Re: [PATCH 4/6] abbrev_sha1_in_line: don't leak memory

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> On Tue, Mar 29, 2016 at 09:30:38PM -0400, Eric Sunshine wrote:
>
>> The implementation of strbuf_list_free() is this:
>> 
>>     struct strbuf **s = sbs;
>>     while (*s) {
>>         strbuf_release(*s);
>>         free(*s++);
>>     }
>>     free(sbs);
>> 
>> which means that wt-status.c is leaking not only 'split', but also
>> each element of split[], right?
>
> Yeah, I didn't notice that, but I think you're right.

Correct.

I suspect that we would be better off in the longer term if
we made conscious effort to deprecate and eradicate the use
of strbuf_split* API functions.  They are easy to write
crappy code with, inefficient, and error prone.  You would
rarely need to have N resulting pieces as strbufs to be
easily manipulatable [*1*].

The function can be written by not using the "split and then
rebuild" pattern, perhaps like so, and the result is even
easier to read and understand, I would say.  A sample rewrite
is attached at the end.


[Footnote]

*1* I wouldn't be this harsh if the function were to fill an
    array of pointers or offsets into the original string.

 wt-status.c | 43 +++++++++++++++++++------------------------
 1 file changed, 19 insertions(+), 24 deletions(-)

diff --git a/wt-status.c b/wt-status.c
index ef74864..4886c35 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -1037,35 +1037,30 @@ static int split_commit_in_progress(struct wt_status *s)
  */
 static void abbrev_sha1_in_line(struct strbuf *line)
 {
-	struct strbuf **split;
-	int i;
+	const char *cp, *ep, *abbrev;
+	unsigned char sha1[20];
 
-	if (starts_with(line->buf, "exec ") ||
-	    starts_with(line->buf, "x "))
+	/* the oddball "exec" does not have 40-hex as the second token */
+	if (starts_with(line->buf, "exec ") || starts_with(line->buf, "x "))
 		return;
 
-	split = strbuf_split_max(line, ' ', 3);
-	if (split[0] && split[1]) {
-		unsigned char sha1[20];
-		const char *abbrev;
+	/* find the second token on the line */
+	cp = strchr(line->buf, ' ');
+	if (!cp)
+		return;
+	cp++;
+	ep = strchr(cp, ' ');
+	if (!ep)
+		return;
 
-		/*
-		 * strbuf_split_max left a space. Trim it and re-add
-		 * it after abbreviation.
-		 */
-		strbuf_trim(split[1]);
-		if (!get_sha1(split[1]->buf, sha1)) {
-			abbrev = find_unique_abbrev(sha1, DEFAULT_ABBREV);
-			strbuf_reset(split[1]);
-			strbuf_addf(split[1], "%s ", abbrev);
-			strbuf_reset(line);
-			for (i = 0; split[i]; i++)
-				strbuf_addf(line, "%s", split[i]->buf);
-		}
-	}
-	for (i = 0; split[i]; i++)
-		strbuf_release(split[i]);
+	/* is it 40-hex? */
+	if (ep - cp != GIT_SHA1_HEXSZ || get_sha1_hex(cp, sha1))
+		return;
 
+	/* replace it with its abbreviation */
+	abbrev = find_unique_abbrev(sha1, DEFAULT_ABBREV);
+	strbuf_splice(line, cp - line->buf, GIT_SHA1_HEXSZ,
+		      abbrev, strlen(abbrev));
 }
 
 static void read_rebase_todolist(const char *fname, struct string_list *lines)