fix event/stream ping (#3553)

api/core/app/apps/base_app_generate_response_converter.py

@@ -26,6 +26,9 @@ class AppGenerateResponseConverter(ABC):
             else:
                 def _generate():
                     for chunk in cls.convert_stream_full_response(response):
+                        if chunk == 'ping':
+                            yield f'event: {chunk}\n\n'
+                        else:
                             yield f'data: {chunk}\n\n'
 
                 return _generate()
@@ -35,6 +38,9 @@ class AppGenerateResponseConverter(ABC):
             else:
                 def _generate():
                     for chunk in cls.convert_stream_simple_response(response):
+                        if chunk == 'ping':
+                            yield f'event: {chunk}\n\n'
+                        else:
                             yield f'data: {chunk}\n\n'
 
                 return _generate()