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`:: 160 161 Add data of given length to the buffer. 162 163`strbuf_addstr`:: 164 165Add a NUL-terminated string to the buffer. 166+ 167NOTE: This function will *always* be implemented as an inline or a macro 168that expands to: 169+ 170---- 171strbuf_add(..., s, strlen(s)); 172---- 173+ 174Meaning that this is efficient to write things like: 175+ 176---- 177strbuf_addstr(sb, "immediate string"); 178---- 179 180`strbuf_addbuf`:: 181 182 Copy the contents of an other buffer at the end of the current one. 183 184`strbuf_adddup`:: 185 186 Copy part of the buffer from a given position till a given length to the 187 end of the buffer. 188 189`strbuf_expand`:: 190 191 This function can be used to expand a format string containing 192 placeholders. To that end, it parses the string and calls the specified 193 function for every percent sign found. 194+ 195The callback function is given a pointer to the character after the `%` 196and a pointer to the struct strbuf. It is expected to add the expanded 197version of the placeholder to the strbuf, e.g. to add a newline 198character if the letter `n` appears after a `%`. The function returns 199the length of the placeholder recognized and `strbuf_expand()` skips 200over it. 201+ 202The format `%%` is automatically expanded to a single `%` as a quoting 203mechanism; callers do not need to handle the `%` placeholder themselves, 204and the callback function will not be invoked for this placeholder. 205+ 206All other characters (non-percent and not skipped ones) are copied 207verbatim to the strbuf. If the callback returned zero, meaning that the 208placeholder is unknown, then the percent sign is copied, too. 209+ 210In order to facilitate caching and to make it possible to give 211parameters to the callback, `strbuf_expand()` passes a context pointer, 212which can be used by the programmer of the callback as she sees fit. 213 214`strbuf_expand_dict_cb`:: 215 216 Used as callback for `strbuf_expand()`, expects an array of 217 struct strbuf_expand_dict_entry as context, i.e. pairs of 218 placeholder and replacement string. The array needs to be 219 terminated by an entry with placeholder set to NULL. 220 221`strbuf_addbuf_percentquote`:: 222 223 Append the contents of one strbuf to another, quoting any 224 percent signs ("%") into double-percents ("%%") in the 225 destination. This is useful for literal data to be fed to either 226 strbuf_expand or to the *printf family of functions. 227 228`strbuf_addf`:: 229 230 Add a formatted string to the buffer. 231 232`strbuf_fread`:: 233 234 Read a given size of data from a FILE* pointer to the buffer. 235+ 236NOTE: The buffer is rewound if the read fails. If -1 is returned, 237`errno` must be consulted, like you would do for `read(3)`. 238`strbuf_read()`, `strbuf_read_file()` and `strbuf_getline()` has the 239same behaviour as well. 240 241`strbuf_read`:: 242 243 Read the contents of a given file descriptor. The third argument can be 244 used to give a hint about the file size, to avoid reallocs. 245 246`strbuf_read_file`:: 247 248 Read the contents of a file, specified by its path. The third argument 249 can be used to give a hint about the file size, to avoid reallocs. 250 251`strbuf_readlink`:: 252 253 Read the target of a symbolic link, specified by its path. The third 254 argument can be used to give a hint about the size, to avoid reallocs. 255 256`strbuf_getline`:: 257 258 Read a line from a FILE* pointer. The second argument specifies the line 259 terminator character, typically `'\n'`. 260 261`stripspace`:: 262 263 Strip whitespace from a buffer. The second parameter controls if 264 comments are considered contents to be removed or not. 265 266`launch_editor`:: 267 268 Launch the user preferred editor to edit a file and fill the buffer 269 with the file's contents upon the user completing their editing. The 270 third argument can be used to set the environment which the editor is 271 run in. If the buffer is NULL the editor is launched as usual but the 272 file's contents are not read into the buffer upon completion.