Error with send_json Function in AsyncJsonWebsocketConsumer

[gaurav-jo1]

Environment Details: Operating System: Ubuntu 24.04 LTS Browser: Google Chrome Django version: 5.0.4 Channels version: 4.1.0

pip freeze output:

asgiref==3.8.1 asyncpg==0.29.0 attrs==23.2.0 autobahn==23.6.2 Automat==22.10.0 cffi==1.16.0 channels==4.1.0 channels-redis==4.2.0 constantly==23.10.4 cryptography==42.0.5 daphne==4.1.2 Django==5.0.4 django-cors-headers==4.3.1 django-redis==5.4.0 djangorestframework==3.15.1 djangorestframework-simplejwt==5.3.1 hyperlink==21.0.0 idna==3.7 incremental==22.10.0 msgpack==1.0.8 psycopg2-binary==2.9.9 pyasn1==0.6.0 pyasn1_modules==0.4.0 pycparser==2.22 PyJWT==2.8.0 pyOpenSSL==24.1.0 python-dotenv==1.0.1 redis==5.0.3 service-identity==24.1.0 setuptools==69.5.1 six==1.16.0 sqlparse==0.5.0 Twisted==24.3.0 txaio==23.1.1 typing_extensions==4.11.0 whitenoise==6.6.0 zope.interface==6.3

---

Expected Behavior:

I anticipated that upon establishing a connection using AsyncJsonWebsocketConsumer, a "welcome message" would be successfully sent to the client side, similar to the behavior observed with JsonWebsocketConsumer.

Expected Behavior Code using JsonWebsocketConsumer:

Expected Response:

Actual Behavior:

I anticipated that upon establishing a connection using AsyncJsonWebsocketConsumer, a "welcome message" would be successfully sent to the client side, similar to the behavior observed with JsonWebsocketConsumer.

Actual Behavior Code:

Error Encountered: The error encountered is as follows:

---

• I am using the command daphne to start the ASGI development server. Upon execution, the server starts successfully and listens for incoming connections at http://127.0.0.1:8000/.

[gaurav-jo1]

After examining the code within the parent class (AsyncJsonWebsocketConsumer), I noticed that the encoding process for the content using json.dumps(content) was utilizing the await keyword. However, I found that removing the await and simply using json.dumps resolved the error. This adjustment allowed the "welcome message" to be sent successfully to the client side without encountering any error.

[carltongibson]

The encode_json method is unchanged since it was introduced:

https://github.com/django/channels/commit/de82aaa660e85af6d1945b445bb6ade4896e2f50#diff-8adaf2e6e01ec2cc05dd10bfd212d6dddfadabe0ddc679b821e03024806647b7R254-R256

    @classmethod
     async def encode_json(cls, content):
         return json.dumps(content)

[gaurav-jo1]

encode_json is defined as an async function, but it uses json.dumps which is a synchronous function.

Error explanation:

When we call await self.encode_json(content), it treats the return value of json.dumps(content) as a coroutine, but since json.dumps returns a string synchronously, it raises the TypeError.

Here is the error message:

If I am misunderstanding something, please let me know.

[carltongibson]

It looks like you've overridden a method maybe and forgotten an async.

Please post code rather than screenshots.

The async send_json method is covered by the test suite. If you could add a test demonstrating your issue, that would help to identify what you're seeing.

[gaurav-jo1]

chats/consumers.py

class ChatConsumer(AsyncJsonWebsocketConsumer):
    async def connect(self):
        # Accept the connection
        await self.accept()

        # Send a welcome message
        await self.send_json(
            {
                "type": "welcome_message",
                "message": "Welcome to the Websocket Connection",
            }
        )

The error traceback is as follows:

python3.12/site-packages/channels/generic/websocket.py", line 282, in send_json
    await super().send(text_data=await self.encode_json(content), close=close)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: object str can't be used in 'await' expression

The full chats/consumers.py file can be found here: ChatConsumer file.

Here is a video demo of the error.

Screencast from 2024-05-20 17-22-47.webm

[carltongibson]

Compare your class:

https://github.com/DevGauravJoshi/python_async/blob/eb0cfb1894fcaaa1aaeed245a032ff1c6ecd40c3/backend/chats/consumers.py#L180-L182

to the base class:

https://github.com/django/channels/blob/42deaca0e25f5dbb6c5133dc969366b93526960f/channels/generic/websocket.py#L288-L290

By overriding this method without using the async keyword, the await call at the error point is receiving a string, rather than a coroutine object. You want to pass UUIDEncoder, but you still need to declare the method async def.