[PATCH 02/17] tree.c: add path_to_sha1()

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Given a tree and a path, it will traverse down the tree, follow the
path and return sha1 of the path.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 tree.c |   35 +++++++++++++++++++++++++++++++++++
 tree.h |    2 ++
 2 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/tree.c b/tree.c
index 5ab90af..2c7ae45 100644
--- a/tree.c
+++ b/tree.c
@@ -284,3 +284,38 @@ struct tree *parse_tree_indirect(const unsigned char *sha1)
 			parse_object(obj->sha1);
 	} while (1);
 }
+
+int path_to_tree_sha1(unsigned char *newsha1, const unsigned char *sha1, const char *path)
+{
+	struct name_entry entry;
+	struct tree_desc desc;
+	enum object_type type;
+	unsigned long size;
+	void *buffer;
+	const char *slash;
+	int len;
+
+	buffer = read_sha1_file(sha1, &type, &size);
+	if (!buffer || type != OBJ_TREE)
+		die("%s is not a tree", sha1_to_hex(sha1));
+
+	slash = strchr(path, '/');
+	len = slash ? slash - path : strlen(path);
+
+	init_tree_desc(&desc, buffer, size);
+	while (tree_entry(&desc, &entry)) {
+		if (!S_ISDIR(entry.mode))
+			continue;
+		if (!strncmp(entry.path, path, len)) {
+			free(buffer);
+			if (slash)
+				return path_to_tree_sha1(newsha1, entry.sha1, slash+1);
+			else {
+				hashcpy(newsha1, entry.sha1);
+				return 1;
+			}
+		}
+	}
+	free(buffer);
+	return 0;
+}
diff --git a/tree.h b/tree.h
index 2ff01a4..d246a6c 100644
--- a/tree.h
+++ b/tree.h
@@ -30,4 +30,6 @@ extern int read_tree_recursive(struct tree *tree,
 
 extern int read_tree(struct tree *tree, int stage, const char **paths);
 
+extern int path_to_tree_sha1(unsigned char *newsha1, const unsigned char *sha1, const char *path);
+
 #endif /* TREE_H */
-- 
1.7.1.rc1.69.g24c2f7