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.

trie/database_wrap.go

@@ -113,8 +113,8 @@ func NewDatabaseWithConfig(diskdb ethdb.Database, config *Config) *Database {
 }
 
 // Reader returns a reader for accessing all trie nodes with provided state root.
-// Nil is returned in case the state is not available.
-func (db *Database) Reader(blockRoot common.Hash) Reader {
+// An error will be returned if the requested state is not available.
+func (db *Database) Reader(blockRoot common.Hash) (Reader, error) {
 	return db.backend.(*hashdb.Database).Reader(blockRoot)
 }
 

trie/errors.go

@@ -17,11 +17,17 @@
 package trie
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/ethereum/go-ethereum/common"
 )
 
+// ErrCommitted is returned when a already committed trie is requested for usage.
+// The potential usages can be `Get`, `Update`, `Delete`, `NodeIterator`, `Prove`
+// and so on.
+var ErrCommitted = errors.New("trie is already committed")
+
 // MissingNodeError is returned by the trie functions (Get, Update, Delete)
 // in the case where a trie node is not present in the local database. It contains
 // information necessary for retrieving the missing node.

trie/iterator_test.go

@@ -34,7 +34,7 @@ import (
 
 func TestEmptyIterator(t *testing.T) {
 	trie := NewEmpty(NewDatabase(rawdb.NewMemoryDatabase()))
-	iter := trie.NodeIterator(nil)
+	iter := trie.MustNodeIterator(nil)
 
 	seen := make(map[string]struct{})
 	for iter.Next(true) {
@@ -67,7 +67,7 @@ func TestIterator(t *testing.T) {
 
 	trie, _ = New(TrieID(root), db)
 	found := make(map[string]string)
-	it := NewIterator(trie.NodeIterator(nil))
+	it := NewIterator(trie.MustNodeIterator(nil))
 	for it.Next() {
 		found[string(it.Key)] = string(it.Value)
 	}
@@ -101,7 +101,7 @@ func TestIteratorLargeData(t *testing.T) {
 		vals[string(value2.k)] = value2
 	}
 
-	it := NewIterator(trie.NodeIterator(nil))
+	it := NewIterator(trie.MustNodeIterator(nil))
 	for it.Next() {
 		vals[string(it.Key)].t = true
 	}
@@ -139,7 +139,7 @@ func testNodeIteratorCoverage(t *testing.T, scheme string) {
 
 	// Gather all the node hashes found by the iterator
 	var elements = make(map[common.Hash]iterationElement)
-	for it := trie.NodeIterator(nil); it.Next(true); {
+	for it := trie.MustNodeIterator(nil); it.Next(true); {
 		if it.Hash() != (common.Hash{}) {
 			elements[it.Hash()] = iterationElement{
 				hash: it.Hash(),
@@ -149,8 +149,12 @@ func testNodeIteratorCoverage(t *testing.T, scheme string) {
 		}
 	}
 	// Cross check the hashes and the database itself
+	reader, err := nodeDb.Reader(trie.Hash())
+	if err != nil {
+		t.Fatalf("state is not available %x", trie.Hash())
+	}
 	for _, element := range elements {
-		if blob, err := nodeDb.Reader(trie.Hash()).Node(common.Hash{}, element.path, element.hash); err != nil {
+		if blob, err := reader.Node(common.Hash{}, element.path, element.hash); err != nil {
 			t.Errorf("failed to retrieve reported node %x: %v", element.hash, err)
 		} else if !bytes.Equal(blob, element.blob) {
 			t.Errorf("node blob is different, want %v got %v", element.blob, blob)
@@ -210,19 +214,19 @@ func TestIteratorSeek(t *testing.T) {
 	}
 
 	// Seek to the middle.
-	it := NewIterator(trie.NodeIterator([]byte("fab")))
+	it := NewIterator(trie.MustNodeIterator([]byte("fab")))
 	if err := checkIteratorOrder(testdata1[4:], it); err != nil {
 		t.Fatal(err)
 	}
 
 	// Seek to a non-existent key.
-	it = NewIterator(trie.NodeIterator([]byte("barc")))
+	it = NewIterator(trie.MustNodeIterator([]byte("barc")))
 	if err := checkIteratorOrder(testdata1[1:], it); err != nil {
 		t.Fatal(err)
 	}
 
 	// Seek beyond the end.
-	it = NewIterator(trie.NodeIterator([]byte("z")))
+	it = NewIterator(trie.MustNodeIterator([]byte("z")))
 	if err := checkIteratorOrder(nil, it); err != nil {
 		t.Fatal(err)
 	}
@@ -264,7 +268,7 @@ func TestDifferenceIterator(t *testing.T) {
 	trieb, _ = New(TrieID(rootB), dbb)
 
 	found := make(map[string]string)
-	di, _ := NewDifferenceIterator(triea.NodeIterator(nil), trieb.NodeIterator(nil))
+	di, _ := NewDifferenceIterator(triea.MustNodeIterator(nil), trieb.MustNodeIterator(nil))
 	it := NewIterator(di)
 	for it.Next() {
 		found[string(it.Key)] = string(it.Value)
@@ -305,7 +309,7 @@ func TestUnionIterator(t *testing.T) {
 	dbb.Update(rootB, types.EmptyRootHash, trienode.NewWithNodeSet(nodesB))
 	trieb, _ = New(TrieID(rootB), dbb)
 
-	di, _ := NewUnionIterator([]NodeIterator{triea.NodeIterator(nil), trieb.NodeIterator(nil)})
+	di, _ := NewUnionIterator([]NodeIterator{triea.MustNodeIterator(nil), trieb.MustNodeIterator(nil)})
 	it := NewIterator(di)
 
 	all := []struct{ k, v string }{
@@ -344,7 +348,7 @@ func TestIteratorNoDups(t *testing.T) {
 	for _, val := range testdata1 {
 		tr.MustUpdate([]byte(val.k), []byte(val.v))
 	}
-	checkIteratorNoDups(t, tr.NodeIterator(nil), nil)
+	checkIteratorNoDups(t, tr.MustNodeIterator(nil), nil)
 }
 
 // This test checks that nodeIterator.Next can be retried after inserting missing trie nodes.
@@ -369,7 +373,7 @@ func testIteratorContinueAfterError(t *testing.T, memonly bool, scheme string) {
 		tdb.Commit(root, false)
 	}
 	tr, _ = New(TrieID(root), tdb)
-	wantNodeCount := checkIteratorNoDups(t, tr.NodeIterator(nil), nil)
+	wantNodeCount := checkIteratorNoDups(t, tr.MustNodeIterator(nil), nil)
 
 	var (
 		paths  [][]byte
@@ -428,7 +432,7 @@ func testIteratorContinueAfterError(t *testing.T, memonly bool, scheme string) {
 		}
 		// Iterate until the error is hit.
 		seen := make(map[string]bool)
-		it := tr.NodeIterator(nil)
+		it := tr.MustNodeIterator(nil)
 		checkIteratorNoDups(t, it, seen)
 		missing, ok := it.Error().(*MissingNodeError)
 		if !ok || missing.NodeHash != rhash {
@@ -496,7 +500,7 @@ func testIteratorContinueAfterSeekError(t *testing.T, memonly bool, scheme strin
 	}
 	// Create a new iterator that seeks to "bars". Seeking can't proceed because
 	// the node is missing.
-	it := tr.NodeIterator([]byte("bars"))
+	it := tr.MustNodeIterator([]byte("bars"))
 	missing, ok := it.Error().(*MissingNodeError)
 	if !ok {
 		t.Fatal("want MissingNodeError, got", it.Error())
@@ -602,7 +606,10 @@ func makeLargeTestTrie() (*Database, *StateTrie, *loggingDb) {
 	}
 	root, nodes := trie.Commit(false)
 	triedb.Update(root, types.EmptyRootHash, trienode.NewWithNodeSet(nodes))
+	triedb.Commit(root, false)
+
 	// Return the generated trie
+	trie, _ = NewStateTrie(TrieID(root), triedb)
 	return triedb, trie, logDb
 }
 
@@ -614,8 +621,8 @@ func TestNodeIteratorLargeTrie(t *testing.T) {
 	// Do a seek operation
 	trie.NodeIterator(common.FromHex("0x77667766776677766778855885885885"))
 	// master: 24 get operations
-	// this pr: 5 get operations
-	if have, want := logDb.getCount, uint64(5); have != want {
+	// this pr: 6 get operations
+	if have, want := logDb.getCount, uint64(6); have != want {
 		t.Fatalf("Too many lookups during seek, have %d want %d", have, want)
 	}
 }
@@ -646,7 +653,7 @@ func testIteratorNodeBlob(t *testing.T, scheme string) {
 
 	var found = make(map[common.Hash][]byte)
 	trie, _ = New(TrieID(root), triedb)
-	it := trie.NodeIterator(nil)
+	it := trie.MustNodeIterator(nil)
 	for it.Next(true) {
 		if it.Hash() == (common.Hash{}) {
 			continue

trie/proof.go

@@ -34,6 +34,10 @@ import (
 // nodes of the longest existing prefix of the key (at least the root node), ending
 // with the node that proves the absence of the key.
 func (t *Trie) Prove(key []byte, proofDb ethdb.KeyValueWriter) error {
+	// Short circuit if the trie is already committed and not usable.
+	if t.committed {
+		return ErrCommitted
+	}
 	// Collect all nodes on the path to key.
 	var (
 		prefix []byte

trie/proof_test.go

@@ -63,7 +63,7 @@ func makeProvers(trie *Trie) []func(key []byte) *memorydb.Database {
 	// Create a leaf iterator based Merkle prover
 	provers = append(provers, func(key []byte) *memorydb.Database {
 		proof := memorydb.New()
-		if it := NewIterator(trie.NodeIterator(key)); it.Next() && bytes.Equal(key, it.Key) {
+		if it := NewIterator(trie.MustNodeIterator(key)); it.Next() && bytes.Equal(key, it.Key) {
 			for _, p := range it.Prove() {
 				proof.Put(crypto.Keccak256(p), p)
 			}

trie/secure_trie.go

@@ -250,12 +250,18 @@ func (t *StateTrie) Copy() *StateTrie {
 	}
 }
 
-// NodeIterator returns an iterator that returns nodes of the underlying trie. Iteration
-// starts at the key after the given start key.
-func (t *StateTrie) NodeIterator(start []byte) NodeIterator {
+// NodeIterator returns an iterator that returns nodes of the underlying trie.
+// Iteration starts at the key after the given start key.
+func (t *StateTrie) NodeIterator(start []byte) (NodeIterator, error) {
 	return t.trie.NodeIterator(start)
 }
 
+// MustNodeIterator is a wrapper of NodeIterator and will omit any encountered
+// error but just print out an error message.
+func (t *StateTrie) MustNodeIterator(start []byte) NodeIterator {
+	return t.trie.MustNodeIterator(start)
+}
+
 // hashKey returns the hash of key as an ephemeral buffer.
 // The caller must not hold onto the return value because it will become
 // invalid on the next call to hashKey or secKey.

trie/sync_test.go

@@ -94,7 +94,7 @@ func checkTrieConsistency(db ethdb.Database, scheme string, root common.Hash) er
 	if err != nil {
 		return nil // Consider a non existent state consistent
 	}
-	it := trie.NodeIterator(nil)
+	it := trie.MustNodeIterator(nil)
 	for it.Next(true) {
 	}
 	return it.Error()
@@ -159,12 +159,16 @@ func testIterativeSync(t *testing.T, count int, bypath bool, scheme string) {
 			syncPath: NewSyncPath([]byte(paths[i])),
 		})
 	}
+	reader, err := srcDb.Reader(srcTrie.Hash())
+	if err != nil {
+		t.Fatalf("State is not available %x", srcTrie.Hash())
+	}
 	for len(elements) > 0 {
 		results := make([]NodeSyncResult, len(elements))
 		if !bypath {
 			for i, element := range elements {
 				owner, inner := ResolvePath([]byte(element.path))
-				data, err := srcDb.Reader(srcTrie.Hash()).Node(owner, inner, element.hash)
+				data, err := reader.Node(owner, inner, element.hash)
 				if err != nil {
 					t.Fatalf("failed to retrieve node data for hash %x: %v", element.hash, err)
 				}
@@ -230,12 +234,16 @@ func testIterativeDelayedSync(t *testing.T, scheme string) {
 			syncPath: NewSyncPath([]byte(paths[i])),
 		})
 	}
+	reader, err := srcDb.Reader(srcTrie.Hash())
+	if err != nil {
+		t.Fatalf("State is not available %x", srcTrie.Hash())
+	}
 	for len(elements) > 0 {
 		// Sync only half of the scheduled nodes
 		results := make([]NodeSyncResult, len(elements)/2+1)
 		for i, element := range elements[:len(results)] {
 			owner, inner := ResolvePath([]byte(element.path))
-			data, err := srcDb.Reader(srcTrie.Hash()).Node(owner, inner, element.hash)
+			data, err := reader.Node(owner, inner, element.hash)
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", element.hash, err)
 			}
@@ -295,12 +303,16 @@ func testIterativeRandomSync(t *testing.T, count int, scheme string) {
 			syncPath: NewSyncPath([]byte(paths[i])),
 		}
 	}
+	reader, err := srcDb.Reader(srcTrie.Hash())
+	if err != nil {
+		t.Fatalf("State is not available %x", srcTrie.Hash())
+	}
 	for len(queue) > 0 {
 		// Fetch all the queued nodes in a random order
 		results := make([]NodeSyncResult, 0, len(queue))
 		for path, element := range queue {
 			owner, inner := ResolvePath([]byte(element.path))
-			data, err := srcDb.Reader(srcTrie.Hash()).Node(owner, inner, element.hash)
+			data, err := reader.Node(owner, inner, element.hash)
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", element.hash, err)
 			}
@@ -358,12 +370,16 @@ func testIterativeRandomDelayedSync(t *testing.T, scheme string) {
 			syncPath: NewSyncPath([]byte(path)),
 		}
 	}
+	reader, err := srcDb.Reader(srcTrie.Hash())
+	if err != nil {
+		t.Fatalf("State is not available %x", srcTrie.Hash())
+	}
 	for len(queue) > 0 {
 		// Sync only half of the scheduled nodes, even those in random order
 		results := make([]NodeSyncResult, 0, len(queue)/2+1)
 		for path, element := range queue {
 			owner, inner := ResolvePath([]byte(element.path))
-			data, err := srcDb.Reader(srcTrie.Hash()).Node(owner, inner, element.hash)
+			data, err := reader.Node(owner, inner, element.hash)
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", element.hash, err)
 			}
@@ -426,13 +442,16 @@ func testDuplicateAvoidanceSync(t *testing.T, scheme string) {
 			syncPath: NewSyncPath([]byte(paths[i])),
 		})
 	}
+	reader, err := srcDb.Reader(srcTrie.Hash())
+	if err != nil {
+		t.Fatalf("State is not available %x", srcTrie.Hash())
+	}
 	requested := make(map[common.Hash]struct{})
-
 	for len(elements) > 0 {
 		results := make([]NodeSyncResult, len(elements))
 		for i, element := range elements {
 			owner, inner := ResolvePath([]byte(element.path))
-			data, err := srcDb.Reader(srcTrie.Hash()).Node(owner, inner, element.hash)
+			data, err := reader.Node(owner, inner, element.hash)
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", element.hash, err)
 			}
@@ -501,12 +520,16 @@ func testIncompleteSync(t *testing.T, scheme string) {
 			syncPath: NewSyncPath([]byte(paths[i])),
 		})
 	}
+	reader, err := srcDb.Reader(srcTrie.Hash())
+	if err != nil {
+		t.Fatalf("State is not available %x", srcTrie.Hash())
+	}
 	for len(elements) > 0 {
 		// Fetch a batch of trie nodes
 		results := make([]NodeSyncResult, len(elements))
 		for i, element := range elements {
 			owner, inner := ResolvePath([]byte(element.path))
-			data, err := srcDb.Reader(srcTrie.Hash()).Node(owner, inner, element.hash)
+			data, err := reader.Node(owner, inner, element.hash)
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", element.hash, err)
 			}
@@ -585,12 +608,15 @@ func testSyncOrdering(t *testing.T, scheme string) {
 		})
 		reqs = append(reqs, NewSyncPath([]byte(paths[i])))
 	}
-
+	reader, err := srcDb.Reader(srcTrie.Hash())
+	if err != nil {
+		t.Fatalf("State is not available %x", srcTrie.Hash())
+	}
 	for len(elements) > 0 {
 		results := make([]NodeSyncResult, len(elements))
 		for i, element := range elements {
 			owner, inner := ResolvePath([]byte(element.path))
-			data, err := srcDb.Reader(srcTrie.Hash()).Node(owner, inner, element.hash)
+			data, err := reader.Node(owner, inner, element.hash)
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", element.hash, err)
 			}
@@ -649,11 +675,15 @@ func syncWith(t *testing.T, root common.Hash, db ethdb.Database, srcDb *Database
 			syncPath: NewSyncPath([]byte(paths[i])),
 		})
 	}
+	reader, err := srcDb.Reader(root)
+	if err != nil {
+		t.Fatalf("State is not available %x", root)
+	}
 	for len(elements) > 0 {
 		results := make([]NodeSyncResult, len(elements))
 		for i, element := range elements {
 			owner, inner := ResolvePath([]byte(element.path))
-			data, err := srcDb.Reader(root).Node(owner, inner, element.hash)
+			data, err := reader.Node(owner, inner, element.hash)
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for hash %x: %v", element.hash, err)
 			}

trie/tracer_test.go

@@ -226,14 +226,14 @@ func TestAccessListLeak(t *testing.T) {
 	}{
 		{
 			func(tr *Trie) {
-				it := tr.NodeIterator(nil)
+				it := tr.MustNodeIterator(nil)
 				for it.Next(true) {
 				}
 			},
 		},
 		{
 			func(tr *Trie) {
-				it := NewIterator(tr.NodeIterator(nil))
+				it := NewIterator(tr.MustNodeIterator(nil))
 				for it.Next() {
 				}
 			},
@@ -300,7 +300,7 @@ func compareSet(setA, setB map[string]struct{}) bool {
 
 func forNodes(tr *Trie) map[string][]byte {
 	var (
-		it    = tr.NodeIterator(nil)
+		it    = tr.MustNodeIterator(nil)
 		nodes = make(map[string][]byte)
 	)
 	for it.Next(true) {
@@ -319,7 +319,7 @@ func iterNodes(db *Database, root common.Hash) map[string][]byte {
 
 func forHashedNodes(tr *Trie) map[string][]byte {
 	var (
-		it    = tr.NodeIterator(nil)
+		it    = tr.MustNodeIterator(nil)
 		nodes = make(map[string][]byte)
 	)
 	for it.Next(true) {

trie/trie.go

@@ -39,6 +39,10 @@ type Trie struct {
 	root  node
 	owner common.Hash
 
+	// Flag whether the commit operation is already performed. If so the
+	// trie is not usable(latest states is invisible).
+	committed bool
+
 	// Keep track of the number leaves which have been inserted since the last
 	// hashing operation. This number will not directly map to the number of
 	// actually unhashed nodes.
@@ -60,11 +64,12 @@ func (t *Trie) newFlag() nodeFlag {
 // Copy returns a copy of Trie.
 func (t *Trie) Copy() *Trie {
 	return &Trie{
-		root:     t.root,
-		owner:    t.owner,
-		unhashed: t.unhashed,
-		reader:   t.reader,
-		tracer:   t.tracer.copy(),
+		root:      t.root,
+		owner:     t.owner,
+		committed: t.committed,
+		unhashed:  t.unhashed,
+		reader:    t.reader,
+		tracer:    t.tracer.copy(),
 	}
 }
 
@@ -74,7 +79,7 @@ func (t *Trie) Copy() *Trie {
 // zero hash or the sha3 hash of an empty string, then trie is initially
 // empty, otherwise, the root node must be present in database or returns
 // a MissingNodeError if not.
-func New(id *ID, db NodeReader) (*Trie, error) {
+func New(id *ID, db *Database) (*Trie, error) {
 	reader, err := newTrieReader(id.StateRoot, id.Owner, db)
 	if err != nil {
 		return nil, err
@@ -100,10 +105,24 @@ func NewEmpty(db *Database) *Trie {
 	return tr
 }
 
+// MustNodeIterator is a wrapper of NodeIterator and will omit any encountered
+// error but just print out an error message.
+func (t *Trie) MustNodeIterator(start []byte) NodeIterator {
+	it, err := t.NodeIterator(start)
+	if err != nil {
+		log.Error("Unhandled trie error in Trie.NodeIterator", "err", err)
+	}
+	return it
+}
+
 // NodeIterator returns an iterator that returns nodes of the trie. Iteration starts at
 // the key after the given start key.
-func (t *Trie) NodeIterator(start []byte) NodeIterator {
-	return newNodeIterator(t, start)
+func (t *Trie) NodeIterator(start []byte) (NodeIterator, error) {
+	// Short circuit if the trie is already committed and not usable.
+	if t.committed {
+		return nil, ErrCommitted
+	}
+	return newNodeIterator(t, start), nil
 }
 
 // MustGet is a wrapper of Get and will omit any encountered error but just
@@ -122,6 +141,10 @@ func (t *Trie) MustGet(key []byte) []byte {
 // If the requested node is not present in trie, no error will be returned.
 // If the trie is corrupted, a MissingNodeError is returned.
 func (t *Trie) Get(key []byte) ([]byte, error) {
+	// Short circuit if the trie is already committed and not usable.
+	if t.committed {
+		return nil, ErrCommitted
+	}
 	value, newroot, didResolve, err := t.get(t.root, keybytesToHex(key), 0)
 	if err == nil && didResolve {
 		t.root = newroot
@@ -181,6 +204,10 @@ func (t *Trie) MustGetNode(path []byte) ([]byte, int) {
 // If the requested node is not present in trie, no error will be returned.
 // If the trie is corrupted, a MissingNodeError is returned.
 func (t *Trie) GetNode(path []byte) ([]byte, int, error) {
+	// Short circuit if the trie is already committed and not usable.
+	if t.committed {
+		return nil, 0, ErrCommitted
+	}
 	item, newroot, resolved, err := t.getNode(t.root, compactToHex(path), 0)
 	if err != nil {
 		return nil, resolved, err
@@ -273,6 +300,10 @@ func (t *Trie) MustUpdate(key, value []byte) {
 // If the requested node is not present in trie, no error will be returned.
 // If the trie is corrupted, a MissingNodeError is returned.
 func (t *Trie) Update(key, value []byte) error {
+	// Short circuit if the trie is already committed and not usable.
+	if t.committed {
+		return ErrCommitted
+	}
 	return t.update(key, value)
 }
 
@@ -387,6 +418,10 @@ func (t *Trie) MustDelete(key []byte) {
 // If the requested node is not present in trie, no error will be returned.
 // If the trie is corrupted, a MissingNodeError is returned.
 func (t *Trie) Delete(key []byte) error {
+	// Short circuit if the trie is already committed and not usable.
+	if t.committed {
+		return ErrCommitted
+	}
 	t.unhashed++
 	k := keybytesToHex(key)
 	_, n, err := t.delete(t.root, nil, k)
@@ -574,7 +609,9 @@ func (t *Trie) Hash() common.Hash {
 // be created with new root and updated trie database for following usage
 func (t *Trie) Commit(collectLeaf bool) (common.Hash, *trienode.NodeSet) {
 	defer t.tracer.reset()
-
+	defer func() {
+		t.committed = true
+	}()
 	nodes := trienode.NewNodeSet(t.owner)
 	t.tracer.markDeletions(nodes)
 
@@ -621,4 +658,5 @@ func (t *Trie) Reset() {
 	t.owner = common.Hash{}
 	t.unhashed = 0
 	t.tracer.reset()
+	t.committed = false
 }

trie/trie_reader.go

@@ -17,9 +17,9 @@
 package trie
 
 import (
-	"fmt"
-
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/log"
 )
 
 // Reader wraps the Node method of a backing trie store.
@@ -30,13 +30,6 @@ type Reader interface {
 	Node(owner common.Hash, path []byte, hash common.Hash) ([]byte, error)
 }
 
-// NodeReader wraps all the necessary functions for accessing trie node.
-type NodeReader interface {
-	// Reader returns a reader for accessing all trie nodes with provided
-	// state root. Nil is returned in case the state is not available.
-	Reader(root common.Hash) Reader
-}
-
 // trieReader is a wrapper of the underlying node reader. It's not safe
 // for concurrent usage.
 type trieReader struct {
@@ -46,10 +39,16 @@ type trieReader struct {
 }
 
 // newTrieReader initializes the trie reader with the given node reader.
-func newTrieReader(stateRoot, owner common.Hash, db NodeReader) (*trieReader, error) {
-	reader := db.Reader(stateRoot)
-	if reader == nil {
-		return nil, fmt.Errorf("state not found #%x", stateRoot)
+func newTrieReader(stateRoot, owner common.Hash, db *Database) (*trieReader, error) {
+	if stateRoot == (common.Hash{}) || stateRoot == types.EmptyRootHash {
+		if stateRoot == (common.Hash{}) {
+			log.Error("Zero state root hash!")
+		}
+		return &trieReader{owner: owner}, nil
+	}
+	reader, err := db.Reader(stateRoot)
+	if err != nil {
+		return nil, &MissingNodeError{Owner: owner, NodeHash: stateRoot, err: err}
 	}
 	return &trieReader{owner: owner, reader: reader}, nil
 }

trie/trie_test.go

@@ -521,7 +521,7 @@ func runRandTest(rt randTest) bool {
 			origin = root
 		case opItercheckhash:
 			checktr := NewEmpty(triedb)
-			it := NewIterator(tr.NodeIterator(nil))
+			it := NewIterator(tr.MustNodeIterator(nil))
 			for it.Next() {
 				checktr.MustUpdate(it.Key, it.Value)
 			}
@@ -530,8 +530,8 @@ func runRandTest(rt randTest) bool {
 			}
 		case opNodeDiff:
 			var (
-				origIter = origTrie.NodeIterator(nil)
-				curIter  = tr.NodeIterator(nil)
+				origIter = origTrie.MustNodeIterator(nil)
+				curIter  = tr.MustNodeIterator(nil)
 				origSeen = make(map[string]struct{})
 				curSeen  = make(map[string]struct{})
 			)
@@ -710,7 +710,7 @@ func TestTinyTrie(t *testing.T) {
 		t.Errorf("3: got %x, exp %x", root, exp)
 	}
 	checktr := NewEmpty(NewDatabase(rawdb.NewMemoryDatabase()))
-	it := NewIterator(trie.NodeIterator(nil))
+	it := NewIterator(trie.MustNodeIterator(nil))
 	for it.Next() {
 		checktr.MustUpdate(it.Key, it.Value)
 	}

trie/triedb/hashdb/database.go

@@ -18,6 +18,7 @@ package hashdb
 
 import (
 	"errors"
+	"fmt"
 	"reflect"
 	"sync"
 	"time"
@@ -621,8 +622,12 @@ func (db *Database) Scheme() string {
 }
 
 // Reader retrieves a node reader belonging to the given state root.
-func (db *Database) Reader(root common.Hash) *reader {
-	return &reader{db: db}
+// An error will be returned if the requested state is not available.
+func (db *Database) Reader(root common.Hash) (*reader, error) {
+	if _, err := db.Node(root); err != nil {
+		return nil, fmt.Errorf("state %#x is not available, %v", root, err)
+	}
+	return &reader{db: db}, nil
 }
 
 // reader is a state reader of Database which implements the Reader interface.