1strbuf API 2========== 3 4strbuf's are meant to be used with all the usual C string and memory 5APIs. Given that the length of the buffer is known, it's often better to 6use the mem* functions than a str* one (memchr vs. strchr e.g.). 7Though, one has to be careful about the fact that str* functions often 8stop on NULs and that strbufs may have embedded NULs. 9 10An strbuf is NUL terminated for convenience, but no function in the 11strbuf API actually relies on the string being free of NULs. 12 13strbufs has some invariants that are very important to keep in mind: 14 15. The `buf` member is never NULL, so it can be used in any usual C 16string operations safely. strbuf's _have_ to be initialized either by 17`strbuf_init()` or by `= STRBUF_INIT` before the invariants, though. 18+ 19Do *not* assume anything on what `buf` really is (e.g. if it is 20allocated memory or not), use `strbuf_detach()` to unwrap a memory 21buffer from its strbuf shell in a safe way. That is the sole supported 22way. This will give you a malloced buffer that you can later `free()`. 23+ 24However, it is totally safe to modify anything in the string pointed by 25the `buf` member, between the indices `0` and `len-1` (inclusive). 26 27. The `buf` member is a byte array that has at least `len + 1` bytes 28 allocated. The extra byte is used to store a `'\0'`, allowing the 29 `buf` member to be a valid C-string. Every strbuf function ensure this 30 invariant is preserved. 31+ 32NOTE: It is OK to "play" with the buffer directly if you work it this 33 way: 34+ 35---- 36strbuf_grow(sb, SOME_SIZE); <1> 37strbuf_setlen(sb, sb->len + SOME_OTHER_SIZE); 38---- 39<1> Here, the memory array starting at `sb->buf`, and of length 40`strbuf_avail(sb)` is all yours, and you can be sure that 41`strbuf_avail(sb)` is at least `SOME_SIZE`. 42+ 43NOTE: `SOME_OTHER_SIZE` must be smaller or equal to `strbuf_avail(sb)`. 44+ 45Doing so is safe, though if it has to be done in many places, adding the 46missing API to the strbuf module is the way to go. 47+ 48WARNING: Do _not_ assume that the area that is yours is of size `alloc 49- 1` even if it's true in the current implementation. Alloc is somehow a 50"private" member that should not be messed with. Use `strbuf_avail()` 51instead. 52 53Data structures 54--------------- 55 56* `struct strbuf` 57 58This is the string buffer structure. The `len` member can be used to 59determine the current length of the string, and `buf` member provides access to 60the string itself. 61 62Functions 63--------- 64 65* Life cycle 66 67`strbuf_init`:: 68 69 Initialize the structure. The second parameter can be zero or a bigger 70 number to allocate memory, in case you want to prevent further reallocs. 71 72`strbuf_release`:: 73 74 Release a string buffer and the memory it used. You should not use the 75 string buffer after using this function, unless you initialize it again. 76 77`strbuf_detach`:: 78 79 Detach the string from the strbuf and returns it; you now own the 80 storage the string occupies and it is your responsibility from then on 81 to release it with `free(3)` when you are done with it. 82 83`strbuf_attach`:: 84 85 Attach a string to a buffer. You should specify the string to attach, 86 the current length of the string and the amount of allocated memory. 87 The amount must be larger than the string length, because the string you 88 pass is supposed to be a NUL-terminated string. This string _must_ be 89 malloc()ed, and after attaching, the pointer cannot be relied upon 90 anymore, and neither be free()d directly. 91 92`strbuf_swap`:: 93 94 Swap the contents of two string buffers. 95 96* Related to the size of the buffer 97 98`strbuf_avail`:: 99 100 Determine the amount of allocated but unused memory. 101 102`strbuf_grow`:: 103 104 Ensure that at least this amount of unused memory is available after 105 `len`. This is used when you know a typical size for what you will add 106 and want to avoid repetitive automatic resizing of the underlying buffer. 107 This is never a needed operation, but can be critical for performance in 108 some cases. 109 110`strbuf_setlen`:: 111 112 Set the length of the buffer to a given value. This function does *not* 113 allocate new memory, so you should not perform a `strbuf_setlen()` to a 114 length that is larger than `len + strbuf_avail()`. `strbuf_setlen()` is 115 just meant as a 'please fix invariants from this strbuf I just messed 116 with'. 117 118`strbuf_reset`:: 119 120 Empty the buffer by setting the size of it to zero. 121 122* Related to the contents of the buffer 123 124`strbuf_rtrim`:: 125 126 Strip whitespace from the end of a string. 127 128`strbuf_cmp`:: 129 130 Compare two buffers. Returns an integer less than, equal to, or greater 131 than zero if the first buffer is found, respectively, to be less than, 132 to match, or be greater than the second buffer. 133 134* Adding data to the buffer 135 136NOTE: All of the functions in this section will grow the buffer as necessary. 137If they fail for some reason other than memory shortage and the buffer hadn't 138been allocated before (i.e. the `struct strbuf` was set to `STRBUF_INIT`), 139then they will free() it. 140 141`strbuf_addch`:: 142 143 Add a single character to the buffer. 144 145`strbuf_insert`:: 146 147 Insert data to the given position of the buffer. The remaining contents 148 will be shifted, not overwritten. 149 150`strbuf_remove`:: 151 152 Remove given amount of data from a given position of the buffer. 153 154`strbuf_splice`:: 155 156 Remove the bytes between `pos..pos+len` and replace it with the given 157 data. 158 159`strbuf_add_commented_lines`:: 160 161 Add a NUL-terminated string to the buffer. Each line will be prepended 162 by a comment character and a blank. 163 164`strbuf_add`:: 165 166 Add data of given length to the buffer. 167 168`strbuf_addstr`:: 169 170Add a NUL-terminated string to the buffer. 171+ 172NOTE: This function will *always* be implemented as an inline or a macro 173that expands to: 174+ 175---- 176strbuf_add(..., s, strlen(s)); 177---- 178+ 179Meaning that this is efficient to write things like: 180+ 181---- 182strbuf_addstr(sb, "immediate string"); 183---- 184 185`strbuf_addbuf`:: 186 187 Copy the contents of an other buffer at the end of the current one. 188 189`strbuf_adddup`:: 190 191 Copy part of the buffer from a given position till a given length to the 192 end of the buffer. 193 194`strbuf_expand`:: 195 196 This function can be used to expand a format string containing 197 placeholders. To that end, it parses the string and calls the specified 198 function for every percent sign found. 199+ 200The callback function is given a pointer to the character after the `%` 201and a pointer to the struct strbuf. It is expected to add the expanded 202version of the placeholder to the strbuf, e.g. to add a newline 203character if the letter `n` appears after a `%`. The function returns 204the length of the placeholder recognized and `strbuf_expand()` skips 205over it. 206+ 207The format `%%` is automatically expanded to a single `%` as a quoting 208mechanism; callers do not need to handle the `%` placeholder themselves, 209and the callback function will not be invoked for this placeholder. 210+ 211All other characters (non-percent and not skipped ones) are copied 212verbatim to the strbuf. If the callback returned zero, meaning that the 213placeholder is unknown, then the percent sign is copied, too. 214+ 215In order to facilitate caching and to make it possible to give 216parameters to the callback, `strbuf_expand()` passes a context pointer, 217which can be used by the programmer of the callback as she sees fit. 218 219`strbuf_expand_dict_cb`:: 220 221 Used as callback for `strbuf_expand()`, expects an array of 222 struct strbuf_expand_dict_entry as context, i.e. pairs of 223 placeholder and replacement string. The array needs to be 224 terminated by an entry with placeholder set to NULL. 225 226`strbuf_addbuf_percentquote`:: 227 228 Append the contents of one strbuf to another, quoting any 229 percent signs ("%") into double-percents ("%%") in the 230 destination. This is useful for literal data to be fed to either 231 strbuf_expand or to the *printf family of functions. 232 233`strbuf_humanise_bytes`:: 234 235 Append the given byte size as a human-readable string (i.e. 12.23 KiB, 236 3.50 MiB). 237 238`strbuf_addf`:: 239 240 Add a formatted string to the buffer. 241 242`strbuf_commented_addf`:: 243 244 Add a formatted string prepended by a comment character and a 245 blank to the buffer. 246 247`strbuf_fread`:: 248 249 Read a given size of data from a FILE* pointer to the buffer. 250+ 251NOTE: The buffer is rewound if the read fails. If -1 is returned, 252`errno` must be consulted, like you would do for `read(3)`. 253`strbuf_read()`, `strbuf_read_file()` and `strbuf_getline()` has the 254same behaviour as well. 255 256`strbuf_read`:: 257 258 Read the contents of a given file descriptor. The third argument can be 259 used to give a hint about the file size, to avoid reallocs. 260 261`strbuf_read_file`:: 262 263 Read the contents of a file, specified by its path. The third argument 264 can be used to give a hint about the file size, to avoid reallocs. 265 266`strbuf_readlink`:: 267 268 Read the target of a symbolic link, specified by its path. The third 269 argument can be used to give a hint about the size, to avoid reallocs. 270 271`strbuf_getline`:: 272 273 Read a line from a FILE *, overwriting the existing contents 274 of the strbuf. The second argument specifies the line 275 terminator character, typically `'\n'`. 276 Reading stops after the terminator or at EOF. The terminator 277 is removed from the buffer before returning. Returns 0 unless 278 there was nothing left before EOF, in which case it returns `EOF`. 279 280`strbuf_getwholeline`:: 281 282 Like `strbuf_getline`, but keeps the trailing terminator (if 283 any) in the buffer. 284 285`strbuf_getwholeline_fd`:: 286 287 Like `strbuf_getwholeline`, but operates on a file descriptor. 288 It reads one character at a time, so it is very slow. Do not 289 use it unless you need the correct position in the file 290 descriptor. 291 292`stripspace`:: 293 294 Strip whitespace from a buffer. The second parameter controls if 295 comments are considered contents to be removed or not. 296 297`strbuf_split_buf`:: 298`strbuf_split_str`:: 299`strbuf_split_max`:: 300`strbuf_split`:: 301 302 Split a string or strbuf into a list of strbufs at a specified 303 terminator character. The returned substrings include the 304 terminator characters. Some of these functions take a `max` 305 parameter, which, if positive, limits the output to that 306 number of substrings. 307 308`strbuf_list_free`:: 309 310 Free a list of strbufs (for example, the return values of the 311 `strbuf_split()` functions). 312 313`launch_editor`:: 314 315 Launch the user preferred editor to edit a file and fill the buffer 316 with the file's contents upon the user completing their editing. The 317 third argument can be used to set the environment which the editor is 318 run in. If the buffer is NULL the editor is launched as usual but the 319 file's contents are not read into the buffer upon completion.