103 lines
3.4 KiB
Python
103 lines
3.4 KiB
Python
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"""HTTP Polling 降级机制 — SSE/WS 不可用时的备选路径。
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按 session_id 维护响应队列，前端通过 HTTP GET 定时轮询获取回复。
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与 SSE 端点协同使用，形成三级降级链：SSE → Polling → 单次 fetch。
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Usage:
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polling = PollingFallback()
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await polling.push("session_abc", {"type": "delta", "data": {"content": "hello"}})
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events = await polling.poll("session_abc")
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"""
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from __future__ import annotations
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import asyncio
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import logging
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import time as _time
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logger = logging.getLogger(__name__)
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DEFAULT_POLL_TTL = 600
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class PollingFallback:
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def __init__(self, max_queue_size: int = 100, ttl_seconds: int = DEFAULT_POLL_TTL):
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self._queues: dict[str, asyncio.Queue[dict]] = {}
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self._ttl = ttl_seconds
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self._last_active: dict[str, float] = {}
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self._max_queue_size = max_queue_size
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self._lock = asyncio.Lock()
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async def ensure(self, session_id: str) -> None:
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async with self._lock:
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if session_id not in self._queues:
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self._queues[session_id] = asyncio.Queue(maxsize=self._max_queue_size)
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self._last_active[session_id] = _time.monotonic()
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async def push(self, session_id: str, event: dict) -> None:
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async with self._lock:
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self._last_active[session_id] = _time.monotonic()
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q = self._queues.get(session_id)
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if q is None:
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q = asyncio.Queue(maxsize=self._max_queue_size)
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self._queues[session_id] = q
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try:
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q.put_nowait(event)
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except asyncio.QueueFull:
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logger.warning("Polling queue full for session %s, dropping event", session_id)
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async def poll(self, session_id: str) -> list[dict]:
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async with self._lock:
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self._last_active[session_id] = _time.monotonic()
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q = self._queues.get(session_id)
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if q is None:
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return []
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events: list[dict] = []
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while not q.empty():
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try:
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events.append(q.get_nowait())
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except asyncio.QueueEmpty:
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break
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return events
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async def cleanup_stale(self) -> int:
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async with self._lock:
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now = _time.monotonic()
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stale = [sid for sid, ts in self._last_active.items() if now - ts > self._ttl]
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for sid in stale:
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self._queues.pop(sid, None)
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self._last_active.pop(sid, None)
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if stale:
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logger.info("PollingFallback cleaned up %d stale sessions", len(stale))
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return len(stale)
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def active_sessions(self) -> int:
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return len(self._queues)
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polling_fallback = PollingFallback()
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async def _polling_cleanup_loop(interval: int = 300) -> None:
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while True:
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await asyncio.sleep(interval)
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await polling_fallback.cleanup_stale()
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_cleanup_task: asyncio.Task | None = None
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def start_polling_cleanup(interval: int = 300) -> None:
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global _cleanup_task
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if _cleanup_task is None or _cleanup_task.done():
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_cleanup_task = asyncio.ensure_future(_polling_cleanup_loop(interval))
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logger.info("PollingFallback cleanup loop started (interval=%ds)", interval)
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def stop_polling_cleanup() -> None:
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global _cleanup_task
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if _cleanup_task and not _cleanup_task.done():
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_cleanup_task.cancel()
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_cleanup_task = None
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