Initial curated ServiceMap source from 7a0a61232d05ba9097432abef6f7f4102a64d0b8

backend/app/events.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+import asyncio
+import json
+from queue import Empty, Full, Queue
+from threading import Lock
+from typing import Any
+
+
+class EventBus:
+    """Small bounded fan-out bus used by the SSE endpoint.
+
+    Persistence is handled by SQLite; this bus only wakes currently connected
+    clients. A queue per client keeps one slow browser from blocking probes or
+    other subscribers.
+    """
+
+    def __init__(self, max_queue_size: int = 100) -> None:
+        self.max_queue_size = max_queue_size
+        self._subscribers: set[Queue[dict[str, Any]]] = set()
+        self._lock = Lock()
+
+    def subscribe(self) -> Queue[dict[str, Any]]:
+        queue: Queue[dict[str, Any]] = Queue(maxsize=self.max_queue_size)
+        with self._lock:
+            self._subscribers.add(queue)
+        return queue
+
+    def unsubscribe(self, queue: Queue[dict[str, Any]]) -> None:
+        with self._lock:
+            self._subscribers.discard(queue)
+
+    def publish(self, payload: dict[str, Any]) -> None:
+        with self._lock:
+            subscribers = tuple(self._subscribers)
+        for queue in subscribers:
+            try:
+                queue.put_nowait(payload)
+            except Full:
+                # Drop the oldest event for a lagging client, then retain the
+                # newest state notification. The durable event journal remains
+                # the source of truth if a client reconnects.
+                try:
+                    queue.get_nowait()
+                except Empty:
+                    pass
+                try:
+                    queue.put_nowait(payload)
+                except Full:
+                    pass
+event_bus = EventBus()
+
+
+def sse_payload(payload: dict[str, Any]) -> str:
+    event_type = str(payload.get("event_type", "update"))
+    return f"event: {event_type}\ndata: {json.dumps(payload, default=str)}\n\n"
+
+
+async def next_event(queue: Queue[dict[str, Any]], timeout: float = 15.0) -> dict[str, Any] | None:
+    try:
+        return await asyncio.to_thread(queue.get, True, timeout)
+    except Empty:
+        return None