Switch to settings-based backend list, start ORM backend

channels/__init__.py

@@ -1,12 +1,18 @@
-from .channel import Channel
-
-# Load a backend
-from .backends.memory import InMemoryChannelBackend
-DEFAULT_CHANNEL_LAYER = "default"
-channel_layers = {
-    DEFAULT_CHANNEL_LAYER: InMemoryChannelBackend(),
-}
+# Load backends
+DEFAULT_CHANNEL_BACKEND = "default"
+from .backends import BackendManager
+from django.conf import settings
+channel_backends = BackendManager(
+    getattr(settings, "CHANNEL_BACKENDS", {
+        DEFAULT_CHANNEL_BACKEND: {
+            "BACKEND": "channels.backends.memory.InMemoryChannelBackend",
+        }
+    })
+)
 
 # Ensure monkeypatching
 from .hacks import monkeypatch_django
 monkeypatch_django()
+
+# Promote channel to top-level (down here to avoid circular import errs)
+from .channel import Channel

channels/adapters.py

@@ -3,7 +3,7 @@ import functools
 from django.core.handlers.base import BaseHandler
 from django.http import HttpRequest, HttpResponse
 
-from channels import Channel, channel_layers, DEFAULT_CHANNEL_LAYER
+from channels import Channel, channel_backends, DEFAULT_CHANNEL_BACKEND
 
 
 class UrlConsumer(object):
@@ -35,7 +35,7 @@ def view_producer(channel_name):
     return producing_view
 
 
-def view_consumer(channel_name, alias=None):
+def view_consumer(channel_name, alias=DEFAULT_CHANNEL_BACKEND):
     """
     Decorates a normal Django view to be a channel consumer.
     Does not run any middleware
@@ -47,7 +47,7 @@ def view_consumer(channel_name, alias=None):
             response = func(request)
             Channel(request.response_channel).send(**response.channel_encode())
         # Get the channel layer and register
-        channel_layer = channel_layers[alias or DEFAULT_CHANNEL_LAYER]
+        channel_layer = channel_backends[DEFAULT_CHANNEL_BACKEND]
         channel_layer.registry.add_consumer(consumer, [channel_name])
         return func
     return inner

channels/backends/__init__.py

@@ -0,0 +1,27 @@
+from django.utils.module_loading import import_string
+
+
+class InvalidChannelBackendError(ValueError):
+    pass
+
+
+class BackendManager(object):
+    """
+    Takes a settings dictionary of backends and initialises them.
+    """
+
+    def __init__(self, backend_configs):
+        self.backends = {}
+        for name, config in backend_configs.items():
+            # Load the backend class
+            try:
+                backend_class = import_string(config['BACKEND'])
+            except KeyError:
+                raise InvalidChannelBackendError("No BACKEND specified for %s" % name)
+            except ImportError:
+                raise InvalidChannelBackendError("Cannot import BACKEND %s specified for %s" % (config['BACKEND'], name))
+            # Initialise and pass config
+            self.backends[name] = backend_class(**{k.lower(): v for k, v in config.items() if k != "BACKEND"})
+
+    def __getitem__(self, key):
+        return self.backends[key]

channels/backends/memory.py

@@ -1,6 +1,5 @@
 import time
-import string
-import random
+import json
 from collections import deque
 from .base import BaseChannelBackend
 
@@ -13,6 +12,8 @@ class InMemoryChannelBackend(BaseChannelBackend):
     """
 
     def send(self, channel, message):
+        # Try JSON encoding it to make sure it would, but store the native version
+        json.dumps(message)
         # Add to the deque, making it if needs be
         queues.setdefault(channel, deque()).append(message)
 

channels/backends/orm.py

@@ -0,0 +1,68 @@
+import time
+import datetime
+
+from django.apps.registry import Apps
+from django.db import models, connections, DEFAULT_DB_ALIAS
+
+from .base import BaseChannelBackend
+
+queues = {}
+
+class ORMChannelBackend(BaseChannelBackend):
+    """
+    ORM-backed channel environment. For development use only; it will span
+    multiple processes fine, but it's going to be pretty bad at throughput.
+    """
+
+    def __init__(self, expiry, db_alias=DEFAULT_DB_ALIAS):
+        super(ORMChannelBackend, self).__init__(expiry)
+        self.connection = connections[db_alias]
+        self.model = self.make_model()
+        self.ensure_schema()
+
+    def make_model(self):
+        """
+        Initialises a new model to store messages; not done as part of a
+        models.py as we don't want to make it for most installs.
+        """
+        class Message(models.Model):
+            # We assume an autoincrementing PK for message order
+            channel = models.CharField(max_length=200, db_index=True)
+            content = models.TextField()
+            expiry = models.DateTimeField(db_index=True)
+            class Meta:
+                apps = Apps()
+                app_label = "channels"
+                db_table = "django_channels"
+        return Message
+
+    def ensure_schema(self):
+        """
+        Ensures the table exists and has the correct schema.
+        """
+        # If the table's there, that's fine - we've never changed its schema
+        # in the codebase.
+        if self.model._meta.db_table in self.connection.introspection.table_names(self.connection.cursor()):
+            return
+        # Make the table
+        with self.connection.schema_editor() as editor:
+            editor.create_model(self.model)
+
+    def send(self, channel, message):
+        self.model.objects.create(
+            channel = channel,
+            message = json.dumps(message),
+            expiry = datetime.datetime.utcnow() + datetime.timedelta(seconds=self.expiry)
+        )
+
+    def receive_many(self, channels):
+        while True:
+            # Delete all expired messages (add 10 second grace period for clock sync)
+            self.model.objects.filter(expiry__lt=datetime.datetime.utcnow() - datetime.timedelta(seconds=10)).delete()
+            # Get a message from one of our channels
+            message = self.model.objects.filter(channel__in=channels).order_by("id").first()
+            if message:
+                return message.channel, json.loads(message.content)
+            # If all empty, sleep for a little bit
+            time.sleep(0.2)
+

channels/channel.py

@@ -3,6 +3,8 @@ import string
 
 from django.utils import six
 
+from channels import channel_backends, DEFAULT_CHANNEL_BACKEND
+
 
 class Channel(object):
     """
@@ -16,13 +18,12 @@ class Channel(object):
     "default" one by default.
     """
 
-    def __init__(self, name, alias=None):
+    def __init__(self, name, alias=DEFAULT_CHANNEL_BACKEND):
         """
         Create an instance for the channel named "name"
         """
-        from channels import channel_layers, DEFAULT_CHANNEL_LAYER
         self.name = name
-        self.channel_layer = channel_layers[alias or DEFAULT_CHANNEL_LAYER]
+        self.channel_layer = channel_backends[alias]
 
     def send(self, **kwargs):
         """
@@ -50,16 +51,15 @@ class Channel(object):
         return view_producer(self.name)
 
     @classmethod
-    def consumer(self, channels, alias=None):
+    def consumer(self, channels, alias=DEFAULT_CHANNEL_BACKEND):
         """
         Decorator that registers a function as a consumer.
         """
-        from channels import channel_layers, DEFAULT_CHANNEL_LAYER
         # Upconvert if you just pass in a string
         if isinstance(channels, six.string_types):
             channels = [channels]
         # Get the channel 
-        channel_layer = channel_layers[alias or DEFAULT_CHANNEL_LAYER]
+        channel_layer = channel_backends[alias]
         # Return a function that'll register whatever it wraps
         def inner(func):
             channel_layer.registry.add_consumer(func, channels)

channels/docs/message-standards.rst

@@ -8,6 +8,9 @@ Note: All consumers also receive the channel name as the keyword argument
 "channel", so there is no need for separate type information to let
 multi-channel consumers distinguish.
 
+The length limit on channel names will be 200 characters.
+
+
 HTTP Request
 ------------
 

channels/management/commands/runserver.py

@@ -3,7 +3,7 @@ import threading
 from django.core.management.commands.runserver import Command as RunserverCommand
 from django.core.handlers.wsgi import WSGIHandler
 from django.http import HttpResponse
-from channels import Channel, channel_layers, DEFAULT_CHANNEL_LAYER
+from channels import Channel, channel_backends, DEFAULT_CHANNEL_BACKEND
 from channels.worker import Worker
 from channels.utils import auto_import_consumers
 from channels.adapters import UrlConsumer
@@ -22,7 +22,7 @@ class Command(RunserverCommand):
         # Force disable reloader for now
         options['use_reloader'] = False
         # Check a handler is registered for http reqs
-        channel_layer = channel_layers[DEFAULT_CHANNEL_LAYER]
+        channel_layer = channel_backends[DEFAULT_CHANNEL_BACKEND]
         auto_import_consumers()
         if not channel_layer.registry.consumer_for_channel("django.wsgi.request"):
             # Register the default one
@@ -43,7 +43,7 @@ class WSGIInterfaceHandler(WSGIHandler):
     def get_response(self, request):
         request.response_channel = Channel.new_name("django.wsgi.response")
         Channel("django.wsgi.request").send(**request.channel_encode())
-        channel, message = channel_layers[DEFAULT_CHANNEL_LAYER].receive_many([request.response_channel])
+        channel, message = channel_backends[DEFAULT_CHANNEL_BACKEND].receive_many([request.response_channel])
         return HttpResponse.channel_decode(message)