starting anvil with port 0

anvil/anvil.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
+	"strconv"
 	"strings"
 	"sync/atomic"
 	"time"
@@ -36,7 +37,8 @@ type Anvil struct {
 }
 
 const (
-	host = "127.0.0.1"
+	host                 = "127.0.0.1"
+	anvilListeningLogStr = "Listening on"
 )
 
 func New(log log.Logger, cfg *Config) *Anvil {
@@ -55,22 +57,22 @@ func (a *Anvil) Start(ctx context.Context) error {
 		return errors.New("anvil already started")
 	}
 
-	tempFile, err := os.CreateTemp("", "genesis-*.json")
-	if err != nil {
-		return fmt.Errorf("error creating temporary genesis file: %w", err)
-	}
-
-	_, err = tempFile.Write(a.cfg.Genesis)
-	if err != nil {
-		return fmt.Errorf("error writing to genesis file: %w", err)
-	}
-
-	// Prep args
 	args := []string{
 		"--host", host,
 		"--chain-id", fmt.Sprintf("%d", a.cfg.ChainId),
 		"--port", fmt.Sprintf("%d", a.cfg.Port),
-		"--init", tempFile.Name(),
+	}
+
+	if len(a.cfg.Genesis) > 0 {
+		tempFile, err := os.CreateTemp("", "genesis-*.json")
+		if err != nil {
+			return fmt.Errorf("error creating temporary genesis file: %w", err)
+		}
+		if _, err = tempFile.Write(a.cfg.Genesis); err != nil {
+			return fmt.Errorf("error writing to genesis file: %w", err)
+		}
+
+		args = append(args, "--init", tempFile.Name())
 	}
 
 	anvilLog := a.log.New("role", "anvil", "chain.id", a.cfg.ChainId)
@@ -81,6 +83,10 @@ func (a *Anvil) Start(ctx context.Context) error {
 		a.resourceCancel()
 	}()
 
+	// In the event anvil is started with port 0, we'll need to block
+	// and see what port anvil eventually binds to when started
+	anvilPortCh := make(chan uint64)
+
 	// Handle stdout/stderr
 	//  - TODO: Figure out best way to dump into logger. Some hex isn't showing appropriately
 	stdout, err := a.cmd.StdoutPipe()
@@ -94,7 +100,17 @@ func (a *Anvil) Start(ctx context.Context) error {
 	go func() {
 		scanner := bufio.NewScanner(stdout)
 		for scanner.Scan() {
-			anvilLog.Info(scanner.Text())
+			txt := scanner.Text()
+			anvilLog.Info(txt)
+
+			// scan for port if applicable
+			if a.cfg.Port == 0 && strings.HasPrefix(txt, anvilListeningLogStr) {
+				port, err := strconv.ParseInt(strings.Split(txt, ":")[1], 10, 64)
+				if err != nil {
+					panic(fmt.Errorf("unexpected anvil listening port log: %w", err))
+				}
+				anvilPortCh <- uint64(port)
+			}
 		}
 	}()
 	go func() {
@@ -110,8 +126,6 @@ func (a *Anvil) Start(ctx context.Context) error {
 	}
 
 	go func() {
-		defer os.Remove(tempFile.Name())
-
 		if err := a.cmd.Wait(); err != nil {
 			anvilLog.Error("anvil terminated with an error", "error", err)
 		} else {
@@ -120,6 +134,17 @@ func (a *Anvil) Start(ctx context.Context) error {
 		a.stoppedCh <- struct{}{}
 	}()
 
+	// wait & update the port if applicable. Since we're in the same routine to which `Start`
+	// is called, we're safe to overrwrite the `Port` field which the caller can observe
+	if a.cfg.Port == 0 {
+		done := ctx.Done()
+		select {
+		case a.cfg.Port = <-anvilPortCh:
+		case <-done:
+			return ctx.Err()
+		}
+	}
+
 	return nil
 }
 
@@ -182,12 +207,9 @@ func waitForAnvilClientToBeReady(ctx context.Context, client *rpc.Client, timeou
 			return fmt.Errorf("timed out waiting for response from client")
 		case <-ticker.C:
 			var result string
-			callErr := client.Call(&result, "web3_clientVersion")
-
-			if callErr != nil {
+			if err := client.Call(&result, "web3_clientVersion"); err != nil {
 				continue
 			}
-
 			if strings.HasPrefix(result, "anvil") {
 				return nil
 			}

anvil/anvil_test.go

@@ -0,0 +1,32 @@
+package anvil
+
+import (
+	"context"
+	"testing"
+
+	"github.com/ethereum-optimism/optimism/op-service/testlog"
+	"github.com/stretchr/testify/require"
+
+	"github.com/ethereum/go-ethereum/common/math"
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/rpc"
+)
+
+func TestAnvil(t *testing.T) {
+	cfg := Config{ChainId: 10, Port: 0}
+	testlog := testlog.Logger(t, log.LevelInfo)
+	anvil := New(testlog, &cfg)
+
+	require.NoError(t, anvil.Start(context.Background()))
+
+	// port overriden on startup
+	require.NotEqual(t, cfg.Port, 0)
+
+	client, err := rpc.Dial(anvil.Endpoint())
+	require.NoError(t, err)
+
+	// query chainId
+	var chainId math.HexOrDecimal64
+	require.NoError(t, client.CallContext(context.Background(), &chainId, "eth_chainId"))
+	require.Equal(t, uint64(chainId), cfg.ChainId)
+}

op-simulator/op_simulator.go

@@ -9,13 +9,18 @@ import (
 	"net/http/httputil"
 	"net/url"
 	"strconv"
+	"strings"
 	"sync/atomic"
 
 	ophttp "github.com/ethereum-optimism/optimism/op-service/httputil"
 	"github.com/ethereum-optimism/supersim/anvil"
 	"github.com/ethereum/go-ethereum/log"
 )
 
+const (
+	host = "127.0.0.1"
+)
+
 type Config struct {
 	Port uint64
 }
@@ -30,10 +35,6 @@ type OpSimulator struct {
 	cfg *Config
 }
 
-const (
-	host = "127.0.0.1"
-)
-
 func New(log log.Logger, cfg *Config, anvil *anvil.Anvil) *OpSimulator {
 	return &OpSimulator{
 		log:   log,
@@ -47,18 +48,27 @@ func (opSim *OpSimulator) Start(ctx context.Context) error {
 	if err != nil {
 		return fmt.Errorf("error creating reverse proxy: %w", err)
 	}
+
 	mux := http.NewServeMux()
 	mux.Handle("/", proxy)
-	endpoint := net.JoinHostPort(host, strconv.Itoa(int(opSim.cfg.Port)))
 
-	hs, err := ophttp.StartHTTPServer(endpoint, mux)
+	hs, err := ophttp.StartHTTPServer(net.JoinHostPort(host, fmt.Sprintf("%d", opSim.cfg.Port)), mux)
 	if err != nil {
 		return fmt.Errorf("failed to start HTTP RPC server: %w", err)
 	}
-	opSim.log.Info(fmt.Sprintf("listening on %v", endpoint), "chain.id", opSim.ChainId())
 
+	opSim.log.Info("started op-simulator", "chain.id", opSim.ChainId(), "addr", hs.Addr())
 	opSim.httpServer = hs
 
+	if opSim.cfg.Port == 0 {
+		port, err := strconv.ParseInt(strings.Split(hs.Addr().String(), ":")[1], 10, 64)
+		if err != nil {
+			panic(fmt.Errorf("unexpected op-simulator listening port: %w", err))
+		}
+
+		opSim.cfg.Port = uint64(port)
+	}
+
 	return nil
 }
 

supersim.go

@@ -32,17 +32,17 @@ var genesisL2JSON []byte
 
 var DefaultConfig = Config{
 	l1Chain: ChainConfig{
-		anvilConfig: anvil.Config{ChainId: 1, Port: 8545, Genesis: genesisL1JSON},
-		opSimConfig: opsim.Config{Port: 8546},
+		anvilConfig: anvil.Config{ChainId: 1, Port: 0, Genesis: genesisL1JSON},
+		opSimConfig: opsim.Config{Port: 0},
 	},
 	l2Chains: []ChainConfig{
 		{
-			anvilConfig: anvil.Config{ChainId: 10, Port: 9545, Genesis: genesisL2JSON},
-			opSimConfig: opsim.Config{Port: 9546},
+			anvilConfig: anvil.Config{ChainId: 10, Port: 0, Genesis: genesisL2JSON},
+			opSimConfig: opsim.Config{Port: 0},
 		},
 		{
-			anvilConfig: anvil.Config{ChainId: 30, Port: 9555, Genesis: genesisL2JSON},
-			opSimConfig: opsim.Config{Port: 9556},
+			anvilConfig: anvil.Config{ChainId: 30, Port: 0, Genesis: genesisL2JSON},
+			opSimConfig: opsim.Config{Port: 0},
 		},
 	},
 }

supersim_test.go

@@ -30,7 +30,6 @@ type TestSuite struct {
 
 func createTestSuite(t *testing.T) *TestSuite {
 	cfg := &DefaultConfig
-
 	testlog := testlog.Logger(t, log.LevelInfo)
 	supersim := NewSupersim(testlog, cfg)
 	t.Cleanup(func() {