feat: add capability to reformat Transactions before broadcasting (#12936)

## Description
Increase customized signing capabilities by:
- Adding a hook to preprocess transactions before broadcasting

This PR introduces the ability to preprocess transactions before broadcasting, a feature that provides the ability to add extensions, or otherwise customize the payload to satisfy a chain's requirements. For adaptability, the parameters include the keytype to allow differentiation between formatting transactions for Ledger vs. software keys.

## PR
This PR introduces a hook to preprocess transactions, chiefly to add extensions, from a higher-level chain. Key changes and relevant files:

- Add `PreprocessTxFn` type and fields to both `Context` and `Factory`
- Instantiate the `Factory` with the `PreprocessTxFn` provided by the `Context`
- Call `PreprocessTx` with the appropriate parameters after signing

Closes: #XXXX



---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/main/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

client/context.go

@@ -18,6 +18,9 @@ import (
 	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
+// PreprocessTxFn defines a hook by which chains can preprocess transactions before broadcasting
+type PreprocessTxFn func(chainID string, key keyring.KeyType, tx TxBuilder) error
+
 // Context implements a typical context created in SDK modules for transaction
 // handling and queries.
 type Context struct {
@@ -50,6 +53,7 @@ type Context struct {
 	FeePayer          sdk.AccAddress
 	FeeGranter        sdk.AccAddress
 	Viper             *viper.Viper
+	PreprocessTxHook  PreprocessTxFn
 
 	// IsAux is true when the signer is an auxiliary signer (e.g. the tipper).
 	IsAux bool
@@ -262,6 +266,13 @@ func (ctx Context) WithAux(isAux bool) Context {
 	return ctx
 }
 
+// WithPreprocessTxHook returns the context with the provided preprocessing hook, which
+// enables chains to preprocess the transaction using the builder.
+func (ctx Context) WithPreprocessTxHook(preprocessFn PreprocessTxFn) Context {
+	ctx.PreprocessTxHook = preprocessFn
+	return ctx
+}
+
 // PrintString prints the raw string to ctx.Output if it's defined, otherwise to os.Stdout
 func (ctx Context) PrintString(str string) error {
 	return ctx.PrintBytes([]byte(str))

client/tx/factory.go

@@ -40,6 +40,7 @@ type Factory struct {
 	gasPrices          sdk.DecCoins
 	signMode           signing.SignMode
 	simulateAndExecute bool
+	preprocessTxHook   client.PreprocessTxFn
 }
 
 // NewFactoryCLI creates a new Factory.
@@ -97,6 +98,8 @@ func NewFactoryCLI(clientCtx client.Context, flagSet *pflag.FlagSet) Factory {
 	gasPricesStr, _ := flagSet.GetString(flags.FlagGasPrices)
 	f = f.WithGasPrices(gasPricesStr)
 
+	f = f.WithPreprocessTxHook(clientCtx.PreprocessTxHook)
+
 	return f
 }
 
@@ -242,6 +245,29 @@ func (f Factory) WithFeePayer(fp sdk.AccAddress) Factory {
 	return f
 }
 
+// WithPreprocessTxHook returns a copy of the Factory with an updated preprocess tx function,
+// allows for preprocessing of transaction data using the TxBuilder.
+func (f Factory) WithPreprocessTxHook(preprocessFn client.PreprocessTxFn) Factory {
+	f.preprocessTxHook = preprocessFn
+	return f
+}
+
+// PreprocessTx calls the preprocessing hook with the factory parameters and
+// returns the result.
+func (f Factory) PreprocessTx(keyname string, builder client.TxBuilder) error {
+	if f.preprocessTxHook == nil {
+		// Allow pass-through
+		return nil
+	}
+
+	key, err := f.Keybase().Key(keyname)
+	if err != nil {
+		return fmt.Errorf("error retrieving key from keyring: %w", err)
+	}
+
+	return f.preprocessTxHook(f.chainID, key.GetType(), builder)
+}
+
 // BuildUnsignedTx builds a transaction to be signed given a set of messages.
 // Once created, the fee, memo, and messages are set.
 func (f Factory) BuildUnsignedTx(msgs ...sdk.Msg) (client.TxBuilder, error) {

client/tx/tx.go

@@ -321,10 +321,19 @@ func Sign(txf Factory, name string, txBuilder client.TxBuilder, overwriteSig boo
 	}
 
 	if overwriteSig {
-		return txBuilder.SetSignatures(sig)
+		err = txBuilder.SetSignatures(sig)
+	} else {
+		prevSignatures = append(prevSignatures, sig)
+		err = txBuilder.SetSignatures(prevSignatures...)
 	}
-	prevSignatures = append(prevSignatures, sig)
-	return txBuilder.SetSignatures(prevSignatures...)
+
+	if err != nil {
+		return fmt.Errorf("unable to set signatures on payload: %w", err)
+	}
+
+	// Run optional preprocessing if specified. By default, this is unset
+	// and will return nil.
+	return txf.PreprocessTx(name, txBuilder)
 }
 
 // GasEstimateResponse defines a response definition for tx gas estimation.

client/tx/tx_test.go

@@ -13,12 +13,15 @@ import (
 	clienttestutil "github.com/cosmos/cosmos-sdk/client/testutil"
 	"github.com/cosmos/cosmos-sdk/client/tx"
 	"github.com/cosmos/cosmos-sdk/codec"
+	codectypes "github.com/cosmos/cosmos-sdk/codec/types"
 	"github.com/cosmos/cosmos-sdk/crypto/hd"
 	"github.com/cosmos/cosmos-sdk/crypto/keyring"
 	cryptotypes "github.com/cosmos/cosmos-sdk/crypto/types"
+	"github.com/cosmos/cosmos-sdk/testutil/testdata"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	txtypes "github.com/cosmos/cosmos-sdk/types/tx"
 	signingtypes "github.com/cosmos/cosmos-sdk/types/tx/signing"
+	ante "github.com/cosmos/cosmos-sdk/x/auth/ante"
 	"github.com/cosmos/cosmos-sdk/x/auth/signing"
 	authtx "github.com/cosmos/cosmos-sdk/x/auth/tx"
 	banktypes "github.com/cosmos/cosmos-sdk/x/bank/types"
@@ -314,6 +317,81 @@ func TestSign(t *testing.T) {
 	}
 }
 
+func TestPreprocessHook(t *testing.T) {
+	txConfig, cdc := newTestTxConfig(t)
+	requireT := require.New(t)
+	path := hd.CreateHDPath(118, 0, 0).String()
+	kb, err := keyring.New(t.Name(), "test", t.TempDir(), nil, cdc)
+	requireT.NoError(err)
+
+	from := "test_key"
+	kr, _, err := kb.NewMnemonic(from, keyring.English, path, keyring.DefaultBIP39Passphrase, hd.Secp256k1)
+	requireT.NoError(err)
+
+	extVal := &testdata.Cat{
+		Moniker: "einstein",
+		Lives:   9,
+	}
+	extAny, err := codectypes.NewAnyWithValue(extVal)
+	requireT.NoError(err)
+
+	coin := sdk.Coin{
+		Denom:  "atom",
+		Amount: sdk.NewInt(20),
+	}
+	newTip := &txtypes.Tip{
+		Amount: sdk.Coins{coin},
+		Tipper: "galaxy",
+	}
+
+	preprocessHook := client.PreprocessTxFn(func(chainID string, key keyring.KeyType, tx client.TxBuilder) error {
+		extensionBuilder, ok := tx.(authtx.ExtensionOptionsTxBuilder)
+		requireT.True(ok)
+
+		// Set new extension and tip
+		extensionBuilder.SetExtensionOptions(extAny)
+		tx.SetTip(newTip)
+
+		return nil
+	})
+
+	txfDirect := tx.Factory{}.
+		WithTxConfig(txConfig).
+		WithAccountNumber(50).
+		WithSequence(23).
+		WithFees("50stake").
+		WithMemo("memo").
+		WithChainID("test-chain").
+		WithKeybase(kb).
+		WithSignMode(signingtypes.SignMode_SIGN_MODE_DIRECT).
+		WithPreprocessTxHook(preprocessHook)
+
+	addr1, err := kr.GetAddress()
+	requireT.NoError(err)
+	msg1 := banktypes.NewMsgSend(addr1, sdk.AccAddress("to"), nil)
+	msg2 := banktypes.NewMsgSend(addr2, sdk.AccAddress("to"), nil)
+	txb, err := txfDirect.BuildUnsignedTx(msg1, msg2)
+
+	err = tx.Sign(txfDirect, from, txb, false)
+	requireT.NoError(err)
+
+	// Run preprocessing
+	err = txfDirect.PreprocessTx(from, txb)
+	requireT.NoError(err)
+
+	hasExtOptsTx, ok := txb.(ante.HasExtensionOptionsTx)
+	requireT.True(ok)
+
+	hasOneExt := len(hasExtOptsTx.GetExtensionOptions()) == 1
+	requireT.True(hasOneExt)
+
+	opt := hasExtOptsTx.GetExtensionOptions()[0]
+	requireT.Equal(opt, extAny)
+
+	tip := txb.GetTx().GetTip()
+	requireT.Equal(tip, newTip)
+}
+
 func testSigners(require *require.Assertions, tr signing.Tx, pks ...cryptotypes.PubKey) []signingtypes.SignatureV2 {
 	sigs, err := tr.GetSignaturesV2()
 	require.Len(sigs, len(pks))