func (b *bolt) Remove(bucket string, key string) error {
	b.Lock()
	defer b.Unlock()
	return b.db.Update(func(tx *boltdb.Tx) error {
		bkt := tx.Bucket([]byte(bucket))
		if bkt == nil {
			return ErrBucketNotFound
		}
		return bkt.Delete([]byte(key))
	})
}
Del is used to delete metadate from boltdb.
package meta
import (
	"os"
	"path"
	"sync"
	"time"
	boltdb "github.com/boltdb/bolt"
	"github.com/pkg/errors"
)
func init() {
	Register("boltdb", NewBolt)
}
type bolt struct {
	db *boltdb.DB
	sync.Mutex
}
func NewBolt(cfg Config) (Backend, error) {
	opt := &boltdb.Options{
		Timeout: time.Second * 10,
	}
	if _, err := os.Stat(cfg.BaseDir); err != nil && os.IsNotExist(err) {
		if err := os.MkdirAll(path.Dir(cfg.BaseDir), 0755); err != nil {
			return nil, errors.Wrap(err, "failed to create metadata path")
		}
	}
	b := &bolt{}
	db, err := boltdb.Open(cfg.BaseDir, 0644, opt)
	if err != nil {
		return nil, err
	}
	for _, bucket := range cfg.Buckets {
		if err := b.prepare(db, []byte(bucket.Name)); err != nil {
			return nil, err
		}
	}
	b.db = db
	return b, nil
}
func (b *bolt) prepare(db *boltdb.DB, bucket []byte) error {
	b.Lock()
	defer b.Unlock()
	return db.Update(func(tx *boltdb.Tx) error {
		_, err := tx.CreateBucketIfNotExists(bucket)
		if err != nil {
			return errors.Wrap(err, "failed to create bucket in boltdb")
		}
		return nil
	})
}
func (b *bolt) Path(key string) string {
	return b.db.Path()
}
func (b *bolt) Keys(bucket string) ([]string, error) {
	keys := make([]string, 0)
	b.Lock()
	defer b.Unlock()
	err := b.db.View(func(tx *boltdb.Tx) error {
		bkt := tx.Bucket([]byte(bucket))
		if bkt == nil {
			return ErrBucketNotFound
		}
		return bkt.ForEach(func(k, v []byte) error {
			keys = append(keys, string(k))
			return nil
		})
	})
	return keys, err
}
func (b *bolt) Put(bucket, key string, value []byte) error {
	b.Lock()
	defer b.Unlock()
	return b.db.Update(func(tx *boltdb.Tx) error {
		bkt := tx.Bucket([]byte(bucket))
		if bkt == nil {
			return ErrBucketNotFound
		}
		if err := bkt.Put([]byte(key), value); err != nil {
			return errors.Wrapf(err, "failed to put key %s in boltdb", key)
		}
		return nil
	})
}