Golang实现请求限流的几种办法

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Golang实现请求限流的几种办法
目录

简单的并发控制

使用计数器实现请求限流

使用golang官方包实现httpserver频率限制

使用Token Bucket（令牌桶算法）实现请求限流

 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。
1. for i, sleeptime := range input {
2. chs[i] = make(chan string, 1)
3. chLimit <- true
4. go limitFunc(chLimit, chs[i], i, sleeptime, timeout)
5. }
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。
1. limitFunc := func(chLimit chan bool, ch chan string, task_id, sleeptime, timeout int) {
2. Run(task_id, sleeptime, timeout, ch)
3. <-chLimit
4. }
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：
1. package main
3. import (
4. "fmt"
5. "time"
6. )
8. func Run(task_id, sleeptime, timeout int, ch chan string) {
9. ch_run := make(chan string)
10. go run(task_id, sleeptime, ch_run)
11. select {
12. case re := <-ch_run:
13. ch <- re
14. case <-time.After(time.Duration(timeout) * time.Second):
15. re := fmt.Sprintf("task id %d , timeout", task_id)
16. ch <- re
17. }
18. }
20. func run(task_id, sleeptime int, ch chan string) {
22. time.Sleep(time.Duration(sleeptime) * time.Second)
23. ch <- fmt.Sprintf("task id %d , sleep %d second", task_id, sleeptime)
24. return
25. }
27. func main() {
28. input := []int{3, 2, 1}
29. timeout := 2
30. chLimit := make(chan bool, 1)
31. chs := make([]chan string, len(input))
32. limitFunc := func(chLimit chan bool, ch chan string, task_id, sleeptime, timeout int) {
33. Run(task_id, sleeptime, timeout, ch)
34. <-chLimit
35. }
36. startTime := time.Now()
37. fmt.Println("Multirun start")
38. for i, sleeptime := range input {
39. chs[i] = make(chan string, 1)
40. chLimit <- true
41. go limitFunc(chLimit, chs[i], i, sleeptime, timeout)
42. }
44. for _, ch := range chs {
45. fmt.Println(<-ch)
46. }
47. endTime := time.Now()
48. fmt.Printf("Multissh finished. Process time %s. Number of task is %d", endTime.Sub(startTime), len(input))
49. }
运行结果：
1. Multirun start
2. task id 0 , timeout
3. task id 1 , timeout
4. task id 2 , sleep 1 second
5. 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：
2. Multirun start
3. task id 0 , timeout
4. task id 1 , timeout
5. task id 2 , sleep 1 second
6. 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：
1. type RequestLimitService struct {
2. Interval time.Duration
3. MaxCount int
4. Lock sync.Mutex
5. ReqCount int
6. }
8. func NewRequestLimitService(interval time.Duration, maxCnt int) *RequestLimitService {
9. reqLimit := &RequestLimitService{
10. Interval: interval,
11. MaxCount: maxCnt,
12. }
14. go func() {
15. ticker := time.NewTicker(interval)
16. for {
17. <-ticker.C
18. reqLimit.Lock.Lock()
19. fmt.Println("Reset Count...")
20. reqLimit.ReqCount = 0
21. reqLimit.Lock.Unlock()
22. }
23. }()
25. return reqLimit
26. }
28. func (reqLimit *RequestLimitService) Increase() {
29. reqLimit.Lock.Lock()
30. defer reqLimit.Lock.Unlock()
32. reqLimit.ReqCount += 1
33. }
35. func (reqLimit *RequestLimitService) IsAvailable() bool {
36. reqLimit.Lock.Lock()
37. defer reqLimit.Lock.Unlock()
39. return reqLimit.ReqCount < reqLimit.MaxCount
40. }
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：
1. var RequestLimit = NewRequestLimitService(10 * time.Second, 5)
3. func helloHandler(w http.ResponseWriter, r *http.Request) {
4. if RequestLimit.IsAvailable() {
5. RequestLimit.Increase()
6. fmt.Println(RequestLimit.ReqCount)
7. io.WriteString(w, "Hello world! ")
8. } else {
9. fmt.Println("Reach request limiting!")
10. io.WriteString(w, "Reach request limit! ")
11. }
12. }
14. func main() {
15. fmt.Println("Server Started!")
16. http.HandleFunc("/", helloHandler)
17. http.ListenAndServe(":8000", nil)
18. }
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：
1. import(
2. "fmt"
3. "net"
4. "golang.org/x/net/netutil"
5. )
7. func main() {
8. l, err := net.Listen("tcp", "127.0.0.1:0")
9. if err != nil {
10. fmt.Fatalf("Listen: %v", err)
11. }
12. defer l.Close()
13. l = LimitListener(l, max)
15. http.Serve(l, http.HandlerFunc())
17. //bla bla bla.................
18. }
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。
1. // Copyright 2013 The Go Authors. All rights reserved.
2. // Use of this source code is governed by a BSD-style
3. // license that can be found in the LICENSE file.
5. // Package netutil provides network utility functions, complementing the more
6. // common ones in the net package.
7. package netutil // import "golang.org/x/net/netutil"
9. import (
10. "net"
11. "sync"
12. )
14. // LimitListener returns a Listener that accepts at most n simultaneous
15. // connections from the provided Listener.
16. func LimitListener(l net.Listener, n int) net.Listener {
17. return &limitListener{
18. Listener: l,
19. sem: make(chan struct{}, n),
20. done: make(chan struct{}),
21. }
22. }
24. type limitListener struct {
25. net.Listener
26. sem chan struct{}
27. closeOnce sync.Once // ensures the done chan is only closed once
28. done chan struct{} // no values sent; closed when Close is called
29. }
31. // acquire acquires the limiting semaphore. Returns true if successfully
32. // accquired, false if the listener is closed and the semaphore is not
33. // acquired.
34. func (l *limitListener) acquire() bool {
35. select {
36. case <-l.done:
37. return false
38. case l.sem <- struct{}{}:
39. return true
40. }
41. }
42. func (l *limitListener) release() { <-l.sem }
44. func (l *limitListener) Accept() (net.Conn, error) {
45. //如果sem满了，就会阻塞在这
46. acquired := l.acquire()
47. // If the semaphore isn't acquired because the listener was closed, expect
48. // that this call to accept won't block, but immediately return an error.
49. c, err := l.Listener.Accept()
50. if err != nil {
51. if acquired {
52. l.release()
53. }
54. return nil, err
55. }
56. return &limitListenerConn{Conn: c, release: l.release}, nil
57. }
59. func (l *limitListener) Close() error {
60. err := l.Listener.Close()
61. l.closeOnce.Do(func() { close(l.done) })
62. return err
63. }
65. type limitListenerConn struct {
66. net.Conn
67. releaseOnce sync.Once
68. release func()
69. }
71. func (l *limitListenerConn) Close() error {
72. err := l.Conn.Close()
73. //close时释放占用的sem
74. l.releaseOnce.Do(l.release)
75. return err
76. }
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：
1. package main
3. import (
4. "net/http"
5. "golang.org/x/time/rate"
6. )
8. var limiter = rate.NewLimiter(2, 5)
9. func limit(next http.Handler) http.Handler {
10. return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
11. if limiter.Allow() == false {
12. http.Error(w, http.StatusText(429), http.StatusTooManyRequests)
13. return
14. }
15. next.ServeHTTP(w, r)
16. })
17. }
19. func main() {
20. mux := http.NewServeMux()
21. mux.HandleFunc("/", okHandler)
22. // Wrap the servemux with the limit middleware.
23. http.ListenAndServe(":4000", limit(mux))
24. }
26. func okHandler(w http.ResponseWriter, r *http.Request) {
27. w.Write([]byte("OK"))
28. }
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；
1. // Copyright 2015 The Go Authors. All rights reserved.
2. // Use of this source code is governed by a BSD-style
3. // license that can be found in the LICENSE file.
4. // Package rate provides a rate limiter.
5. package rate
7. import (
8. "fmt"
9. "math"
10. "sync"
11. "time"
13. "golang.org/x/net/context"
14. )
16. // Limit defines the maximum frequency of some events.
17. // Limit is represented as number of events per second.
18. // A zero Limit allows no events.
19. type Limit float64
21. // Inf is the infinite rate limit; it allows all events (even if burst is zero).
22. const Inf = Limit(math.MaxFloat64)
24. // Every converts a minimum time interval between events to a Limit.
25. func Every(interval time.Duration) Limit {
26. if interval <= 0 {
27. return Inf
28. }
29. return 1 / Limit(interval.Seconds())
30. }
32. // A Limiter controls how frequently events are allowed to happen.
33. // It implements a "token bucket" of size b, initially full and refilled
34. // at rate r tokens per second.
35. // Informally, in any large enough time interval, the Limiter limits the
36. // rate to r tokens per second, with a maximum burst size of b events.
37. // As a special case, if r == Inf (the infinite rate), b is ignored.
38. // See https://en.wikipedia.org/wiki/Token_bucket for more about token buckets.
39. //
40. // The zero value is a valid Limiter, but it will reject all events.
41. // Use NewLimiter to create non-zero Limiters.
42. //
43. // Limiter has three main methods, Allow, Reserve, and Wait.
44. // Most callers should use Wait.
45. //
46. // Each of the three methods consumes a single token.
47. // They differ in their behavior when no token is available.
48. // If no token is available, Allow returns false.
49. // If no token is available, Reserve returns a reservation for a future token
50. // and the amount of time the caller must wait before using it.
51. // If no token is available, Wait blocks until one can be obtained
52. // or its associated context.Context is canceled.
53. //
54. // The methods AllowN, ReserveN, and WaitN consume n tokens.
55. type Limiter struct {
56. //maximum token, token num per second
57. limit Limit
58. //burst field, max token num
59. burst int
60. mu sync.Mutex
61. //tokens num, change
62. tokens float64
63. // last is the last time the limiter's tokens field was updated
64. last time.Time
65. // lastEvent is the latest time of a rate-limited event (past or future)
66. lastEvent time.Time
67. }
69. // Limit returns the maximum overall event rate.
70. func (lim *Limiter) Limit() Limit {
71. lim.mu.Lock()
72. defer lim.mu.Unlock()
73. return lim.limit
74. }
76. // Burst returns the maximum burst size. Burst is the maximum number of tokens
77. // that can be consumed in a single call to Allow, Reserve, or Wait, so higher
78. // Burst values allow more events to happen at once.
79. // A zero Burst allows no events, unless limit == Inf.
80. func (lim *Limiter) Burst() int {
81. return lim.burst
82. }
84. // NewLimiter returns a new Limiter that allows events up to rate r and permits
85. // bursts of at most b tokens.
86. func NewLimiter(r Limit, b int) *Limiter {
87. return &Limiter{
88. limit: r,
89. burst: b,
90. }
91. }
93. // Allow is shorthand for AllowN(time.Now(), 1).
94. func (lim *Limiter) Allow() bool {
95. return lim.AllowN(time.Now(), 1)
96. }
98. // AllowN reports whether n events may happen at time now.
99. // Use this method if you intend to drop / skip events that exceed the rate limit.
100. // Otherwise use Reserve or Wait.
101. func (lim *Limiter) AllowN(now time.Time, n int) bool {
102. return lim.reserveN(now, n, 0).ok
103. }
105. // A Reservation holds information about events that are permitted by a Limiter to happen after a delay.
106. // A Reservation may be canceled, which may enable the Limiter to permit additional events.
107. type Reservation struct {
108. ok bool
109. lim *Limiter
110. tokens int
111. //This is the time to action
112. timeToAct time.Time
113. // This is the Limit at reservation time, it can change later.
114. limit Limit
115. }
117. // OK returns whether the limiter can provide the requested number of tokens
118. // within the maximum wait time. If OK is false, Delay returns InfDuration, and
119. // Cancel does nothing.
120. func (r *Reservation) OK() bool {
121. return r.ok
122. }
124. // Delay is shorthand for DelayFrom(time.Now()).
125. func (r *Reservation) Delay() time.Duration {
126. return r.DelayFrom(time.Now())
127. }
129. // InfDuration is the duration returned by Delay when a Reservation is not OK.
130. const InfDuration = time.Duration(1<<63 - 1)
132. // DelayFrom returns the duration for which the reservation holder must wait
133. // before taking the reserved action. Zero duration means act immediately.
134. // InfDuration means the limiter cannot grant the tokens requested in this
135. // Reservation within the maximum wait time.
136. func (r *Reservation) DelayFrom(now time.Time) time.Duration {
137. if !r.ok {
138. return InfDuration
139. }
140. delay := r.timeToAct.Sub(now)
141. if delay < 0 {
142. return 0
143. }
144. return delay
145. }
147. // Cancel is shorthand for CancelAt(time.Now()).
148. func (r *Reservation) Cancel() {
149. r.CancelAt(time.Now())
150. return
151. }
153. // CancelAt indicates that the reservation holder will not perform the reserved action
154. // and reverses the effects of this Reservation on the rate limit as much as possible,
155. // considering that other reservations may have already been made.
156. func (r *Reservation) CancelAt(now time.Time) {
157. if !r.ok {
158. return
159. }
160. r.lim.mu.Lock()
161. defer r.lim.mu.Unlock()
162. if r.lim.limit == Inf || r.tokens == 0 || r.timeToAct.Before(now) {
163. return
164. }
165. // calculate tokens to restore
166. // The duration between lim.lastEvent and r.timeToAct tells us how many tokens were reserved
167. // after r was obtained. These tokens should not be restored.
168. restoreTokens := float64(r.tokens) - r.limit.tokensFromDuration(r.lim.lastEvent.Sub(r.timeToAct))
169. if restoreTokens <= 0 {
170. return
171. }
172. // advance time to now
173. now, _, tokens := r.lim.advance(now)
174. // calculate new number of tokens
175. tokens += restoreTokens
176. if burst := float64(r.lim.burst); tokens > burst {
177. tokens = burst
178. }
179. // update state
180. r.lim.last = now
181. r.lim.tokens = tokens
182. if r.timeToAct == r.lim.lastEvent {
183. prevEvent := r.timeToAct.Add(r.limit.durationFromTokens(float64(-r.tokens)))
184. if !prevEvent.Before(now) {
185. r.lim.lastEvent = prevEvent
186. }
187. }
188. return
189. }
191. // Reserve is shorthand for ReserveN(time.Now(), 1).
192. func (lim *Limiter) Reserve() *Reservation {
193. return lim.ReserveN(time.Now(), 1)
194. }
196. // ReserveN returns a Reservation that indicates how long the caller must wait before n events happen.
197. // The Limiter takes this Reservation into account when allowing future events.
198. // ReserveN returns false if n exceeds the Limiter's burst size.
199. // Usage example:
200. // r, ok := lim.ReserveN(time.Now(), 1)
201. // if !ok {
202. // // Not allowed to act! Did you remember to set lim.burst to be > 0 ?
203. // }
204. // time.Sleep(r.Delay())
205. // Act()
206. // Use this method if you wish to wait and slow down in accordance with the rate limit without dropping events.
207. // If you need to respect a deadline or cancel the delay, use Wait instead.
208. // To drop or skip events exceeding rate limit, use Allow instead.
209. func (lim *Limiter) ReserveN(now time.Time, n int) *Reservation {
210. r := lim.reserveN(now, n, InfDuration)
211. return &r
212. }
214. // Wait is shorthand for WaitN(ctx, 1).
215. func (lim *Limiter) Wait(ctx context.Context) (err error) {
216. return lim.WaitN(ctx, 1)
217. }
219. // WaitN blocks until lim permits n events to happen.
220. // It returns an error if n exceeds the Limiter's burst size, the Context is
221. // canceled, or the expected wait time exceeds the Context's Deadline.
222. func (lim *Limiter) WaitN(ctx context.Context, n int) (err error) {
223. if n > lim.burst {
224. return fmt.Errorf("rate: Wait(n=%d) exceeds limiter's burst %d", n, lim.burst)
225. }
226. // Check if ctx is already cancelled
227. select {
228. case <-ctx.Done():
229. return ctx.Err()
230. default:
231. }
232. // Determine wait limit
233. now := time.Now()
234. waitLimit := InfDuration
235. if deadline, ok := ctx.Deadline(); ok {
236. waitLimit = deadline.Sub(now)
237. }
238. // Reserve
239. r := lim.reserveN(now, n, waitLimit)
240. if !r.ok {
241. return fmt.Errorf("rate: Wait(n=%d) would exceed context deadline", n)
242. }
243. // Wait
244. t := time.NewTimer(r.DelayFrom(now))
245. defer t.Stop()
246. select {
247. case <-t.C:
248. // We can proceed.
249. return nil
250. case <-ctx.Done():
251. // Context was canceled before we could proceed. Cancel the
252. // reservation, which may permit other events to proceed sooner.
253. r.Cancel()
254. return ctx.Err()
255. }
256. }
258. // SetLimit is shorthand for SetLimitAt(time.Now(), newLimit).
259. func (lim *Limiter) SetLimit(newLimit Limit) {
260. lim.SetLimitAt(time.Now(), newLimit)
261. }
263. // SetLimitAt sets a new Limit for the limiter. The new Limit, and Burst, may be violated
264. // or underutilized by those which reserved (using Reserve or Wait) but did not yet act
265. // before SetLimitAt was called.
266. func (lim *Limiter) SetLimitAt(now time.Time, newLimit Limit) {
267. lim.mu.Lock()
268. defer lim.mu.Unlock()
269. now, _, tokens := lim.advance(now)
270. lim.last = now
271. lim.tokens = tokens
272. lim.limit = newLimit
273. }
275. // reserveN is a helper method for AllowN, ReserveN, and WaitN.
276. // maxFutureReserve specifies the maximum reservation wait duration allowed.
277. // reserveN returns Reservation, not *Reservation, to avoid allocation in AllowN and WaitN.
278. func (lim *Limiter) reserveN(now time.Time, n int, maxFutureReserve time.Duration) Reservation {
279. lim.mu.Lock()
280. defer lim.mu.Unlock()
281. if lim.limit == Inf {
282. return Reservation{
283. ok: true,
284. lim: lim,
285. tokens: n,
286. timeToAct: now,
287. }
288. }
289. now, last, tokens := lim.advance(now)
290. // Calculate the remaining number of tokens resulting from the request.
291. tokens -= float64(n)
292. // Calculate the wait duration
293. var waitDuration time.Duration
294. if tokens < 0 {
295. waitDuration = lim.limit.durationFromTokens(-tokens)
296. }
297. // Decide result
298. ok := n <= lim.burst && waitDuration <= maxFutureReserve
299. // Prepare reservation
300. r := Reservation{
301. ok: ok,
302. lim: lim,
303. limit: lim.limit,
304. }
305. if ok {
306. r.tokens = n
307. r.timeToAct = now.Add(waitDuration)
308. }
309. // Update state
310. if ok {
311. lim.last = now
312. lim.tokens = tokens
313. lim.lastEvent = r.timeToAct
314. } else {
315. lim.last = last
316. }
317. return r
318. }
320. // advance calculates and returns an updated state for lim resulting from the passage of time.
321. // lim is not changed.
322. func (lim *Limiter) advance(now time.Time) (newNow time.Time, newLast time.Time, newTokens float64) {
323. last := lim.last
324. if now.Before(last) {
325. last = now
326. }
327. // Avoid making delta overflow below when last is very old.
328. maxElapsed := lim.limit.durationFromTokens(float64(lim.burst) - lim.tokens)
329. elapsed := now.Sub(last)
330. if elapsed > maxElapsed {
331. elapsed = maxElapsed
332. }
333. // Calculate the new number of tokens, due to time that passed.
334. delta := lim.limit.tokensFromDuration(elapsed)
335. tokens := lim.tokens + delta
336. if burst := float64(lim.burst); tokens > burst {
337. tokens = burst
338. }
339. return now, last, tokens
340. }
342. // durationFromTokens is a unit conversion function from the number of tokens to the duration
343. // of time it takes to accumulate them at a rate of limit tokens per second.
344. func (limit Limit) durationFromTokens(tokens float64) time.Duration {
345. seconds := tokens / float64(limit)
346. return time.Nanosecond * time.Duration(1e9*seconds)
347. }
349. // tokensFromDuration is a unit conversion function from a time duration to the number of tokens
350. // which could be accumulated during that duration at a rate of limit tokens per second.
351. func (limit Limit) tokensFromDuration(d time.Duration) float64 {
352. return d.Seconds() * float64(limit)
353. }
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：
1. package main
2. import (
3. "net/http"
4. "sync"
5. "time"
6. "golang.org/x/time/rate"
7. )
8. // Create a custom visitor struct which holds the rate limiter for each
9. // visitor and the last time that the visitor was seen.
10. type visitor struct {
11. limiter *rate.Limiter
12. lastSeen time.Time
13. }
14. // Change the the map to hold values of the type visitor.
15. var visitors = make(map[string]*visitor)
16. var mtx sync.Mutex
17. // Run a background goroutine to remove old entries from the visitors map.
18. func init() {
19. go cleanupVisitors()
20. }
21. func addVisitor(ip string) *rate.Limiter {
22. limiter := rate.NewLimiter(2, 5)
23. mtx.Lock()
24. // Include the current time when creating a new visitor.
25. visitors[ip] = &visitor{limiter, time.Now()}
26. mtx.Unlock()
27. return limiter
28. }
29. func getVisitor(ip string) *rate.Limiter {
30. mtx.Lock()
31. v, exists := visitors[ip]
32. if !exists {
33. mtx.Unlock()
34. return addVisitor(ip)
35. }
36. // Update the last seen time for the visitor.
37. v.lastSeen = time.Now()
38. mtx.Unlock()
39. return v.limiter
40. }
41. // Every minute check the map for visitors that haven't been seen for
42. // more than 3 minutes and delete the entries.
43. func cleanupVisitors() {
44. for {
45. time.Sleep(time.Minute)
46. mtx.Lock()
47. for ip, v := range visitors {
48. if time.Now().Sub(v.lastSeen) > 3*time.Minute {
49. delete(visitors, ip)
50. }
51. }
52. mtx.Unlock()
53. }
54. }
55. func limit(next http.Handler) http.Handler {
56. return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
57. limiter := getVisitor(r.RemoteAddr)
58. if limiter.Allow() == false {
59. http.Error(w, http.StatusText(429), http.StatusTooManyRequests)
60. return
61. }
62. next.ServeHTTP(w, r)
63. })
64. }
转载: https://blog.csdn.net/micl200110041/article/details/82013032
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原文地址：https://www.cnblogs.com/lovezbs/p/13910575.html

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