golang rate limit per minute

Question

How to rate limit 20 requests per minute?

import "golang.org/x/time/rate"

limiter := rate.NewLimiter(rate.Every(1*time.Minute), 20)

for {
    limiter.Wait()
    //more code
}

This does not work. What that does is, it allows first 20 requests, then only allows 1 request per minute. What is expected is 20 requests on the first minute(Need not be evenly spread like 1 per 3 seconds) and then 20 more requests on the second minute. At any 1 minute interval, there cannot be more than 20 requests sent.

My solution: https://stackoverflow.com/a/72452542

Answer 1

My solution

import (
        "sync"
        "time"
)

type Limiter interface {
        Wait()
}

type limiter struct {
        tick    time.Duration
        count   uint
        entries []time.Time
        index   uint
        mutex   sync.Mutex
}

func NewLimiter(tick time.Duration, count uint) Limiter {
        l := limiter{
                tick:  tick,
                count: count,
                index: 0,
        }
        l.entries = make([]time.Time, count)
        before := time.Now().Add(-2 * tick)
        for i, _ := range l.entries {
                l.entries[i] = before
        }
        return &l
}
func (l *limiter) Wait() {
        l.mutex.Lock()
        defer l.mutex.Unlock()
        last := &l.entries[l.index]
        next := last.Add(l.tick)
        now := time.Now()
        if now.Before(next) {
                time.Sleep(next.Sub(now))
        }
        *last = time.Now()
        l.index = l.index + 1
        if l.index == l.count {
                l.index = 0
        }
}