Problem: export API not supported in memiavl (#924)

* Problem: export API not supported in memiavl

* Update CHANGELOG.md

Signed-off-by: yihuang <huang@crypto.com>

---------

Signed-off-by: yihuang <huang@crypto.com>

CHANGELOG.md

@@ -24,6 +24,7 @@
 
 - [#890](https://github.com/crypto-org-chain/cronos/pull/890) optimize memiavl snapshot format.
 - [#904](https://github.com/crypto-org-chain/cronos/pull/904) Enable "dynamic-level-bytes" on new `application.db`.
+- [#924](https://github.com/crypto-org-chain/cronos/pull/924) memiavl support `Export` API.
 
 *Feb 09, 2022*
 

memiavl/export.go

@@ -0,0 +1,31 @@
+package memiavl
+
+import (
+	"github.com/cosmos/iavl"
+)
+
+type Exporter struct {
+	snapshot *Snapshot
+	i        uint32
+	count    int
+}
+
+func (e *Exporter) Next() (*iavl.ExportNode, error) {
+	if int(e.i) >= e.count {
+		return nil, iavl.ExportDone
+	}
+	node := e.snapshot.Node(e.i)
+	e.i++
+
+	height := node.Height()
+	var value []byte
+	if height == 0 {
+		value = node.Value()
+	}
+	return &iavl.ExportNode{
+		Height:  int8(height),
+		Version: int64(node.Version()),
+		Key:     node.Key(),
+		Value:   value,
+	}, nil
+}

memiavl/snapshot.go

@@ -252,6 +252,11 @@ func (snapshot *Snapshot) KeyValue(offset uint64) ([]byte, []byte) {
 	return key, value
 }
 
+// Export exports the nodes in DFS post-order, resemble the API of existing iavl library
+func (snapshot *Snapshot) Export() *Exporter {
+	return &Exporter{snapshot: snapshot, count: snapshot.nodesLen()}
+}
+
 // WriteSnapshot save the IAVL tree to a new snapshot directory.
 func (t *Tree) WriteSnapshot(snapshotDir string) (returnErr error) {
 	var rootIndex uint32

memiavl/snapshot_test.go

@@ -3,6 +3,7 @@ package memiavl
 import (
 	"testing"
 
+	"github.com/cosmos/iavl"
 	"github.com/stretchr/testify/require"
 )
 
@@ -45,3 +46,42 @@ func TestSnapshotEncodingRoundTrip(t *testing.T) {
 	require.Equal(t, len(ChangeSets), int(v))
 	require.NoError(t, snapshot.Close())
 }
+
+func TestSnapshotExport(t *testing.T) {
+	expNodes := []*iavl.ExportNode{
+		{Key: []byte("hello"), Value: []byte("world1"), Version: 2, Height: 0},
+		{Key: []byte("hello1"), Value: []byte("world1"), Version: 2, Height: 0},
+		{Key: []byte("hello1"), Value: nil, Version: 3, Height: 1},
+		{Key: []byte("hello2"), Value: []byte("world1"), Version: 3, Height: 0},
+		{Key: []byte("hello3"), Value: []byte("world1"), Version: 3, Height: 0},
+		{Key: []byte("hello3"), Value: nil, Version: 3, Height: 1},
+		{Key: []byte("hello2"), Value: nil, Version: 3, Height: 2},
+	}
+
+	// setup test tree
+	tree := NewEmptyTree(0)
+	for _, changes := range ChangeSets[:3] {
+		applyChangeSet(tree, changes)
+		_, _, err := tree.SaveVersion(true)
+		require.NoError(t, err)
+	}
+
+	snapshotDir := t.TempDir()
+	require.NoError(t, tree.WriteSnapshot(snapshotDir))
+
+	snapshot, err := OpenSnapshot(snapshotDir)
+	require.NoError(t, err)
+
+	var nodes []*iavl.ExportNode
+	exporter := snapshot.Export()
+	for {
+		node, err := exporter.Next()
+		if err == iavl.ExportDone {
+			break
+		}
+		require.NoError(t, err)
+		nodes = append(nodes, node)
+	}
+
+	require.Equal(t, expNodes, nodes)
+}