etcd_tools/queue.go

package etcd_tools

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"time"

	etcd "github.com/coreos/etcd/clientv3"
)

var timeFormat = "2006-01-02.15:04:05.000000000"

type Queue struct {
	cli    *EasyClient
	prefix string
	cancel context.CancelFunc
}

func NewQueue(cli *EasyClient, prefix string) *Queue {
	return &Queue{cli: cli, prefix: prefix}
}

func (q *Queue) Client() *EasyClient {
	return q.cli
}

func (q *Queue) Prefix() string {
	return q.prefix
}

func (q *Queue) Put(value interface{}) (string, error) {
	now := time.Now().Format(timeFormat)
	key := fmt.Sprintf("%s/%s", q.prefix, now)
	_, err := q.cli.Put(key, value)
	return key, err
}

func (q *Queue) PutWithTTL(value interface{}, ttl int64) (string, error) {
	lease, err := q.cli.Grant(ttl)
	if err != nil {
		return "", err
	}

	now := time.Now().Format(timeFormat)
	key := fmt.Sprintf("%s/%s", q.prefix, now)
	_, err = q.cli.Put(key, value, etcd.WithLease(lease))
	if err != nil {
		return "", err
	}

	err = q.cli.KeepAliveOnce(lease)
	if err != nil {
		return "", err
	}

	return key, nil
}

func sort() etcd.OpOption {
	return etcd.WithSort(etcd.SortByCreateRevision, etcd.SortAscend)
}

func (q *Queue) Poll() ([]*Pair, error) {
	prefix := fmt.Sprintf("%s/", q.prefix)
	resp, err := q.cli.GetPrefix(prefix, sort())
	return resp, err
}

func (q *Queue) Len() (int, error) {
	prefix := fmt.Sprintf("%s/", q.prefix)
	resp, err := q.cli.GetPrefix(prefix, etcd.WithCountOnly())
	fmt.Println("response to Len query is:", resp)
	return 0, err
}

func (q *Queue) Watch(fn func(q *Queue, pair *Pair)) error {
	prefix := fmt.Sprintf("%s/", q.prefix)
	pairs, err := q.cli.GetPrefix(prefix, etcd.WithLimit(1), sort())
	if err != nil {
		return err
	}
	var fromRev int64 = 0
	if len(pairs) > 0 {
		fromRev = pairs[0].Modified
	}

	ctx, cancel := context.WithCancel(context.Background())
	q.cancel = cancel
	rch := q.cli.Client.Watch(ctx, prefix, etcd.WithPrefix(), etcd.WithRev(fromRev), etcd.WithFilterDelete())
	for wr := range rch {
		for _, ev := range wr.Events {
			fn(q, NewPair(ev.Kv))
		}
	}
	cancel()
	return nil
}

func (q *Queue) CancelWatch() {
	q.cancel()
}

func (q *Queue) ItemName(key string) string {
	prefix := fmt.Sprintf("%s/", q.prefix)
	if !strings.HasPrefix(key, prefix) {
		return ""
	}
	s := strings.Split(key, "/")
	return s[len(s)-1]
}

// Side-effect: from.Key is updated to the new key path
func (q *Queue) Move(from *Pair, to *Queue) error {
	itemName := q.ItemName(from.Key)
	if itemName == "" {
		return errors.New("Invalid fromKey.")
	}
	toKey := fmt.Sprintf("%s/%s", to.prefix, itemName)
	txn := q.cli.Txn()
	txn.If.Version(from.Key, "=", from.Version)
	txn.Then.Put(toKey, from.Value)
	txn.Then.Delete(from.Key)
	err := txn.Commit()
	if !txn.Success {
		return errors.New("Could not move queue item, its version changed.")
	}
	if err == nil {
		from.Key = toKey
	}
	return err
}

func (q *Queue) MoveWithTTL(from *Pair, to *Queue, ttl int64) error {
	lease, err := q.cli.Grant(ttl)
	if err != nil {
		return err
	}

	itemName := q.ItemName(from.Key)
	if itemName == "" {
		return errors.New("Invalid fromKey.")
	}
	toKey := fmt.Sprintf("%s/%s", to.prefix, itemName)
	txn := q.cli.Txn()
	txn.If.Version(from.Key, "=", from.Version)
	txn.Then.Put(toKey, from.Value, etcd.WithLease(lease))
	txn.Then.Delete(from.Key)
	err = txn.Commit()
	if err != nil {
		return err
	}

	from.Key = toKey
	err = q.cli.KeepAliveOnce(lease)
	return err
}