[PATCHv2] fsck.c:fsck_commit() use skip_prefix() and starts_with()

[Othman Darraz <darrazo16@gmail.com>]

make buffer const char* because the content of the memory referenced by this variable doesn't change in this function. 
Add cast to buffer to match fsck_ident signature which is (char**,...)

use skip_prefix() instead of memcmp() to avoid using magic number.

Signed-off-by: Othman Darraz <darrazo16@gmail.com>
---
I am planning to apply for GSOC2014
 fsck.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/fsck.c b/fsck.c
index 5eae856..128d426 100644
--- a/fsck.c
+++ b/fsck.c
@@ -284,21 +284,22 @@ static int fsck_ident(char **ident, struct object *obj, fsck_error error_func)
 
 static int fsck_commit(struct commit *commit, fsck_error error_func)
 {
-	char *buffer = commit->buffer;
+	const char *buffer = commit->buffer;
 	unsigned char tree_sha1[20], sha1[20];
 	struct commit_graft *graft;
 	int parents = 0;
 	int err;
-
-	if (starts_with(buffer, "tree "))
+	buffer = skip_prefix(buffer, "tree ");
+	if (!buffer)
 		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
-	if (get_sha1_hex(buffer+5, tree_sha1) || buffer[45] != '\n')() 
+	if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n')
 		return error_func(&commit->object, FSCK_ERROR, "invalid 'tree' line format - bad sha1");
-	buffer += 46;
-	while (!memcmp(buffer, "parent ", 7)) {
-		if (get_sha1_hex(buffer+7, sha1) || buffer[47] != '\n')
+	buffer += 41;
+	while (starts_with(buffer, "parent ")) {
+		buffer = skip_prefix(buffer, "parent ");
+		if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n')
 			return error_func(&commit->object, FSCK_ERROR, "invalid 'parent' line format - bad sha1");
-		buffer += 48;
+		buffer += 41;
 		parents++;
 	}
 	graft = lookup_commit_graft(commit->object.sha1);
@@ -322,16 +323,16 @@ static int fsck_commit(struct commit *commit, fsck_error error_func)
 		if (p || parents)
 			return error_func(&commit->object, FSCK_ERROR, "parent objects missing");
 	}
-	if (starts_with(buffer, "author "))
+	buffer = skip_prefix(buffer, "author ");
+	if (!buffer)
 		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'author' line");
-	buffer += 7;
-	err = fsck_ident(&buffer, &commit->object, error_func);
+	err = fsck_ident((char **)&buffer, &commit->object, error_func);
 	if (err)
 		return err;
-	buffer = (char* )skip_prefix(buffer,"committer ");
+	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((char **)&buffer, &commit->object, error_func);
 	if (err)
 		return err;
 	if (!commit->tree)
-- 
1.9.0.258.g00eda23.dirty