Add JSONSerializer for records (#22)

* add string serializer for raw data

* document code

* expose json marshal options context func

* fix linter errors

opencdc/data.go

@@ -16,6 +16,8 @@ package opencdc
 
 import (
 	"bytes"
+	"context"
+	"encoding/base64"
 	"fmt"
 
 	opencdcv1 "github.com/conduitio/conduit-commons/proto/opencdc/v1"
@@ -82,3 +84,28 @@ func (d RawData) Bytes() []byte {
 func (d RawData) Clone() Data {
 	return RawData(bytes.Clone(d))
 }
+
+func (d RawData) MarshalJSON(ctx context.Context) ([]byte, error) {
+	if ctx != nil {
+		s := ctx.Value(jsonMarshalOptionsCtxKey{})
+		//nolint:forcetypeassert // We know the type of the value.
+		if s != nil && s.(*JSONMarshalOptions).RawDataAsString {
+			// We should serialize RawData as a string.
+			//nolint:wrapcheck // If we didn't implement MarshalJSON this would be done by the json package.
+			return json.Marshal(string(d))
+		}
+	}
+
+	// We could use json.Marshal([]byte(d)) here, but it would be 3 times slower,
+	// and since this is in the hot path, we need to optimize it.
+
+	if d == nil {
+		return []byte(`null`), nil
+	}
+	encodedLen := base64.StdEncoding.EncodedLen(len(d))
+	out := make([]byte, encodedLen+2)
+	out[0] = '"' // add leading quote
+	base64.StdEncoding.Encode(out[1:], d)
+	out[encodedLen+1] = '"' // add trailing quote
+	return out, nil
+}

opencdc/json.go

@@ -15,11 +15,30 @@
 package opencdc
 
 import (
+	"context"
 	"fmt"
 
 	"github.com/goccy/go-json"
 )
 
+// JSONMarshalOptions can customize how a record is serialized to JSON. It can
+// be attached to a context using WithJSONMarshalOptions and supplied to
+// json.MarshalContext to customize the serialization behavior.
+type JSONMarshalOptions struct {
+	// RawDataAsString is a flag that indicates if the RawData type should be
+	// serialized as a string. If set to false, RawData will be serialized as a
+	// base64 encoded string. If set to true, RawData will be serialized as a
+	// string without conversion.
+	RawDataAsString bool
+}
+
+type jsonMarshalOptionsCtxKey struct{}
+
+// WithJSONMarshalOptions attaches JSONMarshalOptions to a context.
+func WithJSONMarshalOptions(ctx context.Context, options *JSONMarshalOptions) context.Context {
+	return context.WithValue(ctx, jsonMarshalOptionsCtxKey{}, options)
+}
+
 func (r *Record) UnmarshalJSON(b []byte) error {
 	var raw struct {
 		Position  Position  `json:"position"`

opencdc/json_test.go

@@ -23,7 +23,7 @@ import (
 	"github.com/matryer/is"
 )
 
-func TestRecord_UnmarshalJSON(t *testing.T) {
+func TestRecord_JSON(t *testing.T) {
 	is := is.New(t)
 	have := Record{
 		Position:  Position("standing"),
@@ -46,6 +46,7 @@ func TestRecord_UnmarshalJSON(t *testing.T) {
 			},
 		},
 	}
+	wantJSON := `{"position":"c3RhbmRpbmc=","operation":"update","metadata":{"foo":"bar"},"key":"cGFkbG9jay1rZXk=","payload":{"before":"eWVsbG93","after":{"bool":true,"float32":1.2,"float64":1.2,"int":1,"int32":1,"int64":1,"string":"orange"}}}`
 	want := Record{
 		Position:  Position("standing"),
 		Operation: OperationUpdate,
@@ -71,6 +72,8 @@ func TestRecord_UnmarshalJSON(t *testing.T) {
 	b, err := json.Marshal(have)
 	is.NoErr(err)
 
+	is.Equal(cmp.Diff(string(b), wantJSON), "")
+
 	var got Record
 	err = json.Unmarshal(b, &got)
 	is.NoErr(err)

opencdc/serializer.go

@@ -14,8 +14,34 @@
 
 package opencdc
 
+import (
+	"context"
+	"fmt"
+
+	"github.com/goccy/go-json"
+)
+
 // RecordSerializer is a type that can serialize a record to bytes. It's used in
 // destination connectors to change the output structure and format.
 type RecordSerializer interface {
 	Serialize(Record) ([]byte, error)
 }
+
+// JSONSerializer is a RecordSerializer that serializes records to JSON using
+// the configured options.
+type JSONSerializer JSONMarshalOptions
+
+func (s JSONSerializer) Serialize(r Record) ([]byte, error) {
+	ctx := WithJSONMarshalOptions(context.Background(), (*JSONMarshalOptions)(&s))
+	defer func() {
+		// Workaround because of https://github.com/goccy/go-json/issues/499.
+		// TODO: Remove this when the issue is fixed and store value in context
+		//  instead of pointer.
+		s = JSONSerializer{}
+	}()
+	bytes, err := json.MarshalContext(ctx, r)
+	if err != nil {
+		return nil, fmt.Errorf("failed to serialize record to JSON: %w", err)
+	}
+	return bytes, nil
+}

opencdc/serializer_test.go

@@ -0,0 +1,69 @@
+// Copyright © 2024 Meroxa, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package opencdc
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/matryer/is"
+)
+
+func TestJSONSerializer(t *testing.T) {
+	rec := Record{
+		Position:  Position("standing"),
+		Operation: OperationUpdate,
+		Metadata:  Metadata{"foo": "bar"},
+		Key:       RawData("padlock-key"),
+		Payload: Change{
+			Before: RawData("yellow"),
+			After: StructuredData{
+				"bool": true,
+
+				"int":   1,
+				"int32": int32(1),
+				"int64": int64(1),
+
+				"float32": float32(1.2),
+				"float64": 1.2,
+
+				"string": "orange",
+			},
+		},
+	}
+
+	testCases := []struct {
+		name       string
+		serializer JSONSerializer
+		want       string
+	}{{
+		name:       "default",
+		serializer: JSONSerializer{},
+		want:       `{"position":"c3RhbmRpbmc=","operation":"update","metadata":{"foo":"bar"},"key":"cGFkbG9jay1rZXk=","payload":{"before":"eWVsbG93","after":{"bool":true,"float32":1.2,"float64":1.2,"int":1,"int32":1,"int64":1,"string":"orange"}}}`,
+	}, {
+		name:       "raw data as string",
+		serializer: JSONSerializer{RawDataAsString: true},
+		want:       `{"position":"c3RhbmRpbmc=","operation":"update","metadata":{"foo":"bar"},"key":"padlock-key","payload":{"before":"yellow","after":{"bool":true,"float32":1.2,"float64":1.2,"int":1,"int32":1,"int64":1,"string":"orange"}}}`,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			is := is.New(t)
+			rec.SetSerializer(tc.serializer)
+			b := rec.Bytes()
+			is.Equal(cmp.Diff(string(b), tc.want), "")
+		})
+	}
+}