Implementing simple Server Sent Event Stream with Django Channels - django

Question

Django Channels docs has following basic example of a Server Sent Events. AsyncHttpConsumer
from datetime import datetime
from channels.generic.http import AsyncHttpConsumer
class ServerSentEventsConsumer(AsyncHttpConsumer):
async def handle(self, body):
await self.send_headers(headers=[
(b"Cache-Control", b"no-cache"),
(b"Content-Type", b"text/event-stream"),
(b"Transfer-Encoding", b"chunked"),
])
while True:
payload = "data: %s\n\n" % datetime.now().isoformat()
await self.send_body(payload.encode("utf-8"), more_body=True)
await asyncio.sleep(1)
I want to accept messages sent via channel_layer and send them as events.
I changed the handle method, so it subscribes the new channel to a group. And I'm planning to send messages to the channel layer via channel_layer.group_send
But I couldn't figure out how to get the messages sent to the group, within handle method. I tried awaiting for the channel_layer.receive, it doesn't seem to work.
class ServerSentEventsConsumer(AsyncHttpConsumer):
group_name = 'my_message_group'
async def myevent(self, event):
# according to the docs, this method will be called \
# when a group received a message with type 'myevent'
# I'm not sure how to get this event within `handle` method's while loop.
pass
async def handle(self, body):
await self.channel_layer.group_add(
self.group_name,
self.channel_name
)
await self.send_headers(headers=[
(b"Cache-Control", b"no-cache"),
(b"Content-Type", b"text/event-stream"),
(b"Transfer-Encoding", b"chunked"),
])
while True:
payload = "data: %s\n\n" % datetime.now().isoformat()
result = await self.channel_receive()
payload = "data: %s\n\n" % 'received'
I'm sending the messages to channel_layer like below: ( from a management command)
def send_event(event_data):
group_name = 'my_message_group'
channel_layer = get_channel_layer()
async_to_sync(channel_layer.group_send)(
group_name,
{
'type': 'myevent',
'data': [event_data]
}
)

Answer 1

I had the same issue and I even went to dig into Django Channels code but without success.
... Until I found this answer in this (still opened) issue: https://github.com/django/channels/issues/1302#issuecomment-508896846
That should solve your issue.
In your case the code would be (or something quite similar):
class ServerSentEventsConsumer(AsyncHttpConsumer):
group_name = 'my_message_group'
async def http_request(self, message):
if "body" in message:
self.body.append(message["body"])
if not message.get("more_body"):
await self.handle(b"".join(self.body))
async def myevent(self, event):
# according to the docs, this method will be called \
# when a group received a message with type 'myevent'
# I'm not sure how to get this event within `handle` method's while loop.
pass
async def handle(self, body):
await self.channel_layer.group_add(
self.group_name,
self.channel_name
)
await self.send_headers(headers=[
(b"Cache-Control", b"no-cache"),
(b"Content-Type", b"text/event-stream"),
(b"Transfer-Encoding", b"chunked"),
])