[PATCHv3 3/5] Add a common is_gitfile function

[Phil Hord <hordp@cisco.com>]

There are at least two locations in the code that check for
gitfiles.  Each one is slightly different for pretty good
reasons.  Work towards a common API by abstracting the
"is this a gitfile" question into a single function.

Signed-off-by: Phil Hord <hordp@cisco.com>

diff --git a/builtin/clone.c b/builtin/clone.c
index 488f48e..5110399 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -120,13 +120,7 @@ static char *get_repo_path(const char *repo, int *is_bundle)
 			return xstrdup(absolute_path(path));
 		} else if (S_ISREG(st.st_mode) && st.st_size > 8) {
 			/* Is it a "gitfile"? */
-			char signature[8];
-			int len, fd = open(path, O_RDONLY);
-			if (fd < 0)
-				continue;
-			len = read_in_full(fd, signature, 8);
-			close(fd);
-			if (len != 8 || strncmp(signature, "gitdir: ", 8))
+			if (!is_gitfile(path))
 				continue;
 			path = read_gitfile(path);
 			if (path) {
diff --git a/cache.h b/cache.h
index 7eeb8cf..61e1b0f 100644
--- a/cache.h
+++ b/cache.h
@@ -441,6 +441,7 @@ extern const char *get_git_work_tree(void);
 extern const char *read_gitfile(const char *path);
 extern const char *resolve_gitdir(const char *suspect);
 extern void set_git_work_tree(const char *tree);
+extern int is_gitfile(const char *path);
 
 #define ALTERNATE_DB_ENVIRONMENT "GIT_ALTERNATE_OBJECT_DIRECTORIES"
 
diff --git a/setup.c b/setup.c
index 61c22e6..a3d5a41 100644
--- a/setup.c
+++ b/setup.c
@@ -358,7 +358,7 @@ const char *read_gitfile(const char *path)
 
 	if (stat(path, &st))
 		return NULL;
-	if (!S_ISREG(st.st_mode))
+	if (!is_gitfile(path))
 		return NULL;
 	fd = open(path, O_RDONLY);
 	if (fd < 0)
@@ -368,9 +368,6 @@ const char *read_gitfile(const char *path)
 	close(fd);
 	if (len != st.st_size)
 		die("Error reading %s", path);
-	buf[len] = '\0';
-	if (prefixcmp(buf, "gitdir: "))
-		die("Invalid gitfile format: %s", path);
 	while (buf[len - 1] == '\n' || buf[len - 1] == '\r')
 		len--;
 	if (len < 9)
@@ -397,6 +394,32 @@ const char *read_gitfile(const char *path)
 	return path;
 }
 
+/*
+ * See if the referenced file looks like a 'gitfile'.
+ * Does not try to determine if the referenced gitdir is actually valid.
+ */
+int is_gitfile(const char *path)
+{
+	struct stat st;
+	char buf[9];
+	int fd, len;
+	if (stat(path, &st))
+		return 0;
+	if (!S_ISREG(st.st_mode))
+		return 0;
+	if (st.st_size < 10 || st.st_size > PATH_MAX)
+		return 0;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return 0;
+	len = read_in_full(fd, buf, sizeof(buf));
+	close(fd);
+	if (len != sizeof(buf))
+		return 0;
+	return !prefixcmp(buf, "gitdir: ");
+}
+
 static const char *setup_explicit_git_dir(const char *gitdirenv,
 					  char *cwd, int len,
 					  int *nongit_ok)
-- 
1.7.7.505.ga09f6