Snippet

Generator-Based Stateful Token Bucket Rate Limiting logic for Next.js Middleware

Implements a stateful token bucket rate-limiting mechanism using JavaScript generator functions (function*). The generator encapsulates bucket state across requests, dynamically calculates token refills based on timestamp deltas, and receives requested token consumption counts via bidirectional yield evaluation.

snippet.js

javascript

export function* createTokenBucket(capacity, refillRatePerSec) {
  let tokens = capacity;
  let lastRefill = Date.now();
 
  while (true) {
    const now = Date.now();
    const elapsedSeconds = (now - lastRefill) / 1000;
    tokens = Math.min(capacity, tokens + elapsedSeconds * refillRatePerSec);
    lastRefill = now;
 
    const requested = yield { allowed: tokens >= 1, remaining: Math.floor(tokens) };
    if (requested && tokens >= requested) {
      tokens -= requested;
    }
  }
}

nextjs

Breakdown

export function* createTokenBucket(capacity, refillRatePerSec) {

Defines a generator function that produces an iterable state machine for controlling request tokens.

tokens = Math.min(capacity, tokens + elapsedSeconds * refillRatePerSec);

Recalculates current available token balance based on elapsed time and refill rate capped at maximum capacity.

const requested = yield { allowed: tokens >= 1, remaining: Math.floor(tokens) };

Yields rate limit status to the caller and pauses execution, resuming when the caller passes requested token units back via next(count).

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Generator-Based Stateful Token Bucket Rate Limiting logic for Next.js Middleware

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