Add Fee granter field (#7418)

* WIP on adding Fee granter field

* WIP on adding Fee granter field

* WIP on adding Fee granter field

* Update comments, add tests

proto/cosmos/tx/v1beta1/tx.proto

@@ -174,4 +174,9 @@ message Fee {
   // the payer must be a tx signer (and thus have signed this field in AuthInfo).
   // setting this field does *not* change the ordering of required signers for the transaction.
   string payer = 3;
+
+  // if set, the fee payer (either the first signer or the value of the payer field) requests that a fee grant be used
+  // to pay fees instead of the fee payer's own balance. If an appropriate fee grant does not exist or the chain does
+  // not support fee grants, this will fail
+  string granter = 4;
 }

types/tx_msg.go

@@ -62,6 +62,7 @@ type (
 		GetGas() uint64
 		GetFee() Coins
 		FeePayer() AccAddress
+		FeeGranter() AccAddress
 	}
 
 	// Tx must have GetMemo() method to use ValidateMemoDecorator

x/auth/ante/ante.go

@@ -22,6 +22,7 @@ func NewAnteHandler(
 		TxTimeoutHeightDecorator{},
 		NewValidateMemoDecorator(ak),
 		NewConsumeGasForTxSizeDecorator(ak),
+		NewRejectFeeGranterDecorator(),
 		NewSetPubKeyDecorator(ak), // SetPubKeyDecorator must be called before all signature verification decorators
 		NewValidateSigCountDecorator(ak),
 		NewDeductFeeDecorator(ak, bankKeeper),

x/auth/ante/fee_grant.go

@@ -0,0 +1,27 @@
+package ante
+
+import (
+	"github.com/cosmos/cosmos-sdk/types"
+	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
+)
+
+// RejectFeeGranterDecorator is an AnteDecorator which rejects transactions which
+// have the Fee.granter field set. It is to be used by chains which do not support
+// fee grants.
+type RejectFeeGranterDecorator struct{}
+
+// NewRejectFeeGranterDecorator returns a new RejectFeeGranterDecorator.
+func NewRejectFeeGranterDecorator() RejectFeeGranterDecorator {
+	return RejectFeeGranterDecorator{}
+}
+
+var _ types.AnteDecorator = RejectFeeGranterDecorator{}
+
+func (d RejectFeeGranterDecorator) AnteHandle(ctx types.Context, tx types.Tx, simulate bool, next types.AnteHandler) (newCtx types.Context, err error) {
+	feeTx, ok := tx.(types.FeeTx)
+	if ok && len(feeTx.FeeGranter()) != 0 {
+		return ctx, sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "fee grants are not supported")
+	}
+
+	return next(ctx, tx, simulate)
+}

x/auth/ante/fee_grant_test.go

@@ -0,0 +1,32 @@
+package ante_test
+
+import (
+	"github.com/cosmos/cosmos-sdk/codec"
+	"github.com/cosmos/cosmos-sdk/codec/types"
+	"github.com/cosmos/cosmos-sdk/testutil/testdata"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/x/auth/ante"
+	"github.com/cosmos/cosmos-sdk/x/auth/tx"
+)
+
+type setFeeGranter interface {
+	SetFeeGranter(feeGranter sdk.AccAddress)
+}
+
+func (suite *AnteTestSuite) TestRejectFeeGranter() {
+	suite.SetupTest(true) // setup
+	txConfig := tx.NewTxConfig(codec.NewProtoCodec(types.NewInterfaceRegistry()), tx.DefaultSignModes)
+	txBuilder := txConfig.NewTxBuilder()
+	d := ante.NewRejectFeeGranterDecorator()
+	antehandler := sdk.ChainAnteDecorators(d)
+
+	_, err := antehandler(suite.ctx, txBuilder.GetTx(), false)
+	suite.Require().NoError(err)
+
+	setGranterTx := txBuilder.(setFeeGranter)
+	_, _, addr := testdata.KeyTestPubAddr()
+	setGranterTx.SetFeeGranter(addr)
+
+	_, err = antehandler(suite.ctx, txBuilder.GetTx(), false)
+	suite.Require().Error(err)
+}

x/auth/legacy/legacytx/stdtx.go

@@ -264,6 +264,11 @@ func (tx StdTx) FeePayer() sdk.AccAddress {
 	return sdk.AccAddress{}
 }
 
+// FeeGranter always returns nil for StdTx
+func (tx StdTx) FeeGranter() sdk.AccAddress {
+	return nil
+}
+
 func (tx StdTx) UnpackInterfaces(unpacker codectypes.AnyUnpacker) error {
 	for _, m := range tx.Msgs {
 		err := codectypes.UnpackInterfaces(m, unpacker)

x/auth/legacy/legacytx/stdtx_test.go

@@ -67,6 +67,9 @@ func TestStdTx(t *testing.T) {
 
 	feePayer := tx.GetSigners()[0]
 	require.Equal(t, addr, feePayer)
+
+	feeGranter := tx.FeeGranter()
+	require.Empty(t, feeGranter)
 }
 
 func TestStdSignBytes(t *testing.T) {

x/auth/tx/builder.go

@@ -144,6 +144,18 @@ func (w *wrapper) FeePayer() sdk.AccAddress {
 	return w.GetSigners()[0]
 }
 
+func (w *wrapper) FeeGranter() sdk.AccAddress {
+	feePayer := w.tx.AuthInfo.Fee.Granter
+	if feePayer != "" {
+		granterAddr, err := sdk.AccAddressFromBech32(feePayer)
+		if err != nil {
+			panic(err)
+		}
+		return granterAddr
+	}
+	return nil
+}
+
 func (w *wrapper) GetMemo() string {
 	return w.tx.Body.Memo
 }
@@ -255,6 +267,17 @@ func (w *wrapper) SetFeePayer(feePayer sdk.AccAddress) {
 	w.authInfoBz = nil
 }
 
+func (w *wrapper) SetFeeGranter(feeGranter sdk.AccAddress) {
+	if w.tx.AuthInfo.Fee == nil {
+		w.tx.AuthInfo.Fee = &tx.Fee{}
+	}
+
+	w.tx.AuthInfo.Fee.Granter = feeGranter.String()
+
+	// set authInfoBz to nil because the cached authInfoBz no longer matches tx.AuthInfo
+	w.authInfoBz = nil
+}
+
 func (w *wrapper) SetSignatures(signatures ...signing.SignatureV2) error {
 	n := len(signatures)
 	signerInfos := make([]*tx.SignerInfo, n)

x/auth/tx/builder_test.go

@@ -289,3 +289,25 @@ func TestBuilderFeePayer(t *testing.T) {
 		})
 	}
 }
+
+func TestBuilderFeeGranter(t *testing.T) {
+	// keys and addresses
+	_, _, addr1 := testdata.KeyTestPubAddr()
+
+	// msg and signatures
+	msg1 := testdata.NewTestMsg(addr1, addr2)
+	feeAmount := testdata.NewTestFeeAmount()
+	msgs := []sdk.Msg{msg1}
+
+	txBuilder := newBuilder()
+	err := txBuilder.SetMsgs(msgs...)
+	require.NoError(t, err)
+	txBuilder.SetGasLimit(200000)
+	txBuilder.SetFeeAmount(feeAmount)
+
+	require.Empty(t, txBuilder.GetTx().FeeGranter())
+
+	// set fee granter
+	txBuilder.SetFeeGranter(addr1)
+	require.Equal(t, addr1, txBuilder.GetTx().FeeGranter())
+}