fix: 5076 (#5083)

Co-authored-by: Kevin Wan <wanjunfeng@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

gateway/internal/eventhandler_test.go

@@ -2,10 +2,12 @@ package internal
 
 import (
 	"io"
+	"net/http/httptest"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/status"
 )
 
@@ -18,3 +20,145 @@ func TestEventHandler(t *testing.T) {
 	assert.Equal(t, codes.OK, h.Status.Code())
 	h.OnReceiveResponse(nil)
 }
+
+func TestEventHandler_OnReceiveTrailers(t *testing.T) {
+	tests := []struct {
+		name           string
+		writer         io.Writer
+		status         *status.Status
+		metadata       metadata.MD
+		expectedStatus codes.Code
+		expectedHeader map[string][]string
+	}{
+		{
+			name:   "with http.ResponseWriter and metadata",
+			writer: httptest.NewRecorder(),
+			status: status.New(codes.OK, "success"),
+			metadata: metadata.MD{
+				"x-custom-header":  []string{"value1", "value2"},
+				"x-another-header": []string{"single-value"},
+			},
+			expectedStatus: codes.OK,
+			expectedHeader: map[string][]string{
+				"X-Custom-Header":  {"value1", "value2"},
+				"X-Another-Header": {"single-value"},
+			},
+		},
+		{
+			name:           "with http.ResponseWriter and nil metadata",
+			writer:         httptest.NewRecorder(),
+			status:         status.New(codes.Internal, "error"),
+			metadata:       nil,
+			expectedStatus: codes.Internal,
+			expectedHeader: map[string][]string{},
+		},
+		{
+			name:           "with non-http.ResponseWriter",
+			writer:         io.Discard,
+			status:         status.New(codes.OK, "success"),
+			metadata:       metadata.MD{"x-header": []string{"value"}},
+			expectedStatus: codes.OK,
+			expectedHeader: nil, // headers should not be set
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			h := NewEventHandler(tt.writer, nil)
+			
+			h.OnReceiveTrailers(tt.status, tt.metadata)
+			
+			// Check status is set correctly
+			assert.Equal(t, tt.expectedStatus, h.Status.Code())
+			
+			// Check headers are set correctly if writer is http.ResponseWriter
+			if recorder, ok := tt.writer.(*httptest.ResponseRecorder); ok {
+				if tt.expectedHeader != nil {
+					for key, expectedValues := range tt.expectedHeader {
+						actualValues := recorder.Header()[key]
+						assert.Equal(t, expectedValues, actualValues, "Header %s should match", key)
+					}
+				}
+			}
+		})
+	}
+}
+
+func TestEventHandler_OnReceiveHeaders(t *testing.T) {
+	tests := []struct {
+		name           string
+		writer         io.Writer
+		metadata       metadata.MD
+		expectedHeader map[string][]string
+	}{
+		{
+			name:   "with http.ResponseWriter and metadata",
+			writer: httptest.NewRecorder(),
+			metadata: metadata.MD{
+				"content-type":     []string{"application/json"},
+				"x-custom-header":  []string{"value1", "value2"},
+				"x-another-header": []string{"single-value"},
+			},
+			expectedHeader: map[string][]string{
+				"Content-Type":     {"application/json"},
+				"X-Custom-Header":  {"value1", "value2"},
+				"X-Another-Header": {"single-value"},
+			},
+		},
+		{
+			name:           "with http.ResponseWriter and nil metadata",
+			writer:         httptest.NewRecorder(),
+			metadata:       nil,
+			expectedHeader: map[string][]string{},
+		},
+		{
+			name:           "with http.ResponseWriter and empty metadata",
+			writer:         httptest.NewRecorder(),
+			metadata:       metadata.MD{},
+			expectedHeader: map[string][]string{},
+		},
+		{
+			name:           "with non-http.ResponseWriter",
+			writer:         io.Discard,
+			metadata:       metadata.MD{"x-header": []string{"value"}},
+			expectedHeader: nil, // headers should not be set
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			h := NewEventHandler(tt.writer, nil)
+			
+			h.OnReceiveHeaders(tt.metadata)
+			
+			// Check headers are set correctly if writer is http.ResponseWriter
+			if recorder, ok := tt.writer.(*httptest.ResponseRecorder); ok {
+				if tt.expectedHeader != nil {
+					for key, expectedValues := range tt.expectedHeader {
+						actualValues := recorder.Header()[key]
+						assert.Equal(t, expectedValues, actualValues, "Header %s should match", key)
+					}
+				}
+			}
+		})
+	}
+}
+
+func TestEventHandler_OnReceiveHeaders_MultipleValues(t *testing.T) {
+	recorder := httptest.NewRecorder()
+	h := NewEventHandler(recorder, nil)
+	
+	// Test that multiple calls to OnReceiveHeaders accumulate headers
+	h.OnReceiveHeaders(metadata.MD{
+		"x-header-1": []string{"value1"},
+	})
+	
+	h.OnReceiveHeaders(metadata.MD{
+		"x-header-1": []string{"value2"}, // Should add to existing header
+		"x-header-2": []string{"value3"},
+	})
+	
+	// Check that headers are accumulated (not overwritten)
+	assert.Equal(t, []string{"value1", "value2"}, recorder.Header()["X-Header-1"])
+	assert.Equal(t, []string{"value3"}, recorder.Header()["X-Header-2"])
+}