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74 lines
2.6 KiB
Python
74 lines
2.6 KiB
Python
import time
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import json
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import datetime
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from django.apps.registry import Apps
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from django.db import models, connections, DEFAULT_DB_ALIAS
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from django.utils.functional import cached_property
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from django.utils.timezone import now
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from .base import BaseChannelBackend
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class DatabaseChannelBackend(BaseChannelBackend):
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"""
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ORM-backed channel environment. For development use only; it will span
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multiple processes fine, but it's going to be pretty bad at throughput.
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"""
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def __init__(self, expiry=60, db_alias=DEFAULT_DB_ALIAS):
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super(DatabaseChannelBackend, self).__init__(expiry)
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self.db_alias = db_alias
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@property
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def connection(self):
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"""
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Returns the correct connection for the current thread.
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"""
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return connections[self.db_alias]
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@property
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def model(self):
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"""
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Initialises a new model to store messages; not done as part of a
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models.py as we don't want to make it for most installs.
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"""
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# Make the model class
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class Message(models.Model):
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# We assume an autoincrementing PK for message order
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channel = models.CharField(max_length=200, db_index=True)
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content = models.TextField()
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expiry = models.DateTimeField(db_index=True)
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class Meta:
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apps = Apps()
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app_label = "channels"
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db_table = "django_channels"
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# Ensure its table exists
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if Message._meta.db_table not in self.connection.introspection.table_names(self.connection.cursor()):
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with self.connection.schema_editor() as editor:
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editor.create_model(Message)
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return Message
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def send(self, channel, message):
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self.model.objects.create(
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channel = channel,
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content = json.dumps(message),
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expiry = now() + datetime.timedelta(seconds=self.expiry)
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)
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def receive_many(self, channels):
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if not channels:
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raise ValueError("Cannot receive on empty channel list!")
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# Delete all expired messages (add 10 second grace period for clock sync)
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self.model.objects.filter(expiry__lt=now() - datetime.timedelta(seconds=10)).delete()
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# Get a message from one of our channels
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message = self.model.objects.filter(channel__in=channels).order_by("id").first()
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if message:
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self.model.objects.filter(pk=message.pk).delete()
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return message.channel, json.loads(message.content)
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else:
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return None, None
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def __str__(self):
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return "%s(alias=%s)" % (self.__class__.__name__, self.connection.alias)
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