/* * 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 #include #include "libavutil/attributes.h" #include "libavutil/dict.h" #include "libavutil/log.h" #include "libavformat/version_major.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 public fields can be added with minor version bumps. * Removal, reordering and changes to existing public 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 error; /**< contains the error code or 0 if no error happened */ int write_flag; /**< true if open for writing */ int max_packet_size; int min_packet_size; /**< Try to buffer at least this amount of data before flushing it. */ unsigned long checksum; unsigned char *checksum_ptr; unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size); /** * 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; /** * 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; /** * ',' 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; #if FF_API_AVIOCONTEXT_WRITTEN /** * @deprecated field utilized privately by libavformat. For a public * statistic of how many bytes were written out, see * AVIOContext::bytes_written. */ attribute_deprecated int64_t written; #endif /** * 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; /** * Read-only statistic of bytes read for this AVIOContext. */ int64_t bytes_read; /** * Read-only statistic of bytes written for this AVIOContext. */ int64_t bytes_written; } 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); /** * 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 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 taking a va_list. * @return number of bytes written, < 0 on error. */ int avio_vprintf(AVIOContext *s, const char *fmt, va_list ap); /** * 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}) /** * 强制刷新缓冲数据。 * * 对于写流，强制立即将缓冲数据写入输出，而不必等待填充内部缓冲区。 * * 对于读取流，丢弃所有当前缓冲的数据，并将报告的文件位置提前到基础流的位置。 * 这不会读取新数据，也不会执行任何查找。 */ 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 */