limiter.ts

packages/shared/src/limiter.ts

1. import { sleep as realSleep } from './retry.js'
3. /**
4. * Token bucket rate limiter.
5. *
6. * Dependency-free and clock-injectable so it can be tested without real time
7. * passing, and so it runs unchanged in a Cloudflare Worker.
8. */
9. export class TokenBucket {
10. private tokens: number
11. private lastRefill: number
13. constructor(
14. private readonly capacity: number,
15. private readonly refillPerSecond: number,
16. private readonly now: () => number = () => Date.now(),
17. private readonly sleep: (ms: number) => Promise<void> = realSleep,
18. ) {
19. if (capacity <= 0 || refillPerSecond <= 0) {
20. throw new Error('TokenBucket requires positive capacity and refill rate')
21. }
22. this.tokens = capacity
23. this.lastRefill = now()
24. }
26. private refill(): void {
27. const t = this.now()
28. const elapsedSec = (t - this.lastRefill) / 1000
29. if (elapsedSec <= 0) return
30. this.tokens = Math.min(this.capacity, this.tokens + elapsedSec * this.refillPerSecond)
31. this.lastRefill = t
32. }
34. /** Resolves when a token is available. Never rejects. */
35. async acquire(): Promise<void> {
36. // Loop rather than compute-once: other callers may drain the bucket while
37. // this one is sleeping.
38. for (;;) {
39. this.refill()
40. if (this.tokens >= 1) {
41. this.tokens -= 1
42. return
43. }
44. const deficit = 1 - this.tokens
45. const waitMs = Math.ceil((deficit / this.refillPerSecond) * 1000)
46. await this.sleep(Math.max(waitMs, 1))
47. }
48. }
50. /** Test/debug visibility. Not part of the public contract. */
51. get available(): number {
52. this.refill()
53. return this.tokens
54. }
55. }