path: root/libmpv2/libmpv2-sys/include/stream_cb.h

/*
 * yt - A fully featured command line YouTube client
 *
 * Copyright (C) 2017 the mpv developers
 * Copyright (C) 2024 Benedikt Peetz <benedikt.peetz@b-peetz.de>
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 * This file is part of Yt.
 *
 * You should have received a copy of the License along with this program.
 * If not, see <https://www.gnu.org/licenses/gpl-3.0.txt>.
 */

#ifndef MPV_CLIENT_API_STREAM_CB_H_
#define MPV_CLIENT_API_STREAM_CB_H_

#include "client.h"

#ifdef __cplusplus
extern "C"
{
#endif

  /**
   * Warning: this API is not stable yet.
   *
   * Overview
   * --------
   *
   * This API can be used to make mpv read from a stream with a custom
   * implementation. This interface is inspired by funopen on BSD and
   * fopencookie on linux. The stream is backed by user-defined callbacks
   * which can implement customized open, read, seek, size and close behaviors.
   *
   * Usage
   * -----
   *
   * Register your stream callbacks with the mpv_stream_cb_add_ro() function.
   * You have to provide a mpv_stream_cb_open_ro_fn callback to it (open_fn
   * argument).
   *
   * Once registered, you can `loadfile myprotocol://myfile`. Your open_fn will
   * be invoked with the URI and you must fill out the provided
   * mpv_stream_cb_info struct. This includes your stream callbacks (like
   * read_fn), and an opaque cookie, which will be passed as the first argument
   * to all the remaining stream callbacks.
   *
   * Note that your custom callbacks must not invoke libmpv APIs as that would
   * cause a deadlock. (Unless you call a different mpv_handle than the one the
   * callback was registered for, and the mpv_handles refer to different mpv
   * instances.)
   *
   * Stream lifetime
   * ---------------
   *
   * A stream remains valid until its close callback has been called. It's up
   * to libmpv to call the close callback, and the libmpv user cannot close it
   * directly with the stream_cb API.
   *
   * For example, if you consider your custom stream to become suddenly invalid
   * (maybe because the underlying stream died), libmpv will continue using
   * your stream. All you can do is returning errors from each callback, until
   * libmpv gives up and closes it.
   *
   * Protocol registration and lifetime
   * ----------------------------------
   *
   * Protocols remain registered until the mpv instance is terminated. This
   * means in particular that it can outlive the mpv_handle that was used to
   * register it, but once mpv_terminate_destroy() is called, your registered
   * callbacks will not be called again.
   *
   * Protocol unregistration is finished after the mpv core has been destroyed
   * (e.g. after mpv_terminate_destroy() has returned).
   *
   * If you do not call mpv_terminate_destroy() yourself (e.g. plugin-style
   * code), you will have to deal with the registration or even streams
   * outliving your code. Here are some possible ways to do this:
   * - call mpv_terminate_destroy(), which destroys the core, and will make
   * sure all streams are closed once this function returns
   * - you refcount all resources your stream "cookies" reference, so that it
   *   doesn't matter if streams live longer than expected
   * - create "cancellation" semantics: after your protocol has been
   * unregistered, notify all your streams that are still opened, and make them
   * drop all referenced resources - then return errors from the stream
   * callbacks as long as the stream is still opened
   *
   */

  /**
   * Read callback used to implement a custom stream. The semantics of the
   * callback match read(2) in blocking mode. Short reads are allowed (you can
   * return less bytes than requested, and libmpv will retry reading the rest
   * with another call). If no data can be immediately read, the callback must
   * block until there is new data. A return of 0 will be interpreted as final
   * EOF, although libmpv might retry the read, or seek to a different
   * position.
   *
   * @param cookie opaque cookie identifying the stream,
   *               returned from mpv_stream_cb_open_fn
   * @param buf buffer to read data into
   * @param size of the buffer
   * @return number of bytes read into the buffer
   * @return 0 on EOF
   * @return -1 on error
   */
  typedef int64_t (*mpv_stream_cb_read_fn) (void *cookie, char *buf,
                                            uint64_t nbytes);

  /**
   * Seek callback used to implement a custom stream.
   *
   * Note that mpv will issue a seek to position 0 immediately after opening.
   * This is used to test whether the stream is seekable (since seekability
   * might depend on the URI contents, not just the protocol). Return
   * MPV_ERROR_UNSUPPORTED if seeking is not implemented for this stream. This
   * seek also serves to establish the fact that streams start at position 0.
   *
   * This callback can be NULL, in which it behaves as if always returning
   * MPV_ERROR_UNSUPPORTED.
   *
   * @param cookie opaque cookie identifying the stream,
   *               returned from mpv_stream_cb_open_fn
   * @param offset target absolute stream position
   * @return the resulting offset of the stream
   *         MPV_ERROR_UNSUPPORTED or MPV_ERROR_GENERIC if the seek failed
   */
  typedef int64_t (*mpv_stream_cb_seek_fn) (void *cookie, int64_t offset);

  /**
   * Size callback used to implement a custom stream.
   *
   * Return MPV_ERROR_UNSUPPORTED if no size is known.
   *
   * This callback can be NULL, in which it behaves as if always returning
   * MPV_ERROR_UNSUPPORTED.
   *
   * @param cookie opaque cookie identifying the stream,
   *               returned from mpv_stream_cb_open_fn
   * @return the total size in bytes of the stream
   */
  typedef int64_t (*mpv_stream_cb_size_fn) (void *cookie);

  /**
   * Close callback used to implement a custom stream.
   *
   * @param cookie opaque cookie identifying the stream,
   *               returned from mpv_stream_cb_open_fn
   */
  typedef void (*mpv_stream_cb_close_fn) (void *cookie);

  /**
   * Cancel callback used to implement a custom stream.
   *
   * This callback is used to interrupt any current or future read and seek
   * operations. It will be called from a separate thread than the demux
   * thread, and should not block.
   *
   * This callback can be NULL.
   *
   * Available since API 1.106.
   *
   * @param cookie opaque cookie identifying the stream,
   *               returned from mpv_stream_cb_open_fn
   */
  typedef void (*mpv_stream_cb_cancel_fn) (void *cookie);

  /**
   * See mpv_stream_cb_open_ro_fn callback.
   */
  typedef struct mpv_stream_cb_info
  {
    /**
     * Opaque user-provided value, which will be passed to the other callbacks.
     * The close callback will be called to release the cookie. It is not
     * interpreted by mpv. It doesn't even need to be a valid pointer.
     *
     * The user sets this in the mpv_stream_cb_open_ro_fn callback.
     */
    void *cookie;

    /**
     * Callbacks set by the user in the mpv_stream_cb_open_ro_fn callback. Some
     * of them are optional, and can be left unset.
     *
     * The following callbacks are mandatory: read_fn, close_fn
     */
    mpv_stream_cb_read_fn read_fn;
    mpv_stream_cb_seek_fn seek_fn;
    mpv_stream_cb_size_fn size_fn;
    mpv_stream_cb_close_fn close_fn;
    mpv_stream_cb_cancel_fn cancel_fn; /* since API 1.106 */
  } mpv_stream_cb_info;

  /**
   * Open callback used to implement a custom read-only (ro) stream. The user
   * must set the callback fields in the passed info struct. The cookie field
   * also can be set to store state associated to the stream instance.
   *
   * Note that the info struct is valid only for the duration of this callback.
   * You can't change the callbacks or the pointer to the cookie at a later
   * point.
   *
   * Each stream instance created by the open callback can have different
   * callbacks.
   *
   * The close_fn callback will terminate the stream instance. The pointers to
   * your callbacks and cookie will be discarded, and the callbacks will not be
   * called again.
   *
   * @param user_data opaque user data provided via mpv_stream_cb_add()
   * @param uri name of the stream to be opened (with protocol prefix)
   * @param info fields which the user should fill
   * @return 0 on success, MPV_ERROR_LOADING_FAILED if the URI cannot be
   * opened.
   */
  typedef int (*mpv_stream_cb_open_ro_fn) (void *user_data, char *uri,
                                           mpv_stream_cb_info *info);

  /**
   * Add a custom stream protocol. This will register a protocol handler under
   * the given protocol prefix, and invoke the given callbacks if an URI with
   * the matching protocol prefix is opened.
   *
   * The "ro" is for read-only - only read-only streams can be registered with
   * this function.
   *
   * The callback remains registered until the mpv core is registered.
   *
   * If a custom stream with the same name is already registered, then the
   * MPV_ERROR_INVALID_PARAMETER error is returned.
   *
   * @param protocol protocol prefix, for example "foo" for "foo://" URIs
   * @param user_data opaque pointer passed into the mpv_stream_cb_open_fn
   *                  callback.
   * @return error code
   */
  MPV_EXPORT int mpv_stream_cb_add_ro (mpv_handle *ctx, const char *protocol,
                                       void *user_data,
                                       mpv_stream_cb_open_ro_fn open_fn);

#ifdef MPV_CPLUGIN_DYNAMIC_SYM

  MPV_DEFINE_SYM_PTR (mpv_stream_cb_add_ro)
#define mpv_stream_cb_add_ro pfn_mpv_stream_cb_add_ro

#endif

#ifdef __cplusplus
}
#endif

#endif