# strbuf API

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:

1. The `buf` member is never NULL, so 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 is totally safe to modify anything in the string pointed by the `buf` member, between the indices `0` and `len-1` (inclusive).

2. 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 way:

       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()` instead.

## Data structures

- `struct strbuf`

This is the string buffer structure. The `len` member can be used to determine the current length of the string, and `buf` member provides access to the string itself.

## Functions

- Life cycle

  `strbuf_init`

    Initialize the structure. The second parameter can be zero or a bigger number to allocate memory, in case you want to prevent further reallocs.

  `strbuf_release`

    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.

  `strbuf_detach`

    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.

  `strbuf_attach`

    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.

  `strbuf_swap`

    Swap the contents of two string buffers.

- Related to the size of the buffer

  `strbuf_avail`

    Determine the amount of allocated but unused memory.

  `strbuf_grow`

    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 some cases.

  `strbuf_setlen`

    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 with.

  `strbuf_reset`

    Empty the buffer by setting the size of it to zero.

- Related to the contents of the buffer

  `strbuf_rtrim`

    Strip whitespace from the end of a string.

  `strbuf_cmp`

    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 the functions in this section will grow the buffer as necessary. If they fail for some reason other than memory shortage and the buffer hadn’t been allocated before (i.e. the `struct strbuf` was set to `STRBUF_INIT`), then they will free() it.

`strbuf_addch`

  Add a single character to the buffer.

`strbuf_insert`

  Insert data to the given position of the buffer. The remaining contents will be shifted, not overwritten.

`strbuf_remove`

  Remove given amount of data from a given position of the buffer.

`strbuf_splice`

  Remove the bytes between `pos..pos+len` and replace it with the given data.

`strbuf_add`

  Add data of given length to the buffer.

`strbuf_addstr`

  Add a NUL-terminated string to the buffer.

  Note | This function will always be implemented as an inline or a macro that expands to:

      strbuf_add(..., s, strlen(s));

  Meaning that this is efficient to write things like:

      strbuf_addstr(sb, "immediate string");

`strbuf_addbuf`

  Copy the contents of an other buffer at the end of the current one.

`strbuf_adddup`

  Copy part of the buffer from a given position till a given length to the end of the buffer.

`strbuf_expand`

  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 over it.

  The format `%%` is automatically expanded to a single `%` as a quoting mechanism; callers do not need to handle the `%` placeholder themselves, and the callback function will not be invoked for this placeholder.

  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.

`strbuf_expand_dict_cb`

  Used as callback for `strbuf_expand()`, expects an array of struct strbuf_expand_dict_entry as context, i.e. pairs of placeholder and replacement string. The array needs to be terminated by an entry with placeholder set to NULL.

`strbuf_addbuf_percentquote`

  Append the contents of one strbuf to another, quoting any percent signs ("%") into double-percents ("%%") in the destination. This is useful for literal data to be fed to either strbuf_expand or to the *printf family of functions.

`strbuf_addf`

  Add a formatted string to the buffer.

`strbuf_fread`

  Read a given size of data from a FILE* pointer to the buffer.

  Note | The buffer is rewound 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 same behaviour as well.

`strbuf_read`

  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.

`strbuf_read_file`

  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.

`strbuf_readlink`

  Read the target of a symbolic link, specified by its path. The third argument can be used to give a hint about the size, to avoid reallocs.

`strbuf_getline`

  Read a line from a FILE* pointer. The second argument specifies the line terminator character, typically `\n`.

`stripspace`

  Strip whitespace from a buffer. The second parameter controls if comments are considered contents to be removed or not.

`launch_editor`

  Launch the user preferred editor to edit a file and fill the buffer with the file’s contents upon the user completing their editing. The third argument can be used to set the environment which the editor is run in. If the buffer is NULL the editor is launched as usual but the file’s contents are not read into the buffer upon completion.