Charge gas for custom event attributes and messages (Finschia#539)

* Charge gas for custom event attributes

* Introduce gas register for gas costs

* Review feedback

* Tests and minor updates

* Godoc

x/wasm/keeper/api.go

@@ -8,11 +8,11 @@ import (
 )
 
 type cosmwasmAPIImpl struct {
-	gasMultiplier uint64
+	gasMultiplier GasMultiplier
 }
 
 func (a cosmwasmAPIImpl) humanAddress(canon []byte) (string, uint64, error) {
-	gas := 5 * a.gasMultiplier
+	gas := a.gasMultiplier.FromWasmVMGas(5)
 	if len(canon) != sdk.BytesAddrLen {
 		//nolint:stylecheck
 		return "", gas, fmt.Errorf("expected %d byte address", sdk.BytesAddrLen)
@@ -23,7 +23,7 @@ func (a cosmwasmAPIImpl) humanAddress(canon []byte) (string, uint64, error) {
 
 func (a cosmwasmAPIImpl) canonicalAddress(human string) ([]byte, uint64, error) {
 	bz, err := sdk.AccAddressToBytes(human)
-	return bz, 4 * a.gasMultiplier, err
+	return bz, a.gasMultiplier.ToWasmVMGas(4), err
 }
 
 func (k Keeper) cosmwasmAPI(ctx sdk.Context) wasmvm.GoAPI {

x/wasm/keeper/gas_register.go

@@ -0,0 +1,92 @@
+package keeper
+
+import (
+	wasmvmtypes "github.com/line/wasmvm/types"
+	sdk "github.com/line/lbm-sdk/types"
+)
+
+const (
+	// DefaultEventAttributeDataCost is how much SDK gas is charged *per byte* for attribute data in events.
+	// This is used with len(key) + len(value)
+	DefaultEventAttributeDataCost uint64 = 1
+	// DefaultContractMessageDataCost is how much SDK gas is charged *per byte* of the message that goes to the contract
+	// This is used with len(msg)
+	DefaultContractMessageDataCost uint64 = 1
+	// DefaultPerAttributeCost is how much SDK gas we charge per attribute count.
+	DefaultPerAttributeCost uint64 = 10
+	// DefaultEventAttributeDataFreeTier number of bytes of total attribute data we do not charge.
+	DefaultEventAttributeDataFreeTier = 100
+)
+
+// GasRegister abstract source for gas costs
+type GasRegister interface {
+	// NewContractInstanceCosts costs to crate a new contract instance from code
+	// EventCosts costs to persist an event
+	EventCosts(evts []wasmvmtypes.EventAttribute) sdk.Gas
+}
+
+// WasmGasRegisterConfig config type
+type WasmGasRegisterConfig struct {
+	// EventPerAttributeCost is how much SDK gas is charged *per byte* for attribute data in events.
+	// This is used with len(key) + len(value)
+	EventPerAttributeCost sdk.Gas
+	// EventAttributeDataCost is how much SDK gas is charged *per byte* for attribute data in events.
+	// This is used with len(key) + len(value)
+	EventAttributeDataCost sdk.Gas
+	// EventAttributeDataFreeTier number of bytes of total attribute data that is free of charge
+	EventAttributeDataFreeTier int
+	// ContractMessageDataCost SDK gas charged *per byte* of the message that goes to the contract
+	// This is used with len(msg)
+	ContractMessageDataCost sdk.Gas
+}
+
+// DefaultGasRegisterConfig default values
+func DefaultGasRegisterConfig() WasmGasRegisterConfig {
+	return WasmGasRegisterConfig{
+		EventPerAttributeCost:      DefaultPerAttributeCost,
+		EventAttributeDataCost:     DefaultEventAttributeDataCost,
+		EventAttributeDataFreeTier: DefaultEventAttributeDataFreeTier,
+		ContractMessageDataCost:    DefaultContractMessageDataCost,
+	}
+}
+
+// WasmGasRegister implements GasRegister interface
+type WasmGasRegister struct {
+	c WasmGasRegisterConfig
+}
+
+// NewDefaultWasmGasRegister creates instance with default values
+func NewDefaultWasmGasRegister() WasmGasRegister {
+	return NewWasmGasRegister(DefaultGasRegisterConfig())
+}
+
+// NewWasmGasRegister constructor
+func NewWasmGasRegister(c WasmGasRegisterConfig) WasmGasRegister {
+	return WasmGasRegister{
+		c: c,
+	}
+}
+
+// EventCosts costs to persist an event
+func (g WasmGasRegister) EventCosts(evts []wasmvmtypes.EventAttribute) sdk.Gas {
+	if len(evts) == 0 {
+		return 0
+	}
+	var storedBytes int
+	for _, l := range evts {
+		storedBytes += len(l.Key) + len(l.Value)
+	}
+	// apply free tier
+	if storedBytes <= g.c.EventAttributeDataFreeTier {
+		storedBytes = 0
+	} else {
+		storedBytes -= g.c.EventAttributeDataFreeTier
+	}
+	// total Length * costs + attribute count * costs
+	r := sdk.NewIntFromUint64(g.c.EventAttributeDataCost).Mul(sdk.NewIntFromUint64(uint64(storedBytes))).
+		Add(sdk.NewIntFromUint64(g.c.EventPerAttributeCost).Mul(sdk.NewIntFromUint64(uint64(len(evts)))))
+	if !r.IsUint64() {
+		panic(sdk.ErrorOutOfGas{Descriptor: "overflow"})
+	}
+	return r.Uint64()
+}