losant/redis-gcra

Rate limiting based on Generic Cell Rate Algorithm

redis-gcra's Issues

Wrong redis key expire time?

I had check the lua script and found some part unexpected:

// https://github.com/Losant/redis-gcra/blob/master/lib/gcra.lua#L51
redis.call("SET", rate_limit_key, new_tat, "EX", reset_in)

The expire time of the key will be set to reset_in in seconds(EX), but in the reset_in value is in milliseconds.
That means that in most cases, the key will not expire at all(because it requires so much time to expire and will be reset in a short time).
Although this does not influence the whole functionality of the gcra algorithm because it will take the bigger one between now and the value of the key:

// https://github.com/Losant/redis-gcra/blob/master/lib/gcra.lua#L19
tat = math.max(tat, now)

But I think it should be corrected in case of making confusion.

Incorrect retryIn?

I'm trying to set up a simple password rate limiter, and I want to allow 6 attempts per minute.

I set it up like this:

  const {limited, retryIn} = await limiter.limit({
    key: `signin/email/${email.trim().toLowerCase()}`,
    burst: 6,
    rate: 6,
    period: 60000,
    cost: 1
  });

When I do too many sign ins I eventually get a retryIn of 10, but then it gets down to below 5 and then the next request is allowed!

Is this an issue with the rate limiter allowing too many requests through, or an issue with the retryIn?

Or is it an issue in how I'm configuring this?