Server-Sent Events

Compatibility	CPython & MicroPython
Required Microdot source files	sse.py helpers.py
Required external dependencies	None
Examples	counter.py

The Server-Sent Events (SSE) extension simplifies the creation of a streaming endpoint that follows the SSE web standard. The with_sse decorator is used to mark a route as an SSE handler. Decorated routes receive an SSE object as second argument. The SSE object provides a send() asynchronous method to send an event to the client.

Example:

from microdot.sse import with_sse

@app.route('/events')
@with_sse
async def events(request, sse):
    for i in range(10):
        await asyncio.sleep(1)
        await sse.send({'counter': i})  # unnamed event
    await sse.send('end', event='comment')  # named event

To end the SSE connection, the route handler can exit, without returning anything, as shown in the above examples.

If the client ends the SSE connection from their side, the route function is cancelled. The route function can catch the CancelledError exception from asyncio to perform cleanup tasks:

@app.route('/events')
@with_sse
async def events(request, sse):
    try:
        i = 0
        while True:
            await asyncio.sleep(1)
            await sse.send({'counter': i})
            i += 1
    except asyncio.CancelledError:
        print('Client disconnected!')

Note

The SSE protocol is unidirectional, so there is no receive() method in the SSE object. For bidirectional communication with the client, use the WebSocket extension.