context.go

/*
Copyright 2014 The Kubernetes Authors 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 api

import (
	stderrs "errors"
	"time"

	"golang.org/x/net/context"
	"k8s.io/kubernetes/pkg/auth/user"
)

// Context carries values across API boundaries.
// This context matches the context.Context interface
// (https://blog.golang.org/context), for the purposes
// of passing the api.Context through to the storage tier.
// TODO: Determine the extent that this abstraction+interface
// is used by the api, and whether we can remove.
type Context interface {
	// Value returns the value associated with key or nil if none.
	Value(key interface{}) interface{}

	// Deadline returns the time when this Context will be canceled, if any.
	Deadline() (deadline time.Time, ok bool)

	// Done returns a channel that is closed when this Context is canceled
	// or times out.
	Done() <-chan struct{}

	// Err indicates why this context was canceled, after the Done channel
	// is closed.
	Err() error
}

// The key type is unexported to prevent collisions
type key int

// namespaceKey is the context key for the request namespace.
const namespaceKey key = 0

// userKey is the context key for the request user.
const userKey key = 1

// NewContext instantiates a base context object for request flows.
func NewContext() Context {
	return context.TODO()
}

// NewDefaultContext instantiates a base context object for request flows in the default namespace
func NewDefaultContext() Context {
	return WithNamespace(NewContext(), NamespaceDefault)
}

// WithValue returns a copy of parent in which the value associated with key is val.
func WithValue(parent Context, key interface{}, val interface{}) Context {
	internalCtx, ok := parent.(context.Context)
	if !ok {
		panic(stderrs.New("Invalid context type"))
	}
	return context.WithValue(internalCtx, key, val)
}

// WithNamespace returns a copy of parent in which the namespace value is set
func WithNamespace(parent Context, namespace string) Context {
	return WithValue(parent, namespaceKey, namespace)
}

// NamespaceFrom returns the value of the namespace key on the ctx
func NamespaceFrom(ctx Context) (string, bool) {
	namespace, ok := ctx.Value(namespaceKey).(string)
	return namespace, ok
}

// NamespaceValue returns the value of the namespace key on the ctx, or the empty string if none
func NamespaceValue(ctx Context) string {
	namespace, _ := NamespaceFrom(ctx)
	return namespace
}

// ValidNamespace returns false if the namespace on the context differs from the resource.  If the resource has no namespace, it is set to the value in the context.
func ValidNamespace(ctx Context, resource *ObjectMeta) bool {
	ns, ok := NamespaceFrom(ctx)
	if len(resource.Namespace) == 0 {
		resource.Namespace = ns
	}
	return ns == resource.Namespace && ok
}

// WithNamespaceDefaultIfNone returns a context whose namespace is the default if and only if the parent context has no namespace value
func WithNamespaceDefaultIfNone(parent Context) Context {
	namespace, ok := NamespaceFrom(parent)
	if !ok || len(namespace) == 0 {
		return WithNamespace(parent, NamespaceDefault)
	}
	return parent
}

// WithUser returns a copy of parent in which the user value is set
func WithUser(parent Context, user user.Info) Context {
	return WithValue(parent, userKey, user)
}

// UserFrom returns the value of the user key on the ctx
func UserFrom(ctx Context) (user.Info, bool) {
	user, ok := ctx.Value(userKey).(user.Info)
	return user, ok
}