Implement Engine HTTP interfaces for health, enrollment, and tokens

Data/Engine/services/rate_limit.py

@@ -0,0 +1,45 @@
+"""In-process rate limiting utilities for the Borealis Engine."""
+
+from __future__ import annotations
+
+import time
+from collections import deque
+from dataclasses import dataclass
+from threading import Lock
+from typing import Deque, Dict
+
+__all__ = ["RateLimitDecision", "SlidingWindowRateLimiter"]
+
+
+@dataclass(frozen=True, slots=True)
+class RateLimitDecision:
+    """Result of a rate limit check."""
+
+    allowed: bool
+    retry_after: float
+
+
+class SlidingWindowRateLimiter:
+    """Tiny in-memory sliding window limiter suitable for single-process use."""
+
+    def __init__(self) -> None:
+        self._buckets: Dict[str, Deque[float]] = {}
+        self._lock = Lock()
+
+    def check(self, key: str, limit: int, window_seconds: float) -> RateLimitDecision:
+        now = time.monotonic()
+        with self._lock:
+            bucket = self._buckets.get(key)
+            if bucket is None:
+                bucket = deque()
+                self._buckets[key] = bucket
+
+            while bucket and now - bucket[0] > window_seconds:
+                bucket.popleft()
+
+            if len(bucket) >= limit:
+                retry_after = max(0.0, window_seconds - (now - bucket[0]))
+                return RateLimitDecision(False, retry_after)
+
+            bucket.append(now)
+            return RateLimitDecision(True, 0.0)