Initial commit: waitlist microservice

app/rate_limit.py

@@ -0,0 +1,76 @@
+"""
+IP-based sliding-window rate limiter.
+
+Cloudflare-aware: uses CF-Connecting-IP → X-Forwarded-For → client.host
+to identify the real client IP.
+"""
+
+import time
+from collections import defaultdict
+from threading import Lock
+
+from fastapi import Request, Response
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.responses import JSONResponse
+
+from app.config import settings
+
+
+def _get_client_ip(request: Request) -> str:
+    """Extract real client IP behind Cloudflare / reverse proxy."""
+    # Cloudflare always sets this when proxying
+    cf_ip = request.headers.get("cf-connecting-ip")
+    if cf_ip:
+        return cf_ip.strip()
+
+    # Fallback: first entry in X-Forwarded-For (set by most reverse proxies)
+    xff = request.headers.get("x-forwarded-for")
+    if xff:
+        return xff.split(",")[0].strip()
+
+    # Last resort: direct connection IP
+    return request.client.host if request.client else "unknown"
+
+
+# Module-level hits store so tests can clear it
+_hits_store: dict[str, list[float]] = defaultdict(list)
+
+
+class RateLimiter(BaseHTTPMiddleware):
+    """
+    Sliding-window rate limiter keyed on client IP.
+
+    Only applies to POST /api/v1/waitlist.
+    Returns 429 with Retry-After header when exceeded.
+    """
+
+    def __init__(self, app, per_minute: int = settings.RATE_LIMIT_PER_MINUTE):
+        super().__init__(app)
+        self.per_minute = per_minute
+        self.window = 60  # seconds
+        self._hits = _hits_store
+        self._lock = Lock()
+
+    def _prune(self, ip: str, now: float) -> None:
+        cutoff = now - self.window
+        self._hits[ip] = [t for t in self._hits[ip] if t > cutoff]
+
+    async def dispatch(self, request: Request, call_next) -> Response:
+        # Only rate-limit the waitlist POST endpoint
+        if request.method != "POST" or request.url.path != "/api/v1/waitlist":
+            return await call_next(request)
+
+        ip = _get_client_ip(request)
+        now = time.monotonic()
+
+        with self._lock:
+            self._prune(ip, now)
+            if len(self._hits[ip]) >= self.per_minute:
+                return JSONResponse(
+                    status_code=429,
+                    content={"detail": "Too many requests. Please try again later."},
+                    headers={"Retry-After": str(self.window)},
+                )
+            self._hits[ip].append(now)
+
+        return await call_next(request)