PacketStation/server/packetstation/api/events.py

"""`GET /api/events`: the server-sent event stream (session required; locked sessions allowed)."""

from __future__ import annotations

from fastapi import APIRouter, Query, Request
from fastapi.responses import StreamingResponse
from starlette.concurrency import run_in_threadpool

from ..auth.groups import SCREEN_LABELS, SCREENS, role_label
from ..events import EventHub, stream
from .deps import resolve_standalone, settings_of

router = APIRouter(prefix="/api", tags=["events"])

SSE_HEADERS = {"Cache-Control": "no-cache", "X-Accel-Buffering": "no", "Connection": "keep-alive"}


@router.get("/events")
async def events(
    request: Request,
    screen: str | None = Query(None, max_length=32),
    packet_id: int | None = Query(None, ge=1, le=2**62),
) -> StreamingResponse:
    """The event stream. `packet_id` is the packet the page has open; presence carries it, so the packet page can
    show who else is looking at the same packet. The client reopens the stream when the open packet changes.
    Presence names the person with the label of the screen they have open (a screen their roles allow), else their
    primary role. A locked session is left out of presence until it unlocks."""
    # The session check runs on its own pooled connection, returned before the stream starts
    p = await run_in_threadpool(resolve_standalone, request)
    hub: EventHub = request.app.state.events
    open_screen = screen if screen in SCREENS and screen in p.screens else None
    sub = hub.subscribe(
        session_id=p.session_id,
        user_id=p.user_id,
        display_name=p.user["display_name"],
        screen=open_screen,
        packet_id=packet_id,
        role=SCREEN_LABELS[open_screen] if open_screen else role_label(p.roles),
        locked=p.locked,
    )
    hello = {"session_id": str(p.session_id), "build": settings_of(request).ps_build}
    return StreamingResponse(
        stream(hub, sub, hello=hello, is_disconnected=request.is_disconnected),
        media_type="text/event-stream",
        headers=SSE_HEADERS,
    )