Add exponential backoff with jitter algorithm for retry package

common/retry/retry.go

@@ -3,6 +3,8 @@ package retry
 //go:generate go run github.com/v2fly/v2ray-core/v5/common/errors/errorgen
 
 import (
+	"math"
+	"math/rand"
 	"time"
 )
 
@@ -60,3 +62,21 @@ func ExponentialBackoff(attempts int, delay uint32) Strategy {
 		},
 	}
 }
+
+// ExponentialBackoffWithJitter return a retry exponential backoff strategy with jitter
+// http://www.awsarchitectureblog.com/2015/03/backoff.html
+func ExponentialBackoffWithJitter(attempts int, delay uint32) Strategy {
+	rr := rand.New(rand.NewSource(time.Now().UnixNano()))
+	capLevel := delay * 5
+	epoch := 0
+	return &retryer{
+		totalAttempt: attempts,
+		nextDelay: func() uint32 {
+			temp := math.Min(float64(capLevel), float64(delay)*math.Exp2(float64(epoch)))
+			ri := int64(temp / 2)
+			epoch += 1
+			jitter := rr.Int63n(ri)
+			return uint32(ri + jitter)
+		},
+	}
+}

common/retry/retry_test.go

@@ -94,3 +94,20 @@ func TestExponentialBackoff(t *testing.T) {
 		t.Error("duration: ", v)
 	}
 }
+
+func TestExponentialBackoffWithJitter(t *testing.T) {
+	startTime := time.Now()
+	called := 0
+	err := ExponentialBackoffWithJitter(10, 100).On(func() error {
+		called++
+		return errorTestOnly
+	})
+	duration := time.Since(startTime)
+
+	if errors.Cause(err) != ErrRetryFailed {
+		t.Error("cause: ", err)
+	}
+	if v := int64(duration / time.Millisecond); v < 2000 {
+		t.Error("duration: ", v)
+	}
+}