indexer: delay resolving deltas

Not all delta bases are available on the first try. By delaying
resolving all deltas until the end, we avoid decompressing some of the
data twice or even more times, saving effort and time.

src/indexer.c

@@ -169,29 +169,14 @@ cleanup:
 }
 
 /* Try to store the delta so we can try to resolve it later */
-static int store_delta(git_indexer_stream *idx)
+static int store_delta(git_indexer_stream *idx, git_off_t entry_start, size_t entry_size, git_otype type)
 {
-	git_otype type;
 	git_mwindow *w = NULL;
-	git_mwindow_file *mwf = &idx->pack->mwf;
-	git_off_t entry_start = idx->off;
 	struct delta_info *delta;
-	size_t entry_size;
 	git_rawobj obj;
 	int error;
 
-	/*
-	 * ref-delta objects can refer to object that we haven't
-	 * found yet, so give it another opportunity
-	 */
-	if (git_packfile_unpack_header(&entry_size, &type, mwf, &w, &idx->off) < 0)
-		return -1;
-
-	git_mwindow_close(&w);
-
-	/* If it's not a delta, mark it as failure, we can't do anything with it */
-	if (type != GIT_OBJ_REF_DELTA && type != GIT_OBJ_OFS_DELTA)
-		return -1;
+	assert(type == GIT_OBJ_REF_DELTA || type == GIT_OBJ_OFS_DELTA);
 
 	if (type == GIT_OBJ_REF_DELTA) {
 		idx->off += GIT_OID_RAWSZ;
@@ -350,27 +335,44 @@ int git_indexer_stream_add(git_indexer_stream *idx, const void *data, size_t siz
 	while (processed < idx->nr_objects) {
 		git_rawobj obj;
 		git_off_t entry_start = idx->off;
+		size_t entry_size;
+		git_otype type;
+		git_mwindow *w = NULL;
 
 		if (idx->pack->mwf.size <= idx->off + 20)
 			return 0;
 
-		error = git_packfile_unpack(&obj, idx->pack, &idx->off);
+		error = git_packfile_unpack_header(&entry_size, &type, mwf, &w, &idx->off);
 		if (error == GIT_EBUFS) {
 			idx->off = entry_start;
 			return 0;
 		}
+		if (error < 0)
+			return -1;
 
-		if (error < 0) {
-			idx->off = entry_start;
-			error = store_delta(idx);
+		git_mwindow_close(&w);
 
-			if (error == GIT_EBUFS)
+		if (type == GIT_OBJ_REF_DELTA || type == GIT_OBJ_OFS_DELTA) {
+			error = store_delta(idx, entry_start, entry_size, type);
+			if (error == GIT_EBUFS) {
+				idx->off = entry_start;
 				return 0;
+			}
 			if (error < 0)
 				return error;
+
 			continue;
 		}
 
+		idx->off = entry_start;
+		error = git_packfile_unpack(&obj, idx->pack, &idx->off);
+		if (error == GIT_EBUFS) {
+			idx->off = entry_start;
+			return 0;
+		}
+		if (error < 0)
+			return -1;
+
 		if (hash_and_save(idx, &obj, entry_start) < 0)
 			goto on_error;