sse-starlette 1.1.0

"SSE plugin for Starlette"

Server Sent Events for Starlette and FastAPI

Background: https://sysid.github.io/sse/

Installation:

pip install sse-starlette

Usage:

import asyncio
import uvicorn
from starlette.applications import Starlette
from starlette.routing import Route
from sse_starlette.sse import EventSourceResponse

async def numbers(minimum, maximum):
    for i in range(minimum, maximum + 1):
        await asyncio.sleep(0.9)
        yield dict(data=i)

async def sse(request):
    generator = numbers(1, 5)
    return EventSourceResponse(generator)

routes = [
    Route("/", endpoint=sse)
]

app = Starlette(debug=True, routes=routes)

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000, log_level='info')

Output:

Caveat: SSE streaming does not work in combination with GZipMiddleware.

Be aware that for proper server shutdown your application must stop all running tasks (generators). Otherwise you might experience the following warnings at shutdown: Waiting for background tasks to complete. (CTRL+C to force quit).

Client disconnects need to be handled in your Request handler (see example.py):

async def endless(req: Request):
    async def event_publisher():
        i = 0
        try:
          while True:
              i += 1
              yield dict(data=i)
              await asyncio.sleep(0.2)
        except asyncio.CancelledError as e:
          _log.info(f"Disconnected from client (via refresh/close) {req.client}")
          # Do any other cleanup, if any
          raise e
    return EventSourceResponse(event_publisher())

Run the tests:

make test

Special use cases

Fan out Proxies

Fan out proxies usually rely on response being cacheable. To support that, you can set the value of Cache-Control. For example:

return EventSourceResponse(
        generator(), headers={"Cache-Control": "public, max-age=29"}
    )

Changelog

1.1.0 (2022-07-25)

• allow user to set cache-control header for fan-out use-case: Ref: https://www.fastly.com/blog/server-sent-events-fastly

1.0.0 (2022-07-24)

• drop support for python 3.6 and 3.7
• removed unused private attribute _loop from class EventSourceResponse
• updated example in README.md

0.10.3 (2022-01-25)

• fix: use starlette's code to set proper content-type and charset
• fix: update examples

0.10.0 (2021-12-14)

• base EventSourceResponse on latest starlette StreamingResponse (0.17.1) and use anyio
• breaking change: response.wait() and response.stop_streaming() removed

0.9.0 (2021-10-09)

• add sse comment support

0.8.1 (2021-09-30)

• minimum required python version relaxed to python 3.6

0.8.0 (2021-08-26)

• using module-based logger instead of uvicorn logger

0.7.2 (2021-04-18)

• refactoring: Github Actions introduced into build pipeline

0.6.2 (2020-12-19)

• fix: correct shutdown signal handling in case of an endpoint which only yields sporadic messages

0.6.1 (2020-10-24)

• updated example with proper error handling

0.6.0 (2020-10-24)

• In case uvicorn is used: monkeypatch uvicorn signal-handler, in order to gracefully shutdown long-running handlers/generators.