content/django-server-sent-events.md

@@ -1,6 +1,6 @@
 Title: Server-Sent Events and PostgreSQL LISTEN/NOTIFY using Djangos StreamingHttpRequest
 Date: 2023-05-17
-Status: published
+Status: hidden
 Tags: django, sse, postgresql
 Slug: django-sse-postgresql-listen-notify
 Authors: Víðir Valberg Guðmundsson
@@ -79,8 +79,7 @@ the view is an async view, denoted by the `async` keyword.
         )
 
 We tell the `StreamingHttpResponse` class to get its streaming content from the
-`stream_messages` function. The following is my first initial implementation of 
-`stream_messages`:
+`stream_messages` function. I implemented this as follows initially:
 
     ::python
     async def stream_messages() -> AsyncGenerator[str, None]:
@@ -89,7 +88,7 @@ We tell the `StreamingHttpResponse` class to get its streaming content from the
         while True:
             current_message = await ChatMessage.objects.order_by("-id").afirst()
 
-            # If we have a new message yield that
+            # If we have a new foo yield that
             if latest_message != current_message:
                 yield "data: {current_message.text}\n\n"
                 latest_message = current_message
@@ -101,23 +100,23 @@ request from the client every 5 seconds. But we are still doing a query to the
 database every 5 seconds, and that for each client. This is not ideal and is 
 probably something we could have done with a synchronous view.
 
-Let's see if we can do better.
+Let's see if we can do better. But first we'll have to talk about how to run
+this code.
 
 ### More old tech to the rescue: PostgreSQL LISTEN/NOTIFY
 
 This is where we could reach for more infrastructure which could help us giving
 the database a break. This could be listening for data in Redis (this is what
 django-channels does), or even having a queue in RabbitMQ. No matter what, it
-is means more infrastructure.
+is more infrastructure.
 
 But I use PostgreSQL - and PostgreSQL is, like Django, "batteries included".
 
-PostgreSQL has a mechanism called "LISTEN/NOTIFY" where a client can `LISTEN` 
-to a "channel" and then other clients can `NOTIFY` on that same channel which
-will be broadcasted to all listeners .
+PostgreSQL has this mechanism called "LISTEN/NOTIFY" where one client can
+LISTEN to a channel and then anyone can NOTIFY on that same channel.
 
-This seems like something we can use, but the good ol' psycopg2 doesn't have async support, and I'm not
-even sure if `asgiref`'s `sync_to_async`[^3] would help us here.
+This seems like something we can use - but psycopg2 isn't async, so I'm not
+even sure if `sync_to_async` would help us here.
 
 #### Enter psycopg 3
 
@@ -125,7 +124,7 @@ I had put the whole thing on ice until I realized that another big thing (maybe
 a bit bigger than StreamingHttpResponse) in Django 4.2 is the support for
 psycopg 3 - and psycopg 3 is very much async!
 
-So I went for a stroll in the psycopg 3 documentation and struck gold[^4]:
+So I went for a stroll in the psycopg 3 documentation and found this gold[^3]:
 
     ::python
     import psycopg
@@ -142,14 +141,14 @@ This does almost what we want! It just isn't async and isn't getting connection
 info from Django.
 
 So by combining the snippet from the psycopg 3 documentation and my previous
-`stream_messages` I came up with this:
+`stream_foos` I came up with this:
 
     :::python
     from collections.abc import AsyncGenerator
     import psycopg
     from django.db import connection
 
-    async def stream_messages() -> AsyncGenerator[str, None]:
+    async def stream_foos() -> AsyncGenerator[str, None]:
 
         # Get the connection params from Django
         connection_params = connection.get_connection_params()
@@ -165,8 +164,7 @@ So by combining the snippet from the psycopg 3 documentation and my previous
             **connection_params,
             autocommit=True,
         )
-
-        channel_name = "lobby"
+        channel_name = "new_foo"
 
         async with aconnection.cursor() as acursor:
             await acursor.execute(f"LISTEN {channel_name}")
@@ -177,8 +175,6 @@ So by combining the snippet from the psycopg 3 documentation and my previous
 Appart from problems with the `cursor_factory` (which I'll get back to in the 
 [appendix](#difference-between-42-and-421)), this code is pretty straight forward and, most importantly, works!
 
-Whenever a `NOTIFY lobby, '<message>'` is issued, the `stream_messages` function
-will yield the message to the listener.
 
 ### Test the endpoint with curl
 
@@ -192,7 +188,7 @@ If we connect to the endpoint using curl (`-N` disables buffering and is a way t
 And connect to our database and run:
 
     :::sql
-    NOTIFY lobby, 'Hello, world!';
+    NOTIFY new_message, 'Hello, world!';
 
 
 We, excitingly, get the following result :
@@ -453,7 +449,7 @@ So that now looks like so:
             **connection_params,
             autocommit=True,
         )
-        channel_name = "lobby"
+        channel_name = "new_message"
         async with aconnection.cursor() as acursor:
             print(type(acursor))
             await acursor.execute(f"LISTEN {channel_name}")
@@ -462,8 +458,7 @@ So that now looks like so:
                 yield f"data: {notify.payload}\n\n"
 
 
-[^0]: <https://docs.djangoproject.com/en/4.2/releases/4.2/#requests-and-responses>
-[^1]: <https://docs.djangoproject.com/en/4.2/ref/request-response/#django.http.StreamingHttpResponse>
-[^2]: <https://caniuse.com/eventsource>
-[^3]: <https://docs.djangoproject.com/en/4.2/topics/async/#sync-to-async>
-[^4]: <https://www.psycopg.org/psycopg3/docs/advanced/async.html#index-4>
+[^0]: [https://docs.djangoproject.com/en/4.2/releases/4.2/#requests-and-responses]()
+[^1]: [https://docs.djangoproject.com/en/4.2/ref/request-response/#django.http.StreamingHttpResponse]()
+[^2]: [https://caniuse.com/eventsource]()
+[^3]: [https://www.psycopg.org/psycopg3/docs/advanced/async.html#index-4]()