Do not handle lookup by cache if it does not have the key

Cache handles lookups by sending another lookups directly to the backend,
but it is unnecessary when cache does not have the key.

cache/slru_cache.cpp

@@ -395,13 +395,12 @@ int slru_cache_t::lookup(const unsigned char *id, dnet_net_state *st, dnet_cmd *
 	data_t* it = m_treap.find(id);
 	TIMER_STOP("lookup.find");
 
-	dnet_time timestamp;
-	memset(&timestamp, 0, sizeof(timestamp));
-
-	if (it) {
-		timestamp = it->timestamp();
+	if (!it) {
+		return -ENOENT;
 	}
 
+	auto timestamp = it->timestamp();
+
 	guard.unlock();
 
 	// go check object on disk
@@ -415,22 +414,13 @@ int slru_cache_t::lookup(const unsigned char *id, dnet_net_state *st, dnet_cmd *
 	cmd->flags &= ~(DNET_FLAGS_MORE | DNET_FLAGS_NEED_ACK);
 
 	if (err) {
-		if (!it) {
-			// there is no object neither in cache nor on disk,
-			// we want client to notify about that, send him ACK
-			cmd->flags |= DNET_FLAGS_NEED_ACK;
-			return err;
-		}
-
 		// zero size means 'we didn't find key on disk', but yet it exists in cache
 		// lookup by its nature is 'show me what is on disk' command
 		return dnet_send_file_info_ts_without_fd(st, cmd, NULL, 0, &timestamp);
 	}
 
-	dnet_file_info *info = data.skip<dnet_addr>().data<dnet_file_info>();
-	if (it) {
-		info->mtime = timestamp;
-	}
+	auto info = data.skip<dnet_addr>().data<dnet_file_info>();
+	info->mtime = timestamp;
 
 	return dnet_send_reply(st, cmd, data.data(), data.size(), 0);
 }

library/dnet.c

@@ -1601,7 +1601,7 @@ static int dnet_process_cmd_with_backend_raw(struct dnet_backend_io *backend, st
 			if (cmd->cmd == DNET_CMD_LOOKUP && !(cmd->flags & DNET_FLAGS_NOCACHE)) {
 				err = dnet_cmd_cache_lookup(backend, st, cmd);
 
-				if (err != -ENOTSUP) {
+				if (err != -ENOTSUP && err != -ENOENT) {
 					*handled_in_cache = 1;
 					break;
 				}