fix: revert proto changes from #12610 (#12670)

## Description

ref:#12610 (comment)



---

### 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)

proto/cosmos/bank/v1beta1/tx.proto

@@ -40,13 +40,15 @@ message MsgSend {
 // MsgSendResponse defines the Msg/Send response type.
 message MsgSendResponse {}
 
-// MsgMultiSend represents a single input, multi-out send message.
+// MsgMultiSend represents an arbitrary multi-in, multi-out send message.
 message MsgMultiSend {
-  option (cosmos.msg.v1.signer) = "input";
+  option (cosmos.msg.v1.signer) = "inputs";
 
   option (gogoproto.equal) = false;
 
-  Input           input   = 1 [(gogoproto.nullable) = false];
+  // Inputs, despite being `repeated`, only allows one sender input. This is
+  // checked in MsgMultiSend's ValidateBasic.
+  repeated Input  inputs  = 1 [(gogoproto.nullable) = false];
   repeated Output outputs = 2 [(gogoproto.nullable) = false];
 }
 

x/bank/app_test.go

@@ -46,28 +46,32 @@ var (
 	sendMsg1 = types.NewMsgSend(addr1, addr2, coins)
 
 	multiSendMsg1 = &types.MsgMultiSend{
-		Input:   types.NewInput(addr1, coins),
+		Inputs:  []types.Input{types.NewInput(addr1, coins)},
 		Outputs: []types.Output{types.NewOutput(addr2, coins)},
 	}
 	multiSendMsg2 = &types.MsgMultiSend{
-		Input: types.NewInput(addr1, coins),
+		Inputs: []types.Input{types.NewInput(addr1, coins)},
 		Outputs: []types.Output{
 			types.NewOutput(addr2, halfCoins),
 			types.NewOutput(addr3, halfCoins),
 		},
 	}
 	multiSendMsg3 = &types.MsgMultiSend{
-		Input: types.NewInput(addr2, coins),
+		Inputs: []types.Input{types.NewInput(addr2, coins)},
 		Outputs: []types.Output{
 			types.NewOutput(addr1, coins),
 		},
 	}
 	multiSendMsg4 = &types.MsgMultiSend{
-		Input: types.NewInput(addr1, coins),
+		Inputs: []types.Input{types.NewInput(addr1, coins)},
 		Outputs: []types.Output{
 			types.NewOutput(moduleAccAddr, coins),
 		},
 	}
+	invalidMultiSendMsg = &types.MsgMultiSend{
+		Inputs:  []types.Input{types.NewInput(addr1, coins), types.NewInput(addr2, coins)},
+		Outputs: []types.Output{},
+	}
 )
 
 func TestSendNotEnoughBalance(t *testing.T) {
@@ -154,6 +158,15 @@ func TestMsgMultiSendWithAccounts(t *testing.T) {
 			expPass:    false,
 			privKeys:   []cryptotypes.PrivKey{priv1},
 		},
+		{
+			desc:       "multiple inputs not allowed",
+			msgs:       []sdk.Msg{invalidMultiSendMsg},
+			accNums:    []uint64{0},
+			accSeqs:    []uint64{0},
+			expSimPass: false,
+			expPass:    false,
+			privKeys:   []cryptotypes.PrivKey{priv1},
+		},
 	}
 
 	for _, tc := range testCases {

x/bank/client/cli/tx.go

@@ -131,7 +131,7 @@ When using '--dry-run' a key name cannot be used, only a bech32 address.
 				amount = coins.MulInt(totalAddrs)
 			}
 
-			msg := types.NewMsgMultiSend(types.NewInput(clientCtx.FromAddress, amount), output)
+			msg := types.NewMsgMultiSend([]types.Input{types.NewInput(clientCtx.FromAddress, amount)}, output)
 
 			return tx.GenerateOrBroadcastTxCLI(clientCtx, cmd.Flags(), msg)
 		},

x/bank/keeper/keeper_test.go

@@ -361,15 +361,14 @@ func (suite *IntegrationTestSuite) TestInputOutputNewAccount() {
 	suite.Require().Nil(app.AccountKeeper.GetAccount(ctx, addr2))
 	suite.Require().Empty(app.BankKeeper.GetAllBalances(ctx, addr2))
 
-	input := types.Input{
-		Address: addr1.String(),
-		Coins:   sdk.NewCoins(newFooCoin(30), newBarCoin(10)),
+	inputs := []types.Input{
+		{Address: addr1.String(), Coins: sdk.NewCoins(newFooCoin(30), newBarCoin(10))},
 	}
 	outputs := []types.Output{
 		{Address: addr2.String(), Coins: sdk.NewCoins(newFooCoin(30), newBarCoin(10))},
 	}
 
-	suite.Require().NoError(app.BankKeeper.InputOutputCoins(ctx, input, outputs))
+	suite.Require().NoError(app.BankKeeper.InputOutputCoins(ctx, inputs, outputs))
 
 	expected := sdk.NewCoins(newFooCoin(30), newBarCoin(10))
 	acc2Balances := app.BankKeeper.GetAllBalances(ctx, addr2)
@@ -393,9 +392,8 @@ func (suite *IntegrationTestSuite) TestInputOutputCoins() {
 	acc3 := app.AccountKeeper.NewAccountWithAddress(ctx, addr3)
 	app.AccountKeeper.SetAccount(ctx, acc3)
 
-	input := types.Input{
-		Address: addr1.String(),
-		Coins:   sdk.NewCoins(newFooCoin(60), newBarCoin(20)),
+	input := []types.Input{
+		{Address: addr1.String(), Coins: sdk.NewCoins(newFooCoin(60), newBarCoin(20))},
 	}
 	outputs := []types.Output{
 		{Address: addr2.String(), Coins: sdk.NewCoins(newFooCoin(30), newBarCoin(10))},
@@ -407,9 +405,11 @@ func (suite *IntegrationTestSuite) TestInputOutputCoins() {
 
 	suite.Require().NoError(testutil.FundAccount(app.BankKeeper, ctx, addr1, balances))
 
-	insufficientInput := types.Input{
-		Address: addr1.String(),
-		Coins:   sdk.NewCoins(newFooCoin(300), newBarCoin(100)),
+	insufficientInput := []types.Input{
+		{
+			Address: addr1.String(),
+			Coins:   sdk.NewCoins(newFooCoin(300), newBarCoin(100)),
+		},
 	}
 	insufficientOutputs := []types.Output{
 		{Address: addr2.String(), Coins: sdk.NewCoins(newFooCoin(300), newBarCoin(100))},
@@ -613,9 +613,10 @@ func (suite *IntegrationTestSuite) TestMsgMultiSendEvents() {
 	coins := sdk.NewCoins(sdk.NewInt64Coin(fooDenom, 50), sdk.NewInt64Coin(barDenom, 100))
 	newCoins := sdk.NewCoins(sdk.NewInt64Coin(fooDenom, 50))
 	newCoins2 := sdk.NewCoins(sdk.NewInt64Coin(barDenom, 100))
-	input := types.Input{
-		Address: addr.String(),
-		Coins:   coins,
+	input := []types.Input{
+		{Address: addr.String(),
+			Coins: coins,
+		},
 	}
 	outputs := []types.Output{
 		{Address: addr3.String(), Coins: newCoins},

x/bank/keeper/msg_server.go

@@ -76,8 +76,10 @@ func (k msgServer) MultiSend(goCtx context.Context, msg *types.MsgMultiSend) (*t
 	ctx := sdk.UnwrapSDKContext(goCtx)
 
 	// NOTE: totalIn == totalOut should already have been checked
-	if err := k.IsSendEnabledCoins(ctx, msg.Input.Coins...); err != nil {
-		return nil, err
+	for _, in := range msg.Inputs {
+		if err := k.IsSendEnabledCoins(ctx, in.Coins...); err != nil {
+			return nil, err
+		}
 	}
 
 	for _, out := range msg.Outputs {
@@ -88,7 +90,7 @@ func (k msgServer) MultiSend(goCtx context.Context, msg *types.MsgMultiSend) (*t
 		}
 	}
 
-	err := k.InputOutputCoins(ctx, msg.Input, msg.Outputs)
+	err := k.InputOutputCoins(ctx, msg.Inputs, msg.Outputs)
 	if err != nil {
 		return nil, err
 	}

x/bank/keeper/send.go

@@ -18,7 +18,7 @@ import (
 type SendKeeper interface {
 	ViewKeeper
 
-	InputOutputCoins(ctx sdk.Context, input types.Input, outputs []types.Output) error
+	InputOutputCoins(ctx sdk.Context, inputs []types.Input, outputs []types.Output) error
 	SendCoins(ctx sdk.Context, fromAddr sdk.AccAddress, toAddr sdk.AccAddress, amt sdk.Coins) error
 
 	GetParams(ctx sdk.Context) types.Params
@@ -120,30 +120,31 @@ func (k BaseSendKeeper) SetParams(ctx sdk.Context, params types.Params) error {
 // InputOutputCoins performs multi-send functionality. It accepts a series of
 // inputs that correspond to a series of outputs. It returns an error if the
 // inputs and outputs don't line up or if any single transfer of tokens fails.
-func (k BaseSendKeeper) InputOutputCoins(ctx sdk.Context, input types.Input, outputs []types.Output) error {
+func (k BaseSendKeeper) InputOutputCoins(ctx sdk.Context, inputs []types.Input, outputs []types.Output) error {
 	// Safety check ensuring that when sending coins the keeper must maintain the
 	// Check supply invariant and validity of Coins.
-	if err := types.ValidateInputsOutputs(input, outputs); err != nil {
+	if err := types.ValidateInputsOutputs(inputs, outputs); err != nil {
 		return err
 	}
 
-	inAddress, err := sdk.AccAddressFromBech32(input.Address)
-	if err != nil {
-		return err
-	}
+	for _, in := range inputs {
+		inAddress, err := sdk.AccAddressFromBech32(in.Address)
+		if err != nil {
+			return err
+		}
 
-	err = k.subUnlockedCoins(ctx, inAddress, input.Coins)
-	if err != nil {
-		return err
+		err = k.subUnlockedCoins(ctx, inAddress, in.Coins)
+		if err != nil {
+			return err
+		}
+		ctx.EventManager().EmitEvent(
+			sdk.NewEvent(
+				sdk.EventTypeMessage,
+				sdk.NewAttribute(types.AttributeKeySender, in.Address),
+			),
+		)
 	}
 
-	ctx.EventManager().EmitEvent(
-		sdk.NewEvent(
-			sdk.EventTypeMessage,
-			sdk.NewAttribute(types.AttributeKeySender, input.Address),
-		),
-	)
-
 	for _, out := range outputs {
 		outAddress, err := sdk.AccAddressFromBech32(out.Address)
 		if err != nil {