目录
简单的并发控制
利用 channel 的缓冲设定，我们就可以来实现并发的限制。我们只要在执行并发的同时，往一个带有缓冲的 channel 里写入点东西（随便写啥，内容不重要）。让并发的 goroutine在执行完成后把这个 channel 里的东西给读走。这样整个并发的数量就讲控制在这个 channel的缓冲区大小上。
比如我们可以用一个 bool 类型的带缓冲 channel 作为并发限制的计数器。
chLimit := make(chan bool, 1) 然后在并发执行的地方，每创建一个新的 goroutine，都往 chLimit 里塞个东西。
-
for i, sleeptime := range input {
-
chs[i] = make(chan string, 1)
-
chLimit <- true
-
go limitFunc(chLimit, chs[i], i, sleeptime, timeout)
-
}
这里通过 go 关键字并发执行的是新构造的函数。他在执行完后，会把 chLimit的缓冲区里给消费掉一个。
-
limitFunc := func(chLimit chan bool, ch chan string, task_id, sleeptime, timeout int) {
-
Run(task_id, sleeptime, timeout, ch)
-
<-chLimit
-
}
这样一来，当创建的 goroutine 数量到达 chLimit 的缓冲区上限后。主 goroutine 就挂起阻塞了，直到这些 goroutine 执行完毕，消费掉了 chLimit 缓冲区中的数据，程序才会继续创建新的 goroutine 。我们并发数量限制的目的也就达到了。
以下是完整代码：
-
package main
-
-
import (
-
"fmt"
-
"time"
-
)
-
-
func Run(task_id, sleeptime, timeout int, ch chan string) {
-
ch_run := make(chan string)
-
go run(task_id, sleeptime, ch_run)
-
select {
-
case re := <-ch_run:
-
ch <- re
-
case <-time.After(time.Duration(timeout) * time.Second):
-
re := fmt.Sprintf("task id %d , timeout", task_id)
-
ch <- re
-
}
-
}
-
-
func run(task_id, sleeptime int, ch chan string) {
-
-
time.Sleep(time.Duration(sleeptime) * time.Second)
-
ch <- fmt.Sprintf("task id %d , sleep %d second", task_id, sleeptime)
-
return
-
}
-
-
func main() {
-
input := []int{3, 2, 1}
-
timeout := 2
-
chLimit := make(chan bool, 1)
-
chs := make([]chan string, len(input))
-
limitFunc := func(chLimit chan bool, ch chan string, task_id, sleeptime, timeout int) {
-
Run(task_id, sleeptime, timeout, ch)
-
<-chLimit
-
}
-
startTime := time.Now()
-
fmt.Println("Multirun start")
-
for i, sleeptime := range input {
-
chs[i] = make(chan string, 1)
-
chLimit <- true
-
go limitFunc(chLimit, chs[i], i, sleeptime, timeout)
-
}
-
-
for _, ch := range chs {
-
fmt.Println(<-ch)
-
}
-
endTime := time.Now()
-
fmt.Printf("Multissh finished. Process time %s. Number of task is %d", endTime.Sub(startTime), len(input))
-
}
运行结果：
-
Multirun start
-
task id 0 , timeout
-
task id 1 , timeout
-
task id 2 , sleep 1 second
-
Multissh finished. Process time 5s. Number of task is 3
如果修改并发限制为2：
chLimit := make(chan bool, 2)运行结果：
-
-
Multirun start
-
task id 0 , timeout
-
task id 1 , timeout
-
task id 2 , sleep 1 second
-
Multissh finished. Process time 3s. Number of task is 3
使用计数器实现请求限流
限流的要求是在指定的时间间隔内，server 最多只能服务指定数量的请求。实现的原理是我们启动一个计数器，每次服务请求会把计数器加一，同时到达指定的时间间隔后会把计数器清零；这个计数器的实现代码如下所示：
-
type RequestLimitService struct {
-
Interval time.Duration
-
MaxCount int
-
Lock sync.Mutex
-
ReqCount int
-
}
-
-
func NewRequestLimitService(interval time.Duration, maxCnt int) *RequestLimitService {
-
reqLimit := &RequestLimitService{
-
Interval: interval,
-
MaxCount: maxCnt,
-
}
-
-
go func() {
-
ticker := time.NewTicker(interval)
-
for {
-
<-ticker.C
-
reqLimit.Lock.Lock()
-
fmt.Println("Reset Count...")
-
reqLimit.ReqCount = 0
-
reqLimit.Lock.Unlock()
-
}
-
}()
-
-
return reqLimit
-
}
-
-
func (reqLimit *RequestLimitService) Increase() {
-
reqLimit.Lock.Lock()
-
defer reqLimit.Lock.Unlock()
-
-
reqLimit.ReqCount += 1
-
}
-
-
func (reqLimit *RequestLimitService) IsAvailable() bool {
-
reqLimit.Lock.Lock()
-
defer reqLimit.Lock.Unlock()
-
-
return reqLimit.ReqCount < reqLimit.MaxCount
-
}
在服务请求的时候, 我们会对当前计数器和阈值进行比较，只有未超过阈值时才进行服务：
-
var RequestLimit = NewRequestLimitService(10 * time.Second, 5)
-
-
func helloHandler(w http.ResponseWriter, r *http.Request) {
-
if RequestLimit.IsAvailable() {
-
RequestLimit.Increase()
-
fmt.Println(RequestLimit.ReqCount)
-
io.WriteString(w, "Hello world! ")
-
} else {
-
fmt.Println("Reach request limiting!")
-
io.WriteString(w, "Reach request limit! ")
-
}
-
}
-
-
func main() {
-
fmt.Println("Server Started!")
-
http.HandleFunc("/", helloHandler)
-
http.ListenAndServe(":8000", nil)
-
}
完整代码url：https://github.com/hiberabyss/JustDoIt/blob/master/RequestLimit/request_limit.go
使用golang官方包实现httpserver频率限制
使用golang来编写httpserver时，可以使用官方已经有实现好的包：
-
import(
-
"fmt"
-
"net"
-
"golang.org/x/net/netutil"
-
)
-
-
func main() {
-
l, err := net.Listen("tcp", "127.0.0.1:0")
-
if err != nil {
-
fmt.Fatalf("Listen: %v", err)
-
}
-
defer l.Close()
-
l = LimitListener(l, max)
-
-
http.Serve(l, http.HandlerFunc())
-
-
//bla bla bla.................
-
}
源码如下(url : https://github.com/golang/net/blob/master/netutil/listen.go)，基本思路就是为连接数计数，通过make chan来建立一个最大连接数的channel, 每次accept就+1，close时候就-1. 当到达最大连接数时，就等待空闲连接出来之后再accept。
-
// Copyright 2013 The Go Authors. All rights reserved.
-
// Use of this source code is governed by a BSD-style
-
// license that can be found in the LICENSE file.
-
-
// Package netutil provides network utility functions, complementing the more
-
// common ones in the net package.
-
package netutil // import "golang.org/x/net/netutil"
-
-
import (
-
"net"
-
"sync"
-
)
-
-
// LimitListener returns a Listener that accepts at most n simultaneous
-
// connections from the provided Listener.
-
func LimitListener(l net.Listener, n int) net.Listener {
-
return &limitListener{
-
Listener: l,
-
sem: make(chan struct{}, n),
-
done: make(chan struct{}),
-
}
-
}
-
-
type limitListener struct {
-
net.Listener
-
sem chan struct{}
-
closeOnce sync.Once // ensures the done chan is only closed once
-
done chan struct{} // no values sent; closed when Close is called
-
}
-
-
// acquire acquires the limiting semaphore. Returns true if successfully
-
// accquired, false if the listener is closed and the semaphore is not
-
// acquired.
-
func (l *limitListener) acquire() bool {
-
select {
-
case <-l.done:
-
return false
-
case l.sem <- struct{}{}:
-
return true
-
}
-
}
-
func (l *limitListener) release() { <-l.sem }
-
-
func (l *limitListener) Accept() (net.Conn, error) {
-
//如果sem满了，就会阻塞在这
-
acquired := l.acquire()
-
// If the semaphore isn't acquired because the listener was closed, expect
-
// that this call to accept won't block, but immediately return an error.
-
c, err := l.Listener.Accept()
-
if err != nil {
-
if acquired {
-
l.release()
-
}
-
return nil, err
-
}
-
return &limitListenerConn{Conn: c, release: l.release}, nil
-
}
-
-
func (l *limitListener) Close() error {
-
err := l.Listener.Close()
-
l.closeOnce.Do(func() { close(l.done) })
-
return err
-
}
-
-
type limitListenerConn struct {
-
net.Conn
-
releaseOnce sync.Once
-
release func()
-
}
-
-
func (l *limitListenerConn) Close() error {
-
err := l.Conn.Close()
-
//close时释放占用的sem
-
l.releaseOnce.Do(l.release)
-
return err
-
}
使用Token Bucket（令牌桶算法）实现请求限流
在开发高并发系统时有三把利器用来保护系统：缓存、降级和限流!为了保证在业务高峰期，线上系统也能保证一定的弹性和稳定性，最有效的方案就是进行服务降级了，而限流就是降级系统最常采用的方案之一。
这里为大家推荐一个开源库https://github.com/didip/tollbooth，但是，如果您想要一些简单的、轻量级的或者只是想要学习的东西，实现自己的中间件来处理速率限制并不困难。今天我们就来聊聊如何实现自己的一个限流中间件
首先我们需要安装一个提供了 Token bucket (令牌桶算法)的依赖包，上面提到的toolbooth 的实现也是基于它实现的：
$ go get golang.org/x/time/rate先看Demo代码的实现：
-
package main
-
-
import (
-
"net/http"
-
"golang.org/x/time/rate"
-
)
-
-
var limiter = rate.NewLimiter(2, 5)
-
func limit(next http.Handler) http.Handler {
-
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-
if limiter.Allow() == false {
-
http.Error(w, http.StatusText(429), http.StatusTooManyRequests)
-
return
-
}
-
next.ServeHTTP(w, r)
-
})
-
}
-
-
func main() {
-
mux := http.NewServeMux()
-
mux.HandleFunc("/", okHandler)
-
// Wrap the servemux with the limit middleware.
-
http.ListenAndServe(":4000", limit(mux))
-
}
-
-
func okHandler(w http.ResponseWriter, r *http.Request) {
-
w.Write([]byte("OK"))
-
}
然后看看 rate.NewLimiter的源码：
算法描述：用户配置的平均发送速率为r，则每隔1/r秒一个令牌被加入到桶中（每秒会有r个令牌放入桶中），桶中最多可以存放b个令牌。如果令牌到达时令牌桶已经满了，那么这个令牌会被丢弃；
-
// Copyright 2015 The Go Authors. All rights reserved.
-
// Use of this source code is governed by a BSD-style
-
// license that can be found in the LICENSE file.
-
// Package rate provides a rate limiter.
-
package rate
-
-
import (
-
"fmt"
-
"math"
-
"sync"
-
"time"
-
-
"golang.org/x/net/context"
-
)
-
-
// Limit defines the maximum frequency of some events.
-
// Limit is represented as number of events per second.
-
// A zero Limit allows no events.
-
type Limit float64
-
-
// Inf is the infinite rate limit; it allows all events (even if burst is zero).
-
const Inf = Limit(math.MaxFloat64)
-
-
// Every converts a minimum time interval between events to a Limit.
-
func Every(interval time.Duration) Limit {
-
if interval <= 0 {
-
return Inf
-
}
-
return 1 / Limit(interval.Seconds())
-
}
-
-
// A Limiter controls how frequently events are allowed to happen.
-
// It implements a "token bucket" of size b, initially full and refilled
-
// at rate r tokens per second.
-
// Informally, in any large enough time interval, the Limiter limits the
-
// rate to r tokens per second, with a maximum burst size of b events.
-
// As a special case, if r == Inf (the infinite rate), b is ignored.
-
// See https://en.wikipedia.org/wiki/Token_bucket for more about token buckets.
-
//
-
// The zero value is a valid Limiter, but it will reject all events.
-
// Use NewLimiter to create non-zero Limiters.
-
//
-
// Limiter has three main methods, Allow, Reserve, and Wait.
-
// Most callers should use Wait.
-
//
-
// Each of the three methods consumes a single token.
-
// They differ in their behavior when no token is available.
-
// If no token is available, Allow returns false.
-
// If no token is available, Reserve returns a reservation for a future token
-
// and the amount of time the caller must wait before using it.
-
// If no token is available, Wait blocks until one can be obtained
-
// or its associated context.Context is canceled.
-
//
-
// The methods AllowN, ReserveN, and WaitN consume n tokens.
-
type Limiter struct {
-
//maximum token, token num per second
-
limit Limit
-
//burst field, max token num
-
burst int
-
mu sync.Mutex
-
//tokens num, change
-
tokens float64
-
// last is the last time the limiter's tokens field was updated
-
last time.Time
-
// lastEvent is the latest time of a rate-limited event (past or future)
-
lastEvent time.Time
-
}
-
-
// Limit returns the maximum overall event rate.
-
func (lim *Limiter) Limit() Limit {
-
lim.mu.Lock()
-
defer lim.mu.Unlock()
-
return lim.limit
-
}
-
-
// Burst returns the maximum burst size. Burst is the maximum number of tokens
-
// that can be consumed in a single call to Allow, Reserve, or Wait, so higher
-
// Burst values allow more events to happen at once.
-
// A zero Burst allows no events, unless limit == Inf.
-
func (lim *Limiter) Burst() int {
-
return lim.burst
-
}
-
-
// NewLimiter returns a new Limiter that allows events up to rate r and permits
-
// bursts of at most b tokens.
-
func NewLimiter(r Limit, b int) *Limiter {
-
return &Limiter{
-
limit: r,
-
burst: b,
-
}
-
}
-
-
// Allow is shorthand for AllowN(time.Now(), 1).
-
func (lim *Limiter) Allow() bool {
-
return lim.AllowN(time.Now(), 1)
-
}
-
-
// AllowN reports whether n events may happen at time now.
-
// Use this method if you intend to drop / skip events that exceed the rate limit.
-
// Otherwise use Reserve or Wait.
-
func (lim *Limiter) AllowN(now time.Time, n int) bool {
-
return lim.reserveN(now, n, 0).ok
-
}
-
-
// A Reservation holds information about events that are permitted by a Limiter to happen after a delay.
-
// A Reservation may be canceled, which may enable the Limiter to permit additional events.
-
type Reservation struct {
-
ok bool
-
lim *Limiter
-
tokens int
-
//This is the time to action
-
timeToAct time.Time
-
// This is the Limit at reservation time, it can change later.
-
limit Limit
-
}
-
-
// OK returns whether the limiter can provide the requested number of tokens
-
// within the maximum wait time. If OK is false, Delay returns InfDuration, and
-
// Cancel does nothing.
-
func (r *Reservation) OK() bool {
-
return r.ok
-
}
-
-
// Delay is shorthand for DelayFrom(time.Now()).
-
func (r *Reservation) Delay() time.Duration {
-
return r.DelayFrom(time.Now())
-
}
-
-
// InfDuration is the duration returned by Delay when a Reservation is not OK.
-
const InfDuration = time.Duration(1<<63 - 1)
-
-
// DelayFrom returns the duration for which the reservation holder must wait
-
// before taking the reserved action. Zero duration means act immediately.
-
// InfDuration means the limiter cannot grant the tokens requested in this
-
// Reservation within the maximum wait time.
-
func (r *Reservation) DelayFrom(now time.Time) time.Duration {
-
if !r.ok {
-
return InfDuration
-
}
-
delay := r.timeToAct.Sub(now)
-
if delay < 0 {
-
return 0
-
}
-
return delay
-
}
-
-
// Cancel is shorthand for CancelAt(time.Now()).
-
func (r *Reservation) Cancel() {
-
r.CancelAt(time.Now())
-
return
-
}
-
-
// CancelAt indicates that the reservation holder will not perform the reserved action
-
// and reverses the effects of this Reservation on the rate limit as much as possible,
-
// considering that other reservations may have already been made.
-
func (r *Reservation) CancelAt(now time.Time) {
-
if !r.ok {
-
return
-
}
-
r.lim.mu.Lock()
-
defer r.lim.mu.Unlock()
-
if r.lim.limit == Inf || r.tokens == 0 || r.timeToAct.Before(now) {
-
return
-
}
-
// calculate tokens to restore
-
// The duration between lim.lastEvent and r.timeToAct tells us how many tokens were reserved
-
// after r was obtained. These tokens should not be restored.
-
restoreTokens := float64(r.tokens) - r.limit.tokensFromDuration(r.lim.lastEvent.Sub(r.timeToAct))
-
if restoreTokens <= 0 {
-
return
-
}
-
// advance time to now
-
now, _, tokens := r.lim.advance(now)
-
// calculate new number of tokens
-
tokens += restoreTokens
-
if burst := float64(r.lim.burst); tokens > burst {
-
tokens = burst
-
}
-
// update state
-
r.lim.last = now
-
r.lim.tokens = tokens
-
if r.timeToAct == r.lim.lastEvent {
-
prevEvent := r.timeToAct.Add(r.limit.durationFromTokens(float64(-r.tokens)))
-
if !prevEvent.Before(now) {
-
r.lim.lastEvent = prevEvent
-
}
-
}
-
return
-
}
-
-
// Reserve is shorthand for ReserveN(time.Now(), 1).
-
func (lim *Limiter) Reserve() *Reservation {
-
return lim.ReserveN(time.Now(), 1)
-
}
-
-
// ReserveN returns a Reservation that indicates how long the caller must wait before n events happen.
-
// The Limiter takes this Reservation into account when allowing future events.
-
// ReserveN returns false if n exceeds the Limiter's burst size.
-
// Usage example:
-
// r, ok := lim.ReserveN(time.Now(), 1)
-
// if !ok {
-
// // Not allowed to act! Did you remember to set lim.burst to be > 0 ?
-
// }
-
// time.Sleep(r.Delay())
-
// Act()
-
// Use this method if you wish to wait and slow down in accordance with the rate limit without dropping events.
-
// If you need to respect a deadline or cancel the delay, use Wait instead.
-
// To drop or skip events exceeding rate limit, use Allow instead.
-
func (lim *Limiter) ReserveN(now time.Time, n int) *Reservation {
-
r := lim.reserveN(now, n, InfDuration)
-
return &r
-
}
-
-
// Wait is shorthand for WaitN(ctx, 1).
-
func (lim *Limiter) Wait(ctx context.Context) (err error) {
-
return lim.WaitN(ctx, 1)
-
}
-
-
// WaitN blocks until lim permits n events to happen.
-
// It returns an error if n exceeds the Limiter's burst size, the Context is
-
// canceled, or the expected wait time exceeds the Context's Deadline.
-
func (lim *Limiter) WaitN(ctx context.Context, n int) (err error) {
-
if n > lim.burst {
-
return fmt.Errorf("rate: Wait(n=%d) exceeds limiter's burst %d", n, lim.burst)
-
}
-
// Check if ctx is already cancelled
-
select {
-
case <-ctx.Done():
-
return ctx.Err()
-
default:
-
}
-
// Determine wait limit
-
now := time.Now()
-
waitLimit := InfDuration
-
if deadline, ok := ctx.Deadline(); ok {
-
waitLimit = deadline.Sub(now)
-
}
-
// Reserve
-
r := lim.reserveN(now, n, waitLimit)
-
if !r.ok {
-
return fmt.Errorf("rate: Wait(n=%d) would exceed context deadline", n)
-
}
-
// Wait
-
t := time.NewTimer(r.DelayFrom(now))
-
defer t.Stop()
-
select {
-
case <-t.C:
-
// We can proceed.
-
return nil
-
case <-ctx.Done():
-
// Context was canceled before we could proceed. Cancel the
-
// reservation, which may permit other events to proceed sooner.
-
r.Cancel()
-
return ctx.Err()
-
}
-
}
-
-
// SetLimit is shorthand for SetLimitAt(time.Now(), newLimit).
-
func (lim *Limiter) SetLimit(newLimit Limit) {
-
lim.SetLimitAt(time.Now(), newLimit)
-
}
-
-
// SetLimitAt sets a new Limit for the limiter. The new Limit, and Burst, may be violated
-
// or underutilized by those which reserved (using Reserve or Wait) but did not yet act
-
// before SetLimitAt was called.
-
func (lim *Limiter) SetLimitAt(now time.Time, newLimit Limit) {
-
lim.mu.Lock()
-
defer lim.mu.Unlock()
-
now, _, tokens := lim.advance(now)
-
lim.last = now
-
lim.tokens = tokens
-
lim.limit = newLimit
-
}
-
-
// reserveN is a helper method for AllowN, ReserveN, and WaitN.
-
// maxFutureReserve specifies the maximum reservation wait duration allowed.
-
// reserveN returns Reservation, not *Reservation, to avoid allocation in AllowN and WaitN.
-
func (lim *Limiter) reserveN(now time.Time, n int, maxFutureReserve time.Duration) Reservation {
-
lim.mu.Lock()
-
defer lim.mu.Unlock()
-
if lim.limit == Inf {
-
return Reservation{
-
ok: true,
-
lim: lim,
-
tokens: n,
-
timeToAct: now,
-
}
-
}
-
now, last, tokens := lim.advance(now)
-
// Calculate the remaining number of tokens resulting from the request.
-
tokens -= float64(n)
-
// Calculate the wait duration
-
var waitDuration time.Duration
-
if tokens < 0 {
-
waitDuration = lim.limit.durationFromTokens(-tokens)
-
}
-
// Decide result
-
ok := n <= lim.burst && waitDuration <= maxFutureReserve
-
// Prepare reservation
-
r := Reservation{
-
ok: ok,
-
lim: lim,
-
limit: lim.limit,
-
}
-
if ok {
-
r.tokens = n
-
r.timeToAct = now.Add(waitDuration)
-
}
-
// Update state
-
if ok {
-
lim.last = now
-
lim.tokens = tokens
-
lim.lastEvent = r.timeToAct
-
} else {
-
lim.last = last
-
}
-
return r
-
}
-
-
// advance calculates and returns an updated state for lim resulting from the passage of time.
-
// lim is not changed.
-
func (lim *Limiter) advance(now time.Time) (newNow time.Time, newLast time.Time, newTokens float64) {
-
last := lim.last
-
if now.Before(last) {
-
last = now
-
}
-
// Avoid making delta overflow below when last is very old.
-
maxElapsed := lim.limit.durationFromTokens(float64(lim.burst) - lim.tokens)
-
elapsed := now.Sub(last)
-
if elapsed > maxElapsed {
-
elapsed = maxElapsed
-
}
-
// Calculate the new number of tokens, due to time that passed.
-
delta := lim.limit.tokensFromDuration(elapsed)
-
tokens := lim.tokens + delta
-
if burst := float64(lim.burst); tokens > burst {
-
tokens = burst
-
}
-
return now, last, tokens
-
}
-
-
// durationFromTokens is a unit conversion function from the number of tokens to the duration
-
// of time it takes to accumulate them at a rate of limit tokens per second.
-
func (limit Limit) durationFromTokens(tokens float64) time.Duration {
-
seconds := tokens / float64(limit)
-
return time.Nanosecond * time.Duration(1e9*seconds)
-
}
-
-
// tokensFromDuration is a unit conversion function from a time duration to the number of tokens
-
// which could be accumulated during that duration at a rate of limit tokens per second.
-
func (limit Limit) tokensFromDuration(d time.Duration) float64 {
-
return d.Seconds() * float64(limit)
-
}
虽然在某些情况下使用单个全局速率限制器非常有用，但另一种常见情况是基于IP地址或API密钥等标识符为每个用户实施速率限制器。我们将使用IP地址作为标识符。简单实现代码如下：
-
package main
-
import (
-
"net/http"
-
"sync"
-
"time"
-
"golang.org/x/time/rate"
-
)
-
// Create a custom visitor struct which holds the rate limiter for each
-
// visitor and the last time that the visitor was seen.
-
type visitor struct {
-
limiter *rate.Limiter
-
lastSeen time.Time
-
}
-
// Change the the map to hold values of the type visitor.
-
var visitors = make(map[string]*visitor)
-
var mtx sync.Mutex
-
// Run a background goroutine to remove old entries from the visitors map.
-
func init() {
-
go cleanupVisitors()
-
}
-
func addVisitor(ip string) *rate.Limiter {
-
limiter := rate.NewLimiter(2, 5)
-
mtx.Lock()
-
// Include the current time when creating a new visitor.
-
visitors[ip] = &visitor{limiter, time.Now()}
-
mtx.Unlock()
-
return limiter
-
}
-
func getVisitor(ip string) *rate.Limiter {
-
mtx.Lock()
-
v, exists := visitors[ip]
-
if !exists {
-
mtx.Unlock()
-
return addVisitor(ip)
-
}
-
// Update the last seen time for the visitor.
-
v.lastSeen = time.Now()
-
mtx.Unlock()
-
return v.limiter
-
}
-
// Every minute check the map for visitors that haven't been seen for
-
// more than 3 minutes and delete the entries.
-
func cleanupVisitors() {
-
for {
-
time.Sleep(time.Minute)
-
mtx.Lock()
-
for ip, v := range visitors {
-
if time.Now().Sub(v.lastSeen) > 3*time.Minute {
-
delete(visitors, ip)
-
}
-
}
-
mtx.Unlock()
-
}
-
}
-
func limit(next http.Handler) http.Handler {
-
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-
limiter := getVisitor(r.RemoteAddr)
-
if limiter.Allow() == false {
-
http.Error(w, http.StatusText(429), http.StatusTooManyRequests)
-
return
-
}
-
next.ServeHTTP(w, r)
-
})
-
}
转载: https://blog.csdn.net/micl200110041/article/details/82013032