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 {
@@ -58,22 +60,24 @@ func (a *Anvil) Start(ctx context.Context) error {
 	anvilLog := a.log.New("chain.id", a.cfg.ChainId)
 	anvilLog.Info("starting anvil")
 
-	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)
+		}
+
+		defer os.Remove(tempFile.Name())
+		args = append(args, "--init", tempFile.Name())
 	}
 
 	a.cmd = exec.CommandContext(a.resourceCtx, "anvil", args...)
@@ -82,6 +86,10 @@ 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()
@@ -95,7 +103,17 @@ 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() {
@@ -111,8 +129,6 @@ 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 {
@@ -121,6 +137,17 @@ 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
 }
 

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)
+}

supersim.go

@@ -27,8 +27,8 @@ var genesisL2JSON []byte
 var DefaultConfig = Config{
 	l1Chain: anvil.Config{ChainId: 1, Port: 8545, Genesis: genesisL1JSON},
 	l2Chains: []anvil.Config{
-		{ChainId: 10, Port: 9545, Genesis: genesisL2JSON},
-		{ChainId: 30, Port: 9555, Genesis: genesisL2JSON},
+		{ChainId: 10, Port: 0, Genesis: genesisL2JSON},
+		{ChainId: 30, Port: 0, Genesis: genesisL2JSON},
 	},
 }