Flask-socketio: Test Client does not support binary data

[jpowie01]

Hello,
I've found an issue with emitting binary data using Test Client. Is there a way that I can use it in tests? As far as I looked into the code I found that this class always set binary argument to False. Why? Was it done on purpose?

Example use:

web_socket.test_client(app)
...
image = open('example_file.dcm', 'rb')
binary_data = image.read()
web_socket_client.emit('my_event', {'ref_id': 123, 'image': binary_data}, namespace='/my_namespace')

Example error:

venv/lib/python3.6/site-packages/flask_socketio/test_client.py:121: in emit
    self.socketio.server._handle_eio_message(self.sid, pkt.encode())
venv/lib/python3.6/site-packages/socketio/packet.py:71: in encode
    encoded_packet += self.json.dumps(data, separators=(',', ':'))
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/__init__.py:238: in dumps
    **kw).encode(obj)
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py:199: in encode
    chunks = self.iterencode(o, _one_shot=True)
/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py:257: in iterencode
    return _iterencode(o, 0)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <json.encoder.JSONEncoder object at 0x1109da6a0>
o = b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00...00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

    def default(self, o):
        """Implement this method in a subclass such that it returns
            a serializable object for ``o``, or calls the base implementation
            (to raise a ``TypeError``).

            For example, to support arbitrary iterators, you could
            implement default like this::

                def default(self, o):
                    try:
                        iterable = iter(o)
                    except TypeError:
                        pass
                    else:
                        return list(iterable)
                    # Let the base class default method raise the TypeError
                    return JSONEncoder.default(self, o)

            """
        raise TypeError("Object of type '%s' is not JSON serializable" %
>                       o.__class__.__name__)
E       TypeError: Object of type 'bytes' is not JSON serializable

/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py:180: TypeError

FYI: I can properly send binary data from the JS level but I cannot manage Flask-SocketIO itself to be used during testing.

Does anybody managed to workaround this issue somehow or tried to resolve this bug? Maybe am I using it wrong?

[miguelgrinberg]

I'll look into it, seems like it was an oversight on my part.

[jpowie01]

Did you find out where the root cause of this issue is? I've tried to fix it on myself but I don’t have enough knowledge about this library, so I failed :(

Let me know if I could help somehow as this is blocking tests on my project.

[miguelgrinberg]

@jpowie01 Can I ask you to retest your application with the master branch in this repo? I think binary packets should work now.

[jpowie01]

Thank you very much for such quick help :) It works properly!

But I've got another concern. I've used Test Client like above:

web_socket_client = web_socket.test_client(app)
...
image = open('example_file.dcm', 'rb')
binary_data = image.read()
web_socket_client.emit('my_event', {'ref_id': 123, 'image': binary_data}, namespace='/my_namespace')
assert web_socket_client.get_received(namespace='/my_namespace')

... and it failed. I've checked the queue inside of the Test Client and it was empty:

>>> print(web_socket_client.queue)
{'a40cc08de24348c9a0acc957cf9a7da4': []}

But the logs show me that some message has been sent:

------------------------------------------------ Captured stderr call ------------------------------------------------
received event "my_event" from a40cc08de24348c9a0acc957cf9a7da4 [/my_namespace]
emitting event "my_response" to a40cc08de24348c9a0acc957cf9a7da4 [/my_namespace]

Code used for handling such event looks like this:

class MyEventNamespace(Namespace):
    def on_my_event(self, request: Dict) -> None:
        ...
        emit('my_response', {'data': some_data})
web_socket.on_namespace(MyEventNamespace('/my_namespace'))

My solution to this problem was to change the client to work on a specific namespace like this:

web_socket_client = web_socket.test_client(app, namespace='/my_namespace')

...and it works! I've received this message and I could find it on the queue.

Do I have to create Test Client for each of my namespaces? Or is it another bug? Maybe is it a proper behaviour? Could you expain what happened here?

[miguelgrinberg]

Yes, you have to think of the test client in the same way you use a real client. When you create the test client, it "connects" to the server, using the namespace provided. In the most common case the arguments that you pass to the test_client() function are passed directly to connect(), so you definitely need to pass the namespace there.

As a side note, you can call connect() directly if you want, even call it multiple times to connect multiple namespaces.

[jpowie01]

Cool! Thanks for help :)