add fieldmask interceptor

go.mod

@@ -5,6 +5,7 @@ go 1.21
 require (
 	buf.build/gen/go/bufbuild/protovalidate/protocolbuffers/go v1.31.0-20230802163732-1c33ebd9ecfa.1
 	github.com/bufbuild/protovalidate-go v0.2.1
+	github.com/mennanov/fmutils v0.3.0
 	github.com/stretchr/testify v1.8.4
 	golang.org/x/net v0.21.0
 	golang.org/x/oauth2 v0.16.0

interceptors/fieldmask/interceptor.go

@@ -0,0 +1,40 @@
+package fieldmask
+
+import (
+	"context"
+
+	"github.com/mennanov/fmutils"
+	"google.golang.org/grpc"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/types/known/fieldmaskpb"
+)
+
+var DefaultFilterFunc FilterFunc = func(msg proto.Message, paths []string) {
+	fmutils.Filter(msg, paths)
+}
+
+type FilterFunc func(msg proto.Message, paths []string)
+
+// UnaryServerInterceptor returns a new unary server interceptor that will decide whether to which fields should return to clients.
+func UnaryServerInterceptor(filterFunc FilterFunc) grpc.UnaryServerInterceptor {
+	return func(ctx context.Context, req any, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp any, err error) {
+		resp, err = handler(ctx, req)
+		if err != nil {
+			return
+		}
+		reqWithFieldMask, ok := req.(interface {
+			GetFieldMask() *fieldmaskpb.FieldMask
+		})
+		if !ok {
+			return
+		}
+		if len(reqWithFieldMask.GetFieldMask().GetPaths()) > 0 {
+			protoResp, ok := resp.(proto.Message)
+			if !ok {
+				return
+			}
+			filterFunc(protoResp, reqWithFieldMask.GetFieldMask().GetPaths())
+		}
+		return
+	}
+}

interceptors/fieldmask/interceptor_test.go

@@ -0,0 +1,57 @@
+// Copyright (c) The go-grpc-middleware Authors.
+// Licensed under the Apache License 2.0.
+
+// Copyright 2017 David Ackroyd. All Rights Reserved.
+// See LICENSE for licensing terms.
+
+package fieldmask
+
+import (
+	"testing"
+
+	"github.com/grpc-ecosystem/go-grpc-middleware/v2/testing/testpb"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/suite"
+	"google.golang.org/grpc"
+	"google.golang.org/protobuf/types/known/fieldmaskpb"
+)
+
+func TestFieldMaskSuite(t *testing.T) {
+	s := &FieldMaskSuite{
+		InterceptorTestSuite: &testpb.InterceptorTestSuite{
+			TestService: &testpb.TestPingService{},
+			ServerOpts: []grpc.ServerOption{
+				grpc.UnaryInterceptor(
+					UnaryServerInterceptor(DefaultFilterFunc),
+				),
+			},
+		},
+	}
+	suite.Run(t, s)
+}
+
+type FieldMaskSuite struct {
+	*testpb.InterceptorTestSuite
+}
+
+func (s *FieldMaskSuite) TestUnary_ReturnAllResponse() {
+	resp, err := s.Client.Ping(s.SimpleCtx(), &testpb.PingRequest{Value: "1"})
+	assert.Equal(s.T(), nil, err)
+	expected := &testpb.PingResponse{
+		Value: "1",
+	}
+	assert.Equal(s.T(), expected.Counter, resp.Counter)
+	assert.Equal(s.T(), expected.Value, resp.Value)
+}
+
+func (s *FieldMaskSuite) TestUnary_NoReturnValueResponse() {
+	resp, err := s.Client.Ping(s.SimpleCtx(), &testpb.PingRequest{Value: "1", FieldMask: &fieldmaskpb.FieldMask{
+		Paths: []string{"counter"},
+	}})
+	assert.Equal(s.T(), nil, err)
+	expected := &testpb.PingResponse{
+		Value: "",
+	}
+	assert.Equal(s.T(), expected.Counter, resp.Counter)
+	assert.Equal(s.T(), expected.Value, resp.Value)
+}

testing/testpb/v1/test.proto

@@ -1,8 +1,10 @@
 syntax = "proto3";
 
+import "google/protobuf/field_mask.proto";
+
 package testing.testpb.v1;
 
-option go_package = ".;testpb";
+option go_package = "./;testpb";
 
 message PingEmptyRequest {
 }
@@ -14,6 +16,7 @@ message PingRequest {
   string value = 1;
   int32 sleep_time_ms = 2;
   uint32 error_code_returned = 3;
+  google.protobuf.FieldMask field_mask = 4;
 }
 
 message PingResponse {