trie: more node iterator improvements (#14615)

* ethdb: remove Set

Set deadlocks immediately and isn't part of the Database interface.

* trie: add Err to Iterator

This is useful for testing because the underlying NodeIterator doesn't
need to be kept in a separate variable just to get the error.

* trie: add LeafKey to iterator, panic when not at leaf

LeafKey is useful for callers that can't interpret Path.

* trie: retry failed seek/peek in iterator Next

Instead of failing iteration irrecoverably, make it so Next retries the
pending seek or peek every time.

Smaller changes in this commit make this easier to test:

* The iterator previously returned from Next on encountering a hash
  node. This caused it to visit the same path twice.
* Path returned nibbles with terminator symbol for valueNode attached
  to fullNode, but removed it for valueNode attached to shortNode. Now
  the terminator is always present. This makes Path unique to each node
  and simplifies Leaf.

* trie: add Path to MissingNodeError

The light client trie iterator needs to know the path of the node that's
missing so it can retrieve a proof for it. NodeIterator.Path is not
sufficient because it is updated when the node is resolved and actually
visited by the iterator.

Also remove unused fields. They were added a long time ago before we
knew which fields would be needed for the light client.

trie/iterator_test.go

@@ -19,6 +19,7 @@ package trie
 import (
 	"bytes"
 	"fmt"
+	"math/rand"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -239,8 +240,8 @@ func TestUnionIterator(t *testing.T) {
 
 	all := []struct{ k, v string }{
 		{"aardvark", "c"},
-		{"barb", "bd"},
 		{"barb", "ba"},
+		{"barb", "bd"},
 		{"bard", "bc"},
 		{"bars", "bb"},
 		{"bars", "be"},
@@ -267,3 +268,107 @@ func TestUnionIterator(t *testing.T) {
 		t.Errorf("Iterator returned extra values.")
 	}
 }
+
+func TestIteratorNoDups(t *testing.T) {
+	var tr Trie
+	for _, val := range testdata1 {
+		tr.Update([]byte(val.k), []byte(val.v))
+	}
+	checkIteratorNoDups(t, tr.NodeIterator(nil), nil)
+}
+
+// This test checks that nodeIterator.Next can be retried after inserting missing trie nodes.
+func TestIteratorContinueAfterError(t *testing.T) {
+	db, _ := ethdb.NewMemDatabase()
+	tr, _ := New(common.Hash{}, db)
+	for _, val := range testdata1 {
+		tr.Update([]byte(val.k), []byte(val.v))
+	}
+	tr.Commit()
+	wantNodeCount := checkIteratorNoDups(t, tr.NodeIterator(nil), nil)
+	keys := db.Keys()
+	t.Log("node count", wantNodeCount)
+
+	for i := 0; i < 20; i++ {
+		// Create trie that will load all nodes from DB.
+		tr, _ := New(tr.Hash(), db)
+
+		// Remove a random node from the database. It can't be the root node
+		// because that one is already loaded.
+		var rkey []byte
+		for {
+			if rkey = keys[rand.Intn(len(keys))]; !bytes.Equal(rkey, tr.Hash().Bytes()) {
+				break
+			}
+		}
+		rval, _ := db.Get(rkey)
+		db.Delete(rkey)
+
+		// Iterate until the error is hit.
+		seen := make(map[string]bool)
+		it := tr.NodeIterator(nil)
+		checkIteratorNoDups(t, it, seen)
+		missing, ok := it.Error().(*MissingNodeError)
+		if !ok || !bytes.Equal(missing.NodeHash[:], rkey) {
+			t.Fatal("didn't hit missing node, got", it.Error())
+		}
+
+		// Add the node back and continue iteration.
+		db.Put(rkey, rval)
+		checkIteratorNoDups(t, it, seen)
+		if it.Error() != nil {
+			t.Fatal("unexpected error", it.Error())
+		}
+		if len(seen) != wantNodeCount {
+			t.Fatal("wrong node iteration count, got", len(seen), "want", wantNodeCount)
+		}
+	}
+}
+
+// Similar to the test above, this one checks that failure to create nodeIterator at a
+// certain key prefix behaves correctly when Next is called. The expectation is that Next
+// should retry seeking before returning true for the first time.
+func TestIteratorContinueAfterSeekError(t *testing.T) {
+	// Commit test trie to db, then remove the node containing "bars".
+	db, _ := ethdb.NewMemDatabase()
+	ctr, _ := New(common.Hash{}, db)
+	for _, val := range testdata1 {
+		ctr.Update([]byte(val.k), []byte(val.v))
+	}
+	root, _ := ctr.Commit()
+	barNodeHash := common.HexToHash("05041990364eb72fcb1127652ce40d8bab765f2bfe53225b1170d276cc101c2e")
+	barNode, _ := db.Get(barNodeHash[:])
+	db.Delete(barNodeHash[:])
+
+	// Create a new iterator that seeks to "bars". Seeking can't proceed because
+	// the node is missing.
+	tr, _ := New(root, db)
+	it := tr.NodeIterator([]byte("bars"))
+	missing, ok := it.Error().(*MissingNodeError)
+	if !ok {
+		t.Fatal("want MissingNodeError, got", it.Error())
+	} else if missing.NodeHash != barNodeHash {
+		t.Fatal("wrong node missing")
+	}
+
+	// Reinsert the missing node.
+	db.Put(barNodeHash[:], barNode[:])
+
+	// Check that iteration produces the right set of values.
+	if err := checkIteratorOrder(testdata1[2:], NewIterator(it)); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func checkIteratorNoDups(t *testing.T, it NodeIterator, seen map[string]bool) int {
+	if seen == nil {
+		seen = make(map[string]bool)
+	}
+	for it.Next(true) {
+		if seen[string(it.Path())] {
+			t.Fatalf("iterator visited node path %x twice", it.Path())
+		}
+		seen[string(it.Path())] = true
+	}
+	return len(seen)
+}