init

app/services/event_service.py

@@ -0,0 +1,75 @@
+"""
+app/services/event_service.py
+Server-Sent Events (SSE) broadcaster.
+Maintains a set of subscriber asyncio queues and fans out events to all of them.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import json
+import logging
+from datetime import datetime, timezone
+from typing import AsyncGenerator
+
+logger = logging.getLogger(__name__)
+
+# All active SSE subscriber queues
+_subscribers: set[asyncio.Queue] = set()
+
+
+def subscribe() -> asyncio.Queue:
+    """Register a new SSE subscriber and return its queue."""
+    q: asyncio.Queue = asyncio.Queue(maxsize=64)
+    _subscribers.add(q)
+    logger.debug("SSE subscriber added, total=%d", len(_subscribers))
+    return q
+
+
+def unsubscribe(q: asyncio.Queue) -> None:
+    """Remove a subscriber queue."""
+    _subscribers.discard(q)
+    logger.debug("SSE subscriber removed, total=%d", len(_subscribers))
+
+
+def broadcast(event_type: str, data: dict) -> None:
+    """
+    Fan out an event to all current subscribers.
+    Safe to call from synchronous code – uses put_nowait and discards slow consumers.
+    """
+    payload = json.dumps(
+        {
+            "type": event_type,
+            "timestamp": datetime.now(timezone.utc).isoformat(),
+            "data": data,
+        }
+    )
+    dead: list[asyncio.Queue] = []
+    for q in list(_subscribers):
+        try:
+            q.put_nowait(payload)
+        except asyncio.QueueFull:
+            logger.warning("SSE subscriber queue full, dropping event type=%s", event_type)
+            dead.append(q)
+    for q in dead:
+        _subscribers.discard(q)
+
+
+async def event_generator(q: asyncio.Queue) -> AsyncGenerator[str, None]:
+    """
+    Async generator that yields SSE-formatted strings from a subscriber queue.
+    Yields a keep-alive comment every 15 seconds when idle.
+    """
+    try:
+        while True:
+            try:
+                payload = await asyncio.wait_for(q.get(), timeout=15.0)
+                yield f"data: {payload}\n\n"
+            except asyncio.TimeoutError:
+                # Keep-alive ping so browsers don't close the connection
+                yield ": ping\n\n"
+    except asyncio.CancelledError:
+        pass
+    finally:
+        unsubscribe(q)
+