express-rate-limit - catching the message

user_11753322 0
Viewed 5351

In my application, I would like to be able to catch the message that is being produced by the express-rate-limit package. This is an example of the code I have. I would like to be able to catch the message part with middleware so I can post-process it (in this case I have multiple languages ).

const apiCreatingAccountLimiter = rateLimit({
  windowMs: 10 * 60 * 1000, // 10 minutes
  max: 10, // limit each IP to 10 requests per windowMs
  message: {
    limiter: true,
    type: "error",
    message: 'maximum_accounts'
  }
});

and then

router.post('/signup', apiCreatingAccountLimiter, (req, res, next) => {
// handling the post request
})

I have a similar solution middleware setup for some of my other API messages:

// error processing middleware
app.use((err, req, res, next) => {
    const statusCode = err.statusCode || 500;
    res.status(statusCode).send({
        type: 'error', 
        message: err.message, 
        fields: err.fields === '' ? '' : err.fields,
        code: err.code === '' ? '' : err.code,
        section: err.section === '' ? 'general' : err.section
    });
});

However, when trying to read a message from the express-rate-limit package it does not seem to be passing via this middleware at all. I guess it's because it happens before it can even reach any API and trigger this middleware.

Looking at the res part passing through, I can see there is an object with the following data:

rateLimit:
{ limit: 10,
current: 10,
remaining: 0,
resetTime: 2019-10-21T12:35:46.919Z 
},

But that does not seem to be transporting the message object that is set at the very top in the apiCreatingAccountLimiter. I wonder how could I get to it?

Does anyone know how this can be done? I do not want those messages to be translated on the front end. I need the translation to happen on the NodeJS server. I am only interested in the middleware part where I can catch the message and post-process it.

express middleware node.js
2 Answers

In reading the source code, instead of using another middleware, you should play with the handler options as an option.

const apiCreatingAccountLimiter = rateLimit({
  windowMs: 10 * 60 * 1000, // 10 minutes
  max: 10, // limit each IP to 10 requests per windowMs
  message: "my initial message",
      handler: function(req, res /*, next*/) {
        var myCustomMessage = require('anotherModuleYouWannaUse_ForExemple');
        res.status(options.statusCode).send(myCustomMessage);
      },
});

At this end, you'll find an extract of the source code

function RateLimit(options) {
  options = Object.assign(
    {
      windowMs: 60 * 1000, // milliseconds - how long to keep records of requests in memory
      max: 5, // max number of recent connections during `window` milliseconds before sending a 429 response
      message: "Too many requests, please try again later.",
      statusCode: 429, // 429 status = Too Many Requests (RFC 6585)
      headers: true, //Send custom rate limit header with limit and remaining
      skipFailedRequests: false, // Do not count failed requests (status >= 400)
      skipSuccessfulRequests: false, // Do not count successful requests (status < 400)
      // allows to create custom keys (by default user IP is used)
      keyGenerator: function(req /*, res*/) {
        return req.ip;
      },
      skip: function(/*req, res*/) {
        return false;
      },
      handler: function(req, res /*, next*/) {
        res.status(options.statusCode).send(options.message);
      },
      onLimitReached: function(/*req, res, optionsUsed*/) {}
    },
    options
  );
user_24547900

I found that my frontend was only able to catch the message if I set the statusCode to 200, even though technically it should be a 429. So try this instead:

const apiCreatingAccountLimiter = rateLimit({
  windowMs: 10 * 60 * 1000, // 10 minutes
  max: 10, // limit each IP to 10 requests per windowMs,
  statusCode: 200,
  message: {
    status: 429, // optional, of course
    limiter: true,
    type: "error",
    message: 'maximum_accounts'
  }
});

I did my best to match what you already had. Personally mine just looks like this basically:

const loginRatelimiter = rateLimit({
   windowMs: 6 * 60 * 1000,
   max: 10,
   statusCode: 200,
   message: {
    status: 429,
    error: 'You are doing that too much. Please try again in 10 minutes.'
   }
})

Then, on my frontend I just check for res.data.error when the response comes in, and display that to the user if it exists.

user_111405710
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