rateLimit()

in packages/sdk/src/fetch-util.ts [179:212]

• 20 lines of code
• 2 McCabe index (conditional complexity)

  rateLimit(tokenFillRate: number, { maxTokens = tokenFillRate, initialTokens = tokenFillRate } = {}) {
    precondition(tokenFillRate > 0, 'tokenFillRate must be positive');
    let lastRefillTime = Number.NEGATIVE_INFINITY;
    let tokens = initialTokens;
    let nextRun = Promise.resolve();

    return this.compose(next => request => {
      nextRun = nextRun
        // catch the potential abort of the previous run
        .catch(() => {})
        .then(async () => {
          refillTokens();
          // we can only send a request if we have at least one token
          if (tokens < 1) {
            // wait until tokens is one
            await abortableSleep(((1 - tokens) / tokenFillRate) * 1000, request.signal);
          }
        });
      return nextRun.then(() => {
        tokens--;
        return next(request);
      });
    });

    function refillTokens() {
      const currentTime = Date.now();
      // initialTokens might be higher than maxTokens, so we don't refill until we've dropped below maxTokens
      if (Number.isFinite(lastRefillTime) && tokens < maxTokens) {
        const elapsed = (currentTime - lastRefillTime) / 1000;
        tokens = Math.min(maxTokens, tokens + elapsed * tokenFillRate);
      }
      lastRefillTime = currentTime;
    }
  }