[Supplier] Add supplier staking fee (#883)

## Summary

Replace the upstaking requirement with a staking fee when a stake is
added or updated.

The staking fee will become a governance parameter in a follow up PR.

## Issue

- #853 

## Type of change

Select one or more from the following:

- [x] New feature, functionality or library

## Testing

- [x] **Unit Tests**: `make go_develop_and_test`
- [x] **LocalNet E2E Tests**: `make test_e2e`
- [ ] **DevNet E2E Tests**: Add the `devnet-test-e2e` label to the PR.

## Sanity Checklist

- [x] I have tested my changes using the available tooling
- [x] I have commented my code
- [x] I have performed a self-review of my own code; both comments &
source code
- [ ] I create and reference any new tickets, if applicable
- [x] I have left TODOs throughout the codebase, if applicable

e2e/tests/stake_supplier.feature

@@ -2,16 +2,17 @@ Feature: Stake Supplier Namespace
 
     Scenario: User can stake a Supplier
         Given the user has the pocketd binary installed
+        # TODO_UPNEXT: Set the supplier stake fee once it is a param.
         And the user verifies the "supplier" for account "supplier2" is not staked
-        And the account "supplier2" has a balance greater than "1000070" uPOKT
+        And the account "supplier2" has a balance greater than "1000071" uPOKT
         When the user stakes a "supplier" with "1000070" uPOKT for "anvil" service from the account "supplier2"
         Then the user should be able to see standard output containing "txhash:"
         And the user should be able to see standard output containing "code: 0"
         And the pocketd binary should exit without error
         And the user should wait for the "supplier" module "StakeSupplier" message to be submitted
         And the user should wait for the "supplier" module "SupplierStaked" tx event to be broadcast
         And the "supplier" for account "supplier2" is staked with "1000070" uPOKT
-        And the account balance of "supplier2" should be "1000070" uPOKT "less" than before
+        And the account balance of "supplier2" should be "1000071" uPOKT "less" than before
 
     Scenario: User can unstake a Supplier
         Given the user has the pocketd binary installed

testutil/keeper/supplier.go

@@ -33,7 +33,7 @@ type SupplierModuleKeepers struct {
 	*keeper.Keeper
 	types.SharedKeeper
 	// Tracks the amount of funds returned to the supplier owner when the supplier is unbonded.
-	SupplierUnstakedFundsMap map[string]int64
+	SupplierBalanceMap map[string]int64
 }
 
 func SupplierKeeper(t testing.TB) (SupplierModuleKeepers, context.Context) {
@@ -53,17 +53,19 @@ func SupplierKeeper(t testing.TB) (SupplierModuleKeepers, context.Context) {
 	cdc := codec.NewProtoCodec(registry)
 	authority := authtypes.NewModuleAddress(govtypes.ModuleName)
 
-	// Set a simple map to track the where the supplier stake is returned when
-	// the supplier is unbonded.
-	supplierUnstakedFundsMap := make(map[string]int64)
+	// Set a simple map to track the suppliers balances.
+	supplierBalanceMap := make(map[string]int64)
 
 	ctrl := gomock.NewController(t)
 	mockBankKeeper := mocks.NewMockBankKeeper(ctrl)
-	mockBankKeeper.EXPECT().SendCoinsFromAccountToModule(gomock.Any(), gomock.Any(), types.ModuleName, gomock.Any()).AnyTimes()
+	mockBankKeeper.EXPECT().SendCoinsFromAccountToModule(gomock.Any(), gomock.Any(), types.ModuleName, gomock.Any()).AnyTimes().
+		Do(func(ctx context.Context, addr sdk.AccAddress, module string, coins sdk.Coins) {
+			supplierBalanceMap[addr.String()] -= coins[0].Amount.Int64()
+		})
 	mockBankKeeper.EXPECT().SpendableCoins(gomock.Any(), gomock.Any()).AnyTimes()
 	mockBankKeeper.EXPECT().SendCoinsFromModuleToAccount(gomock.Any(), types.ModuleName, gomock.Any(), gomock.Any()).AnyTimes().
 		Do(func(ctx context.Context, module string, addr sdk.AccAddress, coins sdk.Coins) {
-			supplierUnstakedFundsMap[addr.String()] += coins[0].Amount.Int64()
+			supplierBalanceMap[addr.String()] += coins[0].Amount.Int64()
 		})
 
 	// Construct a real shared keeper.
@@ -104,9 +106,9 @@ func SupplierKeeper(t testing.TB) (SupplierModuleKeepers, context.Context) {
 	serviceKeeper.SetService(ctx, sharedtypes.Service{Id: "svcId2"})
 
 	supplierModuleKeepers := SupplierModuleKeepers{
-		Keeper:                   &supplierKeeper,
-		SharedKeeper:             sharedKeeper,
-		SupplierUnstakedFundsMap: supplierUnstakedFundsMap,
+		Keeper:             &supplierKeeper,
+		SharedKeeper:       sharedKeeper,
+		SupplierBalanceMap: supplierBalanceMap,
 	}
 
 	return supplierModuleKeepers, ctx

x/supplier/keeper/msg_server_stake_supplier.go

@@ -8,11 +8,19 @@ import (
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 
+	"github.com/pokt-network/poktroll/app/volatile"
 	"github.com/pokt-network/poktroll/telemetry"
 	sharedtypes "github.com/pokt-network/poktroll/x/shared/types"
 	"github.com/pokt-network/poktroll/x/supplier/types"
 )
 
+var (
+	// TODO_BETA: Make supplier staking fee a governance parameter
+	// TODO_BETA(@red-0ne): Update supplier staking documentation to remove the upstaking
+	// requirement and introduce the staking fee.
+	SupplierStakingFee = sdk.NewInt64Coin(volatile.DenomuPOKT, 1)
+)
+
 func (k msgServer) StakeSupplier(ctx context.Context, msg *types.MsgStakeSupplier) (*types.MsgStakeSupplierResponse, error) {
 	isSuccessful := false
 	defer telemetry.EventSuccessCounter(
@@ -104,9 +112,13 @@ func (k msgServer) StakeSupplier(ctx context.Context, msg *types.MsgStakeSupplie
 		supplier.UnstakeSessionEndHeight = sharedtypes.SupplierNotUnstaking
 	}
 
-	// MUST ALWAYS stake or upstake (> 0 delta)
-	if coinsToEscrow.IsZero() {
-		err = types.ErrSupplierInvalidStake.Wrapf("Signer %q must escrow more than 0 additional coins", msg.Signer)
+	// TODO_BETA: Remove requirement of MUST ALWAYS stake or upstake (>= 0 delta)
+	// TODO_POST_MAINNET: Should we allow stake decrease down to min stake?
+	if coinsToEscrow.IsNegative() {
+		err = types.ErrSupplierInvalidStake.Wrapf(
+			"Supplier signer %q stake (%s) must be greater than or equal to the current stake (%s)",
+			msg.Signer, msg.GetStake(), supplier.Stake,
+		)
 		logger.Info(fmt.Sprintf("WARN: %s", err))
 		return nil, status.Error(codes.InvalidArgument, err.Error())
 	}
@@ -130,7 +142,8 @@ func (k msgServer) StakeSupplier(ctx context.Context, msg *types.MsgStakeSupplie
 	}
 
 	// Send the coins from the message signer account to the staked supplier pool
-	err = k.bankKeeper.SendCoinsFromAccountToModule(ctx, msgSignerAddress, types.ModuleName, []sdk.Coin{coinsToEscrow})
+	stakeWithFee := sdk.NewCoins(coinsToEscrow.Add(SupplierStakingFee))
+	err = k.bankKeeper.SendCoinsFromAccountToModule(ctx, msgSignerAddress, types.ModuleName, stakeWithFee)
 	if err != nil {
 		logger.Info(fmt.Sprintf("ERROR: could not send %v coins from %q to %q module account due to %v", coinsToEscrow, msgSignerAddress, types.ModuleName, err))
 		return nil, status.Error(codes.InvalidArgument, err.Error())
@@ -191,8 +204,12 @@ func (k msgServer) updateSupplier(
 		return types.ErrSupplierInvalidStake.Wrapf("stake amount cannot be nil")
 	}
 
-	if msg.Stake.IsLTE(*supplier.Stake) {
-		return types.ErrSupplierInvalidStake.Wrapf("stake amount %v must be higher than previous stake amount %v", msg.Stake, supplier.Stake)
+	// TODO_BETA: No longer require upstaking. Remove this check.
+	if msg.Stake.IsLT(*supplier.Stake) {
+		return types.ErrSupplierInvalidStake.Wrapf(
+			"stake amount %v must be greater than or equal than previous stake amount %v",
+			msg.Stake, supplier.Stake,
+		)
 	}
 	supplier.Stake = msg.Stake
 

x/supplier/keeper/msg_server_stake_supplier_test.go

@@ -45,9 +45,16 @@ func TestMsgServer_StakeSupplier_SuccessfulCreateAndUpdate(t *testing.T) {
 	require.Equal(t, "svcId", foundSupplier.Services[0].ServiceId)
 	require.Len(t, foundSupplier.Services[0].Endpoints, 1)
 	require.Equal(t, "http://localhost:8080", foundSupplier.Services[0].Endpoints[0].Url)
-
-	// Prepare an updated supplier with a higher stake and a different URL for the service
-	updateMsg := stakeSupplierForServicesMsg(ownerAddr, operatorAddr, 2000000, "svcId2")
+	// Assert that the supplier's account balance was reduced by the staking fee
+	balanceDecrease := keeper.SupplierStakingFee.Amount.Int64() + foundSupplier.Stake.Amount.Int64()
+	// SupplierBalanceMap reflects the relative changes to the supplier's balance
+	// (i.e. it starts from 0 and can go below it).
+	// It is not using coins that enforce non-negativity of the balance nor account
+	// funding and lookups.
+	require.Equal(t, -balanceDecrease, supplierModuleKeepers.SupplierBalanceMap[ownerAddr])
+
+	// Prepare an updated supplier with the same stake and a different URL for the service
+	updateMsg := stakeSupplierForServicesMsg(ownerAddr, operatorAddr, 1000000, "svcId2")
 	updateMsg.Services[0].Endpoints[0].Url = "http://localhost:8082"
 
 	// Update the staked supplier
@@ -56,7 +63,7 @@ func TestMsgServer_StakeSupplier_SuccessfulCreateAndUpdate(t *testing.T) {
 
 	foundSupplier, isSupplierFound = supplierModuleKeepers.GetSupplier(ctx, operatorAddr)
 	require.True(t, isSupplierFound)
-	require.Equal(t, int64(2000000), foundSupplier.Stake.Amount.Int64())
+	require.Equal(t, int64(1000000), foundSupplier.Stake.Amount.Int64())
 	require.Len(t, foundSupplier.Services, 1)
 	require.Equal(t, "svcId2", foundSupplier.Services[0].ServiceId)
 	require.Len(t, foundSupplier.Services[0].Endpoints, 1)

x/supplier/keeper/msg_server_unstake_supplier_test.go

@@ -226,15 +226,19 @@ func TestMsgServer_UnstakeSupplier_OperatorCanUnstake(t *testing.T) {
 	unbondingHeight := sharedtypes.GetSupplierUnbondingHeight(&sharedParams, &foundSupplier)
 	ctx = keepertest.SetBlockHeight(ctx, int64(unbondingHeight))
 
+	// Balance decrease is the total amount deducted from the supplier's balance, including
+	// the initial stake and the staking fee.
+	balanceDecrease := keeper.SupplierStakingFee.Amount.Int64() + foundSupplier.Stake.Amount.Int64()
 	// Ensure that the initial stake is not returned to the owner yet
-	require.Equal(t, int64(0), supplierModuleKeepers.SupplierUnstakedFundsMap[ownerAddr])
+	require.Equal(t, -balanceDecrease, supplierModuleKeepers.SupplierBalanceMap[ownerAddr])
 
 	// Run the endblocker to unbond suppliers
 	err = supplierModuleKeepers.EndBlockerUnbondSuppliers(ctx)
 	require.NoError(t, err)
 
-	// Ensure that the initial stake is returned to the owner
-	require.Equal(t, initialStake, supplierModuleKeepers.SupplierUnstakedFundsMap[ownerAddr])
+	// Ensure that the initial stake is returned to the owner while the staking fee
+	// remains deducted from the supplier's balance.
+	require.Equal(t, -keeper.SupplierStakingFee.Amount.Int64(), supplierModuleKeepers.SupplierBalanceMap[ownerAddr])
 }
 
 func createStakeMsg(supplierOwnerAddr string, stakeAmount int64) *suppliertypes.MsgStakeSupplier {