Re: [PATCHv3 2/2] builtin/commit.c: switch to xstrfmt(), instead of snprintf,

["René Scharfe" <l.s.r@web.de>]

Am 13.01.2017 um 18:58 schrieb Elia Pinto:
> In this patch, instead of using xnprintf instead of snprintf, which asserts
> that we don't truncate, we are switching to dynamic allocation with  xstrfmt(),
> , so we can avoid dealing with magic numbers in the code and reduce the cognitive burden from
> the programmers, because they no longer have to count bytes needed for static allocation.
> As a side effect of this patch we have also reduced the snprintf() calls, that may silently truncate 
> results if the programmer is not careful.
> 
> Helped-by: Junio C Hamano <gitster@pobox.com>
> Helped-by: Jeff King <peff@peff.net> 
> Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
> ---
> This is the third  version of the patch.
> 
> Changes from the first version: I have split the original commit in two, as discussed here
> http://public-inbox.org/git/20161213132717.42965-1-gitter.spiros@gmail.com/.
> 
> Changes from the second version:
> - Changed the commit message to clarify the purpose of the patch (
> as suggested by Junio)
> https://public-inbox.org/git/xmqqtw95mfo3.fsf@gitster.mtv.corp.google.com/T/#m2e6405a8a78a8ca1ed770614c91398290574c4a1
> 
> 
> 
>  builtin/commit.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/builtin/commit.c b/builtin/commit.c
> index 09bcc0f13..37228330c 100644
> --- a/builtin/commit.c
> +++ b/builtin/commit.c
> @@ -1526,12 +1526,10 @@ static int git_commit_config(const char *k, const char *v, void *cb)
>  static int run_rewrite_hook(const unsigned char *oldsha1,
>  			    const unsigned char *newsha1)
>  {
> -	/* oldsha1 SP newsha1 LF NUL */
> -	static char buf[2*40 + 3];
> +	char *buf;
>  	struct child_process proc = CHILD_PROCESS_INIT;
>  	const char *argv[3];
>  	int code;
> -	size_t n;
>  
>  	argv[0] = find_hook("post-rewrite");
>  	if (!argv[0])
> @@ -1547,11 +1545,11 @@ static int run_rewrite_hook(const unsigned char *oldsha1,
>  	code = start_command(&proc);
>  	if (code)
>  		return code;
> -	n = snprintf(buf, sizeof(buf), "%s %s\n",
> -		     sha1_to_hex(oldsha1), sha1_to_hex(newsha1));
> +	buf = xstrfmt("%s %s\n", sha1_to_hex(oldsha1), sha1_to_hex(newsha1));
>  	sigchain_push(SIGPIPE, SIG_IGN);
> -	write_in_full(proc.in, buf, n);
> +	write_in_full(proc.in, buf, strlen(buf));
>  	close(proc.in);
> +	free(buf);
>  	sigchain_pop(SIGPIPE);
>  	return finish_command(&proc);
>  }
> 

Perhaps I missed it from the discussion, but why not use strbuf?  It
would avoid counting the generated string's length.  That's probably
not going to make a measurable difference performance-wise, but it's
easy to avoid and doesn't even take up more lines:
---
 builtin/commit.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index 711f96cc43..73bb72016f 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1525,12 +1525,10 @@ static int git_commit_config(const char *k, const char *v, void *cb)
 static int run_rewrite_hook(const unsigned char *oldsha1,
 			    const unsigned char *newsha1)
 {
-	/* oldsha1 SP newsha1 LF NUL */
-	static char buf[2*40 + 3];
+	struct strbuf sb = STRBUF_INIT;
 	struct child_process proc = CHILD_PROCESS_INIT;
 	const char *argv[3];
 	int code;
-	size_t n;
 
 	argv[0] = find_hook("post-rewrite");
 	if (!argv[0])
@@ -1546,11 +1544,11 @@ static int run_rewrite_hook(const unsigned char *oldsha1,
 	code = start_command(&proc);
 	if (code)
 		return code;
-	n = snprintf(buf, sizeof(buf), "%s %s\n",
-		     sha1_to_hex(oldsha1), sha1_to_hex(newsha1));
+	strbuf_addf(&sb, "%s %s\n", sha1_to_hex(oldsha1), sha1_to_hex(newsha1));
 	sigchain_push(SIGPIPE, SIG_IGN);
-	write_in_full(proc.in, buf, n);
+	write_in_full(proc.in, sb.buf, sb.len);
 	close(proc.in);
+	strbuf_release(&sb);
 	sigchain_pop(SIGPIPE);
 	return finish_command(&proc);
 }
-- 
2.11.0