add function to marshal raw nodes to json

fixes https://github.com/ipfs/go-ipfs/issues/6076

merkledag_test.go

@@ -3,6 +3,7 @@ package merkledag_test
 import (
 	"bytes"
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -640,6 +641,27 @@ func TestCidRawDoesnNeedData(t *testing.T) {
 	}
 }
 
+func TestRawToJson(t *testing.T) {
+	rawData := []byte{1, 2, 3, 4}
+	nd := NewRawNode(rawData)
+	encoded, err := nd.MarshalJSON()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var res interface{}
+	err = json.Unmarshal(encoded, &res)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resBytes, ok := res.(string)
+	if !ok {
+		t.Fatal("expected to marshal to a string")
+	}
+	if string(rawData) != resBytes {
+		t.Fatal("failed to round-trip bytes")
+	}
+}
+
 func TestGetManyDuplicate(t *testing.T) {
 	ctx := context.Background()
 

raw.go

 package merkledag
 
 import (
+	"encoding/json"
 	"fmt"
 	"github.com/ipfs/go-block-format"
 
@@ -94,4 +95,9 @@ func (rn *RawNode) Stat() (*ipld.NodeStat, error) {
 	}, nil
 }
 
+// MarshalJSON is required for our "ipfs dag" commands.
+func (rn *RawNode) MarshalJSON() ([]byte, error) {
+	return json.Marshal(string(rn.RawData()))
+}
+
 var _ ipld.Node = (*RawNode)(nil)