update kvstore to mark transactions as replacements

abci/example/code/code.go

@@ -7,4 +7,5 @@ const (
 	CodeTypeBadNonce      uint32 = 2
 	CodeTypeUnauthorized  uint32 = 3
 	CodeTypeUnknownError  uint32 = 4
+	CodeTypeExecuted      uint32 = 5
 )

abci/example/kvstore/kvstore.go

@@ -68,6 +68,7 @@ type Application struct {
 
 	state        State
 	RetainBlocks int64 // blocks to retain after commit (via ResponseCommit.RetainHeight)
+	txToRemove   map[string]struct{}
 }
 
 func NewApplication() *Application {
@@ -87,6 +88,9 @@ func (app *Application) Info(req types.RequestInfo) (resInfo types.ResponseInfo)
 
 // tx is either "key=value" or just arbitrary bytes
 func (app *Application) DeliverTx(req types.RequestDeliverTx) types.ResponseDeliverTx {
+	if isReplacedTx(req.Tx) {
+		app.txToRemove[string(req.Tx)] = struct{}{}
+	}
 	var key, value []byte
 	parts := bytes.Split(req.Tx, []byte("="))
 	if len(parts) == 2 {
@@ -117,6 +121,11 @@ func (app *Application) DeliverTx(req types.RequestDeliverTx) types.ResponseDeli
 }
 
 func (app *Application) CheckTx(req types.RequestCheckTx) types.ResponseCheckTx {
+	if req.Type == types.CheckTxType_Recheck {
+		if _, ok := app.txToRemove[string(req.Tx)]; ok {
+			return types.ResponseCheckTx{Code: code.CodeTypeExecuted, GasWanted: 1}
+		}
+	}
 	return types.ResponseCheckTx{Code: code.CodeTypeOK, GasWanted: 1}
 }
 
@@ -126,6 +135,9 @@ func (app *Application) Commit() types.ResponseCommit {
 	binary.PutVarint(appHash, app.state.Size)
 	app.state.AppHash = appHash
 	app.state.Height++
+
+	// empty out the set of transactions to remove via rechecktx
+	app.txToRemove = map[string]struct{}{}
 	saveState(app.state)
 
 	resp := types.ResponseCommit{Data: appHash}

abci/example/kvstore/persistent_kvstore.go

@@ -45,7 +45,10 @@ func NewPersistentKVStoreApplication(dbDir string) *PersistentKVStoreApplication
 	state := loadState(db)
 
 	return &PersistentKVStoreApplication{
-		app:                &Application{state: state},
+		app: &Application{
+			state:      state,
+			txToRemove: map[string]struct{}{},
+		},
 		valAddrToPubKeyMap: make(map[string]pc.PublicKey),
 		logger:             log.NewNopLogger(),
 	}
@@ -302,12 +305,19 @@ func (app *PersistentKVStoreApplication) updateValidator(v types.ValidatorUpdate
 
 // -----------------------------
 
-const PreparePrefix = "prepare"
+const (
+	PreparePrefix = "prepare"
+	ReplacePrefix = "replace"
+)
 
 func isPrepareTx(tx []byte) bool {
 	return bytes.HasPrefix(tx, []byte(PreparePrefix))
 }
 
+func isReplacedTx(tx []byte) bool {
+	return bytes.HasPrefix(tx, []byte(ReplacePrefix))
+}
+
 // execPrepareTx is noop. tx data is considered as placeholder
 // and is substitute at the PrepareProposal.
 func (app *PersistentKVStoreApplication) execPrepareTx(tx []byte) types.ResponseDeliverTx {
@@ -323,7 +333,7 @@ func (app *PersistentKVStoreApplication) substPrepareTx(blockData [][]byte, maxT
 	for _, tx := range blockData {
 		txMod := tx
 		if isPrepareTx(tx) {
-			txMod = bytes.TrimPrefix(tx, []byte(PreparePrefix))
+			txMod = bytes.Replace(tx, []byte(PreparePrefix), []byte(ReplacePrefix), 1)
 		}
 		totalBytes += int64(len(txMod))
 		if totalBytes > maxTxBytes {