fee.go

package ante

import (
	"fmt"

	sdk "github.com/cosmos/cosmos-sdk/types"
	"github.com/cosmos/cosmos-sdk/x/auth/exported"
	"github.com/cosmos/cosmos-sdk/x/auth/keeper"
	"github.com/cosmos/cosmos-sdk/x/auth/types"

	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
)

// Tx must implement FeeTx interface to use the FeeDecorators
type FeeTx interface {
	sdk.Tx
	Gas() uint64
	FeeCoins() sdk.Coins
	FeePayer() sdk.AccAddress
}

// MempoolFeeDecorator will check if the transaction's fee is at least as large
// as the local validator's minimum gasFee (defined in validator config).
// If fee is too low, decorator returns error and tx is rejected from mempool.
// Note this only applies when ctx.CheckTx = true
// If fee is high enough or not CheckTx, then call next AnteHandler
// CONTRACT: Tx must implement FeeTx to use MempoolFeeDecorator
type MempoolFeeDecorator struct{}

func NewMempoolFeeDecorator() MempoolFeeDecorator {
	return MempoolFeeDecorator{}
}

func (mfd MempoolFeeDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (newCtx sdk.Context, err error) {
	feeTx, ok := tx.(FeeTx)
	if !ok {
		return ctx, sdkerrors.Wrap(sdkerrors.ErrTxDecode, "Tx must be a FeeTx")
	}
	feeCoins := feeTx.FeeCoins()
	gas := feeTx.Gas()

	// Ensure that the provided fees meet a minimum threshold for the validator,
	// if this is a CheckTx. This is only for local mempool purposes, and thus
	// is only ran on check tx.
	if ctx.IsCheckTx() && !simulate {
		minGasPrices := ctx.MinGasPrices()
		if !minGasPrices.IsZero() {
			requiredFees := make(sdk.Coins, len(minGasPrices))

			// Determine the required fees by multiplying each required minimum gas
			// price by the gas limit, where fee = ceil(minGasPrice * gasLimit).
			glDec := sdk.NewDec(int64(gas))
			for i, gp := range minGasPrices {
				fee := gp.Amount.Mul(glDec)
				requiredFees[i] = sdk.NewCoin(gp.Denom, fee.Ceil().RoundInt())
			}

			if !feeCoins.IsAnyGTE(requiredFees) {
				return ctx, sdkerrors.Wrapf(sdkerrors.ErrInsufficientFee, "insufficient fees; got: %q required: %q", feeCoins, requiredFees)
			}
		}
	}

	return next(ctx, tx, simulate)
}

// DeductFeeDecorator deducts fees from the first signer of the tx
// If the first signer does not have the funds to pay for the fees, return with InsufficientFunds error
// Call next AnteHandler if fees successfully deducted
// CONTRACT: Tx must implement FeeTx interface to use DeductFeeDecorator
type DeductFeeDecorator struct {
	ak           keeper.AccountKeeper
	supplyKeeper types.SupplyKeeper
}

func NewDeductFeeDecorator(ak keeper.AccountKeeper, sk types.SupplyKeeper) DeductFeeDecorator {
	return DeductFeeDecorator{
		ak:           ak,
		supplyKeeper: sk,
	}
}

func (dfd DeductFeeDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (newCtx sdk.Context, err error) {
	feeTx, ok := tx.(FeeTx)
	if !ok {
		return ctx, sdkerrors.Wrap(sdkerrors.ErrTxDecode, "Tx must be a FeeTx")
	}

	if addr := dfd.supplyKeeper.GetModuleAddress(types.FeeCollectorName); addr == nil {
		panic(fmt.Sprintf("%s module account has not been set", types.FeeCollectorName))
	}

	feePayer := feeTx.FeePayer()
	feePayerAcc := dfd.ak.GetAccount(ctx, feePayer)

	// deduct the fees
	if !feeTx.FeeCoins().IsZero() {
		err = DeductFees(dfd.supplyKeeper, ctx, feePayerAcc, feeTx.FeeCoins())
		if err != nil {
			return ctx, err
		}
	}

	return next(ctx, tx, simulate)
}

// DeductFees deducts fees from the given account.
//
// NOTE: We could use the CoinKeeper (in addition to the AccountKeeper, because
// the CoinKeeper doesn't give us accounts), but it seems easier to do this.
func DeductFees(supplyKeeper types.SupplyKeeper, ctx sdk.Context, acc exported.Account, fees sdk.Coins) error {
	blockTime := ctx.BlockHeader().Time
	coins := acc.GetCoins()

	if !fees.IsValid() {
		return sdkerrors.Wrapf(sdkerrors.ErrInsufficientFee, "invalid fee amount: %s", fees)
	}

	// verify the account has enough funds to pay for fees
	_, hasNeg := coins.SafeSub(fees)
	if hasNeg {
		return sdkerrors.Wrapf(sdkerrors.ErrInsufficientFunds,
			"insufficient funds to pay for fees; %s < %s", coins, fees)
	}

	// Validate the account has enough "spendable" coins as this will cover cases
	// such as vesting accounts.
	spendableCoins := acc.SpendableCoins(blockTime)
	if _, hasNeg := spendableCoins.SafeSub(fees); hasNeg {
		return sdkerrors.Wrapf(sdkerrors.ErrInsufficientFunds,
			"insufficient funds to pay for fees; %s < %s", spendableCoins, fees)
	}

	err := supplyKeeper.SendCoinsFromAccountToModule(ctx, acc.GetAddress(), types.FeeCollectorName, fees)
	if err != nil {
		return err
	}

	return nil
}