fix(postage): added postage stamps json marshaling (#4369)

pkg/postage/stamp.go

@@ -6,6 +6,7 @@ package postage
 
 import (
 	"bytes"
+	"encoding/json"
 	"errors"
 	"fmt"
 
@@ -118,6 +119,35 @@ func (s *Stamp) UnmarshalBinary(buf []byte) error {
 	return nil
 }
 
+type stampJson struct {
+	BatchID   []byte `json:"batchID"`
+	Index     []byte `json:"index"`
+	Timestamp []byte `json:"timestamp"`
+	Sig       []byte `json:"sig"`
+}
+
+func (s *Stamp) MarshalJSON() ([]byte, error) {
+	return json.Marshal(&stampJson{
+		s.batchID,
+		s.index,
+		s.timestamp,
+		s.sig,
+	})
+}
+
+func (a *Stamp) UnmarshalJSON(b []byte) error {
+	v := &stampJson{}
+	err := json.Unmarshal(b, v)
+	if err != nil {
+		return err
+	}
+	a.batchID = v.BatchID
+	a.index = v.Index
+	a.timestamp = v.Timestamp
+	a.sig = v.Sig
+	return nil
+}
+
 // ToSignDigest creates a digest to represent the stamp which is to be signed by the owner.
 func ToSignDigest(addr, batchId, index, timestamp []byte) ([]byte, error) {
 	h := swarm.NewHasher()

pkg/postage/stamp_test.go

@@ -6,6 +6,7 @@ package postage_test
 
 import (
 	"bytes"
+	"encoding/json"
 	"math/big"
 	"testing"
 
@@ -31,6 +32,24 @@ func TestStampMarshalling(t *testing.T) {
 	compareStamps(t, sExp, s)
 }
 
+// TestStampMarshalling tests the idempotence  of binary marshal/unmarshals for Stamps.
+func TestStampJsonMarshalling(t *testing.T) {
+	sExp := postagetesting.MustNewStamp()
+
+	b, err := json.Marshal(sExp)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	s := postage.NewStamp(nil, nil, nil, nil)
+	err = json.Unmarshal(b, s)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	compareStamps(t, sExp, s)
+}
+
 func compareStamps(t *testing.T, s1, s2 *postage.Stamp) {
 	t.Helper()
 

pkg/storer/sample.go

@@ -32,7 +32,7 @@ type SampleItem struct {
 	TransformedAddress swarm.Address
 	ChunkAddress       swarm.Address
 	ChunkData          []byte
-	Stamp              swarm.Stamp
+	Stamp              *postage.Stamp
 }
 
 type Sample struct {
@@ -288,7 +288,7 @@ func (db *DB) ReserveSample(
 
 			stats.ValidStampDuration += time.Since(start)
 
-			item.Stamp = stamp
+			item.Stamp = postage.NewStamp(stamp.BatchID(), stamp.Index(), stamp.Timestamp(), stamp.Sig())
 
 			// ensuring to pass the check order function of redistribution contract
 			if index := contains(item.TransformedAddress); index != -1 {