key.go

// Copyright 2016 CoreOS, Inc.
//
// 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 recipe

import (
	"fmt"
	"strings"
	"time"

	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
	"github.com/coreos/etcd/clientv3"
	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
	"github.com/coreos/etcd/lease"
)

// Key is a key/revision pair created by the client and stored on etcd
type RemoteKV struct {
	client *clientv3.Client
	key    string
	rev    int64
	val    string
}

func NewKey(client *clientv3.Client, key string, leaseID lease.LeaseID) (*RemoteKV, error) {
	return NewKV(client, key, "", leaseID)
}

func NewKV(client *clientv3.Client, key, val string, leaseID lease.LeaseID) (*RemoteKV, error) {
	rev, err := putNewKV(client, key, val, leaseID)
	if err != nil {
		return nil, err
	}
	return &RemoteKV{client, key, rev, val}, nil
}

func GetRemoteKV(client *clientv3.Client, key string) (*RemoteKV, error) {
	resp, err := client.KV.Range(
		context.TODO(),
		&pb.RangeRequest{Key: []byte(key)},
	)
	if err != nil {
		return nil, err
	}
	rev := resp.Header.Revision
	val := ""
	if len(resp.Kvs) > 0 {
		rev = resp.Kvs[0].ModRevision
		val = string(resp.Kvs[0].Value)
	}
	return &RemoteKV{
		client: client,
		key:    key,
		rev:    rev,
		val:    val}, nil
}

func NewUniqueKey(client *clientv3.Client, prefix string) (*RemoteKV, error) {
	return NewUniqueKV(client, prefix, "", 0)
}

func NewUniqueKV(client *clientv3.Client, prefix string, val string, leaseID lease.LeaseID) (*RemoteKV, error) {
	for {
		newKey := fmt.Sprintf("%s/%v", prefix, time.Now().UnixNano())
		rev, err := putNewKV(client, newKey, val, 0)
		if err == nil {
			return &RemoteKV{client, newKey, rev, val}, nil
		}
		if err != ErrKeyExists {
			return nil, err
		}
	}
}

// putNewKV attempts to create the given key, only succeeding if the key did
// not yet exist.
func putNewKV(ec *clientv3.Client, key, val string, leaseID lease.LeaseID) (int64, error) {
	cmp := &pb.Compare{
		Result:      pb.Compare_EQUAL,
		Target:      pb.Compare_VERSION,
		Key:         []byte(key),
		TargetUnion: &pb.Compare_Version{Version: 0}}

	req := &pb.RequestUnion{
		Request: &pb.RequestUnion_RequestPut{
			RequestPut: &pb.PutRequest{
				Key:   []byte(key),
				Value: []byte(val),
				Lease: int64(leaseID)}}}
	txnresp, err := ec.KV.Txn(
		context.TODO(),
		&pb.TxnRequest{[]*pb.Compare{cmp}, []*pb.RequestUnion{req}, nil})
	if err != nil {
		return 0, err
	}
	if txnresp.Succeeded == false {
		return 0, ErrKeyExists
	}
	return txnresp.Header.Revision, nil
}

// NewSequentialKV allocates a new sequential key-value pair at <prefix>/nnnnn
func NewSequentialKV(client *clientv3.Client, prefix, val string) (*RemoteKV, error) {
	return newSequentialKV(client, prefix, val, 0)
}

// newSequentialKV allocates a new sequential key <prefix>/nnnnn with a given
// value and lease.  Note: a bookkeeping node __<prefix> is also allocated.
func newSequentialKV(client *clientv3.Client, prefix, val string, leaseID lease.LeaseID) (*RemoteKV, error) {
	resp, err := NewRange(client, prefix).LastKey()
	if err != nil {
		return nil, err
	}

	// add 1 to last key, if any
	newSeqNum := 0
	if len(resp.Kvs) != 0 {
		fields := strings.Split(string(resp.Kvs[0].Key), "/")
		_, err := fmt.Sscanf(fields[len(fields)-1], "%d", &newSeqNum)
		if err != nil {
			return nil, err
		}
		newSeqNum++
	}
	newKey := fmt.Sprintf("%s/%016d", prefix, newSeqNum)

	// base prefix key must be current (i.e., <=) with the server update;
	// the base key is important to avoid the following:
	// N1: LastKey() == 1, start txn.
	// N2: New Key 2, New Key 3, Delete Key 2
	// N1: txn succeeds allocating key 2 when it shouldn't
	baseKey := []byte("__" + prefix)
	cmp := &pb.Compare{
		Result: pb.Compare_LESS,
		Target: pb.Compare_MOD,
		Key:    []byte(baseKey),
		// current revision might contain modification so +1
		TargetUnion: &pb.Compare_ModRevision{ModRevision: resp.Header.Revision + 1},
	}

	reqPrefix := &pb.RequestUnion{
		Request: &pb.RequestUnion_RequestPut{
			RequestPut: &pb.PutRequest{
				Key:   baseKey,
				Lease: int64(leaseID),
			}}}

	reqNewKey := &pb.RequestUnion{
		Request: &pb.RequestUnion_RequestPut{
			RequestPut: &pb.PutRequest{
				Key:   []byte(newKey),
				Value: []byte(val),
				Lease: int64(leaseID),
			}}}

	txnresp, err := client.KV.Txn(
		context.TODO(),
		&pb.TxnRequest{
			[]*pb.Compare{cmp},
			[]*pb.RequestUnion{reqPrefix, reqNewKey}, nil})
	if err != nil {
		return nil, err
	}
	if txnresp.Succeeded == false {
		return newSequentialKV(client, prefix, val, leaseID)
	}
	return &RemoteKV{client, newKey, txnresp.Header.Revision, val}, nil
}

func (rk *RemoteKV) Key() string     { return rk.key }
func (rk *RemoteKV) Revision() int64 { return rk.rev }
func (rk *RemoteKV) Value() string   { return rk.val }

func (rk *RemoteKV) Delete() error {
	if rk.client == nil {
		return nil
	}
	req := &pb.DeleteRangeRequest{Key: []byte(rk.key)}
	_, err := rk.client.KV.DeleteRange(context.TODO(), req)
	rk.client = nil
	return err
}

func (rk *RemoteKV) Put(val string) error {
	req := &pb.PutRequest{Key: []byte(rk.key), Value: []byte(val)}
	_, err := rk.client.KV.Put(context.TODO(), req)
	return err
}

// EphemeralKV is a new key associated with a session lease
type EphemeralKV struct{ RemoteKV }

// NewEphemeralKV creates a new key/value pair associated with a session lease
func NewEphemeralKV(client *clientv3.Client, key, val string) (*EphemeralKV, error) {
	leaseID, err := SessionLease(client)
	if err != nil {
		return nil, err
	}
	k, err := NewKV(client, key, val, leaseID)
	if err != nil {
		return nil, err
	}
	return &EphemeralKV{*k}, nil
}

// NewUniqueEphemeralKey creates a new unique valueless key associated with a session lease
func NewUniqueEphemeralKey(client *clientv3.Client, prefix string) (*EphemeralKV, error) {
	return NewUniqueEphemeralKV(client, prefix, "")
}

// NewUniqueEphemeralKV creates a new unique key/value pair associated with a session lease
func NewUniqueEphemeralKV(client *clientv3.Client, prefix, val string) (ek *EphemeralKV, err error) {
	for {
		newKey := fmt.Sprintf("%s/%v", prefix, time.Now().UnixNano())
		ek, err = NewEphemeralKV(client, newKey, val)
		if err == nil || err != ErrKeyExists {
			break
		}
	}
	return ek, err
}