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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 <stdarg.h>
25 
26 #include "attributes.h"
27 #include "avstring.h"
28 
29 /**
30  * Define a structure with extra padding to a fixed size
31  * This helps ensuring binary compatibility with future versions.
32  */
33 #define FF_PAD_STRUCTURE(size, ...) \
34  __VA_ARGS__ \
35  char reserved_padding[size - sizeof(struct { __VA_ARGS__ })];
36 
37 /**
38  * Buffer to print data progressively
39  *
40  * The string buffer grows as necessary and is always 0-terminated.
41  * The content of the string is never accessed, and thus is
42  * encoding-agnostic and can even hold binary data.
43  *
44  * Small buffers are kept in the structure itself, and thus require no
45  * memory allocation at all (unless the contents of the buffer is needed
46  * after the structure goes out of scope). This is almost as lightweight as
47  * declaring a local "char buf[512]".
48  *
49  * The length of the string can go beyond the allocated size: the buffer is
50  * then truncated, but the functions still keep account of the actual total
51  * length.
52  *
53  * In other words, buf->len can be greater than buf->size and records the
54  * total length of what would have been to the buffer if there had been
55  * enough memory.
56  *
57  * Append operations do not need to be tested for failure: if a memory
58  * allocation fails, data stop being appended to the buffer, but the length
59  * is still updated. This situation can be tested with
60  * av_bprint_is_complete().
61  *
62  * The size_max field determines several possible behaviours:
63  *
64  * size_max = -1 (= UINT_MAX) or any large value will let the buffer be
65  * reallocated as necessary, with an amortized linear cost.
66  *
67  * size_max = 0 prevents writing anything to the buffer: only the total
68  * length is computed. The write operations can then possibly be repeated in
69  * a buffer with exactly the necessary size
70  * (using size_init = size_max = len + 1).
71  *
72  * size_max = 1 is automatically replaced by the exact size available in the
73  * structure itself, thus ensuring no dynamic memory allocation. The
74  * internal buffer is large enough to hold a reasonable paragraph of text,
75  * such as the current paragraph.
76  */
77 typedef struct AVBPrint {
78  FF_PAD_STRUCTURE(1024,
79  char *str; /**< string so far */
80  unsigned len; /**< length so far */
81  unsigned size; /**< allocated memory */
82  unsigned size_max; /**< maximum allocated memory */
83  char reserved_internal_buffer[1];
84  )
85 } AVBPrint;
86 
87 /**
88  * Convenience macros for special values for av_bprint_init() size_max
89  * parameter.
90  */
91 #define AV_BPRINT_SIZE_UNLIMITED ((unsigned)-1)
92 #define AV_BPRINT_SIZE_AUTOMATIC 1
93 #define AV_BPRINT_SIZE_COUNT_ONLY 0
94 
95 /**
96  * Init a print buffer.
97  *
98  * @param buf buffer to init
99  * @param size_init initial size (including the final 0)
100  * @param size_max maximum size;
101  * 0 means do not write anything, just count the length;
102  * 1 is replaced by the maximum value for automatic storage;
103  * any large value means that the internal buffer will be
104  * reallocated as needed up to that limit; -1 is converted to
105  * UINT_MAX, the largest limit possible.
106  * Check also AV_BPRINT_SIZE_* macros.
107  */
108 void av_bprint_init(AVBPrint *buf, unsigned size_init, unsigned size_max);
109 
110 /**
111  * Init a print buffer using a pre-existing buffer.
112  *
113  * The buffer will not be reallocated.
114  *
115  * @param buf buffer structure to init
116  * @param buffer byte buffer to use for the string data
117  * @param size size of buffer
118  */
119 void av_bprint_init_for_buffer(AVBPrint *buf, char *buffer, unsigned size);
120 
121 /**
122  * Append a formatted string to a print buffer.
123  */
124 void av_bprintf(AVBPrint *buf, const char *fmt, ...) av_printf_format(2, 3);
125 
126 /**
127  * Append a formatted string to a print buffer.
128  */
129 void av_vbprintf(AVBPrint *buf, const char *fmt, va_list vl_arg);
130 
131 /**
132  * Append char c n times to a print buffer.
133  */
134 void av_bprint_chars(AVBPrint *buf, char c, unsigned n);
135 
136 /**
137  * Append data to a print buffer.
138  *
139  * param buf bprint buffer to use
140  * param data pointer to data
141  * param size size of data
142  */
143 void av_bprint_append_data(AVBPrint *buf, const char *data, unsigned size);
144 
145 struct tm;
146 /**
147  * Append a formatted date and time to a print buffer.
148  *
149  * param buf bprint buffer to use
150  * param fmt date and time format string, see strftime()
151  * param tm broken-down time structure to translate
152  *
153  * @note due to poor design of the standard strftime function, it may
154  * produce poor results if the format string expands to a very long text and
155  * the bprint buffer is near the limit stated by the size_max option.
156  */
157 void av_bprint_strftime(AVBPrint *buf, const char *fmt, const struct tm *tm);
158 
159 /**
160  * Allocate bytes in the buffer for external use.
161  *
162  * @param[in] buf buffer structure
163  * @param[in] size required size
164  * @param[out] mem pointer to the memory area
165  * @param[out] actual_size size of the memory area after allocation;
166  * can be larger or smaller than size
167  */
168 void av_bprint_get_buffer(AVBPrint *buf, unsigned size,
169  unsigned char **mem, unsigned *actual_size);
170 
171 /**
172  * Reset the string to "" but keep internal allocated data.
173  */
174 void av_bprint_clear(AVBPrint *buf);
175 
176 /**
177  * Test if the print buffer is complete (not truncated).
178  *
179  * It may have been truncated due to a memory allocation failure
180  * or the size_max limit (compare size and size_max if necessary).
181  */
182 static inline int av_bprint_is_complete(const AVBPrint *buf)
183 {
184  return buf->len < buf->size;
185 }
186 
187 /**
188  * Finalize a print buffer.
189  *
190  * The print buffer can no longer be used afterwards,
191  * but the len and size fields are still valid.
192  *
193  * @arg[out] ret_str if not NULL, used to return a permanent copy of the
194  * buffer contents, or NULL if memory allocation fails;
195  * if NULL, the buffer is discarded and freed
196  * @return 0 for success or error code (probably AVERROR(ENOMEM))
197  */
198 int av_bprint_finalize(AVBPrint *buf, char **ret_str);
199 
200 /**
201  * Escape the content in src and append it to dstbuf.
202  *
203  * @param dstbuf already inited destination bprint buffer
204  * @param src string containing the text to escape
205  * @param special_chars string containing the special characters which
206  * need to be escaped, can be NULL
207  * @param mode escape mode to employ, see AV_ESCAPE_MODE_* macros.
208  * Any unknown value for mode will be considered equivalent to
209  * AV_ESCAPE_MODE_BACKSLASH, but this behaviour can change without
210  * notice.
211  * @param flags flags which control how to escape, see AV_ESCAPE_FLAG_* macros
212  */
213 void av_bprint_escape(AVBPrint *dstbuf, const char *src, const char *special_chars,
214  enum AVEscapeMode mode, int flags);
215 
216 #endif /* AVUTIL_BPRINT_H */