forked from premiere/premiere-libtorrent
271 lines
8.7 KiB
ReStructuredText
271 lines
8.7 KiB
ReStructuredText
:Author: Arvid Norberg, arvid@rasterbar.com
|
|
|
|
libtorrent plugins
|
|
==================
|
|
|
|
.. contents::
|
|
|
|
libtorrent has a plugin interface for implementing extensions to the protocol.
|
|
These can be general extensions for transferring metadata or peer exchange
|
|
extensions, or it could be used to provide a way to customize the protocol
|
|
to fit a particular (closed) network.
|
|
|
|
In short, the plugin interface makes it possible to:
|
|
|
|
* register extension messages (sent in the extension handshake), see
|
|
extensions_.
|
|
* add data and parse data from the extension handshake.
|
|
* send extension messages and standard bittorrent messages.
|
|
* override or block the handling of standard bittorrent messages.
|
|
* save and restore state via the session state
|
|
* see all alerts that are posted
|
|
|
|
.. _extensions: extension_protocol.html
|
|
|
|
a word of caution
|
|
-----------------
|
|
|
|
Writing your own plugin is a very easy way to introduce serious bugs such as
|
|
dead locks and race conditions. Since a plugin has access to internal
|
|
structures it is also quite easy to sabotage libtorrent's operation.
|
|
|
|
All the callbacks in this interface are called with the main libtorrent thread
|
|
mutex locked. And they are always called from the libtorrent network thread. In
|
|
case portions of your plugin are called from other threads, typically the main
|
|
thread, you cannot use any of the member functions on the internal structures
|
|
in libtorrent, since those require the mutex to be locked. Futhermore, you would
|
|
also need to have a mutex on your own shared data within the plugin, to make
|
|
sure it is not accessed at the same time from the libtorrent thread (through a
|
|
callback). See `boost thread's mutex`_. If you need to send out a message from
|
|
another thread, it is advised to use an internal queue, and do the actual
|
|
sending in ``tick()``.
|
|
|
|
Since the plugin interface gives you easy access to internal structures, it
|
|
is not supported as a stable API. Plugins should be considered spcific to a
|
|
specific version of libtorrent. Although, in practice the internals mostly
|
|
don't change that dramatically.
|
|
|
|
.. _`boost thread's mutex`: http://www.boost.org/doc/html/mutex.html
|
|
|
|
|
|
plugin interface
|
|
================
|
|
|
|
The plugin interface consists of three base classes that the plugin may
|
|
implement. These are called ``plugin``, ``torrent_plugin`` and ``peer_plugin``.
|
|
They are found in the ``<libtorrent/extensions.hpp>`` header.
|
|
|
|
These plugins are instantiated for each session, torrent and possibly each peer,
|
|
respectively.
|
|
|
|
For plugins that only need per torrent state, it is enough to only implement
|
|
``torrent_plugin`` and pass a constructor function or function object to
|
|
``session::add_extension()`` or ``torrent_handle::add_extension()`` (if the
|
|
torrent has already been started and you want to hook in the extension at
|
|
run-time).
|
|
|
|
The signature of the function is::
|
|
|
|
boost::shared_ptr<torrent_plugin> (*)(torrent*, void*);
|
|
|
|
The first argument is the internal torrent object, the second argument
|
|
is the userdata passed to ``session::add_torrent()`` or
|
|
``torrent_handle::add_extension()``.
|
|
|
|
The function should return a ``boost::shared_ptr<torrent_plugin>`` which
|
|
may or may not be 0. If it is a null pointer, the extension is simply ignored
|
|
for this torrent. If it is a valid pointer (to a class inheriting
|
|
``torrent_plugin``), it will be associated with this torrent and callbacks
|
|
will be made on torrent events.
|
|
|
|
For more elaborate plugins which require session wide state, you would
|
|
implement ``plugin``, construct an object (in a ``boost::shared_ptr``) and pass
|
|
it in to ``session::add_extension()``.
|
|
|
|
plugin
|
|
======
|
|
|
|
::
|
|
|
|
struct plugin
|
|
{
|
|
virtual ~plugin();
|
|
virtual boost::shared_ptr<torrent_plugin> new_torrent(torrent* t, void* user);
|
|
|
|
virtual void added(boost::weak_ptr<aux::session_impl> s);
|
|
virtual void on_alert(alert const* a);
|
|
virtual void on_tick();
|
|
virtual void save_state(entry& ent) const;
|
|
virtual void load_state(lazy_entry const& ent);
|
|
};
|
|
|
|
|
|
torrent_plugin
|
|
==============
|
|
|
|
The synopsis for ``torrent_plugin`` follows::
|
|
|
|
struct torrent_plugin
|
|
{
|
|
virtual ~torrent_plugin();
|
|
virtual boost::shared_ptr<peer_plugin> new_connection(peer_connection*);
|
|
|
|
virtual void on_piece_pass(int index);
|
|
virtual void on_piece_failed(int index);
|
|
|
|
virtual void tick();
|
|
|
|
virtual bool on_pause();
|
|
virtual bool on_resume();
|
|
|
|
virtual void on_files_checked();
|
|
};
|
|
|
|
This is the base class for a torrent_plugin. Your derived class is (if added
|
|
as an extension) instantiated for each torrent in the session. The callback
|
|
hook functions are defined as follows.
|
|
|
|
|
|
new_connection()
|
|
----------------
|
|
|
|
::
|
|
|
|
boost::shared_ptr<peer_plugin> new_connection(peer_connection*);
|
|
|
|
This function is called each time a new peer is connected to the torrent. You
|
|
may choose to ignore this by just returning a default constructed
|
|
``shared_ptr`` (in which case you don't need to override this member
|
|
function).
|
|
|
|
If you need an extension to the peer connection (which most plugins do) you
|
|
are supposed to return an instance of your ``peer_plugin`` class. Which in
|
|
turn will have its hook functions called on event specific to that peer.
|
|
|
|
The ``peer_connection`` will be valid as long as the ``shared_ptr`` is being
|
|
held by the torrent object. So, it is generally a good idea to not keep a
|
|
``shared_ptr`` to your own peer_plugin. If you want to keep references to it,
|
|
use ``weak_ptr``.
|
|
|
|
If this function throws an exception, the connection will be closed.
|
|
|
|
on_piece_pass() on_piece_fail()
|
|
-------------------------------
|
|
|
|
::
|
|
|
|
void on_piece_pass(int index);
|
|
void on_piece_failed(int index);
|
|
|
|
These hooks are called when a piece passes the hash check or fails the hash
|
|
check, respectively. The ``index`` is the piece index that was downloaded.
|
|
It is possible to access the list of peers that participated in sending the
|
|
piece through the ``torrent`` and the ``piece_picker``.
|
|
|
|
tick()
|
|
------
|
|
|
|
::
|
|
|
|
void tick();
|
|
|
|
This hook is called approximately once per second. It is a way of making it
|
|
easy for plugins to do timed events, for sending messages or whatever.
|
|
|
|
|
|
on_pause() on_resume()
|
|
----------------------
|
|
|
|
::
|
|
|
|
bool on_pause();
|
|
bool on_resume();
|
|
|
|
These hooks are called when the torrent is paused and unpaused respectively.
|
|
The return value indicates if the event was handled. A return value of
|
|
``true`` indicates that it was handled, and no other plugin after this one
|
|
will have this hook function called, and the standard handler will also not be
|
|
invoked. So, returning true effectively overrides the standard behavior of
|
|
pause or unpause.
|
|
|
|
Note that if you call ``pause()`` or ``resume()`` on the torrent from your
|
|
handler it will recurse back into your handler, so in order to invoke the
|
|
standard handler, you have to keep your own state on whether you want standard
|
|
behavior or overridden behavior.
|
|
|
|
on_files_checked()
|
|
------------------
|
|
|
|
::
|
|
|
|
void on_files_checked();
|
|
|
|
This function is called when the initial files of the torrent have been
|
|
checked. If there are no files to check, this function is called immediately.
|
|
|
|
i.e. This function is always called when the torrent is in a state where it
|
|
can start downloading.
|
|
|
|
|
|
peer_plugin
|
|
===========
|
|
|
|
::
|
|
|
|
struct peer_plugin
|
|
{
|
|
virtual ~peer_plugin();
|
|
|
|
virtual void add_handshake(entry&);
|
|
virtual bool on_handshake(char const* reserved_bits);
|
|
virtual bool on_extension_handshake(lazy_entry const& h);
|
|
|
|
virtual bool on_choke();
|
|
virtual bool on_unchoke();
|
|
virtual bool on_interested();
|
|
virtual bool on_not_interested();
|
|
virtual bool on_have(int index);
|
|
virtual bool on_bitfield(bitfield const& bits);
|
|
virtual bool on_have_all();
|
|
virtual bool on_have_none();
|
|
virtual bool on_allowed_fast(int index);
|
|
virtual bool on_request(peer_request const& req);
|
|
virtual bool on_piece(peer_request const& piece, disk_buffer_holder& buffer);
|
|
virtual bool on_cancel(peer_request const& req);
|
|
virtual bool on_reject(peer_request const& req);
|
|
virtual bool on_suggest(int index);
|
|
virtual bool on_extended(int length
|
|
, int msg, buffer::const_interval body);
|
|
virtual bool on_unknown_message(int length, int msg
|
|
, buffer::const_interval body);
|
|
virtual void on_piece_pass(int index);
|
|
virtual void on_piece_failed(int index);
|
|
|
|
virtual void tick();
|
|
|
|
virtual bool write_request(peer_request const& r);
|
|
};
|
|
|
|
disk_buffer_holder
|
|
==================
|
|
|
|
::
|
|
|
|
struct disk_buffer_holder
|
|
{
|
|
disk_buffer_holder(aux::session_impl& s, char* b);
|
|
~disk_buffer_holder();
|
|
char* release();
|
|
char* buffer();
|
|
};
|
|
|
|
The disk buffer holder acts like a ``scoped_ptr`` that frees a disk buffer
|
|
when it's destructed, unless it's released. ``release`` returns the disk
|
|
buffer and transferres ownership and responsibility to free it to the caller.
|
|
|
|
A disk buffer is freed by passing it to ``session_impl::free_disk_buffer()``.
|
|
|
|
``buffer()`` returns the pointer without transferring responsibility. If
|
|
this buffer has been released, ``buffer()`` will return 0.
|
|
|