channels_api 0.2.3

Helps build a RESTful API on top of WebSockets using channels.

Channels API

Channels API exposes a RESTful Streaming API over WebSockets using channels. It provides a ResourceBinding which is comparable to Django Rest Framework’s ModelViewSet. It is based on DRF serializer classes.

It requires Python 3, Django 1.8, and Django Rest Framework 3.0

Table of Contents

• Getting Started

• ResourceBinding

• Subscriptions

• Errors

• Roadmap

How does it work?

The API builds on top of channels’ WebsocketBinding class. It works by having the client send a stream and payload parameters. This allows us to route messages to different streams (or resources) for a particular action. So POST /user would have a message that looks like the following

var msg = {
  stream: "users",
  payload: {
    action: "create",
    data: {
      email: "[e-mail]",
      password: "password",
    }
  }
}

ws.send(JSON.stringify(msg))

Why?

You’re already using Django Rest Framework and want to expose similar logic over WebSockets.

WebSockets can publish updates to clients without a request. This is helpful when a resource can be edited by multiple users across many platforms.

Getting Started

This tutorial assumes you’re familiar with channels and have completed the Getting Started

• Add channels_api to requirements.txt

pip install channels_api

• Add channels_api to INSTALLED_APPS

INSTALLED_APPS = (
    'rest_framework',
    'channels',
    'channels_api'
)

• Add a WebsocketDemultiplexer to your channel_routing

# proj/routing.py


from channels.generic.websockets import WebsocketDemultiplexer
from channels.routing import route_class

class APIDemultiplexer(WebsocketDemultiplexer):

    mapping = {
      'questions': 'questions_channel'
    }

channel_routing = [
    route_class(APIDemultiplexer)
]

• Add your first resource binding

# polls/bindings.py

from channels_api.bindings import ResourceBinding

from .models import Question
from .serializers import QuestionSerializer

class QuestionBinding(ResourceBinding):

    model = Question
    stream = "questions"
    serializer_class = QuestionSerializer
    queryset = Question.objects.all()


# proj/routing.py

from channels.routing import route_class, route

from polls.bindings import QuestionBinding

channel_routing = [
  route_class(APIDemultiplexer),
  route("question_channel", QuestionBinding.consumer)
]

That’s it. You can now make REST WebSocket requests to the server.

var ws = new WebSocket("ws://" + window.location.host + "/")

ws.onmessage = function(e){
    console.log(e.data)
}

var msg = {
  stream: "questions",
  payload: {
    action: "create",
    data: {
      question_text: "What is your favorite python package?"
    },
    request_id: "some-guid"
  }
}
ws.send(JSON.stringify(msg))
// response
{
  stream: "questions",
  payload: {
    action: "create",
    data: {
      id: "1",
      question_text: "What is your favorite python package"
    }
    errors: [],
    response_status: 200
    request_id: "some-guid"
  }
}

• Add the channels debugger page (Optional)

This page is helpful to debug API requests from the browser and see the response. It is only designed to be used when DEBUG=TRUE.

# proj/urls.py

from django.conf.urls import include

    urlpatterns = [
        url(r'^channels-api/', include('channels_api.urls'))
    ]

ResourceBinding

By default the ResourceBinding implements the following REST methods:

• create

• retrieve

• update

• list

• delete

• subscribe

See the test suite for usage examples for each method.

List Pagination

Pagination is handled by django.core.paginator.Paginator

You can configure the DEFAULT_PAGE_SIZE by overriding the settings.

# settings.py

CHANNELS_API = {
  'DEFAULT_PAGE_SIZE': 25
}

Subscriptions

Subscriptions are a way to programmatically receive updates from the server whenever a resource is created, updated, or deleted

By default channels-api has implemented the following subscriptions

• create a Resource

• update any Resource

• update this Resource

• delete any Resource

• delete this Resource

To subscribe to a particular event just use the subscribe action with the parameters to filter

// get an event when any question is updated

var msg = {
  stream: "questions",
  payload: {
    action: "subscribe",
    data: {
      action: "update"
    }
  }
}

// get an event when question(1) is updated
var msg = {
  stream: "questions",
  payload: {
    action: "subscribe"
    data: {
      action: "update",
      pk: "1"
    }
  }
}

Roadmap

• 0.3

  • Permissions

  • Custom Methods

  • Test Project