text: /*
   * copyright (c) 2001 Fabrice Bellard
   *
   * This file is part of FFmpeg.
   *
   * FFmpeg is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * FFmpeg is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with FFmpeg; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
   */
  #ifndef AVFORMAT_AVIO_H
  #define AVFORMAT_AVIO_H
  
  /**
   * @file
   * @ingroup lavf_io
   * Buffered I/O operations
   */
  
  #include <stdint.h>
  
  #include "libavutil/common.h"
  #include "libavutil/dict.h"
  #include "libavutil/log.h"
  
  #include "libavformat/version.h"
  
  /**
   * Seeking works like for a local file.
   */
  #define AVIO_SEEKABLE_NORMAL (1 << 0)
  
  /**
   * Seeking by timestamp with avio_seek_time() is possible.
   */
  #define AVIO_SEEKABLE_TIME   (1 << 1)
  
  /**
   * Callback for checking whether to abort blocking functions.
   * AVERROR_EXIT is returned in this case by the interrupted
   * function. During blocking operations, callback is called with
   * opaque as parameter. If the callback returns 1, the
   * blocking operation will be aborted.
   *
   * No members can be added to this struct without a major bump, if
   * new elements have been added after this struct in AVFormatContext
   * or AVIOContext.
   */
  typedef struct AVIOInterruptCB {
      int (*callback)(void*);
      void *opaque;
  } AVIOInterruptCB;
  
  /**
   * Directory entry types.
   */
  enum AVIODirEntryType {
      AVIO_ENTRY_UNKNOWN,
      AVIO_ENTRY_BLOCK_DEVICE,
      AVIO_ENTRY_CHARACTER_DEVICE,
      AVIO_ENTRY_DIRECTORY,
      AVIO_ENTRY_NAMED_PIPE,
      AVIO_ENTRY_SYMBOLIC_LINK,
      AVIO_ENTRY_SOCKET,
      AVIO_ENTRY_FILE,
      AVIO_ENTRY_SERVER,
      AVIO_ENTRY_SHARE,
      AVIO_ENTRY_WORKGROUP,
  };
  
  /**
   * Describes single entry of the directory.
   *
   * Only name and type fields are guaranteed be set.
   * Rest of fields are protocol or/and platform dependent and might be unknown.
   */
  typedef struct AVIODirEntry {
      char *name;                           /**< Filename */
      int type;                             /**< Type of the entry */
      int utf8;                             /**< Set to 1 when name is encoded with UTF-8, 0 otherwise.
                                                 Name can be encoded with UTF-8 even though 0 is set. */
      int64_t size;                         /**< File size in bytes, -1 if unknown. */
      int64_t modification_timestamp;       /**< Time of last modification in microseconds since unix
                                                 epoch, -1 if unknown. */
      int64_t access_timestamp;             /**< Time of last access in microseconds since unix epoch,
                                                 -1 if unknown. */
      int64_t status_change_timestamp;      /**< Time of last status change in microseconds since unix
                                                 epoch, -1 if unknown. */
      int64_t user_id;                      /**< User ID of owner, -1 if unknown. */
      int64_t group_id;                     /**< Group ID of owner, -1 if unknown. */
      int64_t filemode;                     /**< Unix file mode, -1 if unknown. */
  } AVIODirEntry;
  
  typedef struct AVIODirContext {
      struct URLContext *url_context;
  } AVIODirContext;
  
  /**
   * Different data types that can be returned via the AVIO
   * write_data_type callback.
   */
  enum AVIODataMarkerType {
      /**
       * Header data; this needs to be present for the stream to be decodeable.
       */
      AVIO_DATA_MARKER_HEADER,
      /**
       * A point in the output bytestream where a decoder can start decoding
       * (i.e. a keyframe). A demuxer/decoder given the data flagged with
       * AVIO_DATA_MARKER_HEADER, followed by any AVIO_DATA_MARKER_SYNC_POINT,
       * should give decodeable results.
       */
      AVIO_DATA_MARKER_SYNC_POINT,
      /**
       * A point in the output bytestream where a demuxer can start parsing
       * (for non self synchronizing bytestream formats). That is, any
       * non-keyframe packet start point.
       */
      AVIO_DATA_MARKER_BOUNDARY_POINT,
      /**
       * This is any, unlabelled data. It can either be a muxer not marking
       * any positions at all, it can be an actual boundary/sync point
       * that the muxer chooses not to mark, or a later part of a packet/fragment
       * that is cut into multiple write callbacks due to limited IO buffer size.
       */
      AVIO_DATA_MARKER_UNKNOWN,
      /**
       * Trailer data, which doesn't contain actual content, but only for
       * finalizing the output file.
       */
      AVIO_DATA_MARKER_TRAILER,
      /**
       * A point in the output bytestream where the underlying AVIOContext might
       * flush the buffer depending on latency or buffering requirements. Typically
       * means the end of a packet.
       */
      AVIO_DATA_MARKER_FLUSH_POINT,
  };
  
  /**
   * Bytestream IO Context.
   * New fields can be added to the end with minor version bumps.
   * Removal, reordering and changes to existing fields require a major
   * version bump.
   * sizeof(AVIOContext) must not be used outside libav*.
   *
   * @note None of the function pointers in AVIOContext should be called
   *       directly, they should only be set by the client application
   *       when implementing custom I/O. Normally these are set to the
   *       function pointers specified in avio_alloc_context()
   */
  typedef struct AVIOContext {
      /**
       * A class for private options.
       *
       * If this AVIOContext is created by avio_open2(), av_class is set and
       * passes the options down to protocols.
       *
       * If this AVIOContext is manually allocated, then av_class may be set by
       * the caller.
       *
       * warning -- this field can be NULL, be sure to not pass this AVIOContext
       * to any av_opt_* functions in that case.
       */
      const AVClass *av_class;
  
      /*
       * The following shows the relationship between buffer, buf_ptr,
       * buf_ptr_max, buf_end, buf_size, and pos, when reading and when writing
       * (since AVIOContext is used for both):
       *
       **********************************************************************************
       *                                   READING
       **********************************************************************************
       *
       *                            |              buffer_size              |
       *                            |---------------------------------------|
       *                            |                                       |
       *
       *                         buffer          buf_ptr       buf_end
       *                            +---------------+-----------------------+
       *                            |/ / / / / / / /|/ / / / / / /|         |
       *  read buffer:              |/ / consumed / | to be read /|         |
       *                            |/ / / / / / / /|/ / / / / / /|         |
       *                            +---------------+-----------------------+
       *
       *                                                         pos
       *              +-------------------------------------------+-----------------+
       *  input file: |                                           |                 |
       *              +-------------------------------------------+-----------------+
       *
       *
       **********************************************************************************
       *                                   WRITING
       **********************************************************************************
       *
       *                             |          buffer_size                 |
       *                             |--------------------------------------|
       *                             |                                      |
       *
       *                                                buf_ptr_max
       *                          buffer                 (buf_ptr)       buf_end
       *                             +-----------------------+--------------+
       *                             |/ / / / / / / / / / / /|              |
       *  write buffer:              | / / to be flushed / / |              |
       *                             |/ / / / / / / / / / / /|              |
       *                             +-----------------------+--------------+
       *                               buf_ptr can be in this
       *                               due to a backward seek
       *
       *                            pos
       *               +-------------+----------------------------------------------+
       *  output file: |             |                                              |
       *               +-------------+----------------------------------------------+
       *
       */
      unsigned char *buffer;  /**< Start of the buffer. */
      int buffer_size;        /**< Maximum buffer size */
      unsigned char *buf_ptr; /**< Current position in the buffer */
      unsigned char *buf_end; /**< End of the data, may be less than
                                   buffer+buffer_size if the read function returned
                                   less data than requested, e.g. for streams where
                                   no more data has been received yet. */
      void *opaque;           /**< A private pointer, passed to the read/write/seek/...
                                   functions. */
      int (*read_packet)(void *opaque, uint8_t *buf, int buf_size);
      int (*write_packet)(void *opaque, uint8_t *buf, int buf_size);
      int64_t (*seek)(void *opaque, int64_t offset, int whence);
      int64_t pos;            /**< position in the file of the current buffer */
      int eof_reached;        /**< true if was unable to read due to error or eof */
      int write_flag;         /**< true if open for writing */
      int max_packet_size;
      unsigned long checksum;
      unsigned char *checksum_ptr;
      unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size);
      int error;              /**< contains the error code or 0 if no error happened */
      /**
       * Pause or resume playback for network streaming protocols - e.g. MMS.
       */
      int (*read_pause)(void *opaque, int pause);
      /**
       * Seek to a given timestamp in stream with the specified stream_index.
       * Needed for some network streaming protocols which don't support seeking
       * to byte position.
       */
      int64_t (*read_seek)(void *opaque, int stream_index,
                           int64_t timestamp, int flags);
      /**
       * A combination of AVIO_SEEKABLE_ flags or 0 when the stream is not seekable.
       */
      int seekable;
  
      /**
       * max filesize, used to limit allocations
       * This field is internal to include.libavformat and access from outside is not allowed.
       */
      int64_t maxsize;
  
      /**
       * avio_read and avio_write should if possible be satisfied directly
       * instead of going through a buffer, and avio_seek will always
       * call the underlying seek function directly.
       */
      int direct;
  
      /**
       * Bytes read statistic
       * This field is internal to include.libavformat and access from outside is not allowed.
       */
      int64_t bytes_read;
  
      /**
       * seek statistic
       * This field is internal to include.libavformat and access from outside is not allowed.
       */
      int seek_count;
  
      /**
       * writeout statistic
       * This field is internal to include.libavformat and access from outside is not allowed.
       */
      int writeout_count;
  
      /**
       * Original buffer size
       * used internally after probing and ensure seekback to reset the buffer size
       * This field is internal to include.libavformat and access from outside is not allowed.
       */
      int orig_buffer_size;
  
      /**
       * Threshold to favor readahead over seek.
       * This is current internal only, do not use from outside.
       */
      int short_seek_threshold;
  
      /**
       * ',' separated list of allowed protocols.
       */
      const char *protocol_whitelist;
  
      /**
       * ',' separated list of disallowed protocols.
       */
      const char *protocol_blacklist;
  
      /**
       * A callback that is used instead of write_packet.
       */
      int (*write_data_type)(void *opaque, uint8_t *buf, int buf_size,
                             enum AVIODataMarkerType type, int64_t time);
      /**
       * If set, don't call write_data_type separately for AVIO_DATA_MARKER_BOUNDARY_POINT,
       * but ignore them and treat them as AVIO_DATA_MARKER_UNKNOWN (to avoid needlessly
       * small chunks of data returned from the callback).
       */
      int ignore_boundary_point;
  
      /**
       * Internal, not meant to be used from outside of AVIOContext.
       */
      enum AVIODataMarkerType current_type;
      int64_t last_time;
  
      /**
       * A callback that is used instead of short_seek_threshold.
       * This is current internal only, do not use from outside.
       */
      int (*short_seek_get)(void *opaque);
  
      int64_t written;
  
      /**
       * Maximum reached position before a backward seek in the write buffer,
       * used keeping track of already written data for a later flush.
       */
      unsigned char *buf_ptr_max;
  
      /**
       * Try to buffer at least this amount of data before flushing it
       */
      int min_packet_size;
  } AVIOContext;
  
  /**
   * Return the name of the protocol that will handle the passed URL.
   *
   * NULL is returned if no protocol could be found for the given URL.
   *
   * @return Name of the protocol or NULL.
   */
  const char *avio_find_protocol_name(const char *url);
  
  /**
   * Return AVIO_FLAG_* access flags corresponding to the access permissions
   * of the resource in url, or a negative value corresponding to an
   * AVERROR code in case of failure. The returned access flags are
   * masked by the value in flags.
   *
   * @note This function is intrinsically unsafe, in the sense that the
   * checked resource may change its existence or permission status from
   * one call to another. Thus you should not trust the returned value,
   * unless you are sure that no other processes are accessing the
   * checked resource.
   */
  int avio_check(const char *url, int flags);
  
  /**
   * Move or rename a resource.
   *
   * @note url_src and url_dst should share the same protocol and authority.
   *
   * @param url_src url to resource to be moved
   * @param url_dst new url to resource if the operation succeeded
   * @return >=0 on success or negative on error.
   */
  int avpriv_io_move(const char *url_src, const char *url_dst);
  
  /**
   * Delete a resource.
   *
   * @param url resource to be deleted.
   * @return >=0 on success or negative on error.
   */
  int avpriv_io_delete(const char *url);
  
  /**
   * Open directory for reading.
   *
   * @param s       directory read context. Pointer to a NULL pointer must be passed.
   * @param url     directory to be listed.
   * @param options A dictionary filled with protocol-private options. On return
   *                this parameter will be destroyed and replaced with a dictionary
   *                containing options that were not found. May be NULL.
   * @return >=0 on success or negative on error.
   */
  int avio_open_dir(AVIODirContext **s, const char *url, AVDictionary **options);
  
  /**
   * Get next directory entry.
   *
   * Returned entry must be freed with avio_free_directory_entry(). In particular
   * it may outlive AVIODirContext.
   *
   * @param s         directory read context.
   * @param[out] next next entry or NULL when no more entries.
   * @return >=0 on success or negative on error. End of list is not considered an
   *             error.
   */
  int avio_read_dir(AVIODirContext *s, AVIODirEntry **next);
  
  /**
   * Close directory.
   *
   * @note Entries created using avio_read_dir() are not deleted and must be
   * freeded with avio_free_directory_entry().
   *
   * @param s         directory read context.
   * @return >=0 on success or negative on error.
   */
  int avio_close_dir(AVIODirContext **s);
  
  /**
   * Free entry allocated by avio_read_dir().
   *
   * @param entry entry to be freed.
   */
  void avio_free_directory_entry(AVIODirEntry **entry);
  
  /**
   * Allocate and initialize an AVIOContext for buffered I/O. It must be later
   * freed with avio_context_free().
   *
   * @param buffer Memory block for input/output operations via AVIOContext.
   *        The buffer must be allocated with av_malloc() and friends.
   *        It may be freed and replaced with a new buffer by include.libavformat.
   *        AVIOContext.buffer holds the buffer currently in use,
   *        which must be later freed with av_free().
   * @param buffer_size The buffer size is very important for performance.
   *        For protocols with fixed blocksize it should be set to this blocksize.
   *        For others a typical size is a cache page, e.g. 4kb.
   * @param write_flag Set to 1 if the buffer should be writable, 0 otherwise.
   * @param opaque An opaque pointer to user-specific data.
   * @param read_packet  A function for refilling the buffer, may be NULL.
   *                     For stream protocols, must never return 0 but rather
   *                     a proper AVERROR code.
   * @param write_packet A function for writing the buffer contents, may be NULL.
   *        The function may not change the input buffers content.
   * @param seek A function for seeking to specified byte position, may be NULL.
   *
   * @return Allocated AVIOContext or NULL on failure.
   */
  AVIOContext *avio_alloc_context(
                    unsigned char *buffer,
                    int buffer_size,
                    int write_flag,
                    void *opaque,
                    int (*read_packet)(void *opaque, uint8_t *buf, int buf_size),
                    int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),
                    int64_t (*seek)(void *opaque, int64_t offset, int whence));
  
  /**
   * Free the supplied IO context and everything associated with it.
   *
   * @param s Double pointer to the IO context. This function will write NULL
   * into s.
   */
  void avio_context_free(AVIOContext **s);
  
  void avio_w8(AVIOContext *s, int b);
  void avio_write(AVIOContext *s, const unsigned char *buf, int size);
  void avio_wl64(AVIOContext *s, uint64_t val);
  void avio_wb64(AVIOContext *s, uint64_t val);
  void avio_wl32(AVIOContext *s, unsigned int val);
  void avio_wb32(AVIOContext *s, unsigned int val);
  void avio_wl24(AVIOContext *s, unsigned int val);
  void avio_wb24(AVIOContext *s, unsigned int val);
  void avio_wl16(AVIOContext *s, unsigned int val);
  void avio_wb16(AVIOContext *s, unsigned int val);
  
  /**
   * Write a NULL-terminated string.
   * @return number of bytes written.
   */
  int avio_put_str(AVIOContext *s, const char *str);
  
  /**
   * Convert an UTF-8 string to UTF-16LE and write it.
   * @param s the AVIOContext
   * @param str NULL-terminated UTF-8 string
   *
   * @return number of bytes written.
   */
  int avio_put_str16le(AVIOContext *s, const char *str);
  
  /**
   * Convert an UTF-8 string to UTF-16BE and write it.
   * @param s the AVIOContext
   * @param str NULL-terminated UTF-8 string
   *
   * @return number of bytes written.
   */
  int avio_put_str16be(AVIOContext *s, const char *str);
  
  /**
   * Mark the written bytestream as a specific type.
   *
   * Zero-length ranges are omitted from the output.
   *
   * @param time the stream time the current bytestream pos corresponds to
   *             (in AV_TIME_BASE units), or AV_NOPTS_VALUE if unknown or not
   *             applicable
   * @param type the kind of data written starting at the current pos
   */
  void avio_write_marker(AVIOContext *s, int64_t time, enum AVIODataMarkerType type);
  
  /**
   * ORing this as the "whence" parameter to a seek function causes it to
   * return the filesize without seeking anywhere. Supporting this is optional.
   * If it is not supported then the seek function will return <0.
   */
  #define AVSEEK_SIZE 0x10000
  
  /**
   * Passing this flag as the "whence" parameter to a seek function causes it to
   * seek by any means (like reopening and linear reading) or other normally unreasonable
   * means that can be extremely slow.
   * This may be ignored by the seek code.
   */
  #define AVSEEK_FORCE 0x20000
  
  /**
   * fseek() equivalent for AVIOContext.
   * @return new position or AVERROR.
   */
  int64_t avio_seek(AVIOContext *s, int64_t offset, int whence);
  
  /**
   * Skip given number of bytes forward
   * @return new position or AVERROR.
   */
  int64_t avio_skip(AVIOContext *s, int64_t offset);
  
  /**
   * ftell() equivalent for AVIOContext.
   * @return position or AVERROR.
   */
  static av_always_inline int64_t avio_tell(AVIOContext *s)
  {
      return avio_seek(s, 0, SEEK_CUR);
  }
  
  /**
   * Get the filesize.
   * @return filesize or AVERROR
   */
  int64_t avio_size(AVIOContext *s);
  
  /**
   * Similar to feof() but also returns nonzero on read errors.
   * @return non zero if and only if at end of file or a read error happened when reading.
   */
  int avio_feof(AVIOContext *s);
  
  /**
   * Writes a formatted string to the context.
   * @return number of bytes written, < 0 on error.
   */
  int avio_printf(AVIOContext *s, const char *fmt, ...) av_printf_format(2, 3);
  
  /**
   * Write a NULL terminated array of strings to the context.
   * Usually you don't need to use this function directly but its macro wrapper,
   * avio_print.
   */
  void avio_print_string_array(AVIOContext *s, const char *strings[]);
  
  /**
   * Write strings (const char *) to the context.
   * This is a convenience macro around avio_print_string_array and it
   * automatically creates the string array from the variable argument list.
   * For simple string concatenations this function is more performant than using
   * avio_printf since it does not need a temporary buffer.
   */
  #define avio_print(s, ...) \
      avio_print_string_array(s, (const char*[]){__VA_ARGS__, NULL})
  
  /**
   * Force flushing of buffered data.
   *
   * For write streams, force the buffered data to be immediately written to the output,
   * without to wait to fill the internal buffer.
   *
   * For read streams, discard all currently buffered data, and advance the
   * reported file position to that of the underlying stream. This does not
   * read new data, and does not perform any seeks.
   */
  void avio_flush(AVIOContext *s);
  
  /**
   * Read size bytes from AVIOContext into buf.
   * @return number of bytes read or AVERROR
   */
  int avio_read(AVIOContext *s, unsigned char *buf, int size);
  
  /**
   * Read size bytes from AVIOContext into buf. Unlike avio_read(), this is allowed
   * to read fewer bytes than requested. The missing bytes can be read in the next
   * call. This always tries to read at least 1 byte.
   * Useful to reduce latency in certain cases.
   * @return number of bytes read or AVERROR
   */
  int avio_read_partial(AVIOContext *s, unsigned char *buf, int size);
  
  /**
   * @name Functions for reading from AVIOContext
   * @{
   *
   * @note return 0 if EOF, so you cannot use it if EOF handling is
   *       necessary
   */
  int          avio_r8  (AVIOContext *s);
  unsigned int avio_rl16(AVIOContext *s);
  unsigned int avio_rl24(AVIOContext *s);
  unsigned int avio_rl32(AVIOContext *s);
  uint64_t     avio_rl64(AVIOContext *s);
  unsigned int avio_rb16(AVIOContext *s);
  unsigned int avio_rb24(AVIOContext *s);
  unsigned int avio_rb32(AVIOContext *s);
  uint64_t     avio_rb64(AVIOContext *s);
  /**
   * @}
   */
  
  /**
   * Read a string from pb into buf. The reading will terminate when either
   * a NULL character was encountered, maxlen bytes have been read, or nothing
   * more can be read from pb. The result is guaranteed to be NULL-terminated, it
   * will be truncated if buf is too small.
   * Note that the string is not interpreted or validated in any way, it
   * might get truncated in the middle of a sequence for multi-byte encodings.
   *
   * @return number of bytes read (is always <= maxlen).
   * If reading ends on EOF or error, the return value will be one more than
   * bytes actually read.
   */
  int avio_get_str(AVIOContext *pb, int maxlen, char *buf, int buflen);
  
  /**
   * Read a UTF-16 string from pb and convert it to UTF-8.
   * The reading will terminate when either a null or invalid character was
   * encountered or maxlen bytes have been read.
   * @return number of bytes read (is always <= maxlen)
   */
  int avio_get_str16le(AVIOContext *pb, int maxlen, char *buf, int buflen);
  int avio_get_str16be(AVIOContext *pb, int maxlen, char *buf, int buflen);
  
  
  /**
   * @name URL open modes
   * The flags argument to avio_open must be one of the following
   * constants, optionally ORed with other flags.
   * @{
   */
  #define AVIO_FLAG_READ  1                                      /**< read-only */
  #define AVIO_FLAG_WRITE 2                                      /**< write-only */
  #define AVIO_FLAG_READ_WRITE (AVIO_FLAG_READ|AVIO_FLAG_WRITE)  /**< read-write pseudo flag */
  /**
   * @}
   */
  
  /**
   * Use non-blocking mode.
   * If this flag is set, operations on the context will return
   * AVERROR(EAGAIN) if they can not be performed immediately.
   * If this flag is not set, operations on the context will never return
   * AVERROR(EAGAIN).
   * Note that this flag does not affect the opening/connecting of the
   * context. Connecting a protocol will always block if necessary (e.g. on
   * network protocols) but never hang (e.g. on busy devices).
   * Warning: non-blocking protocols is work-in-progress; this flag may be
   * silently ignored.
   */
  #define AVIO_FLAG_NONBLOCK 8
  
  /**
   * Use direct mode.
   * avio_read and avio_write should if possible be satisfied directly
   * instead of going through a buffer, and avio_seek will always
   * call the underlying seek function directly.
   */
  #define AVIO_FLAG_DIRECT 0x8000
  
  /**
   * Create and initialize a AVIOContext for accessing the
   * resource indicated by url.
   * @note When the resource indicated by url has been opened in
   * read+write mode, the AVIOContext can be used only for writing.
   *
   * @param s Used to return the pointer to the created AVIOContext.
   * In case of failure the pointed to value is set to NULL.
   * @param url resource to access
   * @param flags flags which control how the resource indicated by url
   * is to be opened
   * @return >= 0 in case of success, a negative value corresponding to an
   * AVERROR code in case of failure
   */
  int avio_open(AVIOContext **s, const char *url, int flags);
  
  /**
   * Create and initialize a AVIOContext for accessing the
   * resource indicated by url.
   * @note When the resource indicated by url has been opened in
   * read+write mode, the AVIOContext can be used only for writing.
   *
   * @param s Used to return the pointer to the created AVIOContext.
   * In case of failure the pointed to value is set to NULL.
   * @param url resource to access
   * @param flags flags which control how the resource indicated by url
   * is to be opened
   * @param int_cb an interrupt callback to be used at the protocols level
   * @param options  A dictionary filled with protocol-private options. On return
   * this parameter will be destroyed and replaced with a dict containing options
   * that were not found. May be NULL.
   * @return >= 0 in case of success, a negative value corresponding to an
   * AVERROR code in case of failure
   */
  int avio_open2(AVIOContext **s, const char *url, int flags,
                 const AVIOInterruptCB *int_cb, AVDictionary **options);
  
  /**
   * Close the resource accessed by the AVIOContext s and free it.
   * This function can only be used if s was opened by avio_open().
   *
   * The internal buffer is automatically flushed before closing the
   * resource.
   *
   * @return 0 on success, an AVERROR < 0 on error.
   * @see avio_closep
   */
  int avio_close(AVIOContext *s);
  
  /**
   * Close the resource accessed by the AVIOContext *s, free it
   * and set the pointer pointing to it to NULL.
   * This function can only be used if s was opened by avio_open().
   *
   * The internal buffer is automatically flushed before closing the
   * resource.
   *
   * @return 0 on success, an AVERROR < 0 on error.
   * @see avio_close
   */
  int avio_closep(AVIOContext **s);
  
  
  /**
   * Open a write only memory stream.
   *
   * @param s new IO context
   * @return zero if no error.
   */
  int avio_open_dyn_buf(AVIOContext **s);
  
  /**
   * Return the written size and a pointer to the buffer.
   * The AVIOContext stream is left intact.
   * The buffer must NOT be freed.
   * No padding is added to the buffer.
   *
   * @param s IO context
   * @param pbuffer pointer to a byte buffer
   * @return the length of the byte buffer
   */
  int avio_get_dyn_buf(AVIOContext *s, uint8_t **pbuffer);
  
  /**
   * Return the written size and a pointer to the buffer. The buffer
   * must be freed with av_free().
   * Padding of AV_INPUT_BUFFER_PADDING_SIZE is added to the buffer.
   *
   * @param s IO context
   * @param pbuffer pointer to a byte buffer
   * @return the length of the byte buffer
   */
  int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer);
  
  /**
   * Iterate through names of available protocols.
   *
   * @param opaque A private pointer representing current protocol.
   *        It must be a pointer to NULL on first iteration and will
   *        be updated by successive calls to avio_enum_protocols.
   * @param output If set to 1, iterate over output protocols,
   *               otherwise over input protocols.
   *
   * @return A static string containing the name of current protocol or NULL
   */
  const char *avio_enum_protocols(void **opaque, int output);
  
  /**
   * Get AVClass by names of available protocols.
   *
   * @return A AVClass of input protocol name or NULL
   */
  const AVClass *avio_protocol_get_class(const char *name);
  
  /**
   * Pause and resume playing - only meaningful if using a network streaming
   * protocol (e.g. MMS).
   *
   * @param h     IO context from which to call the read_pause function pointer
   * @param pause 1 for pause, 0 for resume
   */
  int     avio_pause(AVIOContext *h, int pause);
  
  /**
   * Seek to a given timestamp relative to some component stream.
   * Only meaningful if using a network streaming protocol (e.g. MMS.).
   *
   * @param h IO context from which to call the seek function pointers
   * @param stream_index The stream index that the timestamp is relative to.
   *        If stream_index is (-1) the timestamp should be in AV_TIME_BASE
   *        units from the beginning of the presentation.
   *        If a stream_index >= 0 is used and the protocol does not support
   *        seeking based on component streams, the call will fail.
   * @param timestamp timestamp in AVStream.time_base units
   *        or if there is no stream specified then in AV_TIME_BASE units.
   * @param flags Optional combination of AVSEEK_FLAG_BACKWARD, AVSEEK_FLAG_BYTE
   *        and AVSEEK_FLAG_ANY. The protocol may silently ignore
   *        AVSEEK_FLAG_BACKWARD and AVSEEK_FLAG_ANY, but AVSEEK_FLAG_BYTE will
   *        fail if used and not supported.
   * @return >= 0 on success
   * @see AVInputFormat::read_seek
   */
  int64_t avio_seek_time(AVIOContext *h, int stream_index,
                         int64_t timestamp, int flags);
  
  /* Avoid a warning. The header can not be included because it breaks c++. */
  struct AVBPrint;
  
  /**
   * Read contents of h into print buffer, up to max_size bytes, or up to EOF.
   *
   * @return 0 for success (max_size bytes read or EOF reached), negative error
   * code otherwise
   */
  int avio_read_to_bprint(AVIOContext *h, struct AVBPrint *pb, size_t max_size);
  
  /**
   * Accept and allocate a client context on a server context.
   * @param  s the server context
   * @param  c the client context, must be unallocated
   * @return   >= 0 on success or a negative value corresponding
   *           to an AVERROR on failure
   */
  int avio_accept(AVIOContext *s, AVIOContext **c);
  
  /**
   * Perform one step of the protocol handshake to accept a new client.
   * This function must be called on a client returned by avio_accept() before
   * using it as a read/write context.
   * It is separate from avio_accept() because it may block.
   * A step of the handshake is defined by places where the application may
   * decide to change the proceedings.
   * For example, on a protocol with a request header and a reply header, each
   * one can constitute a step because the application may use the parameters
   * from the request to change parameters in the reply; or each individual
   * chunk of the request can constitute a step.
   * If the handshake is already finished, avio_handshake() does nothing and
   * returns 0 immediately.
   *
   * @param  c the client context to perform the handshake on
   * @return   0   on a complete and successful handshake
   *           > 0 if the handshake progressed, but is not complete
   *           < 0 for an AVERROR code
   */
  int avio_handshake(AVIOContext *c);
  #endif /* AVFORMAT_AVIO_H */
  