perf: use sliding window (#2066)

src/throttler.service.ts

@@ -1,74 +1,23 @@
-import { Injectable, OnApplicationShutdown } from '@nestjs/common';
-import { ThrottlerStorageOptions } from './throttler-storage-options.interface';
+import { Injectable } from '@nestjs/common';
 import { ThrottlerStorageRecord } from './throttler-storage-record.interface';
 import { ThrottlerStorage } from './throttler-storage.interface';
 
 /**
  * @publicApi
  */
-@Injectable()
-export class ThrottlerStorageService implements ThrottlerStorage, OnApplicationShutdown {
-  private _storage: Map<string, ThrottlerStorageOptions> = new Map();
-  private timeoutIds: Map<string, NodeJS.Timeout[]> = new Map();
-
-  get storage(): Map<string, ThrottlerStorageOptions> {
-    return this._storage;
-  }
-
-  /**
-   * Get the expiration time in seconds from a single record.
-   */
-  private getExpirationTime(key: string): number {
-    return Math.floor((this.storage.get(key).expiresAt - Date.now()) / 1000);
-  }
-
-  /**
-   * Get the block expiration time in seconds from a single record.
-   */
-  private getBlockExpirationTime(key: string): number {
-    return Math.floor((this.storage.get(key).blockExpiresAt - Date.now()) / 1000);
-  }
-
-  /**
-   * Set the expiration time for a given key.
-   */
-  private setExpirationTime(key: string, ttlMilliseconds: number, throttlerName: string): void {
-    const timeoutId = setTimeout(() => {
-      const { totalHits } = this.storage.get(key);
-      totalHits.set(throttlerName, totalHits.get(throttlerName) - 1);
-      clearTimeout(timeoutId);
-      this.timeoutIds.set(
-        throttlerName,
-        this.timeoutIds.get(throttlerName).filter((id) => id !== timeoutId),
-      );
-    }, ttlMilliseconds);
-    this.timeoutIds.get(throttlerName).push(timeoutId);
-  }
-
-  /**
-   * Clear the expiration time related to the throttle
-   */
-  private clearExpirationTimes(throttlerName: string) {
-    this.timeoutIds.get(throttlerName).forEach(clearTimeout);
-    this.timeoutIds.set(throttlerName, []);
-  }
 
-  /**
-   * Reset the request blockage
-   */
-  private resetBlockdRequest(key: string, throttlerName: string) {
-    this.storage.get(key).isBlocked = false;
-    this.storage.get(key).totalHits.set(throttlerName, 0);
-    this.clearExpirationTimes(throttlerName);
-  }
+@Injectable()
+export class ThrottlerStorageService implements ThrottlerStorage {
+  private windows: Map<string, SlidingWindow> = new Map();
 
   /**
-   * Increase the `totalHit` count and sent it to decrease queue
+   * Get or create the current window  by `key` and `throttlerName`
    */
-  private fireHitCount(key: string, throttlerName: string, ttl: number) {
-    const { totalHits } = this.storage.get(key);
-    totalHits.set(throttlerName, totalHits.get(throttlerName) + 1);
-    this.setExpirationTime(key, ttl, throttlerName);
+  private getWindow(key: string, throttlerName: string): SlidingWindow {
+    if (!this.windows.has(`${key}-${throttlerName}`)) {
+      this.windows.set(`${key}-${throttlerName}`, new SlidingWindowImpl());
+    }
+    return this.windows.get(`${key}-${throttlerName}`);
   }
 
   async increment(
@@ -81,57 +30,66 @@ export class ThrottlerStorageService implements ThrottlerStorage, OnApplicationS
     const ttlMilliseconds = ttl;
     const blockDurationMilliseconds = blockDuration;
 
-    if (!this.timeoutIds.has(throttlerName)) {
-      this.timeoutIds.set(throttlerName, []);
-    }
+    const window = this.getWindow(key, throttlerName);
 
-    if (!this.storage.has(key)) {
-      this.storage.set(key, {
-        totalHits: new Map([[throttlerName, 0]]),
-        expiresAt: Date.now() + ttlMilliseconds,
-        blockExpiresAt: 0,
-        isBlocked: false,
-      });
+    if (Date.now() < window.timeToBlockExpireMilliseconds) {
+      return {
+        isBlocked: true,
+        timeToBlockExpire: window.timeToBlockExpire,
+        totalHits: window.currentCount,
+        timeToExpire: window.timeToBlockExpire,
+      };
     }
 
-    let timeToExpire = this.getExpirationTime(key);
-
-    // Reset the timeToExpire once it has been expired.
-    if (timeToExpire <= 0) {
-      this.storage.get(key).expiresAt = Date.now() + ttlMilliseconds;
-      timeToExpire = this.getExpirationTime(key);
+    if (Date.now() - window.currentTime > ttlMilliseconds) {
+      window.currentTime = Date.now();
+      window.previousCount = window.currentCount;
+      window.currentCount = 0;
     }
 
-    if (!this.storage.get(key).isBlocked) {
-      this.fireHitCount(key, throttlerName, ttlMilliseconds);
+    const hits =
+      (window.previousCount * (ttlMilliseconds - (Date.now() - window.currentTime))) /
+        ttlMilliseconds +
+      window.currentCount;
+
+    if (hits > limit) {
+      window.timeToBlockExpireMilliseconds = window.currentTime + blockDurationMilliseconds;
+      return {
+        isBlocked: true,
+        timeToBlockExpire: window.timeToBlockExpire,
+        totalHits: hits,
+        timeToExpire: window.timeToBlockExpire,
+      };
     }
 
-    // Reset the blockExpiresAt once it gets blocked
-    if (
-      this.storage.get(key).totalHits.get(throttlerName) > limit &&
-      !this.storage.get(key).isBlocked
-    ) {
-      this.storage.get(key).isBlocked = true;
-      this.storage.get(key).blockExpiresAt = Date.now() + blockDurationMilliseconds;
-    }
-
-    const timeToBlockExpire = this.getBlockExpirationTime(key);
-
-    // Reset time blocked request
-    if (timeToBlockExpire <= 0 && this.storage.get(key).isBlocked) {
-      this.resetBlockdRequest(key, throttlerName);
-      this.fireHitCount(key, throttlerName, ttlMilliseconds);
-    }
+    window.inc();
 
     return {
-      totalHits: this.storage.get(key).totalHits.get(throttlerName),
-      timeToExpire,
-      isBlocked: this.storage.get(key).isBlocked,
-      timeToBlockExpire: timeToBlockExpire,
+      isBlocked: false,
+      timeToBlockExpire: 0,
+      totalHits: hits + 1,
+      timeToExpire: 0,
     };
   }
+}
+
+interface SlidingWindow {
+  currentTime: number;
+  currentCount: number;
+  previousCount: number;
+  timeToBlockExpireMilliseconds: number;
+  timeToBlockExpire: number;
+  inc(): number;
+}
+
+class SlidingWindowImpl implements SlidingWindow {
+  currentTime = Date.now();
+  currentCount = 0;
+  previousCount = 0;
+  timeToBlockExpireMilliseconds = 0;
+  inc = () => ++this.currentCount;
 
-  onApplicationShutdown() {
-    this.timeoutIds.forEach((timeouts) => timeouts.forEach(clearTimeout));
+  get timeToBlockExpire(): number {
+    return this.timeToBlockExpireMilliseconds / 1000;
   }
 }