// NoLimit can be used as the minDuration arg value to New if no limiting is required.
const NoLimit = time.Duration(-1)

// ErrQueueFull is returned with the queue limit set by WithMaxQueueSize is exceeded.
var ErrQueueFull = errors.New("ratelimiter: queue is full")

// RateLimiter provides functionality to block until ready to ensure a rate limit is not exceeded.
type RateLimiter interface {
    // Wait blocks until the next call is ready based on the minimum time between calls.
    Wait() error
    // NumQueued returns the current number of queued requests. If WithMaxQueueSize is not set, the result will always be 0.
    NumQueued() uint32
}

// New builds a new RateLimiter used to ensure calls adhere to a minimum duration between calls.
func New(minDuration time.Duration, options ...Option) RateLimiter

// WithMaxQueueSize sets the maximum number of requests that can be queued up. If the queue
// limit is reached, ErrQueueFull will be returned when Wait is called.
func WithMaxQueueSize(maxQueue uint32) Option

package main

import (
    "time"

    "github.com/brandenc40/ratelimiter"
)

func main() {
    rl := ratelimiter.New(
        10*time.Millisecond,               // 10ms between calls (100 rps)
        ratelimiter.WithMaxQueueSize(100), // (optional) max of 100 requests queued up before failure
    )

    for i := 0; i < 100; i++ {
        if err := rl.Wait(); err != nil {
            // handle err
        }
        // do some rate limited functionality
    }
}