Function get_size_from_delta

packfile.c:1170–1223

* Read a delta object's header at curpos in p (already inflated as needed) * and return the size of the result object (the post-application target). */

 * and return the size of the result object (the post-application target).
 */
size_t get_size_from_delta(struct packed_git *p,
			   struct pack_window **w_curs,
			   off_t curpos)
{
	const unsigned char *data;
	unsigned char delta_head[20], *in;
	git_zstream stream;
	int st;

	memset(&stream, 0, sizeof(stream));
	stream.next_out = delta_head;
	stream.avail_out = sizeof(delta_head);

	git_inflate_init(&stream);
	do {
		in = use_pack(p, w_curs, curpos, &stream.avail_in);
		stream.next_in = in;
		/*
		 * Note: the window section returned by use_pack() must be
		 * available throughout git_inflate()'s unlocked execution. To
		 * ensure no other thread will modify the window in the
		 * meantime, we rely on the packed_window.inuse_cnt. This
		 * counter is incremented before window reading and checked
		 * before window disposal.
		 *
		 * Other worrying sections could be the call to close_pack_fd(),
		 * which can close packs even with in-use windows, and to
		 * odb_reprepare(). Regarding the former, mmap doc says:
		 * "closing the file descriptor does not unmap the region". And
		 * for the latter, it won't re-open already available packs.
		 */
		obj_read_unlock();
		st = git_inflate(&stream, Z_FINISH);
		obj_read_lock();
		curpos += stream.next_in - in;
	} while ((st == Z_OK || st == Z_BUF_ERROR) &&
		 stream.total_out < sizeof(delta_head));
	git_inflate_end(&stream);
	if ((st != Z_STREAM_END) && stream.total_out != sizeof(delta_head)) {
		error("delta data unpack-initial failed");
		return 0;
	}

	/* Examine the initial part of the delta to figure out
	 * the result size.
	 */
	data = delta_head;

	/* ignore base size */
	get_delta_hdr_size(&data, delta_head+sizeof(delta_head));

	/* Read the result size */
	return get_delta_hdr_size(&data, delta_head+sizeof(delta_head));
}

int unpack_object_header(struct packed_git *p,
			 struct pack_window **w_curs,