Add package libbeat/common/cleanup (elastic#12134)

* Add package libbeat/common/cleanup

The cleanup package adds helpers for deferred optional cleanup on
errors.

For example:

```
ok := False
defer cleanup.IfNot(&ok, func() { ... })

// continue initialization

ok = True
return // some value
```

* Add changelog entry

CHANGELOG-developer.next.asciidoc

@@ -37,3 +37,4 @@ The list below covers the major changes between 7.0.0-rc2 and master only.
 - Update Jinja2 version to 2.10.1. {pull}11817[11817]
 - Reduce idxmgmt.Supporter interface and rework export commands to reuse logic. {pull}11777[11777], {pull}12065[12065], {pull}12067[12067]
 - Update urllib3 version to 1.24.2 {pull}11930[11930]
+- Add libbeat/common/cleanup package. {pull}12134[12134]

libbeat/common/cleanup/cleanup.go

@@ -0,0 +1,74 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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 cleanup provides common helpers for common cleanup patterns on defer
+//
+// Use the helpers with `defer`. For example use IfNot with `defer`, such that
+// cleanup functions will be executed if `check` is false, no matter if an
+// error has been returned or an panic has occured.
+//
+//     initOK := false
+//     defer cleanup.IfNot(&initOK, func() {
+//       cleanup
+//     })
+//
+//     ... // init structures...
+//
+//     initOK = true // notify handler cleanup code must not be executed
+package cleanup
+
+// If will run the cleanup function if the bool value is true.
+func If(check *bool, cleanup func()) {
+	if *check {
+		cleanup()
+	}
+}
+
+// IfNot will run the cleanup function if the bool value is false.
+func IfNot(check *bool, cleanup func()) {
+	if !(*check) {
+		cleanup()
+	}
+}
+
+// IfPred will run the cleanup function if pred returns true.
+func IfPred(pred func() bool, cleanup func()) {
+	if pred() {
+		cleanup()
+	}
+}
+
+// IfNotPred will run the cleanup function if pred returns false.
+func IfNotPred(pred func() bool, cleanup func()) {
+	if !pred() {
+		cleanup()
+	}
+}
+
+// WithError returns a cleanup function calling a custom handler if an error occured.
+func WithError(fn func(error), cleanup func() error) func() {
+	return func() {
+		if err := cleanup(); err != nil {
+			fn(err)
+		}
+	}
+}
+
+// IgnoreError silently ignores errors in the cleanup function.
+func IgnoreError(cleanup func() error) func() {
+	return func() { _ = cleanup() }
+}

libbeat/common/cleanup/cleanup_test.go

@@ -0,0 +1,65 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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 cleanup_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/elastic/beats/libbeat/common/cleanup"
+)
+
+func TestIfBool(t *testing.T) {
+	testcases := []struct {
+		title   string
+		fn      func(*bool, func())
+		value   bool
+		cleanup bool
+	}{
+		{
+			"IfNot runs cleanup",
+			cleanup.IfNot, false, true,
+		},
+		{
+			"IfNot does not run cleanup",
+			cleanup.IfNot, true, false,
+		},
+		{
+			"If runs cleanup",
+			cleanup.If, true, true,
+		},
+		{
+			"If does not run cleanup",
+			cleanup.If, false, false,
+		},
+	}
+
+	for _, test := range testcases {
+		test := test
+		t.Run(test.title, func(t *testing.T) {
+			executed := false
+			func() {
+				v := test.value
+				defer test.fn(&v, func() { executed = true })
+			}()
+
+			assert.Equal(t, test.cleanup, executed)
+		})
+	}
+}

libbeat/common/cleanup/multi.go

@@ -0,0 +1,46 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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 cleanup
+
+// FailClean keeps track of functions to be executed of FailClean did
+// not receive a success signal.
+type FailClean struct {
+	success bool
+	fns     []func()
+}
+
+// Signal sends a success or fail signal to FailClean.
+func (f *FailClean) Signal(success bool) {
+	f.success = success
+}
+
+// Add adds another cleanup handler. The last added handler will be run first.
+func (f *FailClean) Add(fn func()) {
+	f.fns = append(f.fns, fn)
+}
+
+// Cleanup runs all cleanup handlers in reverse order.
+func (f *FailClean) Cleanup() {
+	if f.success {
+		return
+	}
+
+	for i := len(f.fns) - 1; i >= 0; i-- {
+		f.fns[i]()
+	}
+}