storage_codec.go

/*
Copyright 2017 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 (
	"fmt"
	"mime"

	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apimachinery/pkg/runtime/serializer/recognizer"
	"k8s.io/apiserver/pkg/storage/storagebackend"

	"github.com/golang/glog"
)

// StorageCodecConfig are the arguments passed to newStorageCodecFn
type StorageCodecConfig struct {
	StorageMediaType  string
	StorageSerializer runtime.StorageSerializer
	StorageVersion    schema.GroupVersion
	MemoryVersion     schema.GroupVersion
	Config            storagebackend.Config

	EncoderDecoratorFn func(runtime.Encoder) runtime.Encoder
	DecoderDecoratorFn func([]runtime.Decoder) []runtime.Decoder
}

// NewStorageCodec assembles a storage codec for the provided storage media type, the provided serializer, and the requested
// storage and memory versions.
func NewStorageCodec(opts StorageCodecConfig) (runtime.Codec, error) {
	mediaType, _, err := mime.ParseMediaType(opts.StorageMediaType)
	if err != nil {
		return nil, fmt.Errorf("%q is not a valid mime-type", opts.StorageMediaType)
	}
	serializer, ok := runtime.SerializerInfoForMediaType(opts.StorageSerializer.SupportedMediaTypes(), mediaType)
	if !ok {
		return nil, fmt.Errorf("unable to find serializer for %q", opts.StorageMediaType)
	}

	s := serializer.Serializer

	// etcd2 only supports string data - we must wrap any result before returning
	// TODO: storagebackend should return a boolean indicating whether it supports binary data
	if !serializer.EncodesAsText && opts.Config.Type == storagebackend.StorageTypeETCD2 {
		glog.V(4).Infof("Wrapping the underlying binary storage serializer with a base64 encoding for etcd2")
		s = runtime.NewBase64Serializer(s)
	}

	// Give callers the opportunity to wrap encoders and decoders.  For decoders, each returned decoder will
	// be passed to the recognizer so that multiple decoders are available.
	var encoder runtime.Encoder = s
	if opts.EncoderDecoratorFn != nil {
		encoder = opts.EncoderDecoratorFn(encoder)
	}
	decoders := []runtime.Decoder{s, opts.StorageSerializer.UniversalDeserializer()}
	if opts.DecoderDecoratorFn != nil {
		decoders = opts.DecoderDecoratorFn(decoders)
	}

	// Ensure the storage receives the correct version.
	encoder = opts.StorageSerializer.EncoderForVersion(
		encoder,
		runtime.NewMultiGroupVersioner(
			opts.StorageVersion,
			schema.GroupKind{Group: opts.StorageVersion.Group},
			schema.GroupKind{Group: opts.MemoryVersion.Group},
		),
	)
	decoder := opts.StorageSerializer.DecoderToVersion(
		recognizer.NewDecoder(decoders...),
		runtime.NewMultiGroupVersioner(
			opts.MemoryVersion,
			schema.GroupKind{Group: opts.MemoryVersion.Group},
			schema.GroupKind{Group: opts.StorageVersion.Group},
		),
	)

	return runtime.NewCodec(encoder, decoder), nil
}