fix: wrongly switch sync mode from full sync to snap sync issue (#17)

core/blockchain.go

@@ -412,7 +412,7 @@ func NewBlockChain(db ethdb.Database, cacheConfig *CacheConfig, genesis *Genesis
 	// Make sure the state associated with the block is available, or log out
 	// if there is no available state, waiting for state sync.
 	head := bc.CurrentBlock()
-	if !bc.HasState(head.Root) {
+	if !bc.NoTries() && !bc.HasState(head.Root) {
 		if head.Number.Uint64() == 0 {
 			// The genesis state is missing, which is only possible in the path-based
 			// scheme. This situation occurs when the initial state sync is not finished

eth/handler.go

@@ -218,7 +218,7 @@ func newHandler(config *handlerConfig) (*handler, error) {
 			}
 			h.snapSync.Store(true)
 			log.Warn("Switch sync mode from full sync to snap sync", "reason", "snap sync incomplete")
-		} else if !h.chain.HasState(fullBlock.Root) {
+		} else if !h.chain.NoTries() && !h.chain.HasState(fullBlock.Root) {
 			h.snapSync.Store(true)
 			log.Warn("Switch sync mode from full sync to snap sync", "reason", "head state missing")
 		}

eth/sync.go

@@ -213,7 +213,7 @@ func (cs *chainSyncer) modeAndLocalHead() (downloader.SyncMode, *big.Int) {
 	// We are in a full sync, but the associated head state is missing. To complete
 	// the head state, forcefully rerun the snap sync. Note it doesn't mean the
 	// persistent state is corrupted, just mismatch with the head block.
-	if !cs.handler.chain.HasState(head.Root) {
+	if !cs.handler.chain.NoTries() && !cs.handler.chain.HasState(head.Root) {
 		block := cs.handler.chain.CurrentSnapBlock()
 		td := cs.handler.chain.GetTd(block.Hash(), block.Number.Uint64())
 		log.Info("Reenabled snap sync as chain is stateless")