fix: Prevent newExporter crash if tree.ndb is nil

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- [#622](https://github.com/cosmos/iavl/pull/622) `export/newExporter()` and `ImmutableTree.Export()` returns error for nil arguements
 - [#586](https://github.com/cosmos/iavl/pull/586) Remove the `RangeProof` and refactor the ics23_proof to use the internal methods.
 
 ## 0.19.4 (October 28, 2022)

export.go

@@ -13,6 +13,12 @@ const exportBufferSize = 32
 // ErrorExportDone is returned by Exporter.Next() when all items have been exported.
 var ErrorExportDone = errors.New("export is complete")
 
+// ErrorTreeNil is a rare occurance, but it is a clear error
+var ErrorTreeNil = errors.New("iavl/export newExporter failed to create because tree is nil")
+
+// ErrorTreeNodeDbNil encountered when chains introduce a store without initializing data
+var ErrorTreeNodeDbNil = errors.New("iavl/export newExporter failed to create because tree.ndb is nil")
+
 // ExportNode contains exported node data.
 type ExportNode struct {
 	Key     []byte
@@ -33,7 +39,15 @@ type Exporter struct {
 }
 
 // NewExporter creates a new Exporter. Callers must call Close() when done.
-func newExporter(tree *ImmutableTree) *Exporter {
+func newExporter(tree *ImmutableTree) (*Exporter, error) {
+	if tree == nil {
+		return nil, ErrorTreeNil
+	}
+	// CV Prevent crash on incrVersionReaders if tree.ndb == nil
+	if tree.ndb == nil {
+		return nil, ErrorTreeNodeDbNil
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	exporter := &Exporter{
 		tree:   tree,
@@ -44,7 +58,7 @@ func newExporter(tree *ImmutableTree) *Exporter {
 	tree.ndb.incrVersionReaders(tree.version)
 	go exporter.export(ctx)
 
-	return exporter
+	return exporter, nil
 }
 
 // export exports nodes

export_test.go

@@ -160,7 +160,8 @@ func TestExporter(t *testing.T) {
 	}
 
 	actual := make([]*ExportNode, 0, len(expect))
-	exporter := tree.Export()
+	exporter, err := tree.Export()
+	require.NoError(t, err)
 	defer exporter.Close()
 	for {
 		node, err := exporter.Next()
@@ -189,7 +190,8 @@ func TestExporter_Import(t *testing.T) {
 		t.Run(desc, func(t *testing.T) {
 			t.Parallel()
 
-			exporter := tree.Export()
+			exporter, err := tree.Export()
+			require.NoError(t, err)
 			defer exporter.Close()
 
 			newTree, err := NewMutableTree(db.NewMemDB(), 0, false)
@@ -234,7 +236,8 @@ func TestExporter_Import(t *testing.T) {
 
 func TestExporter_Close(t *testing.T) {
 	tree := setupExportTreeSized(t, 4096)
-	exporter := tree.Export()
+	exporter, err := tree.Export()
+	require.NoError(t, err)
 
 	node, err := exporter.Next()
 	require.NoError(t, err)
@@ -273,7 +276,8 @@ func TestExporter_DeleteVersionErrors(t *testing.T) {
 
 	itree, err := tree.GetImmutable(2)
 	require.NoError(t, err)
-	exporter := itree.Export()
+	exporter, err := itree.Export()
+	require.NoError(t, err)
 	defer exporter.Close()
 
 	err = tree.DeleteVersion(2)
@@ -291,7 +295,8 @@ func BenchmarkExport(b *testing.B) {
 	tree := setupExportTreeSized(b, 4096)
 	b.StartTimer()
 	for n := 0; n < b.N; n++ {
-		exporter := tree.Export()
+		exporter, err := tree.Export()
+		require.NoError(b, err)
 		for {
 			_, err := exporter.Next()
 			if err == ErrorExportDone {

immutable_tree.go

@@ -155,7 +155,7 @@ func (t *ImmutableTree) Hash() ([]byte, error) {
 
 // Export returns an iterator that exports tree nodes as ExportNodes. These nodes can be
 // imported with MutableTree.Import() to recreate an identical tree.
-func (t *ImmutableTree) Export() *Exporter {
+func (t *ImmutableTree) Export() (*Exporter, error) {
 	return newExporter(t)
 }
 

import_test.go

@@ -27,7 +27,7 @@ func ExampleImporter() {
 	if err != nil {
 		// handle err
 	}
-	exporter := itree.Export()
+	exporter, err := itree.Export()
 	defer exporter.Close()
 	exported := []*ExportNode{}
 	for {
@@ -218,7 +218,8 @@ func BenchmarkImport(b *testing.B) {
 	b.StopTimer()
 	tree := setupExportTreeSized(b, 4096)
 	exported := make([]*ExportNode, 0, 4096)
-	exporter := tree.Export()
+	exporter, err := tree.Export()
+	require.NoError(b, err)
 	for {
 		item, err := exporter.Next()
 		if err == ErrorExportDone {