eth/protocols/snap, trie: better error-handling (#23657) (#582)

Co-authored-by: Martin Holst Swende <martin@swende.se>

eth/protocols/snap/handler.go

@@ -469,7 +469,7 @@ func handleMessage(backend Backend, peer *Peer) error {
 				// Storage slots requested, open the storage trie and retrieve from there
 				account, err := snap.Account(common.BytesToHash(pathset[0]))
 				loads++ // always account database reads, even for failures
-				if err != nil {
+				if err != nil || account == nil {
 					break
 				}
 				stTrie, err := trie.NewSecure(common.BytesToHash(account.Root), triedb)

trie/trie.go

@@ -174,6 +174,10 @@ func (t *Trie) TryGetNode(path []byte) ([]byte, int, error) {
 }
 
 func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, newnode node, resolved int, err error) {
+	// If non-existent path requested, abort
+	if origNode == nil {
+		return nil, nil, 0, nil
+	}
 	// If we reached the requested path, return the current node
 	if pos >= len(path) {
 		// Although we most probably have the original node expanded, encoding
@@ -193,10 +197,6 @@ func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, new
 	}
 	// Path still needs to be traversed, descend into children
 	switch n := (origNode).(type) {
-	case nil:
-		// Non-existent path requested, abort
-		return nil, nil, 0, nil
-
 	case valueNode:
 		// Path prematurely ended, abort
 		return nil, nil, 0, nil