[PATCH v2] strbuf doc: reuse after strbuf_release is fine
- Date: Tue, 3 Oct 2017 19:39:54 -0700
- From: Jonathan Nieder <jrnieder@xxxxxxxxx>
- Subject: [PATCH v2] strbuf doc: reuse after strbuf_release is fine
strbuf_release leaves the strbuf in a valid, initialized state, so
there is no need to call strbuf_init after it.
Moreover, this is not likely to change in the future: strbuf_release
leaving the strbuf in a valid state has been easy to maintain and has
been very helpful for Git's robustness and simplicity (e.g.,
preventing use-after-free vulnerabilities).
Document the semantics so the next generation of Git developers can
become familiar with them without reading the implementation. It is
still not advisable to call strbuf_release too often because it is
wasteful, so add a note pointing to strbuf_reset for that.
The same semantics apply to strbuf_detach. Add a similar note to its
docstring to make that clear.
Improved-by: Jeff King <peff@xxxxxxxx>
Signed-off-by: Jonathan Nieder <jrnieder@xxxxxxxxx>
Jeff King wrote:
> I think it's actually OK to use the string buffer after this function.
> It's just an empty string.
> Perhaps we should be more explicit: this releases any resources and
> resets to a pristine, empty state. I suspect strbuf_detach() probably
> should make the same claim.
strbuf.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/strbuf.h b/strbuf.h
index 7496cb8ec5..249df86711 100644
@@ -82,8 +82,12 @@ extern char strbuf_slopbuf;
extern void strbuf_init(struct strbuf *, size_t);
- * 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.
+ * Release a string buffer and the memory it used. After this call, the
+ * strbuf points to an empty string that does not need to be free()ed, as
+ * if it had been set to `STRBUF_INIT` and never modified.
+ * To clear a strbuf in preparation for further use without the overhead
+ * of free()ing and malloc()ing again, use strbuf_reset() instead.
extern void strbuf_release(struct strbuf *);
@@ -91,6 +95,9 @@ extern void strbuf_release(struct strbuf *);
* 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.
+ * The strbuf that previously held the string is reset to `STRBUF_INIT` so
+ * it can be reused after calling this function.
extern char *strbuf_detach(struct strbuf *, size_t *);