Implement gateway support Google Cloud Storage

vendor/cloud.google.com/go/internal/optional/optional.go

@@ -0,0 +1,94 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// 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 optional provides versions of primitive types that can
+// be nil. These are useful in methods that update some of an API object's
+// fields.
+package optional
+
+import (
+	"fmt"
+	"strings"
+)
+
+type (
+	// Bool is either a bool or nil.
+	Bool interface{}
+
+	// String is either a string or nil.
+	String interface{}
+
+	// Int is either an int or nil.
+	Int interface{}
+
+	// Uint is either a uint or nil.
+	Uint interface{}
+
+	// Float64 is either a float64 or nil.
+	Float64 interface{}
+)
+
+// ToBool returns its argument as a bool.
+// It panics if its argument is nil or not a bool.
+func ToBool(v Bool) bool {
+	x, ok := v.(bool)
+	if !ok {
+		doPanic("Bool", v)
+	}
+	return x
+}
+
+// ToString returns its argument as a string.
+// It panics if its argument is nil or not a string.
+func ToString(v String) string {
+	x, ok := v.(string)
+	if !ok {
+		doPanic("String", v)
+	}
+	return x
+}
+
+// ToInt returns its argument as an int.
+// It panics if its argument is nil or not an int.
+func ToInt(v Int) int {
+	x, ok := v.(int)
+	if !ok {
+		doPanic("Int", v)
+	}
+	return x
+}
+
+// ToUint returns its argument as a uint.
+// It panics if its argument is nil or not a uint.
+func ToUint(v Uint) uint {
+	x, ok := v.(uint)
+	if !ok {
+		doPanic("Uint", v)
+	}
+	return x
+}
+
+// ToFloat64 returns its argument as a float64.
+// It panics if its argument is nil or not a float64.
+func ToFloat64(v Float64) float64 {
+	x, ok := v.(float64)
+	if !ok {
+		doPanic("Float64", v)
+	}
+	return x
+}
+
+func doPanic(capType string, v interface{}) {
+	panic(fmt.Sprintf("optional.%s value should be %s, got %T", capType, strings.ToLower(capType), v))
+}