k3s/pkg/tools/etcd_tools.go

/*
Copyright 2014 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 tools

import (
	"errors"
	"fmt"
	"reflect"

	"github.com/coreos/go-etcd/etcd"
)

const (
	EtcdErrorCodeNotFound      = 100
	EtcdErrorCodeTestFailed    = 101
	EtcdErrorCodeNodeExist     = 105
	EtcdErrorCodeValueRequired = 200
)

var (
	EtcdErrorNotFound      = &etcd.EtcdError{ErrorCode: EtcdErrorCodeNotFound}
	EtcdErrorTestFailed    = &etcd.EtcdError{ErrorCode: EtcdErrorCodeTestFailed}
	EtcdErrorNodeExist     = &etcd.EtcdError{ErrorCode: EtcdErrorCodeNodeExist}
	EtcdErrorValueRequired = &etcd.EtcdError{ErrorCode: EtcdErrorCodeValueRequired}
)

// Codec provides methods for transforming Etcd values into objects and back.
type Codec interface {
	Encode(obj interface{}) (data []byte, err error)
	Decode(data []byte) (interface{}, error)
	DecodeInto(data []byte, obj interface{}) error
}

// ResourceVersioner provides methods for managing object modification tracking.
type ResourceVersioner interface {
	SetResourceVersion(obj interface{}, version uint64) error
	ResourceVersion(obj interface{}) (uint64, error)
}

// EtcdClient is an injectable interface for testing.
type EtcdClient interface {
	AddChild(key, data string, ttl uint64) (*etcd.Response, error)
	Get(key string, sort, recursive bool) (*etcd.Response, error)
	Set(key, value string, ttl uint64) (*etcd.Response, error)
	Create(key, value string, ttl uint64) (*etcd.Response, error)
	CompareAndSwap(key, value string, ttl uint64, prevValue string, prevIndex uint64) (*etcd.Response, error)
	Delete(key string, recursive bool) (*etcd.Response, error)
	// I'd like to use directional channels here (e.g. <-chan) but this interface mimics
	// the etcd client interface which doesn't, and it doesn't seem worth it to wrap the api.
	Watch(prefix string, waitIndex uint64, recursive bool, receiver chan *etcd.Response, stop chan bool) (*etcd.Response, error)
}

// EtcdGetSet interface exposes only the etcd operations needed by EtcdHelper.
type EtcdGetSet interface {
	Get(key string, sort, recursive bool) (*etcd.Response, error)
	Set(key, value string, ttl uint64) (*etcd.Response, error)
	Create(key, value string, ttl uint64) (*etcd.Response, error)
	Delete(key string, recursive bool) (*etcd.Response, error)
	CompareAndSwap(key, value string, ttl uint64, prevValue string, prevIndex uint64) (*etcd.Response, error)
	Watch(prefix string, waitIndex uint64, recursive bool, receiver chan *etcd.Response, stop chan bool) (*etcd.Response, error)
}

// EtcdHelper offers common object marshalling/unmarshalling operations on an etcd client.
type EtcdHelper struct {
	Client EtcdGetSet
	Codec  Codec
	// optional, no atomic operations can be performed without this interface
	ResourceVersioner ResourceVersioner
}

// IsEtcdNotFound returns true iff err is an etcd not found error.
func IsEtcdNotFound(err error) bool {
	return isEtcdErrorNum(err, EtcdErrorCodeNotFound)
}

// IsEtcdNodeExist returns true iff err is an etcd node aleady exist error.
func IsEtcdNodeExist(err error) bool {
	return isEtcdErrorNum(err, EtcdErrorCodeNodeExist)
}

// IsEtcdTestFailed returns true iff err is an etcd write conflict.
func IsEtcdTestFailed(err error) bool {
	return isEtcdErrorNum(err, EtcdErrorCodeTestFailed)
}

// IsEtcdWatchStoppedByUser returns true iff err is a client triggered stop.
func IsEtcdWatchStoppedByUser(err error) bool {
	return etcd.ErrWatchStoppedByUser == err
}

// isEtcdErrorNum returns true iff err is an etcd error, whose errorCode matches errorCode
func isEtcdErrorNum(err error, errorCode int) bool {
	etcdError, ok := err.(*etcd.EtcdError)
	return ok && etcdError != nil && etcdError.ErrorCode == errorCode
}

// etcdErrorIndex returns the index associated with the error message and whether the
// index was available.
func etcdErrorIndex(err error) (uint64, bool) {
	if etcdError, ok := err.(*etcd.EtcdError); ok {
		return etcdError.Index, true
	}
	return 0, false
}

func (h *EtcdHelper) listEtcdNode(key string) ([]*etcd.Node, uint64, error) {
	result, err := h.Client.Get(key, false, true)
	if err != nil {
		index, ok := etcdErrorIndex(err)
		if !ok {
			index = 0
		}
		nodes := make([]*etcd.Node, 0)
		if IsEtcdNotFound(err) {
			return nodes, index, nil
		} else {
			return nodes, index, err
		}
	}
	return result.Node.Nodes, result.EtcdIndex, nil
}

// ExtractList extracts a go object per etcd node into a slice with the resource version.
func (h *EtcdHelper) ExtractList(key string, slicePtr interface{}, resourceVersion *uint64) error {
	nodes, index, err := h.listEtcdNode(key)
	if resourceVersion != nil {
		*resourceVersion = index
	}
	if err != nil {
		return err
	}
	pv := reflect.ValueOf(slicePtr)
	if pv.Type().Kind() != reflect.Ptr || pv.Type().Elem().Kind() != reflect.Slice {
		// This should not happen at runtime.
		panic("need ptr to slice")
	}
	v := pv.Elem()
	for _, node := range nodes {
		obj := reflect.New(v.Type().Elem())
		err = h.Codec.DecodeInto([]byte(node.Value), obj.Interface())
		if h.ResourceVersioner != nil {
			_ = h.ResourceVersioner.SetResourceVersion(obj.Interface(), node.ModifiedIndex)
			// being unable to set the version does not prevent the object from being extracted
		}
		if err != nil {
			return err
		}
		v.Set(reflect.Append(v, obj.Elem()))
	}
	return nil
}

// ExtractObj unmarshals json found at key into objPtr. On a not found error, will either return
// a zero object of the requested type, or an error, depending on ignoreNotFound. Treats
// empty responses and nil response nodes exactly like a not found error.
func (h *EtcdHelper) ExtractObj(key string, objPtr interface{}, ignoreNotFound bool) error {
	_, _, err := h.bodyAndExtractObj(key, objPtr, ignoreNotFound)
	return err
}

func (h *EtcdHelper) bodyAndExtractObj(key string, objPtr interface{}, ignoreNotFound bool) (body string, modifiedIndex uint64, err error) {
	response, err := h.Client.Get(key, false, false)

	if err != nil && !IsEtcdNotFound(err) {
		return "", 0, err
	}
	if err != nil || response.Node == nil || len(response.Node.Value) == 0 {
		if ignoreNotFound {
			pv := reflect.ValueOf(objPtr)
			pv.Elem().Set(reflect.Zero(pv.Type().Elem()))
			return "", 0, nil
		} else if err != nil {
			return "", 0, err
		}
		return "", 0, fmt.Errorf("key '%v' found no nodes field: %#v", key, response)
	}
	body = response.Node.Value
	err = h.Codec.DecodeInto([]byte(body), objPtr)
	if h.ResourceVersioner != nil {
		_ = h.ResourceVersioner.SetResourceVersion(objPtr, response.Node.ModifiedIndex)
		// being unable to set the version does not prevent the object from being extracted
	}
	return body, response.Node.ModifiedIndex, err
}

// CreateObj adds a new object at a key unless it already exists.
func (h *EtcdHelper) CreateObj(key string, obj interface{}) error {
	data, err := h.Codec.Encode(obj)
	if err != nil {
		return err
	}
	if h.ResourceVersioner != nil {
		if version, err := h.ResourceVersioner.ResourceVersion(obj); err == nil && version != 0 {
			return errors.New("resourceVersion may not be set on objects to be created")
		}
	}

	_, err = h.Client.Create(key, string(data), 0)
	return err
}

// Delete removes the specified key.
func (h *EtcdHelper) Delete(key string, recursive bool) error {
	_, err := h.Client.Delete(key, recursive)
	return err
}

// SetObj marshals obj via json, and stores under key. Will do an
// atomic update if obj's ResourceVersion field is set.
func (h *EtcdHelper) SetObj(key string, obj interface{}) error {
	data, err := h.Codec.Encode(obj)
	if err != nil {
		return err
	}
	if h.ResourceVersioner != nil {
		if version, err := h.ResourceVersioner.ResourceVersion(obj); err == nil && version != 0 {
			_, err = h.Client.CompareAndSwap(key, string(data), 0, "", version)
			return err // err is shadowed!
		}
	}

	// Create will fail if a key already exists.
	_, err = h.Client.Create(key, string(data), 0)
	return err
}

// Pass an EtcdUpdateFunc to EtcdHelper.AtomicUpdate to make an atomic etcd update.
// See the comment for AtomicUpdate for more detail.
type EtcdUpdateFunc func(input interface{}) (output interface{}, err error)

// AtomicUpdate generalizes the pattern that allows for making atomic updates to etcd objects.
// Note, tryUpdate may be called more than once.
//
// Example:
//
// h := &util.EtcdHelper{client, encoding, versioning}
// err := h.AtomicUpdate("myKey", &MyType{}, func(input interface{}) (interface{}, error) {
//	// Before this function is called, currentObj has been reset to etcd's current
//	// contents for "myKey".
//
//	cur := input.(*MyType) // Guaranteed to work.
//
//	// Make a *modification*.
//	cur.Counter++
//
//	// Return the modified object. Return an error to stop iterating.
//	return cur, nil
// })
//
func (h *EtcdHelper) AtomicUpdate(key string, ptrToType interface{}, tryUpdate EtcdUpdateFunc) error {
	pt := reflect.TypeOf(ptrToType)
	if pt.Kind() != reflect.Ptr {
		// Panic is appropriate, because this is a programming error.
		panic("need ptr to type")
	}
	for {
		obj := reflect.New(pt.Elem()).Interface()
		origBody, index, err := h.bodyAndExtractObj(key, obj, true)
		if err != nil {
			return err
		}

		ret, err := tryUpdate(obj)
		if err != nil {
			return err
		}

		data, err := h.Codec.Encode(ret)
		if err != nil {
			return err
		}

		// First time this key has been used, try creating new value.
		if index == 0 {
			_, err = h.Client.Create(key, string(data), 0)
			if IsEtcdNodeExist(err) {
				continue
			}
			return err
		}

		if string(data) == origBody {
			return nil
		}

		_, err = h.Client.CompareAndSwap(key, string(data), 0, origBody, index)
		if IsEtcdTestFailed(err) {
			continue
		}
		return err
	}
}