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RESTful API for WebSockets using django channels.

Project description

Django Channels Rest Framework provides a DRF like interface for building channels-v3 websocket consumers.

This project can be used alongside HyperMediaChannels and ChannelsMultiplexer to create a Hyper Media Style api over websockets. However Django Channels Rest Framework is also a free standing framework with the goal of providing an api that is familiar to DRF users.

theY4Kman has developed a useful Javascript client library dcrf-client to use with DCRF.

Thanks to

DCRF is based of a fork of Channels Api and of course inspired by Django Rest Framework.

Documentation

ReadTheDocs

Install

pip install djangochannelsrestframework

A Generic Api Consumer

In DCRF you can create a GenericAsyncAPIConsumer that works much like a GenericAPIView in DRF: For a more indepth look into Rest-Like Websocket consumers read this blog post.

from . import models
from . import serializers
from djangochannelsrestframework import permissions
from djangochannelsrestframework.generics import GenericAsyncAPIConsumer
from djangochannelsrestframework.mixins import (
    ListModelMixin,
    PatchModelMixin,
    UpdateModelMixin,
    CreateModelMixin,
    DeleteModelMixin,
)

class LiveConsumer(ListModelMixin, GenericAsyncAPIConsumer):
    queryset = models.Test.objects.all()
    serializer_class = serializers.TestSerializer
    permission_classes = (permissions.IsAuthenticated,)

Because this class uses the ListModelMixin, one has access to the list action.

One may use the same exact querysets and serializer_class utilized in their DRF Views, but must omit the DRF permissions. Permissions are to be imported from djangochannelsrestframework, which provides the standard AllowAny and IsAuthenticated permissions.

To call an action from the client send a websocket message: {action: "list", "request_id": 42}

There are a selection of mixins that expose the common CRUD actions:

  • ListModelMixin - list

  • PatchModelMixin - patch

  • CreateModelMixin - create

  • RetrieveModelMixin - retrieve

  • UpdateModelMixin - update

  • DeleteModelMixin - delete

Observing a Model instance

Consumer that let you subscribe to changes on an instance:

class TestConsumer(ObserverModelInstanceMixin, GenericAsyncAPIConsumer):
    queryset = get_user_model().objects.all()
    serializer_class = UserSerializer

this exposes the retrieve, subscribe_instance and unsubscribe_instance actions.

To subscribe send:

{
    "action": "subscribe_instance",
    "pk": 42,  # the id of the instance you are subscribing to
    "request_id": 4  # this id will be used for all result updates.
}

Actions will be sent down out from the server:

{
  "action": "update",
  "errors": [],
  "response_status": 200,
  "request_id": 4,
  "data": {'email': '42@example.com', 'id': 42, 'username': 'thenewname'},
}

Adding Custom actions

class UserConsumer(GenericAsyncAPIConsumer):
    queryset = get_user_model().objects.all()
    serializer_class = UserSerializer

    @action()
    async def send_email(self, pk=None, to=None, **kwargs):
        user = await database_sync_to_async(self.get_object)(pk=pk)
        # ... do some stuff
        # remember to wrap all db actions in `database_sync_to_async`
        return {}, 200  # return the context and the response code.

    @action()  # if the method is not async it is already wrapped in `database_sync_to_async`
    def publish(self, pk=None, **kwargs):
        user = self.get_object(pk=pk)
        # ...
        return {'pk': pk}, 200

Consumers that are not bound to Models

You can also create consumers that are not at all related to any models.

from djangochannelsrestframework.decorators import action
from djangochannelsrestframework.consumers import AsyncAPIConsumer


class MyConsumer(AsyncAPIConsumer):

    @action()
    async def an_async_action(self, some=None, **kwargs):
        # do something async
        return {'response with': 'some message'}, 200

    @action()
    def a_sync_action(self, pk=None, **kwargs):
        # do something sync
        return {'response with': 'some message'}, 200

Using your normal views over a websocket connection

from djangochannelsrestframework.consumers import view_as_consumer

application = ProtocolTypeRouter({
    "websocket": AuthMiddlewareStack(
        URLRouter([
            url(r"^front(end)/$", view_as_consumer(YourDjangoView)),
        ])
    ),
 })

In this situation if your view needs to read the GET query string values you can provides these using the query option. And if the view method reads parameters from the URL you can provides these with the parameters.

Sending the following over your WS connection will result in a GET request being evaluated on your View.

{
  action: "retrieve",
  query: {"user_id": 42}
  parameters: {"project_id": 92}
}

Subscribing to a signal.

One can subscribe to a custom Signal utilizing the observer decorator.

Here we have a custom signal that will be triggered when a user join a chat.

# signals.py
from django.dispatch.dispatcher import Signal

joined_chat_signal = Signal()

Now we will create the consumer with two actions, one for subscribing to our custom signal for specific chat, and another one for manually trigger the signal.

# consumers.py
from djangochannelsrestframework.consumers import AsyncAPIConsumer
from djangochannelsrestframework.decorators import action
from djangochannelsrestframework.observer import observer
from rest_framework import status
from .signals import joined_chat_signal
from .serializers import UserSerializer


class TestConsumer(AsyncAPIConsumer):

    @action()
    def join_chat(self, chat_id, **kwargs):
        serializer = UserSerializer(instance=self.scope['user'])
        joined_chat_signal.send(sender='join_chat', data=serializer.data, **kwargs)
        return {}, status.HTTP_204_NO_CONTENT

    @observer(signal=joined_chat_signal)
    async def joined_chat_handler(self, data, observer=None, action=None, subscribing_request_ids=[], **kwargs):
        for request_id in subscribing_request_ids:
            await self.reply(action='joined_chat', data=data, status=status.HTTP_200_OK, request_id=request_id)

    @joined_chat_handler.serializer
    def join_chat_handler(self, sender, data, **kwargs): # the data comes from the signal.send and will be available in the observer
        return data

    @joined_chat_handler.groups_for_signal
    def joined_chat_handler(self, instance, **kwargs):
        yield f'chat__{instance}'

    @joined_chat_handler.groups_for_consumer
    def joined_chat_handler(self, chat, **kwargs):
        if chat:
            yield f'chat__{chat}'

    @action()
    async def subscribe_joined(self, chat_id, request_id, **kwargs):
        await self.joined_chat_handler.subscribe(chat_id, request_id=request_id)

Subscribing to all instances of a model

One can subscribe to all instances of a model by utilizing the model_observer.

from djangochannelsrestframework.observer import model_observer

@model_observer(models.Test)
async def model_activity(self, message, observer=None, action=None, **kwargs):
    # send activity to your frontend
    await self.send_json(message)

This method will send messages to the client on all CRUD operations made through the Django ORM. The action arg here it will take values such as create, delete and update you should consider passing this to your frontend client.

Note: These notifications do not include bulk updates, such as models.Test.objects.filter(name="abc").update(name="newname")

WARNING When using this to decorate a method to avoid the method firing multiple times you should ensure that if there are multiple @model_observer wrapped methods for the same model type within a single file that each method has a different name.

Subscribing to a model_observer

You can do this in a few placed, a common example is in the websocket_connect method.

async def websocket_connect(self, message):

    # Super Save
    await super().websocket_connect(message)

    # Initialized operation
    await self.activities_change.subscribe()

This method utilizes the previously mentioned model_activity method to subscribe to all instances of the current Consumer’s model.

One can also subscribe by creating a custom action

Another way is override AsyncAPIConsumer.accept(self, **kwargs)

class ModelConsumerObserver(AsyncAPIConsumer):

    async def accept(self, **kwargs):
        await super().accept(** kwargs)
        await self.model_change.subscribe()

    @model_observer(models.Test)
    async def model_change(self, message, action=None, **kwargs):
        """
        This method is evaluated once for every user that subscribed,
        here you have access to info about the user by reading `self.scope`

        However it is best to avoid doing DB quires here since if you have lots of
        subscribers to a given instance you will end up with a LOT of database traffic.
        """
        await self.send_json(message)

    # If you want the data serialized instead of pk
    @model_change.serializer
    def model_serialize(self, instance, action, **kwargs):
        """
        This block is evaluated before the data is sent over the channel layer
        this means you are unable to access information
        such as the user that it will be sent to.

        If you need the user info when serializing then you can do the serialization
        in the above method.
        """
        return TestSerializer(instance).data
class ModelConsumerObserver(AsyncAPIConsumer):

    async def accept(self, **kwargs):
        await super().accept(** kwargs)
        await self.model_change.subscribe()

    @model_observer(models.Test, serializer_class=TestSerializer)
    async def model_change(self, message, action=None, **kwargs):
        # in this case since we subscribe int he `accept` method
        # we do not expect to have any `subscribing_request_ids` to loop over.
        await self.reply(data=message, action=action)

Subscribing to a filtered list of models

In most situations you want to filter the set of models that you subscribe to.

To do this we need to split the model updates into groups and then in the consumer subscribe to the groups that we want/have permission to see.

class MyConsumer(AsyncAPIConsumer):
  # This class MUST subclass `AsyncAPIConsumer` to use `@model_observer`

  @model_observer(models.Classroom)
  async def classroom_change_handler(
      self,
      message,
      observer=None,
      action=None,
      subscribing_request_ids=[],
      **kwargs
  ):
      # due to not being able to make DB QUERIES when selecting a group
      # maybe do an extra check here to be sure the user has permission
      # send activity to your frontend
      for request_id in subscribing_request_ids:
          # we can send a seperate message for each subscribing request
          # this lets ws clients rout these messages.
          await self.send_json(dict(body=message, action=action, request_id=request_id))
      # note if we do not pass `request_id` to the `subscribe` method
      # then `subscribing_request_ids` will be and empty list.

  @classroom_change_handler.groups_for_signal
  def classroom_change_handler(self, instance: models.Classroom, **kwargs):
      # this block of code is called very often *DO NOT make DB QUERIES HERE*
      yield f'-school__{instance.school_id}'
      yield f'-pk__{instance.pk}'

  @classroom_change_handler.groups_for_consumer
  def classroom_change_handler(self, school=None, classroom=None, **kwargs):
      # This is called when you subscribe/unsubscribe
      if school is not None:
          yield f'-school__{school.pk}'
      if classroom is not None:
          yield f'-pk__{classroom.pk}'

  @action()
  async def subscribe_to_classrooms_in_school(self, school_pk, request_id, **kwargs):
      # check user has permission to do this
      await self.classroom_change_handler.subscribe(school=school, request_id=request_id)

  @action()
  async def subscribe_to_classroom(self, classroom_pk, request_id, **kwargs):
      # check user has permission to do this
      await self.classroom_change_handler.subscribe(classroom=classroom, request_id=request_id)

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