+strbuf's are meant to be used with all the usual C string and memory
+APIs. Given that the length of the buffer is known, it's often better to
+use the mem* functions than a str* one (memchr vs. strchr e.g.).
+Though, one has to be careful about the fact that str* functions often
+stop on NULs and that strbufs may have embedded NULs.
+An strbuf is NUL terminated for convenience, but no function in the
+strbuf API actually relies on the string being free of NULs.
+strbufs has some invariants that are very important to keep in mind:
+. The `buf` member is never NULL, so you it can be used in any usual C
+string operations safely. strbuf's _have_ to be initialized either by
+`strbuf_init()` or by `= STRBUF_INIT` before the invariants, though.
+Do *not* assume anything on what `buf` really is (e.g. if it is
+allocated memory or not), use `strbuf_detach()` to unwrap a memory
+buffer from its strbuf shell in a safe way. That is the sole supported
+way. This will give you a malloced buffer that you can later `free()`.
+However, it it totally safe to modify anything in the string pointed by
+the `buf` member, between the indices `0` and `len-1` (inclusive).
+. The `buf` member is a byte array that has at least `len + 1` bytes
+ allocated. The extra byte is used to store a `'\0'`, allowing the
+ `buf` member to be a valid C-string. Every strbuf function ensure this
+ invariant is preserved.
+NOTE: It is OK to "play" with the buffer directly if you work it this
+strbuf_grow(sb, SOME_SIZE); <1>
+strbuf_setlen(sb, sb->len + SOME_OTHER_SIZE);
+<1> Here, the memory array starting at `sb->buf`, and of length
+`strbuf_avail(sb)` is all yours, and you can be sure that
+`strbuf_avail(sb)` is at least `SOME_SIZE`.
+NOTE: `SOME_OTHER_SIZE` must be smaller or equal to `strbuf_avail(sb)`.
+Doing so is safe, though if it has to be done in many places, adding the
+missing API to the strbuf module is the way to go.
+WARNING: Do _not_ assume that the area that is yours is of size `alloc
+- 1` even if it's true in the current implementation. Alloc is somehow a
+"private" member that should not be messed with. Use `strbuf_avail()`
+This is string buffer structure. The `len` member can be used to
+determine the current length of the string, and `buf` member provides access to
+ Initialize the structure. The second parameter can be zero or a bigger
+ number to allocate memory, in case you want to prevent further reallocs.
+ Release a string buffer and the memory it used. You should not use the
+ string buffer after using this function, unless you initialize it again.
+ Detach the string from the strbuf and returns it; you now own the
+ storage the string occupies and it is your responsibility from then on
+ to release it with `free(3)` when you are done with it.
+ Attach a string to a buffer. You should specify the string to attach,
+ the current length of the string and the amount of allocated memory.
+ The amount must be larger than the string length, because the string you
+ pass is supposed to be a NUL-terminated string. This string _must_ be
+ malloc()ed, and after attaching, the pointer cannot be relied upon
+ anymore, and neither be free()d directly.
+ Swap the contents of two string buffers.
+* Related to the size of the buffer
+ Determine the amount of allocated but unused memory.
+ Ensure that at least this amount of unused memory is available after
+ `len`. This is used when you know a typical size for what you will add
+ and want to avoid repetitive automatic resizing of the underlying buffer.
+ This is never a needed operation, but can be critical for performance in
+ Set the length of the buffer to a given value. This function does *not*
+ allocate new memory, so you should not perform a `strbuf_setlen()` to a
+ length that is larger than `len + strbuf_avail()`. `strbuf_setlen()` is
+ just meant as a 'please fix invariants from this strbuf I just messed
+ Empty the buffer by setting the size of it to zero.
+* Related to the contents of the buffer
+ Strip whitespace from the end of a string.
+ Compare two buffers. Returns an integer less than, equal to, or greater
+ than zero if the first buffer is found, respectively, to be less than,
+ to match, or be greater than the second buffer.
+* Adding data to the buffer
+NOTE: All of these functions in this section will grow the buffer as
+ Add a single character to the buffer.
+ Insert data to the given position of the buffer. The remaining contents
+ will be shifted, not overwritten.
+ Remove given amount of data from a given position of the buffer.
+ Remove the bytes between `pos..pos+len` and replace it with the given
+ Add data of given length to the buffer.
+Add a NUL-terminated string to the buffer.
+NOTE: This function will *always* be implemented as an inline or a macro
+strbuf_add(..., s, strlen(s));
+Meaning that this is efficient to write things like:
+strbuf_addstr(sb, "immediate string");
+ Copy the contents of an other buffer at the end of the current one.
+ Copy part of the buffer from a given position till a given length to the
+ This function can be used to expand a format string containing
+ placeholders. To that end, it parses the string and calls the specified
+ function for every percent sign found.
+The callback function is given a pointer to the character after the `%`
+and a pointer to the struct strbuf. It is expected to add the expanded
+version of the placeholder to the strbuf, e.g. to add a newline
+character if the letter `n` appears after a `%`. The function returns
+the length of the placeholder recognized and `strbuf_expand()` skips
+All other characters (non-percent and not skipped ones) are copied
+verbatim to the strbuf. If the callback returned zero, meaning that the
+placeholder is unknown, then the percent sign is copied, too.
+In order to facilitate caching and to make it possible to give
+parameters to the callback, `strbuf_expand()` passes a context pointer,
+which can be used by the programmer of the callback as she sees fit.
+ Add a formatted string to the buffer.
+ Read a given size of data from a FILE* pointer to the buffer.
+NOTE: The buffer is rewinded if the read fails. If -1 is returned,
+`errno` must be consulted, like you would do for `read(3)`.
+`strbuf_read()`, `strbuf_read_file()` and `strbuf_getline()` has the
+ Read the contents of a given file descriptor. The third argument can be
+ used to give a hint about the file size, to avoid reallocs.
+ Read the contents of a file, specified by its path. The third argument
+ can be used to give a hint about the file size, to avoid reallocs.
+ Read a line from a FILE* pointer. The second argument specifies the line
+ terminator character, typically `'\n'`.
+ Strip whitespace from a buffer. The second parameter controls if
+ comments are considered contents to be removed or not.