Add ‘hook’ package for retryable functions

The hook package enables static and backoff retryable functions. This package can be used for calling remote webhooks concurrently in separate goroutines.

util/hook/hook.go

@@ -0,0 +1,111 @@
+// Copyright © 2016 Abcum Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hook
+
+import (
+	"context"
+	"time"
+)
+
+const (
+	Static Kind = iota
+	Backoff
+)
+
+// Kind specifies the policy type.
+type Kind int
+
+// Policy represents a retryable function policy.
+type Policy struct {
+	// Type is the policy type
+	Type Kind
+	// Attempts to retry
+	Retry int
+	// Factor is the backoff rate
+	Factor int
+	// Sleep is the initial duration to wait before retrying
+	Sleep time.Duration
+}
+
+// New creates a new static retryable policy, which retries
+// after the duration of 'sleep', until the number of retries
+// has been reached.
+func NewStatic(retry int, sleep time.Duration) *Policy {
+	return &Policy{
+		Type:  Static,
+		Retry: retry,
+		Sleep: sleep,
+	}
+}
+
+// New creates a new backoff retryable policy, which increases
+// the delay between subsequent retries by the secified factor,
+// until the number of retries has been reached.
+func NewBackoff(retry, factor int, sleep time.Duration) *Policy {
+	return &Policy{
+		Type:   Backoff,
+		Retry:  retry,
+		Sleep:  sleep,
+		Factor: factor,
+	}
+}
+
+// Run executes a function until:
+// 1. A nil error is returned,
+// 2. The max number of retries has been reached,
+// 3. The specified context has been cancelled or timedout.
+func (p *Policy) Run(ctx context.Context, fnc func() error) error {
+
+	c := make(chan error, 1)
+
+	go func() { c <- p.run(ctx, fnc) }()
+
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case err := <-c:
+		return err
+	}
+
+}
+
+func (p *Policy) run(ctx context.Context, fnc func() error) error {
+
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+		if err := fnc(); err != nil {
+			if p.Retry > 0 {
+				p.sleep()
+				p.Retry = p.Retry - 1
+				return p.run(ctx, fnc)
+			}
+		}
+	}
+
+	return nil
+
+}
+
+func (p *Policy) sleep() {
+
+	time.Sleep(p.Sleep)
+
+	if p.Type == Backoff {
+		p.Sleep = p.Sleep * time.Duration(p.Factor)
+	}
+
+}