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bprint.h
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1 /*
2  * Copyright (c) 2012 Nicolas George
3  *
4  * This file is part of FFmpeg.
5  *
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.
10  *
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.
15  *
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
19  */
20 
21 #ifndef AVUTIL_BPRINT_H
22 #define AVUTIL_BPRINT_H
23 
24 #include "attributes.h"
25 #include "avstring.h"
26 
27 /**
28  * Define a structure with extra padding to a fixed size
29  * This helps ensuring binary compatibility with future versions.
30  */
31 #define FF_PAD_STRUCTURE(size, ...) \
32  __VA_ARGS__ \
33  char reserved_padding[size - sizeof(struct { __VA_ARGS__ })];
34 
35 /**
36  * Buffer to print data progressively
37  *
38  * The string buffer grows as necessary and is always 0-terminated.
39  * The content of the string is never accessed, and thus is
40  * encoding-agnostic and can even hold binary data.
41  *
42  * Small buffers are kept in the structure itself, and thus require no
43  * memory allocation at all (unless the contents of the buffer is needed
44  * after the structure goes out of scope). This is almost as lightweight as
45  * declaring a local "char buf[512]".
46  *
47  * The length of the string can go beyond the allocated size: the buffer is
48  * then truncated, but the functions still keep account of the actual total
49  * length.
50  *
51  * In other words, buf->len can be greater than buf->size and records the
52  * total length of what would have been to the buffer if there had been
53  * enough memory.
54  *
55  * Append operations do not need to be tested for failure: if a memory
56  * allocation fails, data stop being appended to the buffer, but the length
57  * is still updated. This situation can be tested with
58  * av_bprint_is_complete().
59  *
60  * The size_max field determines several possible behaviours:
61  *
62  * size_max = -1 (= UINT_MAX) or any large value will let the buffer be
63  * reallocated as necessary, with an amortized linear cost.
64  *
65  * size_max = 0 prevents writing anything to the buffer: only the total
66  * length is computed. The write operations can then possibly be repeated in
67  * a buffer with exactly the necessary size
68  * (using size_init = size_max = len + 1).
69  *
70  * size_max = 1 is automatically replaced by the exact size available in the
71  * structure itself, thus ensuring no dynamic memory allocation. The
72  * internal buffer is large enough to hold a reasonable paragraph of text,
73  * such as the current paragraph.
74  */
75 typedef struct AVBPrint {
76  FF_PAD_STRUCTURE(1024,
77  char *str; /** string so far */
78  unsigned len; /** length so far */
79  unsigned size; /** allocated memory */
80  unsigned size_max; /** maximum allocated memory */
81  char reserved_internal_buffer[1];
82  )
83 } AVBPrint;
84 
85 /**
86  * Convenience macros for special values for av_bprint_init() size_max
87  * parameter.
88  */
89 #define AV_BPRINT_SIZE_UNLIMITED ((unsigned)-1)
90 #define AV_BPRINT_SIZE_AUTOMATIC 1
91 #define AV_BPRINT_SIZE_COUNT_ONLY 0
92 
93 /**
94  * Init a print buffer.
95  *
96  * @param buf buffer to init
97  * @param size_init initial size (including the final 0)
98  * @param size_max maximum size;
99  * 0 means do not write anything, just count the length;
100  * 1 is replaced by the maximum value for automatic storage;
101  * any large value means that the internal buffer will be
102  * reallocated as needed up to that limit; -1 is converted to
103  * UINT_MAX, the largest limit possible.
104  * Check also AV_BPRINT_SIZE_* macros.
105  */
106 void av_bprint_init(AVBPrint *buf, unsigned size_init, unsigned size_max);
107 
108 /**
109  * Init a print buffer using a pre-existing buffer.
110  *
111  * The buffer will not be reallocated.
112  *
113  * @param buf buffer structure to init
114  * @param buffer byte buffer to use for the string data
115  * @param size size of buffer
116  */
117 void av_bprint_init_for_buffer(AVBPrint *buf, char *buffer, unsigned size);
118 
119 /**
120  * Append a formatted string to a print buffer.
121  */
122 void av_bprintf(AVBPrint *buf, const char *fmt, ...) av_printf_format(2, 3);
123 
124 /**
125  * Append char c n times to a print buffer.
126  */
127 void av_bprint_chars(AVBPrint *buf, char c, unsigned n);
128 
129 struct tm;
130 /**
131  * Append a formatted date and time to a print buffer.
132  *
133  * param buf bprint buffer to use
134  * param fmt date and time format string, see strftime()
135  * param tm broken-down time structure to translate
136  *
137  * @note due to poor design of the standard strftime function, it may
138  * produce poor results if the format string expands to a very long text and
139  * the bprint buffer is near the limit stated by the size_max option.
140  */
141 void av_bprint_strftime(AVBPrint *buf, const char *fmt, const struct tm *tm);
142 
143 /**
144  * Allocate bytes in the buffer for external use.
145  *
146  * @param[in] buf buffer structure
147  * @param[in] size required size
148  * @param[out] mem pointer to the memory area
149  * @param[out] actual_size size of the memory area after allocation;
150  * can be larger or smaller than size
151  */
152 void av_bprint_get_buffer(AVBPrint *buf, unsigned size,
153  unsigned char **mem, unsigned *actual_size);
154 
155 /**
156  * Reset the string to "" but keep internal allocated data.
157  */
158 void av_bprint_clear(AVBPrint *buf);
159 
160 /**
161  * Test if the print buffer is complete (not truncated).
162  *
163  * It may have been truncated due to a memory allocation failure
164  * or the size_max limit (compare size and size_max if necessary).
165  */
166 static inline int av_bprint_is_complete(AVBPrint *buf)
167 {
168  return buf->len < buf->size;
169 }
170 
171 /**
172  * Finalize a print buffer.
173  *
174  * The print buffer can no longer be used afterwards,
175  * but the len and size fields are still valid.
176  *
177  * @arg[out] ret_str if not NULL, used to return a permanent copy of the
178  * buffer contents, or NULL if memory allocation fails;
179  * if NULL, the buffer is discarded and freed
180  * @return 0 for success or error code (probably AVERROR(ENOMEM))
181  */
182 int av_bprint_finalize(AVBPrint *buf, char **ret_str);
183 
184 /**
185  * Escape the content in src and append it to dstbuf.
186  *
187  * @param dstbuf already inited destination bprint buffer
188  * @param src string containing the text to escape
189  * @param special_chars string containing the special characters which
190  * need to be escaped, can be NULL
191  * @param mode escape mode to employ, see AV_ESCAPE_MODE_* macros.
192  * Any unknown value for mode will be considered equivalent to
193  * AV_ESCAPE_MODE_BACKSLASH, but this behaviour can change without
194  * notice.
195  * @param flags flags which control how to escape, see AV_ESCAPE_FLAG_* macros
196  */
197 void av_bprint_escape(AVBPrint *dstbuf, const char *src, const char *special_chars,
198  enum AVEscapeMode mode, int flags);
199 
200 #endif /* AVUTIL_BPRINT_H */