func (s *Store) UsedKeys() (out []string) {
	s.Lock()
	defer s.Unlock()
	for xx, yy := range s.Data {
		if (yy.Index > 0) || (yy.Full) {
			out = append(out, xx)
		}
	}
	return
}
UsedKeys reports the used keys in the store.
package storage
import (
	"encoding/json"
	"fmt"
	"math"
	"net/http"
	"sync"
	"time"
	"github.com/open-fresh/data-sidecar/util"
)
const (
	max = 22
)
type storeDetails struct {
	Key        string
	Index      int
	Full       bool
	Last       int64
	Meta       map[string]string
	MetaString string
	Data       [max]util.DataPoint
	LastVal    float64
}
type Store struct {
	*sync.Mutex
	Data map[string]storeDetails
}
func NewStore() *Store {
	var mux sync.Mutex
	s := Store{&mux, nil}
	s.Data = make(map[string]storeDetails)
	return &s
}