Re: [PATCH v3 2/2] fsck.c: Rewrite fsck_commit() to use skip_prefix()

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

Junio C Hamano <gitster@pobox.com> writes:

>> -	if (memcmp(buffer, "tree ", 5))
>> +	buffer = skip_prefix(buffer, "tree ");
>> +	if (buffer == NULL)
>
> We encourage people to write this as:
>
> 	if (!buffer)
>
> The same comment applies to other new lines in this patch.

I also see a lot of repetitions in the code, before or after the
patch.  I wonder if a further refactoring along this line on top of
these two patches might be worth considering.

No, I am not proud of sneaking tree_sha1[] array pointers as a
seemingly boolean-looking must-match-header parameter into the
helper, but this is merely a "how about going in this direction"
weather-balloon patch, so....

 fsck.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 61 insertions(+), 22 deletions(-)

diff --git a/fsck.c b/fsck.c
index 6aab23b..a3eea7f 100644
--- a/fsck.c
+++ b/fsck.c
@@ -279,10 +279,55 @@ static int fsck_ident(const char **ident, struct object *obj, fsck_error error_f
 	return 0;
 }
 
+static int fsck_object_line(struct commit *commit, fsck_error error_func,
+			    const char **buffer, const char *header,
+			    unsigned char must_match_header[])
+{
+	unsigned char sha1_buf[20];
+	unsigned char *sha1 = must_match_header ? must_match_header : sha1_buf;
+	const char *buf;
+
+	buf = skip_prefix(*buffer, header);
+	if (!buf) {
+		if (must_match_header)
+			return error_func(&commit->object, FSCK_ERROR,
+					  "invalid format - expected '%.*s' line",
+					  (int) strlen(header) - 1,
+					  header);
+		return 1;
+	}
+	if (get_sha1_hex(buf, sha1) || buf[40] != '\n')
+		return error_func(&commit->object, FSCK_ERROR,
+				  "invalid '%.*s' line format - bad sha1",
+				  (int) strlen(header) - 1,
+				  header);
+	*buffer = buf + 41;
+	return 0;
+}
+
+static int fsck_ident_line(struct commit *commit, fsck_error error_func,
+			   const char **buffer, const char *header)
+{
+	const char *buf;
+	int err;
+
+	buf = skip_prefix(*buffer, header);
+	if (!buf)
+		return error_func(&commit->object, FSCK_ERROR,
+				  "invalid format - expected '%.*s' line",
+				  (int) strlen(header) - 1,
+				  header);
+	err = fsck_ident(&buf, &commit->object, error_func);
+	if (err)
+		return err;
+	*buffer = buf;
+	return 0;
+}
+
 static int fsck_commit(struct commit *commit, fsck_error error_func)
 {
-	const char *buffer = commit->buffer, *tmp;
-	unsigned char tree_sha1[20], sha1[20];
+	const char *buffer = commit->buffer;
+	unsigned char tree_sha1[20];
 	struct commit_graft *graft;
 	int parents = 0;
 	int err;
@@ -290,18 +335,17 @@ static int fsck_commit(struct commit *commit, fsck_error error_func)
 	if (commit->date == ULONG_MAX)
 		return error_func(&commit->object, FSCK_ERROR, "invalid author/committer line");
 
-	buffer = skip_prefix(buffer, "tree ");
-	if (!buffer)
-		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
-	if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n')
-		return error_func(&commit->object, FSCK_ERROR, "invalid 'tree' line format - bad sha1");
-	buffer += 41;
-	while ((tmp = skip_prefix(buffer, "parent "))) {
-		buffer = tmp;
-		if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n')
-			return error_func(&commit->object, FSCK_ERROR, "invalid 'parent' line format - bad sha1");
-		buffer += 41;
-		parents++;
+	err = fsck_object_line(commit, error_func, &buffer, "tree ", tree_sha1);
+	if (err)
+		return err;
+	while (1) {
+		err = fsck_object_line(commit, error_func, &buffer, "parent ", NULL);
+		if (err < 0)
+			return err;
+		else if (!err)
+			parents++;
+		else
+			break;
 	}
 	graft = lookup_commit_graft(commit->object.sha1);
 	if (graft) {
@@ -324,16 +368,11 @@ static int fsck_commit(struct commit *commit, fsck_error error_func)
 		if (p || parents)
 			return error_func(&commit->object, FSCK_ERROR, "parent objects missing");
 	}
-	buffer = skip_prefix(buffer, "author ");
-	if (!buffer)
-		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'author' line");
-	err = fsck_ident(&buffer, &commit->object, error_func);
+
+	err = fsck_ident_line(commit, error_func, &buffer, "author ");
 	if (err)
 		return err;
-	buffer = skip_prefix(buffer, "committer ");
-	if (!buffer)
-		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'committer' line");
-	err = fsck_ident(&buffer, &commit->object, error_func);
+	err = fsck_ident_line(commit, error_func, &buffer, "committer ");
 	if (err)
 		return err;
 	if (!commit->tree)