Adding gas estimate function

- Added *GasEstimate template.
- Added EstimateGas() in ethutil.go

Author: dimpar

pkg/chain/ethereum/ethutil/ethutil.go

@@ -136,6 +136,37 @@ func CallAtBlock(
 	return nil
 }
 
+// EstimateGas tries to estimate the gas needed to execute a specific transaction based on
+// the current pending state of the backend blockchain. There is no guarantee that this is
+// the true gas limit requirement as other transactions may be added or removed by miners,
+// but it should provide a basis for setting a reasonable default.
+func EstimateGas(
+	from common.Address, 
+	to common.Address,
+	method string,
+	contractABI *abi.ABI,
+	transactor bind.ContractTransactor,
+	parameters ...interface{},
+) (uint64, error) {
+	input, err := contractABI.Pack(method, parameters...)
+	if err != nil {
+		return 0, err
+	}
+
+	msg := ethereum.CallMsg{
+		From: from,
+		To:   &to,
+		Data: input,
+	}
+
+	gas, err := transactor.EstimateGas(context.TODO(), msg)
+	if err != nil {
+		return 0, err
+	}
+
+	return gas, nil
+}
+
 type loggingWrapper struct {
 	bind.ContractBackend
 

tools/generators/ethereum/contract.go.tmpl

@@ -26,13 +26,14 @@ import (
 var {{.ShortVar}}Logger = log.Logger("keep-contract-{{.Class}}")
 
 type {{.Class}} struct {
-	contract          *abi.{{.AbiClass}}
-	contractAddress   common.Address
-	contractABI       *ethereumabi.ABI
-	caller            bind.ContractCaller
-	callerOptions     *bind.CallOpts
-	transactorOptions *bind.TransactOpts
-	errorResolver     *ethutil.ErrorResolver
+	contract           *abi.{{.AbiClass}}
+	contractAddress    common.Address
+	contractABI        *ethereumabi.ABI
+	caller             bind.ContractCaller
+	transactor         bind.ContractTransactor
+	callerOptions      *bind.CallOpts
+	transactorOptions  *bind.TransactOpts
+	errorResolver      *ethutil.ErrorResolver
 
 	transactionMutex *sync.Mutex
 }
@@ -72,6 +73,7 @@ func New{{.Class}}(
 		contractAddress:   contractAddress,
 		contractABI: 	   &contractABI,
 		caller:     	   backend,
+		transactor:        backend,
 		callerOptions:     callerOptions,
 		transactorOptions: transactorOptions,
 		errorResolver:     ethutil.NewErrorResolver(backend, &contractABI, &contractAddress),

tools/generators/ethereum/contract_non_const_methods.go.tmpl

@@ -108,4 +108,21 @@ func ({{$contract.ShortVar}} *{{$contract.Class}}) Call{{$method.CapsName}}(
 	return {{$returnVar}}err
 }
 
+func ({{$contract.ShortVar}} *{{$contract.Class}}) {{$method.CapsName}}GasEstimate(
+	{{$method.ParamDeclarations -}}
+) (uint64, error) {
+	var result uint64
+
+	result, err := ethutil.EstimateGas(
+		{{$contract.ShortVar}}.callerOptions.From,
+		{{$contract.ShortVar}}.contractAddress,
+		"{{$method.LowerName}}",
+		{{$contract.ShortVar}}.contractABI,
+		{{$contract.ShortVar}}.transactor,
+		{{$method.Params}}
+	)
+
+	return result, err
+}
+
 {{- end -}}

tools/generators/ethereum/contract_non_const_methods_template_content.go

@@ -111,5 +111,22 @@ func ({{$contract.ShortVar}} *{{$contract.Class}}) Call{{$method.CapsName}}(
 	return {{$returnVar}}err
 }
 
+func ({{$contract.ShortVar}} *{{$contract.Class}}) {{$method.CapsName}}GasEstimate(
+	{{$method.ParamDeclarations -}}
+) (uint64, error) {
+	var result uint64
+
+	result, err := ethutil.EstimateGas(
+		{{$contract.ShortVar}}.callerOptions.From,
+		{{$contract.ShortVar}}.contractAddress,
+		"{{$method.LowerName}}",
+		{{$contract.ShortVar}}.contractABI,
+		{{$contract.ShortVar}}.transactor,
+		{{$method.Params}}
+	)
+
+	return result, err
+}
+
 {{- end -}}
 `

tools/generators/ethereum/contract_template_content.go

@@ -29,13 +29,14 @@ import (
 var {{.ShortVar}}Logger = log.Logger("keep-contract-{{.Class}}")
 
 type {{.Class}} struct {
-	contract          *abi.{{.AbiClass}}
-	contractAddress   common.Address
-	contractABI       *ethereumabi.ABI
-	caller            bind.ContractCaller
-	callerOptions     *bind.CallOpts
-	transactorOptions *bind.TransactOpts
-	errorResolver     *ethutil.ErrorResolver
+	contract           *abi.{{.AbiClass}}
+	contractAddress    common.Address
+	contractABI        *ethereumabi.ABI
+	caller             bind.ContractCaller
+	transactor         bind.ContractTransactor
+	callerOptions      *bind.CallOpts
+	transactorOptions  *bind.TransactOpts
+	errorResolver      *ethutil.ErrorResolver
 
 	transactionMutex *sync.Mutex
 }
@@ -75,6 +76,7 @@ func New{{.Class}}(
 		contractAddress:   contractAddress,
 		contractABI: 	   &contractABI,
 		caller:     	   backend,
+		transactor:        backend,
 		callerOptions:     callerOptions,
 		transactorOptions: transactorOptions,
 		errorResolver:     ethutil.NewErrorResolver(backend, &contractABI, &contractAddress),