Move Linux client & common packages into a public repo.

logtail/backoff/backoff.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2020 Tailscale Inc & 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 backoff
+
+import (
+	"context"
+	"log"
+	"math/rand"
+	"time"
+)
+
+const MAX_BACKOFF_MSEC = 30000
+
+type Backoff struct {
+	n        int
+	Name     string
+	NewTimer func(d time.Duration) *time.Timer
+}
+
+func (b *Backoff) BackOff(ctx context.Context, err error) {
+	if ctx.Err() == nil && err != nil {
+		b.n++
+		// n^2 backoff timer is a little smoother than the
+		// common choice of 2^n.
+		msec := b.n * b.n * 10
+		if msec > MAX_BACKOFF_MSEC {
+			msec = MAX_BACKOFF_MSEC
+		}
+		// Randomize the delay between 0.5-1.5 x msec, in order
+		// to prevent accidental "thundering herd" problems.
+		msec = rand.Intn(msec) + msec/2
+		log.Printf("%s: backoff: %d msec\n", b.Name, msec)
+		newTimer := b.NewTimer
+		if newTimer == nil {
+			newTimer = time.NewTimer
+		}
+		t := newTimer(time.Duration(msec) * time.Millisecond)
+		select {
+		case <-ctx.Done():
+			t.Stop()
+		case <-t.C:
+		}
+	} else {
+		// not a regular error
+		b.n = 0
+	}
+}