feat: add http.Flusher fallback for SSEWriter in Golang SDK

sdks/community/go/pkg/encoding/sse/writer.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"log/slog"
+	"net/http"
 	"strings"
 	"sync"
 	"time"
@@ -67,6 +68,9 @@ func (w *SSEWriter) WriteBytes(ctx context.Context, writer io.Writer, event []by
 			return fmt.Errorf("SSE flush failed: %w", err)
 		}
 	}
+	if flusher, ok := writer.(flusherWithoutError); ok {
+		flusher.Flush()
+	}
 	return nil
 }
 
@@ -116,6 +120,9 @@ func (w *SSEWriter) WriteEventWithType(ctx context.Context, writer io.Writer, ev
 			return fmt.Errorf("SSE flush failed: %w", err)
 		}
 	}
+	if flusher, ok := writer.(flusherWithoutError); ok {
+		flusher.Flush()
+	}
 
 	return nil
 }
@@ -187,6 +194,10 @@ type flusher interface {
 	Flush() error
 }
 
+// flusherWithoutError is a type alias for http.Flusher.
+// It is used to flush the writer without returning an error.
+type flusherWithoutError = http.Flusher
+
 // CustomEvent is a simple implementation of events.Event for error and custom events
 type CustomEvent struct {
 	events.BaseEvent

sdks/community/go/pkg/encoding/sse/writer_test.go

@@ -68,6 +68,15 @@ func (fw *flushWriter) Flush() error {
 	return fw.flushError
 }
 
+type httpFlushWriter struct {
+	bytes.Buffer
+	flushCalled bool
+}
+
+func (fw *httpFlushWriter) Flush() {
+	fw.flushCalled = true
+}
+
 func TestNewSSEWriter(t *testing.T) {
 	writer := NewSSEWriter()
 	if writer == nil {
@@ -451,6 +460,39 @@ func TestSSEWriter_Flushing(t *testing.T) {
 	}
 }
 
+func TestSSEWriter_HTTPFlusherFallback(t *testing.T) {
+	ctx := context.Background()
+	writer := NewSSEWriter()
+
+	t.Run("WriteEvent", func(t *testing.T) {
+		fw := &httpFlushWriter{}
+		event := &mockEvent{
+			BaseEvent: events.BaseEvent{
+				EventType: events.EventTypeCustom,
+			},
+		}
+
+		if err := writer.WriteEvent(ctx, fw, event); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+
+		if !fw.flushCalled {
+			t.Error("expected fallback flusher to be called")
+		}
+	})
+
+	t.Run("WriteBytes", func(t *testing.T) {
+		fw := &httpFlushWriter{}
+		if err := writer.WriteBytes(ctx, fw, []byte(`{"test":"data"}`)); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+
+		if !fw.flushCalled {
+			t.Error("expected fallback flusher to be called")
+		}
+	})
+}
+
 func TestCustomEvent(t *testing.T) {
 	t.Run("Data operations", func(t *testing.T) {
 		event := &CustomEvent{}