contract-notifier/api/rate-limit.js

const rateLimit = require("express-rate-limit");
const config = require("../config");

class RateLimitMiddleware {
  static setup() {
    const windowMs = config.RATE_LIMIT_TIME;
    const maxReq = config.RATE_LIMIT_MAX_REQ;
    let limiter = rateLimit({
      windowMs: windowMs,
      max: maxReq,
      handler: function(req, res) {
        console.warn(this.message);
        res.status(this.statusCode).send({ error: this.message });
      },
      message: `Rate limit was reached, you are able to do ${maxReq} requests per ${windowMs} milliseconds`
    });

    return limiter;
  }
}

module.exports = RateLimitMiddleware.setup;