Cannot send bytes to clients anymore in 5.14.0

[detoyz]

Describe the bug
After updating to 5.14.0 seems I am not able to send to clients already prepared bytes anymore. It seems like this PR is causing the issue -> #1502

To Reproduce

1. Somewhere in my code I have next:

   async def set_client(self, sid, data):
       await self.emit(
           event='set',
           data=serialize_to_message_pack_as(
               self.client_schemas['set'],
               data,
           ),  # <- this function produces byte object, example: b'\xde\x00\x01\xa5tasks\x90'
           to=sid,
       )

2. When I trigger this function in test suite/local run I get next error:
   ...
   File "/.../.venv/lib/python3.12/site-packages/socketio/async_redis_manager.py", line 118, in _publish
   self.channel, json.dumps(data))
   ...
   TypeError: Object of type bytes is not JSON serializable

Expected behavior
A should be able to send data as bytes to clients, so I can parse as bytes on clients as well according to docs: https://python-socketio.readthedocs.io/en/latest/server.html#emitting-events-to-clients.
On the 5.13.0 all behavior works, 3k tests are all green, I can send and receive bytes.

Logs

Traceback (most recent call last):
  File "/.../.venv/lib/python3.12/site-packages/socketio/async_server.py", line 612, in _handle_event_internal
    r = await server._trigger_event(data[0], namespace, sid, *data[1:])
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/.../.venv/lib/python3.12/site-packages/socketio/async_server.py", line 662, in _trigger_event
    return await handler.trigger_event(event, *args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/.../.venv/lib/python3.12/site-packages/socketio/async_namespace.py", line 38, in trigger_event
    ret = await handler(*args)
          ^^^^^^^^^^^^^^^^^^^^
  File "/.../dashboard.py", line 31, in on_mount_dashboard
    await self.set_client(sid, {'tasks': presentable_tasks})
  File "/.../base_namespace.py", line 255, in set_client
    await self.emit(
  File "/.../.venv/lib/python3.12/site-packages/socketio/async_namespace.py", line 70, in emit
    return await self.server.emit(event, data=data, to=to, room=room,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/.../.venv/lib/python3.12/site-packages/socketio/async_server.py", line 178, in emit
    await self.manager.emit(event, data, namespace, room=room,
  File "/.../.venv/lib/python3.12/site-packages/socketio/async_pubsub_manager.py", line 72, in emit
    await self._publish(message)  # notify other hosts
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/.../.venv/lib/python3.12/site-packages/socketio/async_redis_manager.py", line 118, in _publish
    self.channel, json.dumps(data))
                  ^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/json/encoder.py", line 180, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type bytes is not JSON serializable
Received event "set" [/client]
2025-10-13 17:31:10 INFO     Received event "set" [/client]
Engine.IO connection dropped
2025-10-13 17:31:13 INFO     Engine.IO connection dropped
2025-10-13 17:31:13 INFO     Disconnected :(
2025-10-13 17:31:13 DEBUG    Connection closed on namespace=/client: x7xcl6Rx6KbgZ-kNAAAB

Am I doing something wrong here?

[miguelgrinberg]

Okay, yes, I have missed the use case of binary packets. I'll think about how to re-add support for binary within the new JSON communication format.