accounts, ethclient: minor tweaks on the new simulated backend

accounts/abi/bind/backends/simulated.go

@@ -44,7 +44,7 @@ func (b *SimulatedBackend) Fork(ctx context.Context, parentHash common.Hash) err
 // Deprecated: please use simulated.Backend from package
 // github.com/ethereum/go-ethereum/ethclient/simulated instead.
 func NewSimulatedBackend(alloc core.GenesisAlloc, gasLimit uint64) *SimulatedBackend {
-	b := simulated.New(alloc, gasLimit)
+	b := simulated.NewBackend(alloc, simulated.WithBlockGasLimit(gasLimit))
 	return &SimulatedBackend{
 		Backend: b,
 		Client:  b.Client(),

accounts/abi/bind/util_test.go

@@ -56,11 +56,10 @@ var waitDeployedTests = map[string]struct {
 func TestWaitDeployed(t *testing.T) {
 	t.Parallel()
 	for name, test := range waitDeployedTests {
-		backend := simulated.New(
+		backend := simulated.NewBackend(
 			core.GenesisAlloc{
 				crypto.PubkeyToAddress(testKey.PublicKey): {Balance: big.NewInt(10000000000000000)},
 			},
-			10000000,
 		)
 		defer backend.Close()
 
@@ -102,11 +101,10 @@ func TestWaitDeployed(t *testing.T) {
 }
 
 func TestWaitDeployedCornerCases(t *testing.T) {
-	backend := simulated.New(
+	backend := simulated.NewBackend(
 		core.GenesisAlloc{
 			crypto.PubkeyToAddress(testKey.PublicKey): {Balance: big.NewInt(10000000000000000)},
 		},
-		10000000,
 	)
 	defer backend.Close()
 

ethclient/simulated/backend.go

@@ -34,20 +34,6 @@ import (
 	"github.com/ethereum/go-ethereum/rpc"
 )
 
-// Backend is a simulated blockchain. You can use it to test your contracts or
-// other code that interacts with the Ethereum chain.
-type Backend struct {
-	eth    *eth.Ethereum
-	beacon *catalyst.SimulatedBeacon
-	client simClient
-}
-
-// simClient wraps ethclient. This exists to prevent extracting ethclient.Client
-// from the Client interface returned by Backend.
-type simClient struct {
-	*ethclient.Client
-}
-
 // Client exposes the methods provided by the Ethereum RPC client.
 type Client interface {
 	ethereum.BlockNumberReader
@@ -66,70 +52,81 @@ type Client interface {
 	ethereum.ChainIDReader
 }
 
-// New creates a new binding backend using a simulated blockchain
-// for testing purposes.
+// simClient wraps ethclient. This exists to prevent extracting ethclient.Client
+// from the Client interface returned by Backend.
+type simClient struct {
+	*ethclient.Client
+}
+
+// Backend is a simulated blockchain. You can use it to test your contracts or
+// other code that interacts with the Ethereum chain.
+type Backend struct {
+	eth    *eth.Ethereum
+	beacon *catalyst.SimulatedBeacon
+	client simClient
+}
+
+// NewBackend creates a new simulated blockchain that can be used as a backend for
+// contract bindings in unit tests.
+//
 // A simulated backend always uses chainID 1337.
-func New(alloc core.GenesisAlloc, gasLimit uint64) *Backend {
-	// Setup the node object
+func NewBackend(alloc core.GenesisAlloc, options ...func(nodeConf *node.Config, ethConf *ethconfig.Config)) *Backend {
+	// Create the default configurations for the outer node shell and the Ethereum
+	// service to mutate with the options afterwards
 	nodeConf := node.DefaultConfig
 	nodeConf.DataDir = ""
 	nodeConf.P2P = p2p.Config{NoDiscovery: true}
-	stack, err := node.New(&nodeConf)
-	if err != nil {
-		// This should never happen, if it does, please open an issue
-		panic(err)
-	}
 
-	// Setup ethereum
-	genesis := core.Genesis{
+	ethConf := ethconfig.Defaults
+	ethConf.Genesis = &core.Genesis{
 		Config:   params.AllDevChainProtocolChanges,
-		GasLimit: gasLimit,
+		GasLimit: ethconfig.Defaults.Miner.GasCeil,
 		Alloc:    alloc,
 	}
-	conf := ethconfig.Defaults
-	conf.Genesis = &genesis
-	conf.SyncMode = downloader.FullSync
-	conf.TxPool.NoLocals = true
-	sim, err := newWithNode(stack, &conf, 0)
+	ethConf.SyncMode = downloader.FullSync
+	ethConf.TxPool.NoLocals = true
+
+	for _, option := range options {
+		option(&nodeConf, &ethConf)
+	}
+	// Assemble the Ethereum stack to run the chain with
+	stack, err := node.New(&nodeConf)
+	if err != nil {
+		panic(err) // this should never happen
+	}
+	sim, err := newWithNode(stack, &ethConf, 0)
 	if err != nil {
-		// This should never happen, if it does, please open an issue
-		panic(err)
+		panic(err) // this should never happen
 	}
 	return sim
 }
 
-// newWithNode sets up a simulated backend on an existing node
-// this allows users to do persistent simulations.
-// The provided node must not be started and will be started by newWithNode
+// newWithNode sets up a simulated backend on an existing node. The provided node
+// must not be started and will be started by this method.
 func newWithNode(stack *node.Node, conf *eth.Config, blockPeriod uint64) (*Backend, error) {
 	backend, err := eth.New(stack, conf)
 	if err != nil {
 		return nil, err
 	}
-
 	// Register the filter system
 	filterSystem := filters.NewFilterSystem(backend.APIBackend, filters.Config{})
 	stack.RegisterAPIs([]rpc.API{{
 		Namespace: "eth",
 		Service:   filters.NewFilterAPI(filterSystem, false),
 	}})
-
 	// Start the node
 	if err := stack.Start(); err != nil {
 		return nil, err
 	}
-
 	// Set up the simulated beacon
 	beacon, err := catalyst.NewSimulatedBeacon(blockPeriod, backend)
 	if err != nil {
 		return nil, err
 	}
-
 	// Reorg our chain back to genesis
 	if err := beacon.Fork(backend.BlockChain().GetCanonicalHash(0)); err != nil {
 		return nil, err
 	}
-
 	return &Backend{
 		eth:    backend,
 		beacon: beacon,

ethclient/simulated/backend_test.go

@@ -40,10 +40,10 @@ var (
 )
 
 func simTestBackend(testAddr common.Address) *Backend {
-	return New(
+	return NewBackend(
 		core.GenesisAlloc{
 			testAddr: {Balance: big.NewInt(10000000000000000)},
-		}, 10000000,
+		},
 	)
 }
 
@@ -70,8 +70,8 @@ func newTx(sim *Backend, key *ecdsa.PrivateKey) (*types.Transaction, error) {
 	return types.SignTx(tx, types.LatestSignerForChainID(chainid), key)
 }
 
-func TestNewSim(t *testing.T) {
-	sim := New(core.GenesisAlloc{}, 30_000_000)
+func TestNewBackend(t *testing.T) {
+	sim := NewBackend(core.GenesisAlloc{})
 	defer sim.Close()
 
 	client := sim.Client()
@@ -94,7 +94,7 @@ func TestNewSim(t *testing.T) {
 }
 
 func TestAdjustTime(t *testing.T) {
-	sim := New(core.GenesisAlloc{}, 10_000_000)
+	sim := NewBackend(core.GenesisAlloc{})
 	defer sim.Close()
 
 	client := sim.Client()

ethclient/simulated/options.go

@@ -0,0 +1,39 @@
+// Copyright 2024 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package simulated
+
+import (
+	"github.com/ethereum/go-ethereum/eth/ethconfig"
+	"github.com/ethereum/go-ethereum/node"
+)
+
+// WithBlockGasLimit configures the simulated backend to target a specific gas limit
+// when producing blocks.
+func WithBlockGasLimit(gaslimit uint64) func(nodeConf *node.Config, ethConf *ethconfig.Config) {
+	return func(nodeConf *node.Config, ethConf *ethconfig.Config) {
+		ethConf.Genesis.GasLimit = gaslimit
+		ethConf.Miner.GasCeil = gaslimit
+	}
+}
+
+// WithCallGasLimit configures the simulated backend to cap eth_calls to a specific
+// gas limit when running client operations.
+func WithCallGasLimit(gaslimit uint64) func(nodeConf *node.Config, ethConf *ethconfig.Config) {
+	return func(nodeConf *node.Config, ethConf *ethconfig.Config) {
+		ethConf.RPCGasCap = gaslimit
+	}
+}

ethclient/simulated/options_test.go

@@ -0,0 +1,73 @@
+// Copyright 2024 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package simulated
+
+import (
+	"context"
+	"math/big"
+	"strings"
+	"testing"
+
+	"github.com/ethereum/go-ethereum"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+// Tests that the simulator starts with the initial gas limit in the genesis block,
+// and that it keeps the same target value.
+func TestWithBlockGasLimitOption(t *testing.T) {
+	// Construct a simulator, targeting a different gas limit
+	sim := NewBackend(core.GenesisAlloc{}, WithBlockGasLimit(12_345_678))
+	defer sim.Close()
+
+	client := sim.Client()
+	genesis, err := client.BlockByNumber(context.Background(), big.NewInt(0))
+	if err != nil {
+		t.Fatalf("failed to retrieve genesis block: %v", err)
+	}
+	if genesis.GasLimit() != 12_345_678 {
+		t.Errorf("genesis gas limit mismatch: have %v, want %v", genesis.GasLimit(), 12_345_678)
+	}
+	// Produce a number of blocks and verify the locked in gas target
+	sim.Commit()
+	head, err := client.BlockByNumber(context.Background(), big.NewInt(1))
+	if err != nil {
+		t.Fatalf("failed to retrieve head block: %v", err)
+	}
+	if head.GasLimit() != 12_345_678 {
+		t.Errorf("head gas limit mismatch: have %v, want %v", head.GasLimit(), 12_345_678)
+	}
+}
+
+// Tests that the simulator honors the RPC call caps set by the options.
+func TestWithCallGasLimitOption(t *testing.T) {
+	// Construct a simulator, targeting a different gas limit
+	sim := NewBackend(core.GenesisAlloc{
+		testAddr: {Balance: big.NewInt(10000000000000000)},
+	}, WithCallGasLimit(params.TxGas-1))
+	defer sim.Close()
+
+	client := sim.Client()
+	_, err := client.CallContract(context.Background(), ethereum.CallMsg{
+		From: testAddr,
+		To:   &testAddr,
+		Gas:  21000,
+	}, nil)
+	if !strings.Contains(err.Error(), core.ErrIntrinsicGas.Error()) {
+		t.Fatalf("error mismatch: have %v, want %v", err, core.ErrIntrinsicGas)
+	}
+}