fix(spanner): support custom encoding and decoding of protos

spanner/testdata/protos/custom_singer.go

@@ -0,0 +1,41 @@
+/*
+Copyright 2024 Google LLC
+
+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 protos
+
+import (
+	"errors"
+)
+
+func (c *CustomSingerInfo) EncodeSpanner() (interface{}, error) {
+	if c == nil {
+		return nil, nil
+	}
+	return c.SingerName, nil
+}
+
+func (c CustomGenre) EncodeSpanner() (interface{}, error) {
+	return c.String(), nil
+}
+
+func (c *CustomSingerInfo) DecodeSpanner(input interface{}) error {
+	str, ok := input.(string)
+	if !ok {
+		return errors.New("the interface does not contain a string")
+	}
+	c.SingerName = &str
+	return nil
+}

spanner/testdata/protos/singer.proto

@@ -32,3 +32,14 @@ enum Genre {
   FOLK = 2;
   ROCK = 3;
 }
+
+message CustomSingerInfo {
+  optional string singer_name = 1;
+}
+
+enum CustomGenre {
+  CUSTOM_POP = 0;
+  CUSTOM_JAZZ = 1;
+  CUSTOM_FOLK = 2;
+  CUSTOM_ROCK = 3;
+}

spanner/value.go

@@ -2279,6 +2279,15 @@ func decodeValue(v *proto3.Value, t *sppb.Type, ptr interface{}, opts ...DecodeO
 		reflect.ValueOf(p.ProtoEnumVal).Elem().SetInt(y)
 		p.Valid = true
 	case proto.Message:
+		// Check if the pointer is a custom type that implements spanner.Decoder
+		// interface.
+		if decodedVal, ok := ptr.(Decoder); ok {
+			x, err := getGenericValue(t, v)
+			if err != nil {
+				return err
+			}
+			return decodedVal.DecodeSpanner(x)
+		}
 		if p == nil {
 			return errNilDst(p)
 		}
@@ -4429,6 +4438,16 @@ func encodeValue(v interface{}) (*proto3.Value, *sppb.Type, error) {
 	case []GenericColumnValue:
 		return nil, nil, errEncoderUnsupportedType(v)
 	case protoreflect.Enum:
+		// Check if the value is of protoreflect.Enum type that implements spanner.Encoder
+		// interface.
+		if encodedVal, ok := v.(Encoder); ok {
+			nv, err := encodedVal.EncodeSpanner()
+			if err != nil {
+				return nil, nil, err
+			}
+			return encodeValue(nv)
+		}
+
 		if v != nil {
 			var protoEnumfqn string
 			rv := reflect.ValueOf(v)
@@ -4447,6 +4466,16 @@ func encodeValue(v interface{}) (*proto3.Value, *sppb.Type, error) {
 		}
 		return nil, nil, errNotValidSrc(v)
 	case proto.Message:
+		// Check if the value is of proto.Message type that implements spanner.Encoder
+		// interface.
+		if encodedVal, ok := v.(Encoder); ok {
+			nv, err := encodedVal.EncodeSpanner()
+			if err != nil {
+				return nil, nil, err
+			}
+			return encodeValue(nv)
+		}
+
 		if v != nil {
 			if v.ProtoReflect().IsValid() {
 				bytes, err := proto.Marshal(v)

spanner/value_test.go

@@ -563,6 +563,9 @@ func TestEncodeValue(t *testing.T) {
 		{[]*pb.Genre{nil, (*pb.Genre)(nil)}, listProto(nullProto(), nullProto()), listType(tProtoEnum), "Array of Proto Enum with nil values"},
 		{[]*pb.SingerInfo{singer1ProtoMsg, singer2ProtoMsg, nil, (*pb.SingerInfo)(nil)}, listProto(protoMessageProto(singer1ProtoMsg), protoMessageProto(singer2ProtoMsg), nullProto(), nullProto()), listType(tProtoMessage), "Array of Proto Message with non-nil and nil values"},
 		{[]*pb.Genre{&singer1ProtoEnum, &singer2ProtoEnum, nil, (*pb.Genre)(nil)}, listProto(protoEnumProto(singer1ProtoEnum), protoEnumProto(singer2ProtoEnum), nullProto(), nullProto()), listType(tProtoEnum), "Array of Proto Enum with non-nil and nil values"},
+		// PROTO MESSAGE AND ENUM WITH CUSTOM ENCODER
+		{&pb.CustomSingerInfo{SingerName: &sValue}, stringProto("abc"), tString, "Proto message with encoder interface to string"},
+		{pb.CustomGenre_CUSTOM_ROCK, stringProto("CUSTOM_ROCK"), tString, "Proto Enum with encoder interface to string"},
 	} {
 		got, gotType, err := encodeValue(test.in)
 		if err != nil {
@@ -1996,6 +1999,8 @@ func TestDecodeValue(t *testing.T) {
 		{desc: "decode all NULL elements in ARRAY<PROTO<>> to []*pb.SingerInfo", proto: listProto(nullProto(), nullProto()), protoType: listType(protoMessageType(protoMessagefqn)), want: []*pb.SingerInfo{nil, nil}},
 		{desc: "decode ARRAY<ENUM<>> to []*pb.Genre", proto: listProto(nullProto(), protoEnumProto(pb.Genre_ROCK), protoEnumProto(pb.Genre_FOLK)), protoType: listType(protoEnumType(protoEnumfqn)), want: []*pb.Genre{nil, &singerEnumValue, &singer2ProtoEnum}},
 		{desc: "decode all NULL elements in ARRAY<ENUM<>> to []*pb.Genre", proto: listProto(nullProto(), nullProto()), protoType: listType(protoEnumType(protoEnumfqn)), want: []*pb.Genre{nil, nil}},
+		// PROTO MESSAGE WITH CUSTOM DECODER
+		{desc: "decode STRING to Proto message", proto: stringProto("abc"), protoType: stringType(), want: pb.CustomSingerInfo{SingerName: proto.String("abc")}},
 	} {
 		gotp := reflect.New(reflect.TypeOf(test.want))
 		v := gotp.Interface()