fix: harden gateway control-plane restart protections

src/gateway/control-plane-rate-limit.ts

@@ -0,0 +1,79 @@
+import type { GatewayClient } from "./server-methods/types.js";
+
+const CONTROL_PLANE_RATE_LIMIT_MAX_REQUESTS = 3;
+const CONTROL_PLANE_RATE_LIMIT_WINDOW_MS = 60_000;
+
+type Bucket = {
+  count: number;
+  windowStartMs: number;
+};
+
+const controlPlaneBuckets = new Map<string, Bucket>();
+
+function normalizePart(value: unknown, fallback: string): string {
+  if (typeof value !== "string") {
+    return fallback;
+  }
+  const normalized = value.trim();
+  return normalized.length > 0 ? normalized : fallback;
+}
+
+export function resolveControlPlaneRateLimitKey(client: GatewayClient | null): string {
+  const deviceId = normalizePart(client?.connect?.device?.id, "unknown-device");
+  const clientIp = normalizePart(client?.clientIp, "unknown-ip");
+  return `${deviceId}|${clientIp}`;
+}
+
+export function consumeControlPlaneWriteBudget(params: {
+  client: GatewayClient | null;
+  nowMs?: number;
+}): {
+  allowed: boolean;
+  retryAfterMs: number;
+  remaining: number;
+  key: string;
+} {
+  const nowMs = params.nowMs ?? Date.now();
+  const key = resolveControlPlaneRateLimitKey(params.client);
+  const bucket = controlPlaneBuckets.get(key);
+
+  if (!bucket || nowMs - bucket.windowStartMs >= CONTROL_PLANE_RATE_LIMIT_WINDOW_MS) {
+    controlPlaneBuckets.set(key, {
+      count: 1,
+      windowStartMs: nowMs,
+    });
+    return {
+      allowed: true,
+      retryAfterMs: 0,
+      remaining: CONTROL_PLANE_RATE_LIMIT_MAX_REQUESTS - 1,
+      key,
+    };
+  }
+
+  if (bucket.count >= CONTROL_PLANE_RATE_LIMIT_MAX_REQUESTS) {
+    const retryAfterMs = Math.max(
+      0,
+      bucket.windowStartMs + CONTROL_PLANE_RATE_LIMIT_WINDOW_MS - nowMs,
+    );
+    return {
+      allowed: false,
+      retryAfterMs,
+      remaining: 0,
+      key,
+    };
+  }
+
+  bucket.count += 1;
+  return {
+    allowed: true,
+    retryAfterMs: 0,
+    remaining: Math.max(0, CONTROL_PLANE_RATE_LIMIT_MAX_REQUESTS - bucket.count),
+    key,
+  };
+}
+
+export const __testing = {
+  resetControlPlaneRateLimitState() {
+    controlPlaneBuckets.clear();
+  },
+};