2 * copyright (c) 2001 Fabrice Bellard
4 * This file is part of FFmpeg.
6 * FFmpeg is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
11 * FFmpeg is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with FFmpeg; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 #ifndef AVFORMAT_AVIO_H
21 #define AVFORMAT_AVIO_H
26 * Buffered I/O operations
31 #include "libavutil/common.h"
32 #include "libavutil/dict.h"
33 #include "libavutil/log.h"
35 #include "libavformat/version.h"
37 #define AVIO_SEEKABLE_NORMAL 0x0001 /**< Seeking works like for a local file */
40 * Callback for checking whether to abort blocking functions.
41 * AVERROR_EXIT is returned in this case by the interrupted
42 * function. During blocking operations, callback is called with
43 * opaque as parameter. If the callback returns 1, the
44 * blocking operation will be aborted.
46 * No members can be added to this struct without a major bump, if
47 * new elements have been added after this struct in AVFormatContext
50 typedef struct AVIOInterruptCB {
51 int (*callback)(void*);
56 * Directory entry types.
58 enum AVIODirEntryType {
60 AVIO_ENTRY_BLOCK_DEVICE,
61 AVIO_ENTRY_CHARACTER_DEVICE,
63 AVIO_ENTRY_NAMED_PIPE,
64 AVIO_ENTRY_SYMBOLIC_LINK,
73 * Describes single entry of the directory.
75 * Only name and type fields are guaranteed be set.
76 * Rest of fields are protocol or/and platform dependent and might be unknown.
78 typedef struct AVIODirEntry {
79 char *name; /**< Filename */
80 int type; /**< Type of the entry */
81 int utf8; /**< Set to 1 when name is encoded with UTF-8, 0 otherwise.
82 Name can be encoded with UTF-8 even though 0 is set. */
83 int64_t size; /**< File size in bytes, -1 if unknown. */
84 int64_t modification_timestamp; /**< Time of last modification in microseconds since unix
85 epoch, -1 if unknown. */
86 int64_t access_timestamp; /**< Time of last access in microseconds since unix epoch,
88 int64_t status_change_timestamp; /**< Time of last status change in microseconds since unix
89 epoch, -1 if unknown. */
90 int64_t user_id; /**< User ID of owner, -1 if unknown. */
91 int64_t group_id; /**< Group ID of owner, -1 if unknown. */
92 int64_t filemode; /**< Unix file mode, -1 if unknown. */
95 typedef struct AVIODirContext {
96 struct URLContext *url_context;
100 * Different data types that can be returned via the AVIO
101 * write_data_type callback.
103 enum AVIODataMarkerType {
105 * Header data; this needs to be present for the stream to be decodeable.
107 AVIO_DATA_MARKER_HEADER,
109 * A point in the output bytestream where a decoder can start decoding
110 * (i.e. a keyframe). A demuxer/decoder given the data flagged with
111 * AVIO_DATA_MARKER_HEADER, followed by any AVIO_DATA_MARKER_SYNC_POINT,
112 * should give decodeable results.
114 AVIO_DATA_MARKER_SYNC_POINT,
116 * A point in the output bytestream where a demuxer can start parsing
117 * (for non self synchronizing bytestream formats). That is, any
118 * non-keyframe packet start point.
120 AVIO_DATA_MARKER_BOUNDARY_POINT,
122 * This is any, unlabelled data. It can either be a muxer not marking
123 * any positions at all, it can be an actual boundary/sync point
124 * that the muxer chooses not to mark, or a later part of a packet/fragment
125 * that is cut into multiple write callbacks due to limited IO buffer size.
127 AVIO_DATA_MARKER_UNKNOWN,
129 * Trailer data, which doesn't contain actual content, but only for
130 * finalizing the output file.
132 AVIO_DATA_MARKER_TRAILER
136 * Bytestream IO Context.
137 * New fields can be added to the end with minor version bumps.
138 * Removal, reordering and changes to existing fields require a major
140 * sizeof(AVIOContext) must not be used outside libav*.
142 * @note None of the function pointers in AVIOContext should be called
143 * directly, they should only be set by the client application
144 * when implementing custom I/O. Normally these are set to the
145 * function pointers specified in avio_alloc_context()
147 typedef struct AVIOContext {
149 * A class for private options.
151 * If this AVIOContext is created by avio_open2(), av_class is set and
152 * passes the options down to protocols.
154 * If this AVIOContext is manually allocated, then av_class may be set by
157 * warning -- this field can be NULL, be sure to not pass this AVIOContext
158 * to any av_opt_* functions in that case.
160 const AVClass *av_class;
163 * The following shows the relationship between buffer, buf_ptr, buf_end, buf_size,
164 * and pos, when reading and when writing (since AVIOContext is used for both):
166 **********************************************************************************
168 **********************************************************************************
171 * |---------------------------------------|
174 * buffer buf_ptr buf_end
175 * +---------------+-----------------------+
176 * |/ / / / / / / /|/ / / / / / /| |
177 * read buffer: |/ / consumed / | to be read /| |
178 * |/ / / / / / / /|/ / / / / / /| |
179 * +---------------+-----------------------+
182 * +-------------------------------------------+-----------------+
184 * +-------------------------------------------+-----------------+
187 **********************************************************************************
189 **********************************************************************************
192 * |-------------------------------|
195 * buffer buf_ptr buf_end
196 * +-------------------+-----------+
197 * |/ / / / / / / / / /| |
198 * write buffer: | / to be flushed / | |
199 * |/ / / / / / / / / /| |
200 * +-------------------+-----------+
203 * +--------------------------+-----------------------------------+
205 * +--------------------------+-----------------------------------+
208 unsigned char *buffer; /**< Start of the buffer. */
209 int buffer_size; /**< Maximum buffer size */
210 unsigned char *buf_ptr; /**< Current position in the buffer */
211 unsigned char *buf_end; /**< End of the data, may be less than
212 buffer+buffer_size if the read function returned
213 less data than requested, e.g. for streams where
214 no more data has been received yet. */
215 void *opaque; /**< A private pointer, passed to the read/write/seek/...
217 int (*read_packet)(void *opaque, uint8_t *buf, int buf_size);
218 int (*write_packet)(void *opaque, uint8_t *buf, int buf_size);
219 int64_t (*seek)(void *opaque, int64_t offset, int whence);
220 int64_t pos; /**< position in the file of the current buffer */
221 int must_flush; /**< true if the next seek should flush */
222 int eof_reached; /**< true if eof reached */
223 int write_flag; /**< true if open for writing */
225 unsigned long checksum;
226 unsigned char *checksum_ptr;
227 unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size);
228 int error; /**< contains the error code or 0 if no error happened */
230 * Pause or resume playback for network streaming protocols - e.g. MMS.
232 int (*read_pause)(void *opaque, int pause);
234 * Seek to a given timestamp in stream with the specified stream_index.
235 * Needed for some network streaming protocols which don't support seeking
238 int64_t (*read_seek)(void *opaque, int stream_index,
239 int64_t timestamp, int flags);
241 * A combination of AVIO_SEEKABLE_ flags or 0 when the stream is not seekable.
246 * max filesize, used to limit allocations
247 * This field is internal to libavformat and access from outside is not allowed.
252 * avio_read and avio_write should if possible be satisfied directly
253 * instead of going through a buffer, and avio_seek will always
254 * call the underlying seek function directly.
259 * Bytes read statistic
260 * This field is internal to libavformat and access from outside is not allowed.
266 * This field is internal to libavformat and access from outside is not allowed.
272 * This field is internal to libavformat and access from outside is not allowed.
277 * Original buffer size
278 * used internally after probing and ensure seekback to reset the buffer size
279 * This field is internal to libavformat and access from outside is not allowed.
281 int orig_buffer_size;
284 * Threshold to favor readahead over seek.
285 * This is current internal only, do not use from outside.
287 int short_seek_threshold;
290 * ',' separated list of allowed protocols.
292 const char *protocol_whitelist;
295 * ',' separated list of disallowed protocols.
297 const char *protocol_blacklist;
300 * A callback that is used instead of write_packet.
302 int (*write_data_type)(void *opaque, uint8_t *buf, int buf_size,
303 enum AVIODataMarkerType type, int64_t time);
305 * If set, don't call write_data_type separately for AVIO_DATA_MARKER_BOUNDARY_POINT,
306 * but ignore them and treat them as AVIO_DATA_MARKER_UNKNOWN (to avoid needlessly
307 * small chunks of data returned from the callback).
309 int ignore_boundary_point;
312 * Internal, not meant to be used from outside of AVIOContext.
314 enum AVIODataMarkerType current_type;
318 * A callback that is used instead of short_seek_threshold.
319 * This is current internal only, do not use from outside.
321 int (*short_seek_get)(void *opaque);
325 * Return the name of the protocol that will handle the passed URL.
327 * NULL is returned if no protocol could be found for the given URL.
329 * @return Name of the protocol or NULL.
331 const char *avio_find_protocol_name(const char *url);
334 * Return AVIO_FLAG_* access flags corresponding to the access permissions
335 * of the resource in url, or a negative value corresponding to an
336 * AVERROR code in case of failure. The returned access flags are
337 * masked by the value in flags.
339 * @note This function is intrinsically unsafe, in the sense that the
340 * checked resource may change its existence or permission status from
341 * one call to another. Thus you should not trust the returned value,
342 * unless you are sure that no other processes are accessing the
345 int avio_check(const char *url, int flags);
348 * Move or rename a resource.
350 * @note url_src and url_dst should share the same protocol and authority.
352 * @param url_src url to resource to be moved
353 * @param url_dst new url to resource if the operation succeeded
354 * @return >=0 on success or negative on error.
356 int avpriv_io_move(const char *url_src, const char *url_dst);
361 * @param url resource to be deleted.
362 * @return >=0 on success or negative on error.
364 int avpriv_io_delete(const char *url);
367 * Open directory for reading.
369 * @param s directory read context. Pointer to a NULL pointer must be passed.
370 * @param url directory to be listed.
371 * @param options A dictionary filled with protocol-private options. On return
372 * this parameter will be destroyed and replaced with a dictionary
373 * containing options that were not found. May be NULL.
374 * @return >=0 on success or negative on error.
376 int avio_open_dir(AVIODirContext **s, const char *url, AVDictionary **options);
379 * Get next directory entry.
381 * Returned entry must be freed with avio_free_directory_entry(). In particular
382 * it may outlive AVIODirContext.
384 * @param s directory read context.
385 * @param[out] next next entry or NULL when no more entries.
386 * @return >=0 on success or negative on error. End of list is not considered an
389 int avio_read_dir(AVIODirContext *s, AVIODirEntry **next);
394 * @note Entries created using avio_read_dir() are not deleted and must be
395 * freeded with avio_free_directory_entry().
397 * @param s directory read context.
398 * @return >=0 on success or negative on error.
400 int avio_close_dir(AVIODirContext **s);
403 * Free entry allocated by avio_read_dir().
405 * @param entry entry to be freed.
407 void avio_free_directory_entry(AVIODirEntry **entry);
410 * Allocate and initialize an AVIOContext for buffered I/O. It must be later
411 * freed with av_free().
413 * @param buffer Memory block for input/output operations via AVIOContext.
414 * The buffer must be allocated with av_malloc() and friends.
415 * It may be freed and replaced with a new buffer by libavformat.
416 * AVIOContext.buffer holds the buffer currently in use,
417 * which must be later freed with av_free().
418 * @param buffer_size The buffer size is very important for performance.
419 * For protocols with fixed blocksize it should be set to this blocksize.
420 * For others a typical size is a cache page, e.g. 4kb.
421 * @param write_flag Set to 1 if the buffer should be writable, 0 otherwise.
422 * @param opaque An opaque pointer to user-specific data.
423 * @param read_packet A function for refilling the buffer, may be NULL.
424 * @param write_packet A function for writing the buffer contents, may be NULL.
425 * The function may not change the input buffers content.
426 * @param seek A function for seeking to specified byte position, may be NULL.
428 * @return Allocated AVIOContext or NULL on failure.
430 AVIOContext *avio_alloc_context(
431 unsigned char *buffer,
435 int (*read_packet)(void *opaque, uint8_t *buf, int buf_size),
436 int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),
437 int64_t (*seek)(void *opaque, int64_t offset, int whence));
439 void avio_w8(AVIOContext *s, int b);
440 void avio_write(AVIOContext *s, const unsigned char *buf, int size);
441 void avio_wl64(AVIOContext *s, uint64_t val);
442 void avio_wb64(AVIOContext *s, uint64_t val);
443 void avio_wl32(AVIOContext *s, unsigned int val);
444 void avio_wb32(AVIOContext *s, unsigned int val);
445 void avio_wl24(AVIOContext *s, unsigned int val);
446 void avio_wb24(AVIOContext *s, unsigned int val);
447 void avio_wl16(AVIOContext *s, unsigned int val);
448 void avio_wb16(AVIOContext *s, unsigned int val);
451 * Write a NULL-terminated string.
452 * @return number of bytes written.
454 int avio_put_str(AVIOContext *s, const char *str);
457 * Convert an UTF-8 string to UTF-16LE and write it.
458 * @param s the AVIOContext
459 * @param str NULL-terminated UTF-8 string
461 * @return number of bytes written.
463 int avio_put_str16le(AVIOContext *s, const char *str);
466 * Convert an UTF-8 string to UTF-16BE and write it.
467 * @param s the AVIOContext
468 * @param str NULL-terminated UTF-8 string
470 * @return number of bytes written.
472 int avio_put_str16be(AVIOContext *s, const char *str);
475 * Mark the written bytestream as a specific type.
477 * Zero-length ranges are omitted from the output.
479 * @param time the stream time the current bytestream pos corresponds to
480 * (in AV_TIME_BASE units), or AV_NOPTS_VALUE if unknown or not
482 * @param type the kind of data written starting at the current pos
484 void avio_write_marker(AVIOContext *s, int64_t time, enum AVIODataMarkerType type);
487 * ORing this as the "whence" parameter to a seek function causes it to
488 * return the filesize without seeking anywhere. Supporting this is optional.
489 * If it is not supported then the seek function will return <0.
491 #define AVSEEK_SIZE 0x10000
494 * Passing this flag as the "whence" parameter to a seek function causes it to
495 * seek by any means (like reopening and linear reading) or other normally unreasonable
496 * means that can be extremely slow.
497 * This may be ignored by the seek code.
499 #define AVSEEK_FORCE 0x20000
502 * fseek() equivalent for AVIOContext.
503 * @return new position or AVERROR.
505 int64_t avio_seek(AVIOContext *s, int64_t offset, int whence);
508 * Skip given number of bytes forward
509 * @return new position or AVERROR.
511 int64_t avio_skip(AVIOContext *s, int64_t offset);
514 * ftell() equivalent for AVIOContext.
515 * @return position or AVERROR.
517 static av_always_inline int64_t avio_tell(AVIOContext *s)
519 return avio_seek(s, 0, SEEK_CUR);
524 * @return filesize or AVERROR
526 int64_t avio_size(AVIOContext *s);
529 * feof() equivalent for AVIOContext.
530 * @return non zero if and only if end of file
532 int avio_feof(AVIOContext *s);
535 * @deprecated use avio_feof()
538 int url_feof(AVIOContext *s);
541 /** @warning Writes up to 4 KiB per call */
542 int avio_printf(AVIOContext *s, const char *fmt, ...) av_printf_format(2, 3);
545 * Force flushing of buffered data.
547 * For write streams, force the buffered data to be immediately written to the output,
548 * without to wait to fill the internal buffer.
550 * For read streams, discard all currently buffered data, and advance the
551 * reported file position to that of the underlying stream. This does not
552 * read new data, and does not perform any seeks.
554 void avio_flush(AVIOContext *s);
557 * Read size bytes from AVIOContext into buf.
558 * @return number of bytes read or AVERROR
560 int avio_read(AVIOContext *s, unsigned char *buf, int size);
563 * @name Functions for reading from AVIOContext
566 * @note return 0 if EOF, so you cannot use it if EOF handling is
569 int avio_r8 (AVIOContext *s);
570 unsigned int avio_rl16(AVIOContext *s);
571 unsigned int avio_rl24(AVIOContext *s);
572 unsigned int avio_rl32(AVIOContext *s);
573 uint64_t avio_rl64(AVIOContext *s);
574 unsigned int avio_rb16(AVIOContext *s);
575 unsigned int avio_rb24(AVIOContext *s);
576 unsigned int avio_rb32(AVIOContext *s);
577 uint64_t avio_rb64(AVIOContext *s);
583 * Read a string from pb into buf. The reading will terminate when either
584 * a NULL character was encountered, maxlen bytes have been read, or nothing
585 * more can be read from pb. The result is guaranteed to be NULL-terminated, it
586 * will be truncated if buf is too small.
587 * Note that the string is not interpreted or validated in any way, it
588 * might get truncated in the middle of a sequence for multi-byte encodings.
590 * @return number of bytes read (is always <= maxlen).
591 * If reading ends on EOF or error, the return value will be one more than
592 * bytes actually read.
594 int avio_get_str(AVIOContext *pb, int maxlen, char *buf, int buflen);
597 * Read a UTF-16 string from pb and convert it to UTF-8.
598 * The reading will terminate when either a null or invalid character was
599 * encountered or maxlen bytes have been read.
600 * @return number of bytes read (is always <= maxlen)
602 int avio_get_str16le(AVIOContext *pb, int maxlen, char *buf, int buflen);
603 int avio_get_str16be(AVIOContext *pb, int maxlen, char *buf, int buflen);
607 * @name URL open modes
608 * The flags argument to avio_open must be one of the following
609 * constants, optionally ORed with other flags.
612 #define AVIO_FLAG_READ 1 /**< read-only */
613 #define AVIO_FLAG_WRITE 2 /**< write-only */
614 #define AVIO_FLAG_READ_WRITE (AVIO_FLAG_READ|AVIO_FLAG_WRITE) /**< read-write pseudo flag */
620 * Use non-blocking mode.
621 * If this flag is set, operations on the context will return
622 * AVERROR(EAGAIN) if they can not be performed immediately.
623 * If this flag is not set, operations on the context will never return
625 * Note that this flag does not affect the opening/connecting of the
626 * context. Connecting a protocol will always block if necessary (e.g. on
627 * network protocols) but never hang (e.g. on busy devices).
628 * Warning: non-blocking protocols is work-in-progress; this flag may be
631 #define AVIO_FLAG_NONBLOCK 8
635 * avio_read and avio_write should if possible be satisfied directly
636 * instead of going through a buffer, and avio_seek will always
637 * call the underlying seek function directly.
639 #define AVIO_FLAG_DIRECT 0x8000
642 * Create and initialize a AVIOContext for accessing the
643 * resource indicated by url.
644 * @note When the resource indicated by url has been opened in
645 * read+write mode, the AVIOContext can be used only for writing.
647 * @param s Used to return the pointer to the created AVIOContext.
648 * In case of failure the pointed to value is set to NULL.
649 * @param url resource to access
650 * @param flags flags which control how the resource indicated by url
652 * @return >= 0 in case of success, a negative value corresponding to an
653 * AVERROR code in case of failure
655 int avio_open(AVIOContext **s, const char *url, int flags);
658 * Create and initialize a AVIOContext for accessing the
659 * resource indicated by url.
660 * @note When the resource indicated by url has been opened in
661 * read+write mode, the AVIOContext can be used only for writing.
663 * @param s Used to return the pointer to the created AVIOContext.
664 * In case of failure the pointed to value is set to NULL.
665 * @param url resource to access
666 * @param flags flags which control how the resource indicated by url
668 * @param int_cb an interrupt callback to be used at the protocols level
669 * @param options A dictionary filled with protocol-private options. On return
670 * this parameter will be destroyed and replaced with a dict containing options
671 * that were not found. May be NULL.
672 * @return >= 0 in case of success, a negative value corresponding to an
673 * AVERROR code in case of failure
675 int avio_open2(AVIOContext **s, const char *url, int flags,
676 const AVIOInterruptCB *int_cb, AVDictionary **options);
679 * Close the resource accessed by the AVIOContext s and free it.
680 * This function can only be used if s was opened by avio_open().
682 * The internal buffer is automatically flushed before closing the
685 * @return 0 on success, an AVERROR < 0 on error.
688 int avio_close(AVIOContext *s);
691 * Close the resource accessed by the AVIOContext *s, free it
692 * and set the pointer pointing to it to NULL.
693 * This function can only be used if s was opened by avio_open().
695 * The internal buffer is automatically flushed before closing the
698 * @return 0 on success, an AVERROR < 0 on error.
701 int avio_closep(AVIOContext **s);
705 * Open a write only memory stream.
707 * @param s new IO context
708 * @return zero if no error.
710 int avio_open_dyn_buf(AVIOContext **s);
713 * Return the written size and a pointer to the buffer.
714 * The AVIOContext stream is left intact.
715 * The buffer must NOT be freed.
716 * No padding is added to the buffer.
718 * @param s IO context
719 * @param pbuffer pointer to a byte buffer
720 * @return the length of the byte buffer
722 int avio_get_dyn_buf(AVIOContext *s, uint8_t **pbuffer);
725 * Return the written size and a pointer to the buffer. The buffer
726 * must be freed with av_free().
727 * Padding of AV_INPUT_BUFFER_PADDING_SIZE is added to the buffer.
729 * @param s IO context
730 * @param pbuffer pointer to a byte buffer
731 * @return the length of the byte buffer
733 int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer);
736 * Iterate through names of available protocols.
738 * @param opaque A private pointer representing current protocol.
739 * It must be a pointer to NULL on first iteration and will
740 * be updated by successive calls to avio_enum_protocols.
741 * @param output If set to 1, iterate over output protocols,
742 * otherwise over input protocols.
744 * @return A static string containing the name of current protocol or NULL
746 const char *avio_enum_protocols(void **opaque, int output);
749 * Pause and resume playing - only meaningful if using a network streaming
750 * protocol (e.g. MMS).
752 * @param h IO context from which to call the read_pause function pointer
753 * @param pause 1 for pause, 0 for resume
755 int avio_pause(AVIOContext *h, int pause);
758 * Seek to a given timestamp relative to some component stream.
759 * Only meaningful if using a network streaming protocol (e.g. MMS.).
761 * @param h IO context from which to call the seek function pointers
762 * @param stream_index The stream index that the timestamp is relative to.
763 * If stream_index is (-1) the timestamp should be in AV_TIME_BASE
764 * units from the beginning of the presentation.
765 * If a stream_index >= 0 is used and the protocol does not support
766 * seeking based on component streams, the call will fail.
767 * @param timestamp timestamp in AVStream.time_base units
768 * or if there is no stream specified then in AV_TIME_BASE units.
769 * @param flags Optional combination of AVSEEK_FLAG_BACKWARD, AVSEEK_FLAG_BYTE
770 * and AVSEEK_FLAG_ANY. The protocol may silently ignore
771 * AVSEEK_FLAG_BACKWARD and AVSEEK_FLAG_ANY, but AVSEEK_FLAG_BYTE will
772 * fail if used and not supported.
773 * @return >= 0 on success
774 * @see AVInputFormat::read_seek
776 int64_t avio_seek_time(AVIOContext *h, int stream_index,
777 int64_t timestamp, int flags);
779 /* Avoid a warning. The header can not be included because it breaks c++. */
783 * Read contents of h into print buffer, up to max_size bytes, or up to EOF.
785 * @return 0 for success (max_size bytes read or EOF reached), negative error
788 int avio_read_to_bprint(AVIOContext *h, struct AVBPrint *pb, size_t max_size);
791 * Accept and allocate a client context on a server context.
792 * @param s the server context
793 * @param c the client context, must be unallocated
794 * @return >= 0 on success or a negative value corresponding
795 * to an AVERROR on failure
797 int avio_accept(AVIOContext *s, AVIOContext **c);
800 * Perform one step of the protocol handshake to accept a new client.
801 * This function must be called on a client returned by avio_accept() before
802 * using it as a read/write context.
803 * It is separate from avio_accept() because it may block.
804 * A step of the handshake is defined by places where the application may
805 * decide to change the proceedings.
806 * For example, on a protocol with a request header and a reply header, each
807 * one can constitute a step because the application may use the parameters
808 * from the request to change parameters in the reply; or each individual
809 * chunk of the request can constitute a step.
810 * If the handshake is already finished, avio_handshake() does nothing and
811 * returns 0 immediately.
813 * @param c the client context to perform the handshake on
814 * @return 0 on a complete and successful handshake
815 * > 0 if the handshake progressed, but is not complete
816 * < 0 for an AVERROR code
818 int avio_handshake(AVIOContext *c);
819 #endif /* AVFORMAT_AVIO_H */