
all peers. The rates are given as the number of bytes per second. The
<tt class="docutils literal"><span class="pre">download_payload_rate</span></tt> and <tt class="docutils literal"><span class="pre">upload_payload_rate</span></tt> respectively is the
total transfer rate of payload only, not counting protocol chatter. This might
be slightly smaller than the other rates, but if projected over a long time
(e.g. when calculating ETA:s) the difference may be noticable.</p>
<p><tt class="docutils literal"><span class="pre">num_peers</span></tt> is the number of peers this torrent currently is connected to.</p>
<p><tt class="docutils literal"><span class="pre">num_complete</span></tt> and <tt class="docutils literal"><span class="pre">num_incomplete</span></tt> are set to -1 if the tracker did not
send any scrape data in its announce reply. This data is optional and may
not be available from all trackers. If these are not -1, they are the total
number of peers that are seeding (complete) and the total number of peers
that are still downloading (incomplete) this torrent.</p>
<p><tt class="docutils literal"><span class="pre">total_done</span></tt> is the total number of bytes of the file(s) that we have. All
this does not necessarily has to be downloaded during this session (that's
<tt class="docutils literal"><span class="pre">total_download_payload</span></tt>).</p>
<p><tt class="docutils literal"><span class="pre">total_wanted_done</span></tt> is the number of bytes we have downloadd, only counting the
pieces that we actually want to download. i.e. excluding any pieces that we have but
are filtered as not wanted.</p>
<p><tt class="docutils literal"><span class="pre">total_wanted</span></tt> is the total number of bytes we want to download. This is also
excluding pieces that have been filtered.</p>
<p><tt class="docutils literal"><span class="pre">num_seeds</span></tt> is the number of peers that are seeding that this client is
currently connected to.</p>
<p><tt class="docutils literal"><span class="pre">distributed_copies</span></tt> is the number of distributed copies of the torrent.
Note that one copy may be spread out among many peers. The integer part
tells how many copies there are currently of the rarest piece(s) among the
peers this client is connected to. The fractional part tells the share of
pieces that have more copies than the rarest piece(s). For example: 2.5 would
mean that the rarest pieces have only 2 copies among the peers this torrent is
connected to, and that 50% of all the pieces have more than two copies.</p>
<p><tt class="docutils literal"><span class="pre">block_size</span></tt> is the size of a block, in bytes. A block is a sub piece, it
is the number of bytes that each piece request asks for and the number of
bytes that each bit in the <tt class="docutils literal"><span class="pre">partial_piece_info</span></tt>'s bitset represents
(see <a class="reference" href="#get-download-queue">get_download_queue()</a>). This is typically 16 kB, but it may be
larger if the pieces are larger.</p>
</div>
<div class="section" id="peer-info">
<h1><a name="peer-info">peer_info</a></h1>
<p>It contains the following fields:</p>
<pre class="literal-block">
struct peer_info
{
enum
{
interesting = 0x1,
choked = 0x2,
remote_interested = 0x4,
remote_choked = 0x8,
supports_extensions = 0x10,
local_connection = 0x20
};
unsigned int flags;
address ip;
float up_speed;
float down_speed;
float payload_up_speed;
float payload_down_speed;
size_type total_download;
size_type total_upload;
peer_id id;
std::vector&lt;bool&gt; pieces;
bool seed;
int upload_limit;
int upload_ceiling;
size_type load_balancing;
int download_queue_length;
int upload_queue_length;
int downloading_piece_index;
int downloading_block_index;
int downloading_progress;
int downloading_total;
};
</pre>
<p>The <tt class="docutils literal"><span class="pre">flags</span></tt> attribute tells you in which state the peer is. It is set to
any combination of the enums above. The following table describes each flag:</p>
<table border="1" class="docutils">
<colgroup>
<col width="31%" />
<col width="69%" />
</colgroup>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">interesting</span></tt></td>
<td><strong>we</strong> are interested in pieces from this peer.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">choked</span></tt></td>
<td><strong>we</strong> have choked this peer.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">remote_interested</span></tt></td>
<td>the peer is interested in <strong>us</strong></td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">remote_choked</span></tt></td>
<td>the peer has choked <strong>us</strong>.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">support_extensions</span></tt></td>
<td>means that this peer supports the
<a class="reference" href="http://nolar.com/azureus/extended.htm">extension protocol</a>.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">local_connection</span></tt></td>
<td>The connection was initiated by us, the peer has a
listen port open, and that port is the same as in the
<a class="reference" href="#address">address</a> of this peer. If this flag is not set, this
peer connection was opened by this peer connecting to
us.</td>
</tr>
</tbody>
</table>
<p>The <tt class="docutils literal"><span class="pre">ip</span></tt> field is the IP-address to this peer. Its type is a wrapper around the
actual address and the port number. See <a class="reference" href="#address">address</a> class.</p>
<p><tt class="docutils literal"><span class="pre">up_speed</span></tt> and <tt class="docutils literal"><span class="pre">down_speed</span></tt> contains the current upload and download speed
we have to and from this peer (including any protocol messages). The transfer rates
of payload data only are found in <tt class="docutils literal"><span class="pre">payload_up_speed</span></tt> and <tt class="docutils literal"><span class="pre">payload_down_speed</span></tt>.
These figures are updated aproximately once every second.</p>
<p><tt class="docutils literal"><span class="pre">total_download</span></tt> and <tt class="docutils literal"><span class="pre">total_upload</span></tt> are the total number of bytes downloaded
from and uploaded to this peer. These numbers do not include the protocol chatter, but only
the payload data.</p>
<p><tt class="docutils literal"><span class="pre">id</span></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. See identify_client()_</p>
<p><tt class="docutils literal"><span class="pre">pieces</span></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>
<p><tt class="docutils literal"><span class="pre">seed</span></tt> is true if this peer is a seed.</p>
<p><tt class="docutils literal"><span class="pre">upload_limit</span></tt> is the number of bytes per second we are allowed to send to this
peer every second. It may be -1 if there's no limit. The upload limits of all peers
should sum up to the upload limit set by <tt class="docutils literal"><span class="pre">session::set_upload_limit</span></tt>.</p>
<p><tt class="docutils literal"><span class="pre">upload_ceiling</span></tt> is the current maximum allowed upload rate given the cownload
rate and share ratio. If the global upload rate is inlimited, the <tt class="docutils literal"><span class="pre">upload_limit</span></tt>
for every peer will be the same as their <tt class="docutils literal"><span class="pre">upload_ceiling</span></tt>.</p>
<p><tt class="docutils literal"><span class="pre">load_balancing</span></tt> is a measurment of the balancing of free download (that we get)
and free upload that we give. Every peer gets a certain amount of free upload, but
this member says how much <em>extra</em> free upload this peer has got. If it is a negative
number it means that this was a peer from which we have got this amount of free
download.</p>
<p><tt class="docutils literal"><span class="pre">download_queue_length</span></tt> is the number of piece-requests we have sent to this peer
that hasn't been answered with a piece yet.</p>
<p><tt class="docutils literal"><span class="pre">upload_queue_length</span></tt> is the number of piece-requests we have received from this peer
that we haven't answered with a piece yet.</p>
<p>You can know which piece, and which part of that piece, that is currently being
downloaded from a specific peer by looking at the next four members.
<tt class="docutils literal"><span class="pre">downloading_piece_index</span></tt> is the index of the piece that is currently being downloaded.
This may be set to -1 if there's currently no piece downloading from this peer. If it is
&gt;= 0, the other three members are valid. <tt class="docutils literal"><span class="pre">downloading_block_index</span></tt> is the index of the
block (or sub-piece) that is being downloaded. <tt class="docutils literal"><span class="pre">downloading_progress</span></tt> is the number
of bytes of this block we have received from the peer, and <tt class="docutils literal"><span class="pre">downloading_total</span></tt> is
the total number of bytes in this block.</p>
</div>
<div class="section" id="address">
<h1><a name="address">address</a></h1>
<p>The <tt class="docutils literal"><span class="pre">address</span></tt> class represents a name of a network endpoint (usually referred to as
IP-address) and a port number. This is the same thing as a <tt class="docutils literal"><span class="pre">sockaddr_in</span></tt> would contain.
Its declaration looks like this:</p>
<pre class="literal-block">
class address
{
public:
address();
address(unsigned char a
, unsigned char b
, unsigned char c
, unsigned char d
, unsigned short port);
address(unsigned int addr, unsigned short port);
address(const std::string&amp; addr, unsigned short port);
address(const address&amp; a);
~address();
std::string as_string() const;
unsigned int ip() const;
unsigned short port() const;
bool operator&lt;(const address&amp; a) const;
bool operator!=(const address&amp; a) const;
bool operator==(const address&amp; a) const;
};
</pre>
<p>It is less-than comparable to make it possible to use it as a key in a map. <tt class="docutils literal"><span class="pre">as_string()</span></tt> may block
while it does the DNS lookup, it returns a string that points to the address represented by the object.</p>
<p><tt class="docutils literal"><span class="pre">ip()</span></tt> will return the 32-bit ip-address as an integer. <tt class="docutils literal"><span class="pre">port()</span></tt> returns the port number.</p>
</div>
<div class="section" id="http-settings">
<h1><a name="http-settings">http_settings</a></h1>
<p>You have some control over tracker requests through the <tt class="docutils literal"><span class="pre">http_settings</span></tt> object. You
create it and fill it with your settings and then use <tt class="docutils literal"><span class="pre">session::set_http_settings()</span></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 class="literal-block">
struct http_settings
{
http_settings();
std::string proxy_ip;
int proxy_port;
std::string proxy_login;
std::string proxy_password;
std::string user_agent;
int tracker_timeout;
int tracker_maximum_response_length;
};
</pre>
<p><tt class="docutils literal"><span class="pre">proxy_ip</span></tt> may be a hostname or ip to a http proxy to use. If this is
an empty string, no http proxy will be used.</p>
<p><tt class="docutils literal"><span class="pre">proxy_port</span></tt> is the port on which the http proxy listens. If <tt class="docutils literal"><span class="pre">proxy_ip</span></tt>
is empty, this will be ignored.</p>
<p><tt class="docutils literal"><span class="pre">proxy_login</span></tt> should be the login username for the http proxy, if this
empty, the http proxy will be tried to be used without authentication.</p>
<p><tt class="docutils literal"><span class="pre">proxy_password</span></tt> the password string for the http proxy.</p>
<p><tt class="docutils literal"><span class="pre">user_agent</span></tt> this is the client identification to the tracker. It will
be followed by the string &quot;(libtorrent)&quot; to identify that this library
is being used. This should be set to your client's name and version number.</p>
<p><tt class="docutils literal"><span class="pre">tracker_timeout</span></tt> is the number of seconds the tracker connection will
wait until it considers the tracker to have timed-out. Default value is 10
seconds.</p>
<p><tt class="docutils literal"><span class="pre">tracker_maximum_response_length</span></tt> is the maximum number of bytes in a
tracker response. If a response size passes this number it will be rejected
and the connection will be closed. On gzipped responses this size is measured
on the uncompressed data. So, if you get 20 bytes of gzip response that'll
expand to 2 megs, it will be interrupted before the entire response has been
uncompressed (given your limit is lower than 2 megs). Default limit is
1 megabyte.</p>
</div>
<div class="section" id="ip-filter">
<h1><a name="ip-filter">ip_filter</a></h1>
<p>The <tt class="docutils literal"><span class="pre">ip_filter</span></tt> class is a set of rules that uniquely categorizes all
ip addresses as allowed or disallowed. The default constructor creates
a single rule that allowes all addresses (0.0.0.0 - 255.255.255.255).</p>
<blockquote>
<pre class="literal-block">
class ip_filter
{
public:
enum access_flags { blocked = 1 };
ip_filter();
void add_rule(address first, address last, int flags);
int access(address const&amp; addr) const;
struct ip_range
{
address first;
address last;
int flags;
};
std::vector&lt;ip_range&gt; export_filter() const;
};
</pre>
</blockquote>
<div class="section" id="id14">
<h2><a name="id14">ip_filter()</a></h2>
<blockquote>
<pre class="literal-block">
ip_filter()
</pre>
</blockquote>
<p>Creates a default filter that doesn't filter any address.</p>
<p>postcondition:
<tt class="docutils literal"><span class="pre">access(x)</span> <span class="pre">==</span> <span class="pre">0</span></tt> for every <tt class="docutils literal"><span class="pre">x</span></tt></p>
</div>
<div class="section" id="add-rule">
<h2><a name="add-rule">add_rule()</a></h2>
<blockquote>
<pre class="literal-block">
void add_rule(address first, address last, int flags);
</pre>
</blockquote>
<p>Adds a rule to the filter. <tt class="docutils literal"><span class="pre">first</span></tt> and <tt class="docutils literal"><span class="pre">last</span></tt> defines a range of
ip addresses that will be marked with the given flags. The <tt class="docutils literal"><span class="pre">flags</span></tt>
can currenly be 0, which means allowed, or <tt class="docutils literal"><span class="pre">ip_filter::blocked</span></tt>, which
means disallowed.</p>
<p>postcondition:
<tt class="docutils literal"><span class="pre">access(x)</span> <span class="pre">==</span> <span class="pre">flags</span></tt> for every <tt class="docutils literal"><span class="pre">x</span></tt> in the range [<tt class="docutils literal"><span class="pre">first</span></tt>, <tt class="docutils literal"><span class="pre">last</span></tt>]</p>
<p>This means that in a case of overlapping ranges, the last one applied takes
precedence.</p>
</div>
<div class="section" id="access">
<h2><a name="access">access()</a></h2>
<blockquote>
<pre class="literal-block">
int access(address const&amp; addr) const;
</pre>
</blockquote>
<p>Returns the access permissions for the given address (<tt class="docutils literal"><span class="pre">addr</span></tt>). The permission
can currently be 0 or <tt class="docutils literal"><span class="pre">ip_filter::blocked</span></tt>. The complexity of this operation
is O(<tt class="docutils literal"><span class="pre">log</span></tt> n), where n is the minimum number of non-overlapping ranges to describe
the current filter.</p>
</div>
<div class="section" id="export-filter">
<h2><a name="export-filter">export_filter()</a></h2>
<blockquote>
<pre class="literal-block">
std::vector&lt;ip_range&gt; export_filter() const;
</pre>
</blockquote>
<p>This function will return the current state of the filter in the minimum number of
ranges possible. They are sorted from ranges in low addresses to high addresses. Each
entry in the returned vector is a range with the access control specified in its
<tt class="docutils literal"><span class="pre">flags</span></tt> field.</p>
</div>
</div>
<div class="section" id="big-number">
<h1><a name="big-number">big_number</a></h1>
<p>Both the <tt class="docutils literal"><span class="pre">peer_id</span></tt> and <tt class="docutils literal"><span class="pre">sha1_hash</span></tt> types are typedefs of the class
<tt class="docutils literal"><span class="pre">big_number</span></tt>. It represents 20 bytes of data. Its synopsis follows:</p>
<pre class="literal-block">
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>
</div>
<div class="section" id="hasher">
<h1><a name="hasher">hasher</a></h1>
<p>This class creates sha1-hashes. Its declaration looks like this:</p>
<pre class="literal-block">
class hasher
{
public:
hasher();
void update(const char* data, unsigned int len);
sha1_hash final();
void reset();
};
</pre>
<p>You use it by first instantiating it, then call <tt class="docutils literal"><span class="pre">update()</span></tt> to feed it
with data. i.e. you don't have to keep the entire buffer of which you want to
create the hash in memory. You can feed the hasher parts of it at a time. When
You have fed the hasher with all the data, you call <tt class="docutils literal"><span class="pre">final()</span></tt> and it
will return the sha1-hash of the data.</p>
<p>If you want to reuse the hasher object once you have created a hash, you have to
call <tt class="docutils literal"><span class="pre">reset()</span></tt> to reinitialize it.</p>
<p>The sha1-algorithm used was implemented by Steve Reid and released as public domain.
For more info, see <tt class="docutils literal"><span class="pre">src/sha1.cpp</span></tt>.</p>
</div>
<div class="section" id="fingerprint">
<h1><a name="fingerprint">fingerprint</a></h1>
<p>The fingerprint class represents information about a client and its version. It is used
to encode this information into the client's peer id.</p>
<p>This is the class declaration:</p>
<pre class="literal-block">
struct fingerprint
{
fingerprint(const char* id_string, int major, int minor, int revision, int tag);
std::string to_string() const;
char id[2];
char major_version;
char minor_version;
char revision_version;
char tag_version;
};
</pre>
<p>The constructor takes a <tt class="docutils literal"><span class="pre">char</span> <span class="pre">const*</span></tt> that should point to a string constant containing
exactly two characters. These are the characters that should be unique for your client. Make
sure not to clash with anybody else. Here are some taken id's:</p>
<table border="1" class="docutils">
<colgroup>
<col width="30%" />
<col width="70%" />
</colgroup>
<thead valign="bottom">
<tr><th>id chars</th>
<th>client</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>'AZ'</td>
<td>Azureus</td>
</tr>
<tr><td>'LT'</td>
<td>libtorrent (default)</td>
</tr>
<tr><td>'BX'</td>
<td>BittorrentX</td>
</tr>
<tr><td>'MT'</td>
<td>Moonlight Torrent</td>
</tr>
<tr><td>'TS'</td>
<td>Torrent Storm</td>
</tr>
<tr><td>'SS'</td>
<td>Swarm Scope</td>
</tr>
<tr><td>'XT'</td>
<td>Xan Torrent</td>
</tr>
</tbody>
</table>
<p>The <tt class="docutils literal"><span class="pre">major</span></tt>, <tt class="docutils literal"><span class="pre">minor</span></tt>, <tt class="docutils literal"><span class="pre">revision</span></tt> and <tt class="docutils literal"><span class="pre">tag</span></tt> parameters are used to identify the
version of your client. All these numbers must be within the range [0, 9].</p>
<p><tt class="docutils literal"><span class="pre">to_string()</span></tt> will generate the actual string put in the peer-id, and return it.</p>
</div>
<div class="section" id="free-functions">
<h1><a name="free-functions">free functions</a></h1>
<div class="section" id="identify-client">
<h2><a name="identify-client">identify_client()</a></h2>
<blockquote>
<pre class="literal-block">
std::string identify_client(peer_id const&amp; id);
</pre>
</blockquote>
<p>This function is declared in the header <tt class="docutils literal"><span class="pre">&lt;libtorrent/identify_client.hpp&gt;</span></tt>. It can can be used
to extract a string describing a client version from its peer-id. It will recognize most clients
that have this kind of identification in the peer-id.</p>
</div>
<div class="section" id="bdecode-bencode">
<h2><a name="bdecode-bencode">bdecode() bencode()</a></h2>
<blockquote>
<pre class="literal-block">
template&lt;class InIt&gt; entry bdecode(InIt start, InIt end);
template&lt;class OutIt&gt; void bencode(OutIt out, const entry&amp; e);
</pre>
</blockquote>
<p>These functions will encode data to <a class="reference" href="http://wiki.theory.org/index.php/BitTorrentSpecification">bencoded</a> or decode <a class="reference" href="http://wiki.theory.org/index.php/BitTorrentSpecification">bencoded</a> data.</p>
<p>The <a class="reference" href="#entry">entry</a> class is the internal representation of the bencoded data
and it can be used to retreive information, an <a class="reference" href="#entry">entry</a> can also be build by
the program and given to <tt class="docutils literal"><span class="pre">bencode()</span></tt> to encode it into the <tt class="docutils literal"><span class="pre">OutIt</span></tt>
iterator.</p>
<p>The <tt class="docutils literal"><span class="pre">OutIt</span></tt> and <tt class="docutils literal"><span class="pre">InIt</span></tt> are iterators
(<a class="reference" href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</a> and <a class="reference" href="http://www.sgi.com/tech/stl/OutputIterator.html">OutputIterator</a> respectively). They
are templates and are usually instantiated as <a class="reference" href="http://www.sgi.com/tech/stl/ostream_iterator.html">ostream_iterator</a>,
<a class="reference" href="http://www.sgi.com/tech/stl/back_insert_iterator.html">back_insert_iterator</a> or <a class="reference" href="http://www.sgi.com/tech/stl/istream_iterator.html">istream_iterator</a>. These
functions will assume that the iterator refers to a character
(<tt class="docutils literal"><span class="pre">char</span></tt>). So, if you want to encode entry <tt class="docutils literal"><span class="pre">e</span></tt> into a buffer
in memory, you can do it like this:</p>
<pre class="literal-block">
std::vector&lt;char&gt; buffer;
bencode(std::back_inserter(buf), e);
</pre>
<p>If you want to decode a torrent file from a buffer in memory, you can do it like this:</p>
<pre class="literal-block">
std::vector&lt;char&gt; buffer;
// ...
entry e = bdecode(buf.begin(), buf.end());
</pre>
<p>Or, if you have a raw char buffer:</p>
<pre class="literal-block">
const char* buf;
// ...
entry e = bdecode(buf, buf + data_size);
</pre>
<p>Now we just need to know how to retrieve information from the <a class="reference" href="#entry">entry</a>.</p>
<p>If <tt class="docutils literal"><span class="pre">bdecode()</span></tt> encounters invalid encoded data in the range given to it
it will throw <a class="reference" href="#invalid-encoding">invalid_encoding</a>.</p>
</div>
</div>
<div class="section" id="alerts">
<h1><a name="alerts">alerts</a></h1>
<p>The <tt class="docutils literal"><span class="pre">pop_alert()</span></tt> function on session is the interface for retrieving
alerts, warnings, messages and errors from libtorrent. If there hasn't
occured any errors (matching your severity level) <tt class="docutils literal"><span class="pre">pop_alert()</span></tt> will
return a zero pointer. If there has been some error, it will return a pointer
to an alert object describing it. You can then use the alert object and query
it for information about the error or message. To retrieve any alerts, you have
to select a severity level using <tt class="docutils literal"><span class="pre">session::set_severity_level()</span></tt>. It defaults to
<tt class="docutils literal"><span class="pre">alert::none</span></tt>, which means that you don't get any messages at all, ever.
You have the following levels to select among:</p>
<table border="1" class="docutils">
<colgroup>
<col width="19%" />
<col width="81%" />
</colgroup>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">none</span></tt></td>
<td>No alert will ever have this severity level, which
effectively filters all messages.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">fatal</span></tt></td>
<td>Fatal errors will have this severity level. Examples can
be disk full or something else that will make it
impossible to continue normal execution.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">critical</span></tt></td>
<td>Signals errors that requires user interaction or
messages that almost never should be ignored. For
example, a chat message received from another peer is
announced as severity <tt class="docutils literal"><span class="pre">critical</span></tt>.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">warning</span></tt></td>
<td>Messages with the warning severity can be a tracker that
times out or responds with invalid data. It will be
retried automatically, and the possible next tracker in
a multitracker sequence will be tried. It does not
require any user interaction.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">info</span></tt></td>
<td>Events that can be considered normal, but still deserves
an event. This could be a piece hash that fails.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">debug</span></tt></td>
<td>This will include alot of debug events that can be used
both for debugging libtorrent but also when debugging
other clients that are connected to libtorrent. It will
report strange behaviors among the connected peers.</td>
</tr>
</tbody>
</table>
<p>When setting a severity level, you will receive messages of that severity and all
messages that are more sever. If you set <tt class="docutils literal"><span class="pre">alert::none</span></tt> (the default) you will not recieve
any events at all.</p>
<p>When you set a severuty level other than <tt class="docutils literal"><span class="pre">none</span></tt>, you have the responsibility to call
<tt class="docutils literal"><span class="pre">pop_alert()</span></tt> from time to time. If you don't do that, the alert queue will just grow.</p>
<p>When you get an alert, you can use <tt class="docutils literal"><span class="pre">typeid()</span></tt> or <tt class="docutils literal"><span class="pre">dynamic_cast&lt;&gt;</span></tt> to get more detailed
information on exactly which type it is. i.e. what kind of error it is. You can also use a
<a class="reference" href="#dispatcher">dispatcher</a> mechanism that's available in libtorrent.</p>
<p>All alert types are defined in the <tt class="docutils literal"><span class="pre">&lt;libtorrent/alert_types.hpp&gt;</span></tt> header file.</p>
<p>The <tt class="docutils literal"><span class="pre">alert</span></tt> class is the base class that specific messages are derived from. This
is its synopsis:</p>
<pre class="literal-block">
class alert
{
public:
enum severity_t { debug, info, warning, critital, fatal, none };
alert(severity_t severity, const std::string&amp; msg);
virtual ~alert();
std::string const&amp; msg() const;
severity_t severity() const;
virtual std::auto_ptr&lt;alert&gt; clone() const = 0;
};
</pre>
<p>This means that all alerts have at least a string describing it. They also
have a severity level that can be used to sort them or present them to the
user in different ways.</p>
<p>The specific alerts, that all derives from <tt class="docutils literal"><span class="pre">alert</span></tt>, are:</p>
<div class="section" id="listen-failed-alert">
<h2><a name="listen-failed-alert">listen_failed_alert</a></h2>
<p>This alert is generated when none of the ports, given in the port range, to
<a class="reference" href="#session">session</a> can be opened for listening. This alert is generated as severity
level <tt class="docutils literal"><span class="pre">fatal</span></tt>.</p>
<pre class="literal-block">
struct listen_failed_alert: alert
{
listen_failed_alert(const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
};
</pre>
</div>
<div class="section" id="file-error-alert">
<h2><a name="file-error-alert">file_error_alert</a></h2>
<p>If the storage fails to read or write files that it needs access to, this alert is
generated and the torrent is paused. It is generated as severity level <tt class="docutils literal"><span class="pre">fatal</span></tt>.</p>
<pre class="literal-block">
struct file_error_alert: alert
{
file_error_alert(
const torrent_handle&amp; h
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
};
</pre>
</div>
<div class="section" id="tracker-announce-alert">
<h2><a name="tracker-announce-alert">tracker_announce_alert</a></h2>
<p>This alert is generated each time a tracker announce is sent (or attempted to be sent).
It is generated at severity level <tt class="docutils literal"><span class="pre">info</span></tt>.</p>
<pre class="literal-block">
struct tracker_announce_alert: alert
{
tracker_announce_alert(
const torrent_handle&amp; h
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
};
</pre>
</div>
<div class="section" id="tracker-alert">
<h2><a name="tracker-alert">tracker_alert</a></h2>
<p>This alert is generated on tracker time outs, premature disconnects, invalid response or
a HTTP response other than &quot;200 OK&quot;. From the alert you can get the handle to the torrent
the tracker belongs to. This alert is generated as severity level <tt class="docutils literal"><span class="pre">warning</span></tt>.</p>
<p>The <tt class="docutils literal"><span class="pre">times_in_row</span></tt> member says how many times in a row this tracker has failed.
<tt class="docutils literal"><span class="pre">status_code</span></tt> is the code returned from the HTTP server. 401 means the tracker needs
authentication, 404 means not found etc. If the tracker timed out, the code will be set
to 0.</p>
<pre class="literal-block">
struct tracker_alert: alert
{
tracker_alert(const torrent_handle&amp; h, int times, int status
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
int times_in_row;
int status_code;
};
</pre>
</div>
<div class="section" id="tracker-reply-alert">
<h2><a name="tracker-reply-alert">tracker_reply_alert</a></h2>
<p>This alert is only for informational purpose. It is generated when a tracker announce
succeeds. It is generated with severity level <tt class="docutils literal"><span class="pre">info</span></tt>.</p>
<pre class="literal-block">
struct tracker_reply_alert: alert
{
tracker_reply_alert(const torrent_handle&amp; h
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
};
</pre>
</div>
<div class="section" id="hash-failed-alert">
<h2><a name="hash-failed-alert">hash_failed_alert</a></h2>
<p>This alert is generated when a finished piece fails its hash check. You can get the handle
to the torrent which got the failed piece and the index of the piece itself from the alert.
This alert is generated as severity level <tt class="docutils literal"><span class="pre">info</span></tt>.</p>
<pre class="literal-block">
struct hash_failed_alert: alert
{
hash_failed_alert(
const torrent_handle&amp; h
, int index
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
int piece_index;
};
</pre>
</div>
<div class="section" id="peer-ban-alert">
<h2><a name="peer-ban-alert">peer_ban_alert</a></h2>
<p>This alert is generated when a peer is banned because it has sent too many corrupt pieces
to us. It is generated at severity level <tt class="docutils literal"><span class="pre">info</span></tt>. The <tt class="docutils literal"><span class="pre">handle</span></tt> member is a <a class="reference" href="#torrent-handle">torrent_handle</a>
to the torrent that this peer was a member of.</p>
<pre class="literal-block">
struct peer_ban_alert: alert
{
peer_ban_alert(
address const&amp; pip
, torrent_handle h
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
address ip;
torrent_handle handle;
};
</pre>
</div>
<div class="section" id="peer-error-alert">
<h2><a name="peer-error-alert">peer_error_alert</a></h2>
<p>This alert is generated when a peer sends invalid data over the peer-peer protocol. The peer
will be disconnected, but you get its ip address from the alert, to identify it. This alert
is generated as severity level <tt class="docutils literal"><span class="pre">debug</span></tt>.</p>
<pre class="literal-block">
struct peer_error_alert: alert
{
peer_error_alert(
address const&amp; pip
, peer_id const&amp; pid
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
address ip;
peer_id id;
};
</pre>
</div>
<div class="section" id="invalid-request-alert">
<h2><a name="invalid-request-alert">invalid_request_alert</a></h2>
<p>This is a debug alert that is generated by an incoming invalid piece request. The <tt class="docutils literal"><span class="pre">handle</span></tt>
is a handle to the torrent the peer is a member of. <tt class="docutils literal"><span class="pre">ìp</span></tt> is the address of the peer and the
<tt class="docutils literal"><span class="pre">request</span></tt> is the actual incoming request from the peer. The alert is generated as severity level
<tt class="docutils literal"><span class="pre">debug</span></tt>.</p>
<pre class="literal-block">
struct invalid_request_alert: alert
{
invalid_request_alert(
peer_request const&amp; r
, torrent_handle const&amp; h
, address const&amp; send
, peer_id const&amp; pid
, std::string const&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
address ip;
peer_request request;
peer_id id;
};
struct peer_request
{
int piece;
int start;
int length;
bool operator==(peer_request const&amp; r) const;
};
</pre>
<p>The <tt class="docutils literal"><span class="pre">peer_request</span></tt> contains the values the client sent in its <tt class="docutils literal"><span class="pre">request</span></tt> message. <tt class="docutils literal"><span class="pre">piece</span></tt> is
the index of the piece it want data from, <tt class="docutils literal"><span class="pre">start</span></tt> is the offset within the piece where the data
should be read, and <tt class="docutils literal"><span class="pre">length</span></tt> is the amount of data it wants.</p>
</div>
<div class="section" id="torrent-finished-alert">
<h2><a name="torrent-finished-alert">torrent_finished_alert</a></h2>
<p>This alert is generated when a torrent switches from being a downloader to a seed.
It will only be generated once per torrent. It contains a torrent_handle to the
torrent in question. This alert is generated as severity level <tt class="docutils literal"><span class="pre">info</span></tt>.</p>
<pre class="literal-block">
struct torrent_finished_alert: alert
{
torrent_finished_alert(
const torrent_handle&amp; h
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
};
</pre>
</div>
<div class="section" id="metadata-received-alert">
<h2><a name="metadata-received-alert">metadata_received_alert</a></h2>
<p>This alert is generated when the metadata has been completely received and the torrent
can start downloading. It is not generated on torrents that are started with metadata, but
only those that needs to download it from peers (when utilizing the libtorrent extension).
It is generated at severity level <tt class="docutils literal"><span class="pre">info</span></tt>.</p>
<pre class="literal-block">
struct metadata_received_alert: alert
{
metadata_received_alert(
const torrent_handle&amp; h
, const std::string&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
};
</pre>
</div>
<div class="section" id="fastresume-rejected-alert">
<h2><a name="fastresume-rejected-alert">fastresume_rejected_alert</a></h2>
<p>This alert is generated when a fastresume file has been passed to <tt class="docutils literal"><span class="pre">add_torrent</span></tt> but the
files on disk did not match the fastresume file. The string explaints the reason why the
resume file was rejected. It is generated at severity level <tt class="docutils literal"><span class="pre">warning</span></tt>.</p>
<pre class="literal-block">
struct fastresume_rejected_alert: alert
{
fastresume_rejected_alert(torrent_handle const&amp; h
, std::string const&amp; msg);
virtual std::auto_ptr&lt;alert&gt; clone() const;
torrent_handle handle;
};
</pre>
<!-- chat_message_alert
- - - - - - - - - - - - - - - - - -
This alert is generated when you receive a chat message from another peer. Chat messages
are supported as an extension ("chat"). It is generated as severity level ``critical``,
even though it doesn't necessarily require any user intervention, it's high priority
since you would almost never want to ignore such a message. The alert class contain
a torrent_handle_ to the torrent in which the sender-peer is a member and the ip
of the sending peer.
::
struct chat_message_alert: alert
{
chat_message_alert(const torrent_handle& h
, const address& sender
, const std::string& msg);
virtual std::auto_ptr<alert> clone() const;
torrent_handle handle;
address ip;
}; -->
</div>
<div class="section" id="dispatcher">
<h2><a name="dispatcher">dispatcher</a></h2>
<p><em>TODO: describe the dispatcher mechanism</em></p>
</div>
</div>
<div class="section" id="exceptions">
<h1><a name="exceptions">exceptions</a></h1>
<p>There are a number of exceptions that can be thrown from different places in libtorrent,
here's a complete list with description.</p>
<div class="section" id="invalid-handle">
<h2><a name="invalid-handle">invalid_handle</a></h2>
<p>This exception is thrown when querying information from a <a class="reference" href="#torrent-handle">torrent_handle</a> that hasn't
been initialized or that has become invalid.</p>
<pre class="literal-block">
struct invalid_handle: std::exception
{
const char* what() const throw();
};
</pre>
</div>
<div class="section" id="duplicate-torrent">
<h2><a name="duplicate-torrent">duplicate_torrent</a></h2>
<p>This is thrown by <a class="reference" href="#add-torrent">add_torrent()</a> if the torrent already has been added to
the session.</p>
<pre class="literal-block">
struct duplicate_torrent: std::exception
{
const char* what() const throw();
};
</pre>
</div>
<div class="section" id="invalid-encoding">
<h2><a name="invalid-encoding">invalid_encoding</a></h2>
<p>This is thrown by <tt class="docutils literal"><span class="pre">bdecode()</span></tt> if the input data is not a valid bencoding.</p>
<pre class="literal-block">
struct invalid_encoding: std::exception
{
const char* what() const throw();
};
</pre>
</div>
<div class="section" id="type-error">
<h2><a name="type-error">type_error</a></h2>
<p>This is thrown from the accessors of <tt class="docutils literal"><span class="pre">entry</span></tt> if the data type of the <tt class="docutils literal"><span class="pre">entry</span></tt> doesn't
match the type you want to extract from it.</p>
<pre class="literal-block">
struct type_error: std::runtime_error
{
type_error(const char* error);
};
</pre>
</div>
<div class="section" id="invalid-torrent-file">
<h2><a name="invalid-torrent-file">invalid_torrent_file</a></h2>
<p>This exception is thrown from the constructor of <tt class="docutils literal"><span class="pre">torrent_info</span></tt> if the given bencoded information
doesn't meet the requirements on what information has to be present in a torrent file.</p>
<pre class="literal-block">
struct invalid_torrent_file: std::exception
{
const char* what() const throw();
};
</pre>
</div>
</div>
<div class="section" id="examples">
<h1><a name="examples">examples</a></h1>
<div class="section" id="dump-torrent">
<h2><a name="dump-torrent">dump_torrent</a></h2>
<p>This is an example of a program that will take a torrent-file as a parameter and
print information about it to std out:</p>
<pre class="literal-block">
#include &lt;iostream&gt;
#include &lt;fstream&gt;
#include &lt;iterator&gt;
#include &lt;exception&gt;
#include &lt;iomanip&gt;
#include &quot;libtorrent/entry.hpp&quot;
#include &quot;libtorrent/bencode.hpp&quot;
#include &quot;libtorrent/torrent_info.hpp&quot;
int main(int argc, char* argv[])
{
using namespace libtorrent;
if (argc != 2)
{
std::cerr &lt;&lt; &quot;usage: dump_torrent torrent-file\n&quot;;
return 1;
}
try
{
std::ifstream in(argv[1], std::ios_base::binary);
in.unsetf(std::ios_base::skipws);
entry e = bdecode(std::istream_iterator&lt;char&gt;(in), std::istream_iterator&lt;char&gt;());
torrent_info t(e);
// print info about torrent
std::cout &lt;&lt; &quot;\n\n----- torrent file info -----\n\n&quot;;
std::cout &lt;&lt; &quot;trackers:\n&quot;;
for (std::vector&lt;announce_entry&gt;::const_iterator i = t.trackers().begin();
i != t.trackers().end(); ++i)
{
std::cout &lt;&lt; i-&gt;tier &lt;&lt; &quot;: &quot; &lt;&lt; i-&gt;url &lt;&lt; &quot;\n&quot;;
}
std::cout &lt;&lt; &quot;number of pieces: &quot; &lt;&lt; t.num_pieces() &lt;&lt; &quot;\n&quot;;
std::cout &lt;&lt; &quot;piece length: &quot; &lt;&lt; t.piece_length() &lt;&lt; &quot;\n&quot;;
std::cout &lt;&lt; &quot;files:\n&quot;;
for (torrent_info::file_iterator i = t.begin_files();
i != t.end_files();
++i)
{
std::cout &lt;&lt; &quot; &quot; &lt;&lt; std::setw(11) &lt;&lt; i-&gt;size
&lt;&lt; &quot; &quot; &lt;&lt; i-&gt;path &lt;&lt; &quot; &quot; &lt;&lt; i-&gt;filename &lt;&lt; &quot;\n&quot;;
}
}
catch (std::exception&amp; e)
{
std::cout &lt;&lt; e.what() &lt;&lt; &quot;\n&quot;;
}
return 0;
}
</pre>
</div>
<div class="section" id="simple-client">
<h2><a name="simple-client">simple client</a></h2>
<p>This is a simple client. It doesn't have much output to keep it simple:</p>
<pre class="literal-block">
#include &lt;iostream&gt;
#include &lt;fstream&gt;
#include &lt;iterator&gt;
#include &lt;exception&gt;
#include &lt;boost/format.hpp&gt;
#include &lt;boost/date_time/posix_time/posix_time.hpp&gt;
#include &quot;libtorrent/entry.hpp&quot;
#include &quot;libtorrent/bencode.hpp&quot;
#include &quot;libtorrent/session.hpp&quot;
#include &quot;libtorrent/http_settings.hpp&quot;
int main(int argc, char* argv[])
{
using namespace libtorrent;
if (argc != 2)
{
std::cerr &lt;&lt; &quot;usage: ./simple_cient torrent-file\n&quot;
&quot;to stop the client, press return.\n&quot;;
return 1;
}
try
{
session s;
s.listen_on(std::make_pair(6881, 6889));
std::ifstream in(argv[1], std::ios_base::binary);
in.unsetf(std::ios_base::skipws);
entry e = bdecode(std::istream_iterator&lt;char&gt;(in), std::istream_iterator&lt;char&gt;());
s.add_torrent(e, &quot;&quot;);
// wait for the user to end
char a;
std::cin.unsetf(std::ios_base::skipws);
std::cin &gt;&gt; a;
}
catch (std::exception&amp; e)
{
std::cout &lt;&lt; e.what() &lt;&lt; &quot;\n&quot;;
}
return 0;
}
</pre>
</div>
<div class="section" id="make-torrent">
<h2><a name="make-torrent">make_torrent</a></h2>
<p>Shows how to create a torrent from a directory tree:</p>
<pre class="literal-block">
#include &lt;iostream&gt;
#include &lt;fstream&gt;
#include &lt;iterator&gt;
#include &lt;iomanip&gt;
#include &quot;libtorrent/entry.hpp&quot;
#include &quot;libtorrent/bencode.hpp&quot;
#include &quot;libtorrent/torrent_info.hpp&quot;
#include &quot;libtorrent/file.hpp&quot;
#include &quot;libtorrent/storage.hpp&quot;
#include &quot;libtorrent/hasher.hpp&quot;
#include &lt;boost/filesystem/operations.hpp&gt;
#include &lt;boost/filesystem/path.hpp&gt;
#include &lt;boost/filesystem/fstream.hpp&gt;
using namespace boost::filesystem;
using namespace libtorrent;
void add_files(
torrent_info&amp; t
, path const&amp; p
, path const&amp; l)
{
path f(p / l);
if (is_directory(f))
{
for (directory_iterator i(f), end; i != end; ++i)
add_files(t, p, l / i-&gt;leaf());
}
else
{
std::cerr &lt;&lt; &quot;adding \&quot;&quot; &lt;&lt; l.string() &lt;&lt; &quot;\&quot;\n&quot;;
file fi(f, file::in);
fi.seek(0, file::end);
libtorrent::size_type size = fi.tell();
t.add_file(l, size);
}
}
int main(int argc, char* argv[])
{
using namespace libtorrent;
using namespace boost::filesystem;
if (argc != 4)
{
std::cerr &lt;&lt; &quot;usage: make_torrent &lt;output torrent-file&gt; &lt;announce url&gt; &quot;
&quot;&lt;file or directory to create torrent from&gt;\n&quot;;
return 1;
}
boost::filesystem::path::default_name_check(native);
try
{
torrent_info t;
path full_path = initial_path() / path(argv[3]);
ofstream out(initial_path() / path(argv[1]), std::ios_base::binary);
int piece_size = 256 * 1024;
char const* creator_str = &quot;libtorrent&quot;;
add_files(t, full_path.branch_path(), full_path.leaf());
t.set_piece_size(piece_size);
storage st(t, full_path.branch_path());
t.add_tracker(argv[2]);
// calculate the hash for all pieces
int num = t.num_pieces();
std::vector&lt;char&gt; buf(piece_size);
for (int i = 0; i &lt; num; ++i)
{
st.read(&amp;buf[0], i, 0, t.piece_size(i));
hasher h(&amp;buf[0], t.piece_size(i));
t.set_hash(i, h.final());
std::cerr &lt;&lt; (i+1) &lt;&lt; &quot;/&quot; &lt;&lt; num &lt;&lt; &quot;\r&quot;;
}
t.set_creator(creator_str);
// create the torrent and print it to out
entry e = t.create_torrent();
libtorrent::bencode(std::ostream_iterator&lt;char&gt;(out), e);
}
catch (std::exception&amp; e)
{
std::cerr &lt;&lt; e.what() &lt;&lt; &quot;\n&quot;;
}
return 0;
}
</pre>
</div>
</div>
<div class="section" id="fast-resume">
<h1><a name="fast-resume">fast resume</a></h1>
<p>The fast resume mechanism is a way to remember which pieces are downloaded and where they
are put between sessions. You can generate fast resume data by calling
<tt class="docutils literal"><span class="pre">torrent_handle::write_resume_data()</span></tt> on <a class="reference" href="#torrent-handle">torrent_handle</a>. You can then save this data
to disk and use it when resuming the torrent. libtorrent will not check the piece hashes
then, and rely on the information given in the fast-resume data. The fast-resume data
also contains information about which blocks, in the unfinished pieces, were downloaded,
so it will not have to start from scratch on the partially downloaded pieces.</p>
<p>To use the fast-resume data you simply give it to <a class="reference" href="#add-torrent">add_torrent()</a>, and it
will skip the time consuming checks. It may have to do the checking anyway, if the
fast-resume data is corrupt or doesn't fit the storage for that torrent, then it will
not trust the fast-resume data and just do the checking.</p>
<div class="section" id="file-format">
<h2><a name="file-format">file format</a></h2>
<p>The file format is a bencoded dictionary containing the following fields:</p>
<table border="1" class="docutils">
<colgroup>
<col width="26%" />
<col width="74%" />
</colgroup>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">file-format</span></tt></td>
<td>string: &quot;libtorrent resume file&quot;</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">file-version</span></tt></td>
<td>integer: 1</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">info-hash</span></tt></td>
<td>string, the info hash of the torrent this data is saved for.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">blocks</span> <span class="pre">per</span> <span class="pre">piece</span></tt></td>
<td>integer, the number of blocks per piece. Must be: piece_size
/ (16 * 1024). Clamped to be within the range [1, 256]. It
is the number of blocks per (normal sized) piece. Usually
each block is 16 * 1024 bytes in size. But if piece size is
greater than 4 megabytes, the block size will increase.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">slots</span></tt></td>
<td><p class="first">list of integers. The list mappes slots to piece indices. It
tells which piece is on which slot. If piece index is -2 it
means it is free, that there's no piece there. If it is -1,
means the slot isn't allocated on disk yet. The pieces have
to meet the following requirement:</p>
<p class="last">If there's a slot at the position of the piece index,
the piece must be located in that slot.</p>
</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">peers</span></tt></td>
<td><p class="first">list of dictionaries. Each dictionary has the following
layout:</p>
<table border="1" class="docutils">
<colgroup>
<col width="18%" />
<col width="82%" />
</colgroup>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">ip</span></tt></td>
<td>string, the ip address of the peer.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">port</span></tt></td>
<td>integer, the listen port of the peer</td>
</tr>
</tbody>
</table>
<p class="last">These are the local peers we were connected to when this
fast-resume data was saved.</p>
</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">unfinished</span></tt></td>
<td><p class="first">list of dictionaries. Each dictionary represents an
piece, and has the following layout:</p>
<table border="1" class="last docutils">
<colgroup>
<col width="23%" />
<col width="77%" />
</colgroup>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">piece</span></tt></td>
<td>integer, the index of the piece this entry
refers to.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">bitmask</span></tt></td>
<td>string, a binary bitmask representing the
blocks that have been downloaded in this
piece.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">adler32</span></tt></td>
<td>The adler32 checksum of the data in the
blocks specified by <tt class="docutils literal"><span class="pre">bitmask</span></tt>.</td>
</tr>
</tbody>
</table>
</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">file</span> <span class="pre">sizes</span></tt></td>
<td>list where each entry corresponds to a file in the file list
in the metadata. Each entry has a list of two values, the
first value is the size of the file in bytes, the second
is the timestamp when the last time someone wrote to it.
This information is used to compare with the files on disk.
All the files must match exactly this information in order
to consider the resume data as current. Otherwise a full
re-check is issued.</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" id="threads">
<h1><a name="threads">threads</a></h1>
<p>libtorrent starts 3 threads.</p>
<blockquote>
<ul class="simple">
<li>The first thread is the main thread that will sit
idle in a <tt class="docutils literal"><span class="pre">select()</span></tt> call most of the time. This thread runs the main loop
that will send and receive data on all connections.</li>
<li>The second thread is a hash-check thread. Whenever a torrent is added it will
first be passed to this thread for checking the files that may already have been
downloaded. If there is any resume data this thread will make sure it is valid
and matches the files. Once the torrent has been checked, it is passed on to the
main thread that will start it. The hash-check thread has a queue of torrents,
it will only check one torrent at a time.</li>
<li>The third thread is spawned the first time a tracker is contacted. It is used
for doing calls to <tt class="docutils literal"><span class="pre">gethostbyname()</span></tt>. Since this call is blocking (and may block
for several seconds if the dns server is down or slow) it is necessary to run this
in its own thread to avoid stalling the main thread.</li>
</ul>
</blockquote>
</div>
<div class="section" id="storage-allocation">
<h1><a name="storage-allocation">storage allocation</a></h1>
<p>There are two modes in which storage (files on disk) are allocated in libtorrent.</p>
<blockquote>
<ul class="simple">
<li>The traditional <em>full allocation</em> mode, where the entire files are filled up with
zeroes before anything is downloaded.</li>
<li>And the <em>compact allocation</em> mode, where only files are allocated for actual
pieces that have been downloaded. This is the default allocation mode in libtorrent.</li>
</ul>
</blockquote>
<p>The allocation mode is selected when a torrent is started. It is passed as a boolean
argument to <tt class="docutils literal"><span class="pre">session::add_torrent()</span></tt> (see <a class="reference" href="#add-torrent">add_torrent()</a>). These two modes have
different drawbacks and benefits.</p>
<div class="section" id="full-allocation">
<h2><a name="full-allocation">full allocation</a></h2>
<p>When a torrent is started in full allocation mode, the checker thread (see <a class="reference" href="#threads">threads</a>)
will make sure that the entire storage is allocated, and fill any gaps with zeroes.
It will of course still check for existing pieces and fast resume data. The main
drawbacks of this mode are:</p>
<blockquote>
<ul class="simple">
<li>It will take longer to start the torrent, since it will need to fill the files
with zeroes. This delay is linearly dependent on the size of the download.</li>
<li>The download will occupy unnecessary disk space between download sessions.</li>
</ul>
</blockquote>
<p>The benefit of thise mode are:</p>
<blockquote>
<ul class="simple">
<li>Downloaded pieces are written directly to their final place in the files and the
total number of disk operations will be fewer and may also play nicer to
filesystems' file allocation, and reduce fragmentation.</li>
<li>No risk of a download failing because of a full disk during download.</li>
</ul>
</blockquote>
</div>
<div class="section" id="compact-allocation">
<h2><a name="compact-allocation">compact allocation</a></h2>
<p>The compact allocation will only allocate as much storage as it needs to keep the
pieces downloaded so far. This means that pieces will be moved around to be placed
at their final position in the files while downloading (to make sure the completed
download has all its pieces in the correct place). So, the main drawbacks are:</p>
<blockquote>
<ul class="simple">
<li>More disk operations while downloading since pieces are moved around.</li>
<li>Potentially more fragmentation in the filesystem.</li>
</ul>
</blockquote>
<p>The benefits though, are:</p>
<blockquote>
<ul class="simple">
<li>No startup delay, since the files doesn't need allocating.</li>
<li>The download will not use unnecessary disk space.</li>
</ul>
</blockquote>
<p>The algorithm that is used when allocating pieces and slots isn't very complicated.
For the interested, a description follows.</p>
<p>storing a piece:</p>
<ol class="arabic simple">
<li>let <strong>A</strong> be a newly downloaded piece, with index <strong>n</strong>.</li>
<li>let <strong>s</strong> be the number of slots allocated in the file we're
downloading to. (the number of pieces it has room for).</li>
<li>if <strong>n</strong> &gt;= <strong>s</strong> then allocate a new slot and put the piece there.</li>
<li>if <strong>n</strong> &lt; <strong>s</strong> then allocate a new slot, move the data at
slot <strong>n</strong> to the new slot and put <strong>A</strong> in slot <strong>n</strong>.</li>
</ol>
<p>allocating a new slot:</p>
<ol class="arabic simple">
<li>if there's an unassigned slot (a slot that doesn't
contain any piece), return that slot index.</li>
<li>append the new slot at the end of the file (or find an unused slot).</li>
<li>let <strong>i</strong> be the index of newly allocated slot</li>
<li>if we have downloaded piece index <strong>i</strong> already (to slot <strong>j</strong>) then<ol class="arabic">
<li>move the data at slot <strong>j</strong> to slot <strong>i</strong>.</li>
<li>return slot index <strong>j</strong> as the newly allocated free slot.</li>
</ol>
</li>
<li>return <strong>i</strong> as the newly allocated slot.</li>
</ol>
</div>
</div>
<div class="section" id="extensions">
<h1><a name="extensions">extensions</a></h1>
<p>These extensions all operates within the <a class="reference" href="http://nolar.com/azureus/extended.html">extension protocol</a>. The
name of the extension is the name used in the extension-list packets,
and the payload is the data in the extended message (not counting the
length-prefix, message-id nor extension-id).</p>
<p>Note that since this protocol relies on one of the reserved bits in the
handshake, it may be incompatible with future versions of the mainline
bittorrent client.</p>
<p>These are the extensions that are currently implemented.</p>
<div class="section" id="chat-messages">
<h2><a name="chat-messages">chat messages</a></h2>
<p>Extension name: &quot;chat&quot;</p>
<p>The payload in the packet is a bencoded dictionary with any
combination of the following entries:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="15%" />
<col width="85%" />
</colgroup>
<tbody valign="top">
<tr><td>&quot;msg&quot;</td>
<td>This is a string that contains a message that
should be displayed to the user.</td>
</tr>
<tr><td>&quot;ctrl&quot;</td>
<td>This is a control string that can tell a client that
it is ignored (to make the user aware of that) and
it can also tell a client that it is no longer ignored.
These notifications are encoded as the strings:
&quot;ignored&quot; and &quot;not ignored&quot;.
Any unrecognized strings should be ignored.</td>
</tr>
</tbody>
</table>
</blockquote>
</div>
<div class="section" id="metadata-from-peers">
<h2><a name="metadata-from-peers">metadata from peers</a></h2>
<p>Extension name: &quot;metadata&quot;</p>
<p>The point with this extension is that you don't have to distribute the
metadata (.torrent-file) separately. The metadata can be distributed
through the bittorrent swarm. The only thing you need to download such
a torrent is the tracker url and the info-hash of the torrent.</p>
<p>It works by assuming that the initial seeder has the metadata and that
the metadata will propagate through the network as more peers join.</p>
<p>There are three kinds of messages in the metadata extension. These packets
are put as payload to the extension message. The three packets are:</p>
<blockquote>
<ul class="simple">
<li>request metadata</li>
<li>metadata</li>
<li>don't have metadata</li>
</ul>
</blockquote>
<p>request metadata:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="17%" />
<col width="23%" />
<col width="61%" />
</colgroup>
<thead valign="bottom">
<tr><th>size</th>
<th>name</th>
<th>description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>uint8_t</td>
<td>msg_type</td>
<td>Determines the kind of message this is
0 means 'request metadata'</td>
</tr>
<tr><td>uint8_t</td>
<td>start</td>
<td>The start of the metadata block that
is requested. It is given in 256:ths
of the total size of the metadata,
since the requesting client don't know
the size of the metadata.</td>
</tr>
<tr><td>uint8_t</td>
<td>size</td>
<td>The size of the metadata block that is
requested. This is also given in
256:ths of the total size of the
metadata. The size is given as size-1.
That means that if this field is set
0, the request wants one 256:th of the
metadata.</td>
</tr>
</tbody>
</table>
</blockquote>
<p>metadata:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="17%" />
<col width="23%" />
<col width="61%" />
</colgroup>
<thead valign="bottom">
<tr><th>size</th>
<th>name</th>
<th>description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>uint8_t</td>
<td>msg_type</td>
<td>1 means 'metadata'</td>
</tr>
<tr><td>int32_t</td>
<td>total_size</td>
<td>The total size of the metadata, given
in number of bytes.</td>
</tr>
<tr><td>int32_t</td>
<td>offset</td>
<td>The offset of where the metadata block
in this message belongs in the final
metadata. This is given in bytes.</td>
</tr>
<tr><td>uint8_t[]</td>
<td>metadata</td>
<td>The actual metadata block. The size of
this part is given implicit by the
length prefix in the bittorrent
protocol packet.</td>
</tr>
</tbody>
</table>
</blockquote>
<p>Don't have metadata:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="17%" />
<col width="23%" />
<col width="61%" />
</colgroup>
<thead valign="bottom">
<tr><th>size</th>
<th>name</th>
<th>description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>uint8_t</td>
<td>msg_type</td>
<td>2 means 'I don't have metadata'.
This message is sent as a reply to a
metadata request if the the client
doesn't have any metadata.</td>
</tr>
</tbody>
</table>
</blockquote>
<p>The current implementation of this extension in libtorrent is experimental,
and not optimal in any way.</p>
</div>
</div>
<div class="section" id="filename-checks">
<h1><a name="filename-checks">filename checks</a></h1>
<p>Boost.Filesystem will by default check all its paths to make sure they conform
to filename requirements on many platforms. If you don't want this check, you can
set it to either only check for native filesystem requirements or turn it off
alltogether. You can use:</p>
<pre class="literal-block">
boost::filesystem::path::default_name_check(boost::filesystem::native);
</pre>
<p>for example. For more information, see the <a class="reference" href="http://www.boost.org/libs/filesystem/doc/index.htm">Boost.Filesystem docs</a>.</p>
</div>
<div class="section" id="acknowledgements">
<h1><a name="acknowledgements">acknowledgements</a></h1>
<p>Written by Arvid Norberg. Copyright (c) 2003-2005</p>
<p>Contributions by Magnus Jonsson, Daniel Wallin and Cory Nelson</p>
<p>Thanks to Reimond Retz for bugfixes, suggestions and testing</p>
<p>Thanks to <a class="reference" href="http://www.cs.umu.se">University of Umeå</a> for providing development and
test hardware.</p>
<p>Project is hosted by sourceforge.</p>
<p><a class="reference" href="http://sourceforge.net"><img alt="sf_logo" src="http://sourceforge.net/sflogo.php?group_id=7994" /></a></p>
</div>
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