2fc647004a
Make all strbuf functions that can fail free() their memory on error if they have allocated it. They don't shrink buffers that have been grown, though. This allows for easier error handling, as callers only need to call strbuf_release() if A) the command succeeded or B) if they would have had to do so anyway because they added something to the strbuf themselves. Bonus hunk: document strbuf_readlink. Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <gitster@pobox.com>
256 lines
8.0 KiB
Plaintext
256 lines
8.0 KiB
Plaintext
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:
|
|
|
|
. 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
|
|
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 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.
|
|
+
|
|
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_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 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
|
|
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`::
|