protovalidate: send violations as error details

Amend the unary and streaming interceptors to send validation errors to
the client as an error detail. This allows client code to easily parse
and work with the structured validation information: for example, a UI
might want to display validation errors next to the relevant fields in a
form.

Signed-off-by: Akshay Shah <[email protected]>

Author: akshayjshah

interceptors/protovalidate/protovalidate.go

@@ -29,7 +29,7 @@ func UnaryServerInterceptor(validator *protovalidate.Validator, opts ...Option)
 				break
 			}
 			if err = validator.Validate(msg); err != nil {
-				return nil, status.Error(codes.InvalidArgument, err.Error())
+				return nil, validationErrToStatus(err).Err()
 			}
 		default:
 			return nil, errors.New("unsupported message type")
@@ -71,7 +71,7 @@ func (w *wrappedServerStream) RecvMsg(m interface{}) error {
 		return nil
 	}
 	if err := w.validator.Validate(msg); err != nil {
-		return status.Error(codes.InvalidArgument, err.Error())
+		return validationErrToStatus(err).Err()
 	}
 
 	return nil
@@ -96,3 +96,17 @@ func (w *wrappedServerStream) Context() context.Context {
 func wrapServerStream(stream grpc.ServerStream) *wrappedServerStream {
 	return &wrappedServerStream{ServerStream: stream, wrappedContext: stream.Context()}
 }
+
+func validationErrToStatus(err error) *status.Status {
+	// Message is invalid.
+	if valErr := new(protovalidate.ValidationError); errors.As(err, &valErr) {
+		st := status.New(codes.InvalidArgument, err.Error())
+		ds, detErr := st.WithDetails(valErr.ToProto())
+		if detErr != nil {
+			return st
+		}
+		return ds
+	}
+	// CEL expression doesn't compile or type-check.
+	return status.New(codes.Unknown, err.Error())
+}

interceptors/protovalidate/protovalidate_test.go

@@ -9,16 +9,19 @@ import (
 	"net"
 	"testing"
 
+	"buf.build/gen/go/bufbuild/protovalidate/protocolbuffers/go/buf/validate"
 	"github.com/bufbuild/protovalidate-go"
 	protovalidate_middleware "github.com/grpc-ecosystem/go-grpc-middleware/v2/interceptors/protovalidate"
 	"github.com/grpc-ecosystem/go-grpc-middleware/v2/testing/testvalidate"
 	testvalidatev1 "github.com/grpc-ecosystem/go-grpc-middleware/v2/testing/testvalidate/v1"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/grpc/status"
 	"google.golang.org/grpc/test/bufconn"
+	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/reflect/protoreflect"
 )
 
@@ -41,8 +44,11 @@ func TestUnaryServerInterceptor(t *testing.T) {
 
 	t.Run("invalid_email", func(t *testing.T) {
 		_, err = interceptor(context.TODO(), testvalidate.BadUnaryRequest, info, handler)
-		assert.Error(t, err)
-		assert.Equal(t, codes.InvalidArgument, status.Code(err))
+		assertEqualViolation(t, &validate.Violation{
+			FieldPath:    "message",
+			ConstraintId: "string.email",
+			Message:      "value must be a valid email address",
+		}, err)
 	})
 
 	t.Run("not_protobuf", func(t *testing.T) {
@@ -140,8 +146,11 @@ func TestStreamServerInterceptor(t *testing.T) {
 		assert.Nil(t, err)
 
 		_, err = out.Recv()
-		assert.Error(t, err)
-		assert.Equal(t, codes.InvalidArgument, status.Code(err))
+		assertEqualViolation(t, &validate.Violation{
+			FieldPath:    "message",
+			ConstraintId: "string.email",
+			Message:      "value must be a valid email address",
+		}, err)
 	})
 
 	t.Run("invalid_email_ignored", func(t *testing.T) {
@@ -156,3 +165,19 @@ func TestStreamServerInterceptor(t *testing.T) {
 		assert.Nil(t, err)
 	})
 }
+
+func assertEqualViolation(tb testing.TB, want *validate.Violation, got error) bool {
+	require.Error(tb, got)
+	st := status.Convert(got)
+	assert.Equal(tb, codes.InvalidArgument, st.Code())
+	details := st.Proto().GetDetails()
+	require.Len(tb, details, 1)
+	gotpb, unwrapErr := details[0].UnmarshalNew()
+	require.Nil(tb, unwrapErr)
+	violations := &validate.Violations{
+		Violations: []*validate.Violation{want},
+	}
+	tb.Logf("got: %v", gotpb)
+	tb.Logf("want: %v", violations)
+	return assert.True(tb, proto.Equal(gotpb, violations))
+}