From bce45c237973c2b0defb07a5b91b079fd06a7879 Mon Sep 17 00:00:00 2001
From: Edward <crazybber@outlook.com>
Date: Tue, 28 Apr 2020 22:48:09 +0800
Subject: [PATCH] add circuit_breaker /rate_limiting

---
 .../circuit_breaker/circuit_breaker_test.go   |  57 ++++++++++
 gomore/rate_limiting/rate_limiting_test.go    | 105 ++++++++++++++++++
 2 files changed, 162 insertions(+)
 create mode 100644 gomore/circuit_breaker/circuit_breaker_test.go
 create mode 100644 gomore/rate_limiting/rate_limiting_test.go

diff --git a/gomore/circuit_breaker/circuit_breaker_test.go b/gomore/circuit_breaker/circuit_breaker_test.go
new file mode 100644
index 0000000..355c9e4
--- /dev/null
+++ b/gomore/circuit_breaker/circuit_breaker_test.go
@@ -0,0 +1,57 @@
+package circuit
+
+import (
+	"context"
+	"time"
+)
+
+type State int
+
+const (
+	UnknownState State = iota
+	FailureState
+	SuccessState
+)
+
+type Counter interface {
+	Count(State)
+	ConsecutiveFailures() uint32
+	LastActivity() time.Time
+	Reset()
+}
+
+type Circuit func(context.Context) error
+
+func Breaker(c Circuit, failureThreshold uint32) Circuit {
+	cnt := NewCounter()
+
+	return func(ctx context) error {
+		if cnt.ConsecutiveFailures() >= failureThreshold {
+			canRetry := func(cnt Counter) {
+				backoffLevel := Cnt.ConsecutiveFailures() - failureThreshold
+
+				// Calculates when should the circuit breaker resume propagating requests
+				// to the service
+				shouldRetryAt := cnt.LastActivity().Add(time.Seconds * 2 << backoffLevel)
+
+				return time.Now().After(shouldRetryAt)
+			}
+
+			if !canRetry(cnt) {
+				// Fails fast instead of propagating requests to the circuit since
+				// not enough time has passed since the last failure to retry
+				return ErrServiceUnavailable
+			}
+		}
+
+		// Unless the failure threshold is exceeded the wrapped service mimics the
+		// old behavior and the difference in behavior is seen after consecutive failures
+		if err := c(ctx); err != nil {
+			cnt.Count(FailureState)
+			return err
+		}
+
+		cnt.Count(SuccessState)
+		return nil
+	}
+}
diff --git a/gomore/rate_limiting/rate_limiting_test.go b/gomore/rate_limiting/rate_limiting_test.go
new file mode 100644
index 0000000..57f10df
--- /dev/null
+++ b/gomore/rate_limiting/rate_limiting_test.go
@@ -0,0 +1,105 @@
+package ratelimit
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+/*
+
+Rate limiting is an very important mechanism
+With limiting you can controll resource utilization and maintain quality of service.
+Go  supports rate limiting by using goroutines, channels, and tickers.
+*/
+
+func TestRateLimiting(t *testing.T) {
+	requests := make(chan int, 5)
+	for i := 1; i <= 5; i++ {
+		requests <- i
+	}
+	close(requests)
+
+	limiter := time.Tick(200 * time.Millisecond)
+
+	for req := range requests {
+		<-limiter
+		t.Log("Sev request by 2000 Millisecond", req, time.Now())
+	}
+
+	burstyLimiter := make(chan struct{}, 3)
+
+	//init burstyLimiter
+	for i := 0; i < 3; i++ {
+		burstyLimiter <- struct{}{}
+	}
+	go func() {
+		for {
+			select {
+			case <-time.Tick(200 * time.Millisecond):
+				burstyLimiter <- struct{}{}
+			}
+
+		}
+	}()
+
+	//max request queue
+	burstyRequestsQueue := make(chan int, 5)
+	for i := 1; i <= 5; i++ {
+		burstyRequestsQueue <- i
+	}
+	close(burstyRequestsQueue)
+
+	for req := range burstyRequestsQueue {
+		<-burstyLimiter
+		if len(burstyLimiter) > 0 {
+			fmt.Println("working current in bursting status!")
+		} else {
+			fmt.Println("working current in normal status!")
+		}
+		fmt.Println("request handled", req, time.Now())
+	}
+
+	rateLimiting()
+
+}
+
+func rateLimiting() {
+
+	requests := make(chan int, 5)
+	for i := 1; i <= 5; i++ {
+		requests <- i
+	}
+	close(requests)
+
+	limiter := time.Tick(200 * time.Millisecond)
+
+	for req := range requests {
+		<-limiter
+		fmt.Println("request", req, time.Now())
+	}
+
+	//突发限流器
+	burstyLimiter := make(chan time.Time, 3)
+
+	for i := 0; i < 3; i++ {
+		burstyLimiter <- time.Now()
+	}
+
+	go func() {
+		for t := range time.Tick(200 * time.Millisecond) {
+			burstyLimiter <- t
+		}
+	}()
+
+	//请求队列
+	burstyRequests := make(chan int, 5)
+	for i := 1; i <= 5; i++ {
+		burstyRequests <- i
+	}
+	close(burstyRequests)
+	for req := range burstyRequests {
+		<-burstyLimiter
+		fmt.Println("request", req, time.Now())
+	}
+}