Upd.

content/django-server-sent-events.md

@@ -330,6 +330,56 @@ And that's it! We can now open two browser windows and see the messages appear i
 
 Check out the repo for the full code where I've also added a simple form for submitting new messages.
 
+### Dealing with reconnections
+
+One of the nice things about SSE is that it will automatically reconnect if the connection is lost. It even has a
+mechanism for dealing with the fact that the client might have missed some events while it was disconnected.
+
+This is done by sending a `Last-Event-ID` header with the request. The value of this header is the `id` of the last
+event that the client received. The server can then use this to determine which events to send to the client.
+
+To deal with this we can expand on our `stream_messages` function and view as follows:
+
+    :::python
+    async def stream_messages(last_id: int | None = None) -> AsyncGenerator[str, None]:
+        connection_params = connection.get_connection_params()
+        connection_params.pop('cursor_factory')
+        aconnection = await psycopg.AsyncConnection.connect(
+            **connection_params,
+            autocommit=True,
+        )
+        channel_name = "lobby"
+
+        if last_id:
+            messages = ChatMessage.objects.filter(id__gt=last_id)
+            async for message in messages:
+                yield f"id: {message.id}\nevent: message_created\ndata: {message.as_json()}\n\n"
+
+        async with aconnection.cursor() as acursor:
+            await acursor.execute(f"LISTEN {channel_name}")
+            gen = aconnection.notifies()
+            async for notify in gen:
+                payload = json.loads(notify.payload)
+                event = payload.get("event")
+                event_id = payload.get("event_id")
+                data = payload.get("data")
+                yield f"id: {event_id}\nevent: {event}\ndata: {data}\n\n"
+
+
+    async def stream_messages_view(
+        request: HttpRequest,
+    ) -> StreamingHttpResponse:
+        last_id = request.headers.get("Last-Event-ID")
+        return StreamingHttpResponse(
+            streaming_content=stream_messages(last_id=last_id),
+            content_type="text/event-stream",
+        )
+
+We now send the `id` of each message, and whenever a (re)connection is made we check if the client sent a `Last-Event-ID`
+and if so we send all messages with an `id` greater than that.
+
+This change does also require some changes to our utility functions and model. Those are to be found in the git repo.
+
 ### Conclusion
 
 Django is boring, which is a good thing, to the degree where it is always the safe option. But with the advances in