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"
38 * Seeking works like for a local file.
40 #define AVIO_SEEKABLE_NORMAL (1 << 0)
43 * Seeking by timestamp with avio_seek_time() is possible.
45 #define AVIO_SEEKABLE_TIME (1 << 1)
48 * Callback for checking whether to abort blocking functions.
49 * AVERROR_EXIT is returned in this case by the interrupted
50 * function. During blocking operations, callback is called with
51 * opaque as parameter. If the callback returns 1, the
52 * blocking operation will be aborted.
54 * No members can be added to this struct without a major bump, if
55 * new elements have been added after this struct in AVFormatContext
58 typedef struct AVIOInterruptCB {
59 int (*callback)(void*);
64 * Directory entry types.
66 enum AVIODirEntryType {
68 AVIO_ENTRY_BLOCK_DEVICE,
69 AVIO_ENTRY_CHARACTER_DEVICE,
71 AVIO_ENTRY_NAMED_PIPE,
72 AVIO_ENTRY_SYMBOLIC_LINK,
81 * Describes single entry of the directory.
83 * Only name and type fields are guaranteed be set.
84 * Rest of fields are protocol or/and platform dependent and might be unknown.
86 typedef struct AVIODirEntry {
87 char *name; /**< Filename */
88 int type; /**< Type of the entry */
89 int utf8; /**< Set to 1 when name is encoded with UTF-8, 0 otherwise.
90 Name can be encoded with UTF-8 even though 0 is set. */
91 int64_t size; /**< File size in bytes, -1 if unknown. */
92 int64_t modification_timestamp; /**< Time of last modification in microseconds since unix
93 epoch, -1 if unknown. */
94 int64_t access_timestamp; /**< Time of last access in microseconds since unix epoch,
96 int64_t status_change_timestamp; /**< Time of last status change in microseconds since unix
97 epoch, -1 if unknown. */
98 int64_t user_id; /**< User ID of owner, -1 if unknown. */
99 int64_t group_id; /**< Group ID of owner, -1 if unknown. */
100 int64_t filemode; /**< Unix file mode, -1 if unknown. */
103 typedef struct AVIODirContext {
104 struct URLContext *url_context;
108 * Different data types that can be returned via the AVIO
109 * write_data_type callback.
111 enum AVIODataMarkerType {
113 * Header data; this needs to be present for the stream to be decodeable.
115 AVIO_DATA_MARKER_HEADER,
117 * A point in the output bytestream where a decoder can start decoding
118 * (i.e. a keyframe). A demuxer/decoder given the data flagged with
119 * AVIO_DATA_MARKER_HEADER, followed by any AVIO_DATA_MARKER_SYNC_POINT,
120 * should give decodeable results.
122 AVIO_DATA_MARKER_SYNC_POINT,
124 * A point in the output bytestream where a demuxer can start parsing
125 * (for non self synchronizing bytestream formats). That is, any
126 * non-keyframe packet start point.
128 AVIO_DATA_MARKER_BOUNDARY_POINT,
130 * This is any, unlabelled data. It can either be a muxer not marking
131 * any positions at all, it can be an actual boundary/sync point
132 * that the muxer chooses not to mark, or a later part of a packet/fragment
133 * that is cut into multiple write callbacks due to limited IO buffer size.
135 AVIO_DATA_MARKER_UNKNOWN,
137 * Trailer data, which doesn't contain actual content, but only for
138 * finalizing the output file.
140 AVIO_DATA_MARKER_TRAILER
144 * Bytestream IO Context.
145 * New fields can be added to the end with minor version bumps.
146 * Removal, reordering and changes to existing fields require a major
148 * sizeof(AVIOContext) must not be used outside libav*.
150 * @note None of the function pointers in AVIOContext should be called
151 * directly, they should only be set by the client application
152 * when implementing custom I/O. Normally these are set to the
153 * function pointers specified in avio_alloc_context()
155 typedef struct AVIOContext {
157 * A class for private options.
159 * If this AVIOContext is created by avio_open2(), av_class is set and
160 * passes the options down to protocols.
162 * If this AVIOContext is manually allocated, then av_class may be set by
165 * warning -- this field can be NULL, be sure to not pass this AVIOContext
166 * to any av_opt_* functions in that case.
168 const AVClass *av_class;
171 * The following shows the relationship between buffer, buf_ptr, buf_end, buf_size,
172 * and pos, when reading and when writing (since AVIOContext is used for both):
174 **********************************************************************************
176 **********************************************************************************
179 * |---------------------------------------|
182 * buffer buf_ptr buf_end
183 * +---------------+-----------------------+
184 * |/ / / / / / / /|/ / / / / / /| |
185 * read buffer: |/ / consumed / | to be read /| |
186 * |/ / / / / / / /|/ / / / / / /| |
187 * +---------------+-----------------------+
190 * +-------------------------------------------+-----------------+
192 * +-------------------------------------------+-----------------+
195 **********************************************************************************
197 **********************************************************************************
200 * |-------------------------------|
203 * buffer buf_ptr buf_end
204 * +-------------------+-----------+
205 * |/ / / / / / / / / /| |
206 * write buffer: | / to be flushed / | |
207 * |/ / / / / / / / / /| |
208 * +-------------------+-----------+
211 * +--------------------------+-----------------------------------+
213 * +--------------------------+-----------------------------------+
216 unsigned char *buffer; /**< Start of the buffer. */
217 int buffer_size; /**< Maximum buffer size */
218 unsigned char *buf_ptr; /**< Current position in the buffer */
219 unsigned char *buf_end; /**< End of the data, may be less than
220 buffer+buffer_size if the read function returned
221 less data than requested, e.g. for streams where
222 no more data has been received yet. */
223 void *opaque; /**< A private pointer, passed to the read/write/seek/...
225 int (*read_packet)(void *opaque, uint8_t *buf, int buf_size);
226 int (*write_packet)(void *opaque, uint8_t *buf, int buf_size);
227 int64_t (*seek)(void *opaque, int64_t offset, int whence);
228 int64_t pos; /**< position in the file of the current buffer */
229 int must_flush; /**< true if the next seek should flush */
230 int eof_reached; /**< true if eof reached */
231 int write_flag; /**< true if open for writing */
233 unsigned long checksum;
234 unsigned char *checksum_ptr;
235 unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size);
236 int error; /**< contains the error code or 0 if no error happened */
238 * Pause or resume playback for network streaming protocols - e.g. MMS.
240 int (*read_pause)(void *opaque, int pause);
242 * Seek to a given timestamp in stream with the specified stream_index.
243 * Needed for some network streaming protocols which don't support seeking
246 int64_t (*read_seek)(void *opaque, int stream_index,
247 int64_t timestamp, int flags);
249 * A combination of AVIO_SEEKABLE_ flags or 0 when the stream is not seekable.
254 * max filesize, used to limit allocations
255 * This field is internal to libavformat and access from outside is not allowed.
260 * avio_read and avio_write should if possible be satisfied directly
261 * instead of going through a buffer, and avio_seek will always
262 * call the underlying seek function directly.
267 * Bytes read statistic
268 * This field is internal to libavformat and access from outside is not allowed.
274 * This field is internal to libavformat and access from outside is not allowed.
280 * This field is internal to libavformat and access from outside is not allowed.
285 * Original buffer size
286 * used internally after probing and ensure seekback to reset the buffer size
287 * This field is internal to libavformat and access from outside is not allowed.
289 int orig_buffer_size;
292 * Threshold to favor readahead over seek.
293 * This is current internal only, do not use from outside.
295 int short_seek_threshold;
298 * ',' separated list of allowed protocols.
300 const char *protocol_whitelist;
303 * ',' separated list of disallowed protocols.
305 const char *protocol_blacklist;
308 * A callback that is used instead of write_packet.
310 int (*write_data_type)(void *opaque, uint8_t *buf, int buf_size,
311 enum AVIODataMarkerType type, int64_t time);
313 * If set, don't call write_data_type separately for AVIO_DATA_MARKER_BOUNDARY_POINT,
314 * but ignore them and treat them as AVIO_DATA_MARKER_UNKNOWN (to avoid needlessly
315 * small chunks of data returned from the callback).
317 int ignore_boundary_point;
320 * Internal, not meant to be used from outside of AVIOContext.
322 enum AVIODataMarkerType current_type;
326 * A callback that is used instead of short_seek_threshold.
327 * This is current internal only, do not use from outside.
329 int (*short_seek_get)(void *opaque);
335 * Return the name of the protocol that will handle the passed URL.
337 * NULL is returned if no protocol could be found for the given URL.
339 * @return Name of the protocol or NULL.
341 const char *avio_find_protocol_name(const char *url);
344 * Return AVIO_FLAG_* access flags corresponding to the access permissions
345 * of the resource in url, or a negative value corresponding to an
346 * AVERROR code in case of failure. The returned access flags are
347 * masked by the value in flags.
349 * @note This function is intrinsically unsafe, in the sense that the
350 * checked resource may change its existence or permission status from
351 * one call to another. Thus you should not trust the returned value,
352 * unless you are sure that no other processes are accessing the
355 int avio_check(const char *url, int flags);
358 * Move or rename a resource.
360 * @note url_src and url_dst should share the same protocol and authority.
362 * @param url_src url to resource to be moved
363 * @param url_dst new url to resource if the operation succeeded
364 * @return >=0 on success or negative on error.
366 int avpriv_io_move(const char *url_src, const char *url_dst);
371 * @param url resource to be deleted.
372 * @return >=0 on success or negative on error.
374 int avpriv_io_delete(const char *url);
377 * Open directory for reading.
379 * @param s directory read context. Pointer to a NULL pointer must be passed.
380 * @param url directory to be listed.
381 * @param options A dictionary filled with protocol-private options. On return
382 * this parameter will be destroyed and replaced with a dictionary
383 * containing options that were not found. May be NULL.
384 * @return >=0 on success or negative on error.
386 int avio_open_dir(AVIODirContext **s, const char *url, AVDictionary **options);
389 * Get next directory entry.
391 * Returned entry must be freed with avio_free_directory_entry(). In particular
392 * it may outlive AVIODirContext.
394 * @param s directory read context.
395 * @param[out] next next entry or NULL when no more entries.
396 * @return >=0 on success or negative on error. End of list is not considered an
399 int avio_read_dir(AVIODirContext *s, AVIODirEntry **next);
404 * @note Entries created using avio_read_dir() are not deleted and must be
405 * freeded with avio_free_directory_entry().
407 * @param s directory read context.
408 * @return >=0 on success or negative on error.
410 int avio_close_dir(AVIODirContext **s);
413 * Free entry allocated by avio_read_dir().
415 * @param entry entry to be freed.
417 void avio_free_directory_entry(AVIODirEntry **entry);
420 * Allocate and initialize an AVIOContext for buffered I/O. It must be later
421 * freed with av_free().
423 * @param buffer Memory block for input/output operations via AVIOContext.
424 * The buffer must be allocated with av_malloc() and friends.
425 * It may be freed and replaced with a new buffer by libavformat.
426 * AVIOContext.buffer holds the buffer currently in use,
427 * which must be later freed with av_free().
428 * @param buffer_size The buffer size is very important for performance.
429 * For protocols with fixed blocksize it should be set to this blocksize.
430 * For others a typical size is a cache page, e.g. 4kb.
431 * @param write_flag Set to 1 if the buffer should be writable, 0 otherwise.
432 * @param opaque An opaque pointer to user-specific data.
433 * @param read_packet A function for refilling the buffer, may be NULL.
434 * @param write_packet A function for writing the buffer contents, may be NULL.
435 * The function may not change the input buffers content.
436 * @param seek A function for seeking to specified byte position, may be NULL.
438 * @return Allocated AVIOContext or NULL on failure.
440 AVIOContext *avio_alloc_context(
441 unsigned char *buffer,
445 int (*read_packet)(void *opaque, uint8_t *buf, int buf_size),
446 int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),
447 int64_t (*seek)(void *opaque, int64_t offset, int whence));
449 void avio_w8(AVIOContext *s, int b);
450 void avio_write(AVIOContext *s, const unsigned char *buf, int size);
451 void avio_wl64(AVIOContext *s, uint64_t val);
452 void avio_wb64(AVIOContext *s, uint64_t val);
453 void avio_wl32(AVIOContext *s, unsigned int val);
454 void avio_wb32(AVIOContext *s, unsigned int val);
455 void avio_wl24(AVIOContext *s, unsigned int val);
456 void avio_wb24(AVIOContext *s, unsigned int val);
457 void avio_wl16(AVIOContext *s, unsigned int val);
458 void avio_wb16(AVIOContext *s, unsigned int val);
461 * Write a NULL-terminated string.
462 * @return number of bytes written.
464 int avio_put_str(AVIOContext *s, const char *str);
467 * Convert an UTF-8 string to UTF-16LE and write it.
468 * @param s the AVIOContext
469 * @param str NULL-terminated UTF-8 string
471 * @return number of bytes written.
473 int avio_put_str16le(AVIOContext *s, const char *str);
476 * Convert an UTF-8 string to UTF-16BE and write it.
477 * @param s the AVIOContext
478 * @param str NULL-terminated UTF-8 string
480 * @return number of bytes written.
482 int avio_put_str16be(AVIOContext *s, const char *str);
485 * Mark the written bytestream as a specific type.
487 * Zero-length ranges are omitted from the output.
489 * @param time the stream time the current bytestream pos corresponds to
490 * (in AV_TIME_BASE units), or AV_NOPTS_VALUE if unknown or not
492 * @param type the kind of data written starting at the current pos
494 void avio_write_marker(AVIOContext *s, int64_t time, enum AVIODataMarkerType type);
497 * ORing this as the "whence" parameter to a seek function causes it to
498 * return the filesize without seeking anywhere. Supporting this is optional.
499 * If it is not supported then the seek function will return <0.
501 #define AVSEEK_SIZE 0x10000
504 * Passing this flag as the "whence" parameter to a seek function causes it to
505 * seek by any means (like reopening and linear reading) or other normally unreasonable
506 * means that can be extremely slow.
507 * This may be ignored by the seek code.
509 #define AVSEEK_FORCE 0x20000
512 * fseek() equivalent for AVIOContext.
513 * @return new position or AVERROR.
515 int64_t avio_seek(AVIOContext *s, int64_t offset, int whence);
518 * Skip given number of bytes forward
519 * @return new position or AVERROR.
521 int64_t avio_skip(AVIOContext *s, int64_t offset);
524 * ftell() equivalent for AVIOContext.
525 * @return position or AVERROR.
527 static av_always_inline int64_t avio_tell(AVIOContext *s)
529 return avio_seek(s, 0, SEEK_CUR);
534 * @return filesize or AVERROR
536 int64_t avio_size(AVIOContext *s);
539 * feof() equivalent for AVIOContext.
540 * @return non zero if and only if end of file
542 int avio_feof(AVIOContext *s);
545 * @deprecated use avio_feof()
548 int url_feof(AVIOContext *s);
551 /** @warning Writes up to 4 KiB per call */
552 int avio_printf(AVIOContext *s, const char *fmt, ...) av_printf_format(2, 3);
555 * Force flushing of buffered data.
557 * For write streams, force the buffered data to be immediately written to the output,
558 * without to wait to fill the internal buffer.
560 * For read streams, discard all currently buffered data, and advance the
561 * reported file position to that of the underlying stream. This does not
562 * read new data, and does not perform any seeks.
564 void avio_flush(AVIOContext *s);
567 * Read size bytes from AVIOContext into buf.
568 * @return number of bytes read or AVERROR
570 int avio_read(AVIOContext *s, unsigned char *buf, int size);
573 * @name Functions for reading from AVIOContext
576 * @note return 0 if EOF, so you cannot use it if EOF handling is
579 int avio_r8 (AVIOContext *s);
580 unsigned int avio_rl16(AVIOContext *s);
581 unsigned int avio_rl24(AVIOContext *s);
582 unsigned int avio_rl32(AVIOContext *s);
583 uint64_t avio_rl64(AVIOContext *s);
584 unsigned int avio_rb16(AVIOContext *s);
585 unsigned int avio_rb24(AVIOContext *s);
586 unsigned int avio_rb32(AVIOContext *s);
587 uint64_t avio_rb64(AVIOContext *s);
593 * Read a string from pb into buf. The reading will terminate when either
594 * a NULL character was encountered, maxlen bytes have been read, or nothing
595 * more can be read from pb. The result is guaranteed to be NULL-terminated, it
596 * will be truncated if buf is too small.
597 * Note that the string is not interpreted or validated in any way, it
598 * might get truncated in the middle of a sequence for multi-byte encodings.
600 * @return number of bytes read (is always <= maxlen).
601 * If reading ends on EOF or error, the return value will be one more than
602 * bytes actually read.
604 int avio_get_str(AVIOContext *pb, int maxlen, char *buf, int buflen);
607 * Read a UTF-16 string from pb and convert it to UTF-8.
608 * The reading will terminate when either a null or invalid character was
609 * encountered or maxlen bytes have been read.
610 * @return number of bytes read (is always <= maxlen)
612 int avio_get_str16le(AVIOContext *pb, int maxlen, char *buf, int buflen);
613 int avio_get_str16be(AVIOContext *pb, int maxlen, char *buf, int buflen);
617 * @name URL open modes
618 * The flags argument to avio_open must be one of the following
619 * constants, optionally ORed with other flags.
622 #define AVIO_FLAG_READ 1 /**< read-only */
623 #define AVIO_FLAG_WRITE 2 /**< write-only */
624 #define AVIO_FLAG_READ_WRITE (AVIO_FLAG_READ|AVIO_FLAG_WRITE) /**< read-write pseudo flag */
630 * Use non-blocking mode.
631 * If this flag is set, operations on the context will return
632 * AVERROR(EAGAIN) if they can not be performed immediately.
633 * If this flag is not set, operations on the context will never return
635 * Note that this flag does not affect the opening/connecting of the
636 * context. Connecting a protocol will always block if necessary (e.g. on
637 * network protocols) but never hang (e.g. on busy devices).
638 * Warning: non-blocking protocols is work-in-progress; this flag may be
641 #define AVIO_FLAG_NONBLOCK 8
645 * avio_read and avio_write should if possible be satisfied directly
646 * instead of going through a buffer, and avio_seek will always
647 * call the underlying seek function directly.
649 #define AVIO_FLAG_DIRECT 0x8000
652 * Create and initialize a AVIOContext for accessing the
653 * resource indicated by url.
654 * @note When the resource indicated by url has been opened in
655 * read+write mode, the AVIOContext can be used only for writing.
657 * @param s Used to return the pointer to the created AVIOContext.
658 * In case of failure the pointed to value is set to NULL.
659 * @param url resource to access
660 * @param flags flags which control how the resource indicated by url
662 * @return >= 0 in case of success, a negative value corresponding to an
663 * AVERROR code in case of failure
665 int avio_open(AVIOContext **s, const char *url, int flags);
668 * Create and initialize a AVIOContext for accessing the
669 * resource indicated by url.
670 * @note When the resource indicated by url has been opened in
671 * read+write mode, the AVIOContext can be used only for writing.
673 * @param s Used to return the pointer to the created AVIOContext.
674 * In case of failure the pointed to value is set to NULL.
675 * @param url resource to access
676 * @param flags flags which control how the resource indicated by url
678 * @param int_cb an interrupt callback to be used at the protocols level
679 * @param options A dictionary filled with protocol-private options. On return
680 * this parameter will be destroyed and replaced with a dict containing options
681 * that were not found. May be NULL.
682 * @return >= 0 in case of success, a negative value corresponding to an
683 * AVERROR code in case of failure
685 int avio_open2(AVIOContext **s, const char *url, int flags,
686 const AVIOInterruptCB *int_cb, AVDictionary **options);
689 * Close the resource accessed by the AVIOContext s and free it.
690 * This function can only be used if s was opened by avio_open().
692 * The internal buffer is automatically flushed before closing the
695 * @return 0 on success, an AVERROR < 0 on error.
698 int avio_close(AVIOContext *s);
701 * Close the resource accessed by the AVIOContext *s, free it
702 * and set the pointer pointing to it to NULL.
703 * This function can only be used if s was opened by avio_open().
705 * The internal buffer is automatically flushed before closing the
708 * @return 0 on success, an AVERROR < 0 on error.
711 int avio_closep(AVIOContext **s);
715 * Open a write only memory stream.
717 * @param s new IO context
718 * @return zero if no error.
720 int avio_open_dyn_buf(AVIOContext **s);
723 * Return the written size and a pointer to the buffer.
724 * The AVIOContext stream is left intact.
725 * The buffer must NOT be freed.
726 * No padding is added to the buffer.
728 * @param s IO context
729 * @param pbuffer pointer to a byte buffer
730 * @return the length of the byte buffer
732 int avio_get_dyn_buf(AVIOContext *s, uint8_t **pbuffer);
735 * Return the written size and a pointer to the buffer. The buffer
736 * must be freed with av_free().
737 * Padding of AV_INPUT_BUFFER_PADDING_SIZE is added to the buffer.
739 * @param s IO context
740 * @param pbuffer pointer to a byte buffer
741 * @return the length of the byte buffer
743 int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer);
746 * Iterate through names of available protocols.
748 * @param opaque A private pointer representing current protocol.
749 * It must be a pointer to NULL on first iteration and will
750 * be updated by successive calls to avio_enum_protocols.
751 * @param output If set to 1, iterate over output protocols,
752 * otherwise over input protocols.
754 * @return A static string containing the name of current protocol or NULL
756 const char *avio_enum_protocols(void **opaque, int output);
759 * Pause and resume playing - only meaningful if using a network streaming
760 * protocol (e.g. MMS).
762 * @param h IO context from which to call the read_pause function pointer
763 * @param pause 1 for pause, 0 for resume
765 int avio_pause(AVIOContext *h, int pause);
768 * Seek to a given timestamp relative to some component stream.
769 * Only meaningful if using a network streaming protocol (e.g. MMS.).
771 * @param h IO context from which to call the seek function pointers
772 * @param stream_index The stream index that the timestamp is relative to.
773 * If stream_index is (-1) the timestamp should be in AV_TIME_BASE
774 * units from the beginning of the presentation.
775 * If a stream_index >= 0 is used and the protocol does not support
776 * seeking based on component streams, the call will fail.
777 * @param timestamp timestamp in AVStream.time_base units
778 * or if there is no stream specified then in AV_TIME_BASE units.
779 * @param flags Optional combination of AVSEEK_FLAG_BACKWARD, AVSEEK_FLAG_BYTE
780 * and AVSEEK_FLAG_ANY. The protocol may silently ignore
781 * AVSEEK_FLAG_BACKWARD and AVSEEK_FLAG_ANY, but AVSEEK_FLAG_BYTE will
782 * fail if used and not supported.
783 * @return >= 0 on success
784 * @see AVInputFormat::read_seek
786 int64_t avio_seek_time(AVIOContext *h, int stream_index,
787 int64_t timestamp, int flags);
789 /* Avoid a warning. The header can not be included because it breaks c++. */
793 * Read contents of h into print buffer, up to max_size bytes, or up to EOF.
795 * @return 0 for success (max_size bytes read or EOF reached), negative error
798 int avio_read_to_bprint(AVIOContext *h, struct AVBPrint *pb, size_t max_size);
801 * Accept and allocate a client context on a server context.
802 * @param s the server context
803 * @param c the client context, must be unallocated
804 * @return >= 0 on success or a negative value corresponding
805 * to an AVERROR on failure
807 int avio_accept(AVIOContext *s, AVIOContext **c);
810 * Perform one step of the protocol handshake to accept a new client.
811 * This function must be called on a client returned by avio_accept() before
812 * using it as a read/write context.
813 * It is separate from avio_accept() because it may block.
814 * A step of the handshake is defined by places where the application may
815 * decide to change the proceedings.
816 * For example, on a protocol with a request header and a reply header, each
817 * one can constitute a step because the application may use the parameters
818 * from the request to change parameters in the reply; or each individual
819 * chunk of the request can constitute a step.
820 * If the handshake is already finished, avio_handshake() does nothing and
821 * returns 0 immediately.
823 * @param c the client context to perform the handshake on
824 * @return 0 on a complete and successful handshake
825 * > 0 if the handshake progressed, but is not complete
826 * < 0 for an AVERROR code
828 int avio_handshake(AVIOContext *c);
829 #endif /* AVFORMAT_AVIO_H */