builtin/commit.c: switch to strbuf, instead of snprintf()

Switch to dynamic allocation with strbuf, so we can avoid dealing
with magic numbers in the code and reduce the cognitive burden from
the programmers.  The original code is correct, but programmers no
longer have to count bytes needed for static allocation to know that.

As a side effect of this change, we also reduce the snprintf()
calls, that may silently truncate results if the programmer is not
careful.

Helped-by: René Scharfe <[email protected]>
Helped-by: Junio C Hamano <[email protected]>
Helped-by: Jeff King <[email protected]>
Signed-off-by: Elia Pinto <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: devzero2000

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 child_process proc = CHILD_PROCESS_INIT;
 	const char *argv[3];
 	int code;
-	size_t n;
+	struct strbuf sb = STRBUF_INIT;
 
 	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);
 }