spife-ratelimiter

Middleware that adds [Token Bucket]-style ratelimiting to [Spife].

``javascript
// settings.js:
module.exports.MIDDLEWARE = {
['@npm/spife-ratelimiting', {
redisUrl: 'redis://localhost:6379', // let it connect to redis
redisClient, // (or give it a client)

costHeader: 'npm-cost', // the "cost" header to use
// for determining how many
// tokens a request took

clock: Date.now, // if you would like time to
// move to the beat of a
// different drum

getBucket (spifeRequest) { // given a request, return
// an object describing its
// token bucket
return {
capacity: 100, // how many tokens does
// the bucket hold?

interval: 60, // in minutes, how long
// does the bucket take to
// fill up?

key: String // what should the bucket be
// named?
}
}
}]
}

// views.js:
const reply = require('@npm/spife/reply')
const cost = require('@npm/spife-ratelimiter/decorator')

module.exports = {
// a view can declare how much it costs up-front:
index: cost(index, 5),
other
}

function index (req, context) {
return 'I cost five tokens!'
}

function other (req, context) {
return reply.header(
'I cost a hundred tokens sometimes',
'npm-cost',
Math.random() > 0.5 ? 100 : 0
)
}
`

This is implemented in redis by keeping two keys per bucket: one that
tracks the current number of tokens, and one that tracks the last update
time. Both keys are expired at interval`, and updated atomically using a
Lua script.

[Token Bucket]: https://en.wikipedia.org/wiki/Token_bucket
[Spife]: https://github.com/npm/spife