Lesson 22 · One interface, many limiters

One interface, many limiters

Every algorithm you built answers Allow(now) the same way, so they are interchangeable. Today you make that explicit with a Limiter interface and a Replay helper that runs a scripted stream of timestamps through any limiter, returning its allow/deny timeline.

The goal

Define the common Limiter interface and a driver that replays a timestamp stream.

Start here - the target

TO DO

Scenario: Replay runs a timestamp stream through any limiter

Givena FixedWindow with limit 2 and window 10, treated as a Limiter

WhenReplay(limiter, [0, 1, 2, 10]) runs the four ticks through it in order

Thenit returns [true, true, false, true] - ticks 0 and 1 fill window 0, tick 2 is denied, and tick 10 opens window 1

Andthe same Replay works unchanged on a SlidingCounter or a TokenBucket, since all of them satisfy the Limiter interface

Background

Every algorithm in this project - fixed window, sliding log, sliding counter, token bucket, leaky bucket - exposes the exact same method, Allow(now) Decision. That shared shape is a Limiter interface, and once it is named, code can accept any limiter without caring which algorithm it is. Nothing about the limiters changes; naming the interface just records the contract they already share since lesson 2.

The payoff is Replay: a driver that takes any Limiter and a scripted list of request ticks, calls Allow for each in order, and returns the allow/deny timeline as a slice of booleans. Because it speaks only to the interface, the same helper drives a fixed window, a sliding counter, or a token bucket unchanged. That is exactly the tool the capstone needs - a way to push one identical request stream through several algorithms and line up their timelines. Confirm it on a fixed window today; tomorrow you point it at three limiters at once.

Make it work

type Limiter interface {
  Allow(now int64) Decision
}
func Replay(l Limiter, times []int64) []bool {
  out := make([]bool, len(times))
  for i, t := range times {
    out[i] = l.Allow(t).Allowed
  }
  return out
}

CheckpointDONE

Any limiter can be driven through a scripted stream by one helper. Commit and stop here.