Add client interceptors

docs/interceptors.md

@@ -4,11 +4,15 @@ title: "Interceptors"
 sidebar_label: "Interceptors"
 ---
 
-The service constructor can use the option `twirp.WithServerInterceptors(interceptors ...twirp.Interceptor)`
+The client and service constructors can use the options
+`twirp.WithClientInterceptors(interceptors ...twirp.Interceptor)`
+and `twirp.WithServerInterceptors(interceptors ...twirp.Interceptor)`
 to plug in additional functionality:
 
 ```go
-server := NewHaberdasherServer(svcImpl, twirp.WithInterceptor(NewLogInterceptor(logger.New(os.Stderr, "", 0))))
+client := NewHaberdasherProtobufClient(url, &http.Client{}, twirp.WithClientInterceptors(NewLogInterceptor(logger.New(os.Stderr, "", 0))))
+
+server := NewHaberdasherServer(svcImpl, twirp.WithServerInterceptors(NewLogInterceptor(logger.New(os.Stderr, "", 0))))
 
 // NewLogInterceptor logs various parts of a request using a standard Logger.
 func NewLogInterceptor(l *log.Logger) twirp.Interceptor {

internal/twirptest/client_test.go

@@ -402,6 +402,67 @@ func TestClientContextToHook(t *testing.T) {
 	}
 }
 
+func TestClientInterceptor(t *testing.T) {
+	interceptor := func(next twirp.Method) twirp.Method {
+		return func(ctx context.Context, request interface{}) (interface{}, error) {
+			methodName, _ := twirp.MethodName(ctx)
+			if methodName != "MakeHat" {
+				return nil, fmt.Errorf("unexpected methodName: %q", methodName)
+			}
+			serviceName, _ := twirp.ServiceName(ctx)
+			if serviceName != "Haberdasher" {
+				return nil, fmt.Errorf("unexpected serviceName: %q", serviceName)
+			}
+			packageName, _ := twirp.PackageName(ctx)
+			if packageName != "twirp.internal.twirptest" {
+				return nil, fmt.Errorf("unexpected packageName: %q", packageName)
+			}
+			size, ok := request.(*Size)
+			if !ok {
+				return nil, fmt.Errorf("could not cast %T to a *Size", request)
+			}
+			size.Inches = size.Inches + 1
+			response, err := next(ctx, request)
+			hat, ok := response.(*Hat)
+			if ok && hat != nil {
+				hat.Color = hat.Color + "x"
+				return hat, err
+			}
+			return nil, err
+		}
+	}
+	h := PickyHatmaker(3)
+
+	s := httptest.NewServer(NewHaberdasherServer(h))
+	defer s.Close()
+	client := NewHaberdasherProtobufClient(
+		s.URL,
+		http.DefaultClient,
+		twirp.WithClientInterceptors(
+			interceptor,
+			interceptor,
+		),
+	)
+	hat, clientErr := client.MakeHat(context.Background(), &Size{Inches: 1})
+	if clientErr != nil {
+		t.Fatalf("client err=%q", clientErr)
+	}
+	if hat.Size != 3 {
+		t.Errorf("hat size expected=3 actual=%v", hat.Size)
+	}
+	if hat.Color != "bluexx" {
+		t.Errorf("hat color expected=bluexx actual=%v", hat.Color)
+	}
+	_, clientErr = client.MakeHat(context.Background(), &Size{Inches: 3})
+	twerr, ok := clientErr.(twirp.Error)
+	if !ok {
+		t.Fatalf("expected twirp.Error type error, have %T", clientErr)
+	}
+	if twerr.Code() != twirp.InvalidArgument {
+		t.Errorf("expected error type to be InvalidArgument, buf found %q", twerr.Code())
+	}
+}
+
 func TestClientIntermediaryErrors(t *testing.T) {
 	testcase := func(body string, code int, expectedErrorCode twirp.ErrorCode, clientMaker func(string, HTTPClient, ...twirp.ClientOption) Haberdasher) func(*testing.T) {
 		return func(t *testing.T) {