func (app *Application) Query(reqQuery types.RequestQuery) (resQuery types.ResponseQuery) {
	if reqQuery.Prove {
		value, err := app.state.db.Get(prefixKey(reqQuery.Data))
		if err != nil {
			panic(err)
		}
		if value == nil {
			resQuery.Log = "does not exist"
		} else {
			resQuery.Log = "exists"
		}
		resQuery.Index = -1  
		resQuery.Key = reqQuery.Data
		resQuery.Value = value
		resQuery.Height = app.state.Height
		return
	}
	resQuery.Key = reqQuery.Data
	value, err := app.state.db.Get(prefixKey(reqQuery.Data))
	if err != nil {
		panic(err)
	}
	if value == nil {
		resQuery.Log = "does not exist"
	} else {
		resQuery.Log = "exists"
	}
	resQuery.Value = value
	resQuery.Height = app.state.Height
	return resQuery
}
Returns an associated value or nil if missing.
package kvstore
import (
	"bytes"
	"encoding/binary"
	"encoding/json"
	"fmt"
	dbm "github.com/line/tm-db/v2"
	"github.com/line/tm-db/v2/memdb"
	"github.com/line/ostracon/abci/example/code"
	"github.com/line/ostracon/abci/types"
	"github.com/line/ostracon/version"
)
var (
	stateKey        = []byte("stateKey")
	kvPairPrefixKey = []byte("kvPairKey:")
	ProtocolVersion uint64 = 0x1
)
type State struct {
	db      dbm.DB
	Size    int64  `json:"size"`
	Height  int64  `json:"height"`
	AppHash []byte `json:"app_hash"`
}
func loadState(db dbm.DB) State {
	var state State
	state.db = db
	stateBytes, err := db.Get(stateKey)
	if err != nil {
		panic(err)
	}
	if len(stateBytes) == 0 {
		return state
	}
	err = json.Unmarshal(stateBytes, &state)
	if err != nil {
		panic(err)
	}
	return state
}
func saveState(state State) {
	stateBytes, err := json.Marshal(state)
	if err != nil {
		panic(err)
	}
	err = state.db.Set(stateKey, stateBytes)
	if err != nil {
		panic(err)
	}
}
func prefixKey(key []byte) []byte {
	return append(kvPairPrefixKey, key...)
}
var _ types.Application = (*Application)(nil)
type Application struct {
	types.BaseApplication
	state        State
	RetainBlocks int64  
}
func NewApplication() *Application {
	state := loadState(memdb.NewDB())
	return &Application{state: state}
}
func (app *Application) Info(req types.RequestInfo) (resInfo types.ResponseInfo) {
	return types.ResponseInfo{
		Data:             fmt.Sprintf("{\"size\":%v}", app.state.Size),
		Version:          version.ABCIVersion,
		AppVersion:       ProtocolVersion,
		LastBlockHeight:  app.state.Height,
		LastBlockAppHash: app.state.AppHash,
	}
}
func (app *Application) DeliverTx(req types.RequestDeliverTx) types.ResponseDeliverTx {
	var key, value []byte
	parts := bytes.Split(req.Tx, []byte("="))
	if len(parts) == 2 {
		key, value = parts[0], parts[1]
	} else {
		key, value = req.Tx, req.Tx
	}
	err := app.state.db.Set(prefixKey(key), value)
	if err != nil {
		panic(err)
	}
	app.state.Size++
	events := []types.Event{
		{
			Type: "app",
			Attributes: []types.EventAttribute{
				{Key: []byte("creator"), Value: []byte("Cosmoshi Netowoko"), Index: true},
				{Key: []byte("key"), Value: key, Index: true},
				{Key: []byte("index_key"), Value: []byte("index is working"), Index: true},
				{Key: []byte("noindex_key"), Value: []byte("index is working"), Index: false},
			},
		},
	}
	return types.ResponseDeliverTx{Code: code.CodeTypeOK, Events: events}
}
func (app *Application) CheckTxSync(req types.RequestCheckTx) types.ResponseCheckTx {
	return app.checkTx(req)
}
func (app *Application) CheckTxAsync(req types.RequestCheckTx, callback types.CheckTxCallback) {
	callback(app.checkTx(req))
}
func (app *Application) checkTx(req types.RequestCheckTx) types.ResponseCheckTx {
	return types.ResponseCheckTx{Code: code.CodeTypeOK, GasWanted: 1}
}
func (app *Application) Commit() types.ResponseCommit {
	appHash := make([]byte, 8)
	binary.PutVarint(appHash, app.state.Size)
	app.state.AppHash = appHash
	app.state.Height++
	saveState(app.state)
	resp := types.ResponseCommit{Data: appHash}
	if app.RetainBlocks > 0 && app.state.Height >= app.RetainBlocks {
		resp.RetainHeight = app.state.Height - app.RetainBlocks + 1
	}
	return resp
}