Subject: [PATCH 08/12] index-pack: parse v4 tree format

From: Nguyễn Thái Ngọc Duy <[email-masked]>
Date: Sat, 7 Sep 2013 17:43:15 +0700

Signed-off-by: Nguyễn Thái Ngọc Duy <[email-masked]>
---
 builtin/index-pack.c | 104 +++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 100 insertions(+), 4 deletions(-)

diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 210b78d..51ca64b 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -319,6 +319,21 @@ static const unsigned char *read_sha1ref(void)
 	return sha1_table + index * 20;
 }
 
+static const unsigned char *read_sha1table_ref(void)
+{
+	const unsigned char *sha1 = read_sha1ref();
+	if (sha1 < sha1_table || sha1 >= sha1_table + nr_objects * 20) {
+		unsigned char *found;
+		found = bsearch(sha1, sha1_table, nr_objects, 20,
+				(int (*)(const void *, const void *))hashcmp);
+		if (!found)
+			bad_object(consumed_bytes,
+				   _("SHA-1 %s not found in SHA-1 table"),
+				   sha1_to_hex(sha1));
+	}
+	return sha1;
+}
+
 static const unsigned char *read_dictref(struct packv4_dict *dict)
 {
 	unsigned int index = read_varint();
@@ -561,17 +576,93 @@ static void *unpack_commit_v4(unsigned int offset,
 	return dst.buf;
 }
 
-static void *unpack_entry_data(unsigned long offset, unsigned long size,
-			       enum object_type type, unsigned char *sha1)
+/*
+ * v4 trees are actually kind of deltas and we don't do delta in the
+ * first pass. This function only walks through a tree object to find
+ * the end offset, register object dependencies and performs limited
+ * validation.
+ */
+static void *unpack_tree_v4(struct object_entry *obj,
+			    unsigned int offset, unsigned long size,
+			    unsigned char *sha1)
+{
+	unsigned int nr = read_varint();
+	const unsigned char *last_base = NULL;
+	struct strbuf sb = STRBUF_INIT;
+	while (nr) {
+		unsigned int copy_start_or_path = read_varint();
+		if (copy_start_or_path & 1) { /* copy_start */
+			unsigned int copy_count = read_varint();
+			if (copy_count & 1) { /* first delta */
+				last_base = read_sha1table_ref();
+			} else if (!last_base)
+				bad_object(offset,
+					   _("bad copy count index in unpack_tree_v4"));
+			copy_count >>= 1;
+			if (!copy_count)
+				bad_object(offset,
+					   _("bad copy count index in unpack_tree_v4"));
+			nr -= copy_count;
+		} else {	/* path */
+			unsigned int path_idx = copy_start_or_path >> 1;
+			const unsigned char *entry_sha1;
+
+			if (path_idx >= path_dict->nb_entries)
+				bad_object(offset,
+					   _("bad path index in unpack_tree_v4"));
+			entry_sha1 = read_sha1ref();
+			nr--;
+
+			if (!last_base) {
+				const unsigned char *path;
+				unsigned mode;
+
+				path = path_dict->data + path_dict->offsets[path_idx];
+				mode = (path[0] << 8) | path[1];
+				strbuf_addf(&sb, "%o %s%c", mode, path+2, '\0');
+				strbuf_add(&sb, entry_sha1, 20);
+				if (sb.len > size)
+					bad_object(offset,
+						   _("tree larger than expected"));
+			}
+		}
+	}
+
+	if (last_base) {
+		strbuf_release(&sb);
+		return NULL;
+	} else {
+		git_SHA_CTX ctx;
+		char hdr[32];
+		int hdrlen;
+
+		if (sb.len != size)
+			bad_object(offset, _("tree size mismatch"));
+
+		hdrlen = sprintf(hdr, "tree %lu", size) + 1;
+		git_SHA1_Init(&ctx);
+		git_SHA1_Update(&ctx, hdr, hdrlen);
+		git_SHA1_Update(&ctx, sb.buf, size);
+		git_SHA1_Final(sha1, &ctx);
+		return strbuf_detach(&sb, NULL);
+	}
+}
+
+static void *unpack_entry_data(struct object_entry *obj, unsigned char *sha1)
 {
 	static char fixed_buf[8192];
 	void *buf;
 	git_SHA_CTX c;
 	char hdr[32];
 	int hdrlen;
+	unsigned long offset = obj->idx.offset;
+	unsigned long size = obj->size;
+	enum object_type type = obj->type;
 
 	if (type == OBJ_PV4_COMMIT)
 		return unpack_commit_v4(offset, size, sha1);
+	if (type == OBJ_PV4_TREE)
+		return unpack_tree_v4(obj, offset, size, sha1);
 
 	if (!is_delta_type(type)) {
 		hdrlen = sprintf(hdr, "%s %lu", typename(type), size) + 1;
@@ -640,16 +731,19 @@ static void *unpack_raw_entry(struct object_entry *obj,
 	case OBJ_BLOB:
 	case OBJ_TAG:
 		break;
-
 	case OBJ_PV4_COMMIT:
 		obj->real_type = OBJ_COMMIT;
 		break;
+	case OBJ_PV4_TREE:
+		obj->real_type = OBJ_TREE;
+		break;
+
 	default:
 		bad_object(obj->idx.offset, _("unknown object type %d"), obj->type);
 	}
 	obj->hdr_size = consumed_bytes - obj->idx.offset;
 
-	data = unpack_entry_data(obj->idx.offset, obj->size, obj->type, sha1);
+	data = unpack_entry_data(obj, sha1);
 	obj->idx.crc32 = input_crc32;
 	return data;
 }
@@ -1186,6 +1280,8 @@ static void parse_pack_objects(unsigned char *sha1)
 			nr_deltas++;
 			delta->obj_no = i;
 			delta++;
+		} else if (!data && obj->type == OBJ_PV4_TREE) {
+			/* delay sha1_object() until second pass */
 		} else if (!data) {
 			/* large blobs, check later */
 			obj->real_type = OBJ_BAD;
-- 
1.8.2.83.gc99314b