Add --custom-spec-support flag for non-mainnet SSZ presets

Build the go-eth2-client HTTP client with WithCustomSpecSupport when the new
--custom-spec-support persistent flag is set, switching from the static
mainnet fastssz decoder to dynamic-ssz. Without it, decoding a non-mainnet
preset beacon state (e.g. Gnosis) fails with:

  invalid ssz encoding. first variable element offset indexes into fixed value data

because the static mainnet-preset decoder misreads the variable-length
offsets of a Gnosis-preset BeaconState. This blocks
"validator exit --prepare-offline" against a Gnosis node, which fetches the
full beacon state via SSZ.

Threads the flag through ConnectOpts and connectToBeaconNode, and wires it
into the validator exit command's ConnectToBeaconNode call, mirroring the
existing --allow-insecure-connections plumbing.

Author: AntiD2ta

cmd/root.go

@@ -253,6 +253,10 @@ func addPersistentFlags() {
 	if err := viper.BindPFlag("allow-insecure-connections", RootCmd.PersistentFlags().Lookup("allow-insecure-connections")); err != nil {
 		panic(err)
 	}
+	RootCmd.PersistentFlags().Bool("custom-spec-support", false, "use dynamic SSZ to support non-mainnet presets (e.g. Gnosis); slower than the static decoder")
+	if err := viper.BindPFlag("custom-spec-support", RootCmd.PersistentFlags().Lookup("custom-spec-support")); err != nil {
+		panic(err)
+	}
 }
 
 // initConfig reads in config file and ENV variables if set.

cmd/validator/exit/command.go

@@ -50,6 +50,7 @@ type command struct {
 	timeout                  time.Duration
 	connection               string
 	allowInsecureConnections bool
+	customSpecSupport        bool
 
 	// Information required to generate the operations.
 	chainInfo *beacon.ChainInfo
@@ -73,6 +74,7 @@ func newCommand(_ context.Context) (*command, error) {
 		timeout:                  viper.GetDuration("timeout"),
 		connection:               viper.GetString("connection"),
 		allowInsecureConnections: viper.GetBool("allow-insecure-connections"),
+		customSpecSupport:        viper.GetBool("custom-spec-support"),
 		prepareOffline:           viper.GetBool("prepare-offline"),
 		passphrases:              util.GetPassphrases(),
 		mnemonic:                 viper.GetString("mnemonic"),

cmd/validator/exit/process.go

@@ -595,10 +595,11 @@ func (c *command) setup(ctx context.Context) error {
 	// Connect to the consensus node.
 	var err error
 	c.consensusClient, err = util.ConnectToBeaconNode(ctx, &util.ConnectOpts{
-		Address:       c.connection,
-		Timeout:       c.timeout,
-		AllowInsecure: c.allowInsecureConnections,
-		LogFallback:   !c.quiet,
+		Address:           c.connection,
+		Timeout:           c.timeout,
+		AllowInsecure:     c.allowInsecureConnections,
+		CustomSpecSupport: c.customSpecSupport,
+		LogFallback:       !c.quiet,
 	})
 	if err != nil {
 		return err

util/beaconnode.go

@@ -38,10 +38,11 @@ var defaultBeaconNodeAddresses = []string{
 var fallbackBeaconNode = "http://mainnet-consensus.attestant.io/"
 
 type ConnectOpts struct {
-	Address       string
-	Timeout       time.Duration
-	AllowInsecure bool
-	LogFallback   bool
+	Address           string
+	Timeout           time.Duration
+	AllowInsecure     bool
+	CustomSpecSupport bool
+	LogFallback       bool
 }
 
 // ConnectToBeaconNode connects to a beacon node at the given address.
@@ -56,12 +57,12 @@ func ConnectToBeaconNode(ctx context.Context, opts *ConnectOpts) (eth2client.Ser
 
 	if opts.Address != "" {
 		// We have an explicit address; use it.
-		return connectToBeaconNode(ctx, opts.Address, opts.Timeout, opts.AllowInsecure)
+		return connectToBeaconNode(ctx, opts.Address, opts.Timeout, opts.AllowInsecure, opts.CustomSpecSupport)
 	}
 
 	// Try the defaults.
 	for _, address := range defaultBeaconNodeAddresses {
-		client, err := connectToBeaconNode(ctx, address, opts.Timeout, opts.AllowInsecure)
+		client, err := connectToBeaconNode(ctx, address, opts.Timeout, opts.AllowInsecure, opts.CustomSpecSupport)
 		if err == nil {
 			return client, nil
 		}
@@ -71,15 +72,15 @@ func ConnectToBeaconNode(ctx context.Context, opts *ConnectOpts) (eth2client.Ser
 	if opts.LogFallback {
 		fmt.Fprintf(os.Stderr, "No connection supplied with --connection parameter and no local beacon node found, attempting to use mainnet fallback\n")
 	}
-	client, err := connectToBeaconNode(ctx, fallbackBeaconNode, opts.Timeout, true)
+	client, err := connectToBeaconNode(ctx, fallbackBeaconNode, opts.Timeout, true, opts.CustomSpecSupport)
 	if err == nil {
 		return client, nil
 	}
 
 	return nil, errors.New("failed to connect to any beacon node")
 }
 
-func connectToBeaconNode(ctx context.Context, address string, timeout time.Duration, allowInsecure bool) (eth2client.Service, error) {
+func connectToBeaconNode(ctx context.Context, address string, timeout time.Duration, allowInsecure bool, customSpecSupport bool) (eth2client.Service, error) {
 	if !strings.HasPrefix(address, "http") {
 		address = fmt.Sprintf("http://%s", address)
 	}
@@ -101,6 +102,7 @@ func connectToBeaconNode(ctx context.Context, address string, timeout time.Durat
 		http.WithLogLevel(zerolog.Disabled),
 		http.WithAddress(address),
 		http.WithTimeout(timeout),
+		http.WithCustomSpecSupport(customSpecSupport),
 	)
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to connect to beacon node")