simonw/server_sent_events.py

## server_sent_events.py
import asyncio
from pprint import pprint


async def app(scope, receive, send):
    if scope["type"] == "http":
        if scope["path"] == "/":
            await homepage(send)
        elif scope["path"] == "/subscribe":
            await subscribe(scope, send)


async def homepage(send):
    await send(
        {
            "type": "http.response.start",
            "status": 200,
            "headers": [
                [b"content-type", b"text/html"],
            ],
        }
    )
    await send(
        {
            "type": "http.response.body",
            "body": b"""
        <html>
            <head>
                <title>Subscribe Endpoint Demonstration</title>
                <script>
                    let eventSource;
                    function start() {
                        const id = 1234;
                        eventSource = new EventSource(`/subscribe?id=${id}`);
                        eventSource.onmessage = function (event) {
                            const para = document.createElement("p");
                            para.innerText = event.data;
                            document.body.appendChild(para);
                        };
                    }
                    function stop() {
                        eventSource.close();
                    }
                </script>
            </head>
            <body>
                <button onclick="start()">Start</button>
                <button onclick="stop()">Stop</button>
            </body>
        </html>
        """,
        }
    )


async def subscribe(scope, send):
    pprint(scope)
    last_event_id = next(
        (value for key, value in scope["headers"] if key == b"last-event-id"), b"0"
    ).decode()
    id = int(scope["query_string"].decode().split("=")[1])
    start = id if last_event_id == "0" else int(last_event_id)
    await send(
        {
            "type": "http.response.start",
            "status": 200,
            "headers": [
                [b"content-type", b"text/event-stream"],
            ],
        }
    )
    for i in range(start, start + 10):
        await send(
            {
                "type": "http.response.body",
                "body": f"id: {i}\ndata: {i}\n\n".encode(),
                "more_body": True,
            }
        )
        await asyncio.sleep(1)
    await send(
        {
            "type": "http.response.body",
            "body": b"",
        }
    )


if __name__ == "__main__":
    import uvicorn

    uvicorn.run(app, host="0.0.0.0", port=8000)
	import asyncio
	from pprint import pprint


	async def app(scope, receive, send):
	if scope["type"] == "http":
	if scope["path"] == "/":
	await homepage(send)
	elif scope["path"] == "/subscribe":
	await subscribe(scope, send)


	async def homepage(send):
	await send(
	{
	"type": "http.response.start",
	"status": 200,
	"headers": [
	[b"content-type", b"text/html"],
	],
	}
	)
	await send(
	{
	"type": "http.response.body",
	"body": b"""
	<html>
	<head>
	<title>Subscribe Endpoint Demonstration</title>
	<script>
	let eventSource;
	function start() {
	const id = 1234;
	eventSource = new EventSource(`/subscribe?id=${id}`);
	eventSource.onmessage = function (event) {
	const para = document.createElement("p");
	para.innerText = event.data;
	document.body.appendChild(para);
	};
	}
	function stop() {
	eventSource.close();
	}
	</script>
	</head>
	<body>
	<button onclick="start()">Start</button>
	<button onclick="stop()">Stop</button>
	</body>
	</html>
	""",
	}
	)


	async def subscribe(scope, send):
	pprint(scope)
	last_event_id = next(
	(value for key, value in scope["headers"] if key == b"last-event-id"), b"0"
	).decode()
	id = int(scope["query_string"].decode().split("=")[1])
	start = id if last_event_id == "0" else int(last_event_id)
	await send(
	{
	"type": "http.response.start",
	"status": 200,
	"headers": [
	[b"content-type", b"text/event-stream"],
	],
	}
	)
	for i in range(start, start + 10):
	await send(
	{
	"type": "http.response.body",
	"body": f"id: {i}\ndata: {i}\n\n".encode(),
	"more_body": True,
	}
	)
	await asyncio.sleep(1)
	await send(
	{
	"type": "http.response.body",
	"body": b"",
	}
	)


	if __name__ == "__main__":
	import uvicorn

	uvicorn.run(app, host="0.0.0.0", port=8000)