Svc REST: Add a transaction API

This will be used in upcoming commits, but for easier history and review
it is pretty stand-alone.

pkg/registry/core/service/storage/transaction.go

@@ -0,0 +1,62 @@
+/*
+Copyright 2020 The Kubernetes Authors.
+
+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 storage
+
+// transaction represents something that may need to be finalized on success or
+// failure of the larger transaction.
+type transaction interface {
+	// Commit tells the transaction to finalize any changes it may have
+	// pending.  This cannot fail, so errors must be handled internally.
+	Commit()
+
+	// Revert tells the transaction to abandon or undo any changes it may have
+	// pending.  This cannot fail, so errors must be handled internally.
+	Revert()
+}
+
+// metaTransaction is a collection of transactions.
+type metaTransaction []transaction
+
+func (mt metaTransaction) Commit() {
+	for _, t := range mt {
+		t.Commit()
+	}
+}
+
+func (mt metaTransaction) Revert() {
+	for _, t := range mt {
+		t.Revert()
+	}
+}
+
+// callbackTransaction is a transaction which calls arbitrary functions.
+type callbackTransaction struct {
+	commit func()
+	revert func()
+}
+
+func (cb callbackTransaction) Commit() {
+	if cb.commit != nil {
+		cb.commit()
+	}
+}
+
+func (cb callbackTransaction) Revert() {
+	if cb.revert != nil {
+		cb.revert()
+	}
+}

pkg/registry/core/service/storage/transaction_test.go

@@ -0,0 +1,167 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+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 storage
+
+import (
+	"testing"
+)
+
+func Test_metaTransaction(t *testing.T) {
+	const initial = 10
+	var temp int
+
+	tests := []struct {
+		name  string
+		mt    metaTransaction
+		start int
+		want  int
+	}{{
+		name: "commit and revert match",
+		mt: metaTransaction{
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 1
+				},
+				revert: func() {
+					temp = temp - 1
+				},
+			},
+		},
+		want: 10,
+	}, {
+		name: "commit and revert match multiple times",
+		mt: metaTransaction{
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 1
+				},
+				revert: func() {
+					temp = temp - 1
+				},
+			},
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 2
+				},
+				revert: func() {
+					temp = temp - 2
+				},
+			},
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 3
+				},
+				revert: func() {
+					temp = temp - 3
+				},
+			},
+		},
+		want: 10,
+	}, {
+		name: "missing revert",
+		mt: metaTransaction{
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 1
+				},
+				revert: func() {
+					temp = temp - 1
+				},
+			},
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 2
+				},
+			},
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 3
+				},
+				revert: func() {
+					temp = temp - 3
+				},
+			},
+		},
+		want: 12,
+	}, {
+		name: "missing commit",
+		mt: metaTransaction{
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 1
+				},
+				revert: func() {
+					temp = temp - 1
+				},
+			},
+			callbackTransaction{
+				revert: func() {
+					temp = temp - 2
+				},
+			},
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 3
+				},
+				revert: func() {
+					temp = temp - 3
+				},
+			},
+		},
+		want: 8,
+	}, {
+		name: "commit and revert match multiple but different order",
+		mt: metaTransaction{
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 1
+				},
+				revert: func() {
+					temp = temp - 2
+				},
+			},
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 2
+				},
+				revert: func() {
+					temp = temp - 1
+				},
+			},
+			callbackTransaction{
+				commit: func() {
+					temp = temp + 3
+				},
+				revert: func() {
+					temp = temp - 3
+				},
+			},
+		},
+		want: 10,
+	}}
+	t.Parallel()
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			temp = initial
+			tt.mt.Commit()
+			tt.mt.Revert()
+			if temp != tt.want {
+				t.Fatalf("expected %d got %d", tt.want, temp)
+			}
+		})
+	}
+}