Implement fee pool pseudo-account in sdk.AccountMapper

types/account.go

@@ -48,6 +48,8 @@ type AccountMapper interface {
 	NewAccountWithAddress(ctx Context, addr Address) Account
 	GetAccount(ctx Context, addr Address) Account
 	SetAccount(ctx Context, acc Account)
+	GetFeePool(ctx Context) Coins
+	SetFeePool(ctx Context, coins Coins)
 }
 
 // AccountDecoder unmarshals account bytes

x/auth/ante.go

@@ -74,6 +74,9 @@ func NewAnteHandler(accountMapper sdk.AccountMapper) sdk.AnteHandler {
 				// TODO: min fee
 				if !fee.Amount.IsZero() {
 					signerAcc, res = deductFees(signerAcc, fee)
+					pool := accountMapper.GetFeePool(ctx)
+					pool = pool.Plus(fee.Amount)
+					accountMapper.SetFeePool(ctx, pool)
 					if !res.IsOK() {
 						return ctx, res, true
 					}

x/auth/mapper.go

@@ -51,6 +51,33 @@ func (am accountMapper) Seal() sealedAccountMapper {
 	return sealedAccountMapper{am}
 }
 
+var feePoolKey = []byte("feePool")
+
+// Implements sdk.AccountMapper.
+func (am accountMapper) GetFeePool(ctx sdk.Context) sdk.Coins {
+	store := ctx.KVStore(am.key)
+	bz := store.Get(feePoolKey)
+	if bz == nil {
+		return sdk.Coins{}
+	}
+	var coins sdk.Coins
+	err := am.cdc.UnmarshalBinaryBare(bz, &coins)
+	if err != nil {
+		panic(err)
+	}
+	return coins
+}
+
+// Implements sdk.AccountMapper.
+func (am accountMapper) SetFeePool(ctx sdk.Context, coins sdk.Coins) {
+	store := ctx.KVStore(am.key)
+	bz, err := am.cdc.MarshalBinaryBare(coins)
+	if err != nil {
+		panic(err)
+	}
+	store.Set(feePoolKey, bz)
+}
+
 // Implements sdk.AccountMapper.
 func (am accountMapper) NewAccountWithAddress(ctx sdk.Context, addr sdk.Address) sdk.Account {
 	acc := am.clonePrototype()