Add async buffered pubsub, websocket updates endpoint and initial fast hashing of objects

yacv_server/pubsub.py

@@ -0,0 +1,54 @@
+import asyncio
+from typing import List, TypeVar, \
+    Generic, AsyncGenerator
+
+T = TypeVar('T')
+
+
+class BufferedPubSub(Generic[T]):
+    """A simple implementation of publish-subscribe pattern using asyncio and buffering all previous events"""
+
+    _buffer: List[T]
+    _subscribers: List[asyncio.Queue[T]]
+    _lock = asyncio.Lock()
+
+    def __init__(self):
+        self._buffer = []
+        self._subscribers = []
+
+    async def publish(self, event: T):
+        """Publishes an event"""
+        async with self._lock:
+            self._buffer.append(event)
+            for q in self._subscribers:
+                await q.put(event)
+
+    def publish_nowait(self, event: T):
+        """Publishes an event without blocking"""
+        self._buffer.append(event)
+        for q in self._subscribers:
+            q.put_nowait(event)
+
+    async def _subscribe(self, include_buffered: bool = True) -> asyncio.Queue[T]:
+        """Subscribes to events"""
+        q = asyncio.Queue()
+        async with self._lock:
+            self._subscribers.append(q)
+            if include_buffered:
+                for event in self._buffer:
+                    await q.put(event)
+        return q
+
+    async def _unsubscribe(self, q: asyncio.Queue[T]):
+        """Unsubscribes from events"""
+        async with self._lock:
+            self._subscribers.remove(q)
+
+    async def subscribe(self, include_buffered: bool = True) -> AsyncGenerator[T, None]:
+        """Subscribes to events as an async generator that yields events and automatically unsubscribes"""
+        q = await self._subscribe(include_buffered)
+        try:
+            while True:
+                yield await q.get()
+        finally:
+            await self._unsubscribe(q)