Add "decrease" parameter to allow reading the values without changing them

[nicokaiser]

In some scenarios it might be useful to be able to read the current "remaining" value for a limiter.

In this example, new login attempts are rejected when more at least 10 unsuccessful login attempts happened in the last 60 seconds.

const rateLimiter = new RateLimiter({
  db: new Redis()
  max: 10
  duration: 60 * 1000
})

const loginHandler = async (req, res, next) => {
  const limit = await rateLimiter.get({ id: req.clientIp, decrease: false })
  if (!limit.remaining) return sendError(req, res, 429)

  try {
    await doLogin(req);// or something like this
  } catch (err) {
    if (err) {
      await rateLimiter.get({ id: req.clientIp })
      return sendError(req, res, 401)
    }
  }

  next(req, res)
}

This is done with a new decrease parameter that controls if the remaining value should actually be decreased (default: true) or if the request is only done to read the current value.

What do you think?

[coveralls]

Pull Request Test Coverage Report for Build 40

• 10 of 10 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.7%) to 98.077%

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Totals
Change from base Build 39:	0.7%
Covered Lines:	34
Relevant Lines:	34

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💛 - Coveralls

[nicokaiser]

If you think this PR is useful, I can try to also implement this for tj/node-ratelimiter to make it consistent again.

[Kikobeats]

why not read the value directly from redis?

[nicokaiser]

why not read the value directly from redis?

That would be possible, but the "sliding window" effect would be gone then. When reading the value directly from Redis (with zcard), the count is only reset to 0 at duration after the last get call. When using get (or the PR implementation), the count is decreased duration after the first get call.

[Kikobeats]

Hello @nicokaiser, can you implement it at tj/node-ratelimiter? I interested in be 1:1 replacement

[ghmeier]

Any updates on this? It seems like essential functionality :)

[Kikobeats]

Sorry for the delay! Added into the codebase, also I'm going to add the example as part of the documentation.

Thanks for all 🙂

[ghmeier]

Oh yay! Thanks a bunch @Kikobeats!