Create packages client/internal/ retry and lhttp.

client/internal/retry/retry.go

Index: client/internal/retry/retry.go
diff --git a/client/internal/retry/retry.go b/client/internal/retry/retry.go
new file mode 100644
index 0000000000000000000000000000000000000000..35582cb7bb542ca1f76be84146c48b3a9eeaa4e5
--- /dev/null
+++ b/client/internal/retry/retry.go
@@ -0,0 +1,66 @@
+// Copyright 2015 The Chromium 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 retry
+
+import (
+	"io"
+	"time"
+)
+
+// Default defines the default retry parameters that should be used throughout
+// the program. It is fine to update this variable on start up.
+var Default = &Config{
+	10,
+	100 * time.Millisecond,
+	500 * time.Millisecond,
+	5 * time.Second,
+}
+
+// Config defines the retry properties.
+type Config struct {
+	MaxTries            int           // Maximum number of retries.
+	SleepMax            time.Duration // Maximum duration of a single sleep.
+	SleepBase           time.Duration // Base sleep duration.
+	SleepMultiplicative time.Duration // Incremental sleep duration for each additional try.
+}
+
+// Do runs a Retriable, potentially retrying it multiple times.
+func (c *Config) Do(r Retriable) (err error) {
+	defer func() {
+		if err2 := r.Close(); err == nil {
+			err = err2
+		}
+	}()
+	for i := 0; i < c.MaxTries; i++ {
+		err = r.Do()
+		if _, ok := err.(Error); !ok {
+			return err
+		}
+		if i != c.MaxTries-1 {
+			s := c.SleepBase + time.Duration(i)*c.SleepMultiplicative
+			if s > c.SleepMax {
+				s = c.SleepMax
+			}
+			time.Sleep(s)
+		}
+	}
+	return
+}
+
+// Error is an error that can be retried.
+type Error struct {
+	Err error
+}
+
+func (e Error) Error() string {
+	return e.Err.Error()
+}
+
+// Retriable is a task that can be retried. It is important that Do be
+// idempotent.
+type Retriable interface {
+	io.Closer
+	Do() error
+}