cmd, core/state, eth, tests, trie: improve state reader (#27428)

The state availability is checked during the creation of a state reader.

-    In hash-based database, if the specified root node does not exist on disk disk, then
    the state reader won't be created and an error will be returned.

-    In path-based database, if the specified state layer is not available, then the
    state reader won't be created and an error will be returned.

This change also contains a stricter semantics regarding the `Commit` operation: once it has been performed, the trie is no longer usable, and certain operations will return an error.

cmd/geth/dbcmd.go

@@ -519,8 +519,12 @@ func dbDumpTrie(ctx *cli.Context) error {
 	if err != nil {
 		return err
 	}
+	trieIt, err := theTrie.NodeIterator(start)
+	if err != nil {
+		return err
+	}
 	var count int64
-	it := trie.NewIterator(theTrie.NodeIterator(start))
+	it := trie.NewIterator(trieIt)
 	for it.Next() {
 		if max > 0 && count == max {
 			fmt.Printf("Exiting after %d values\n", count)

cmd/geth/snapshot.go

@@ -292,7 +292,12 @@ func traverseState(ctx *cli.Context) error {
 		lastReport time.Time
 		start      = time.Now()
 	)
-	accIter := trie.NewIterator(t.NodeIterator(nil))
+	acctIt, err := t.NodeIterator(nil)
+	if err != nil {
+		log.Error("Failed to open iterator", "root", root, "err", err)
+		return err
+	}
+	accIter := trie.NewIterator(acctIt)
 	for accIter.Next() {
 		accounts += 1
 		var acc types.StateAccount
@@ -307,7 +312,12 @@ func traverseState(ctx *cli.Context) error {
 				log.Error("Failed to open storage trie", "root", acc.Root, "err", err)
 				return err
 			}
-			storageIter := trie.NewIterator(storageTrie.NodeIterator(nil))
+			storageIt, err := storageTrie.NodeIterator(nil)
+			if err != nil {
+				log.Error("Failed to open storage iterator", "root", acc.Root, "err", err)
+				return err
+			}
+			storageIter := trie.NewIterator(storageIt)
 			for storageIter.Next() {
 				slots += 1
 			}
@@ -385,7 +395,11 @@ func traverseRawState(ctx *cli.Context) error {
 		hasher     = crypto.NewKeccakState()
 		got        = make([]byte, 32)
 	)
-	accIter := t.NodeIterator(nil)
+	accIter, err := t.NodeIterator(nil)
+	if err != nil {
+		log.Error("Failed to open iterator", "root", root, "err", err)
+		return err
+	}
 	for accIter.Next(true) {
 		nodes += 1
 		node := accIter.Hash()
@@ -422,7 +436,11 @@ func traverseRawState(ctx *cli.Context) error {
 					log.Error("Failed to open storage trie", "root", acc.Root, "err", err)
 					return errors.New("missing storage trie")
 				}
-				storageIter := storageTrie.NodeIterator(nil)
+				storageIter, err := storageTrie.NodeIterator(nil)
+				if err != nil {
+					log.Error("Failed to open storage iterator", "root", acc.Root, "err", err)
+					return err
+				}
 				for storageIter.Next(true) {
 					nodes += 1
 					node := storageIter.Hash()