fix: Multiple network flags should prevent the BN to start

cmd/beacon-chain/main.go

@@ -212,6 +212,10 @@ func before(ctx *cli.Context) error {
 		return errors.Wrap(err, "failed to set max fd limits")
 	}
 
+	if err := features.ValidateNetworkFlags(ctx); err != nil {
+		return errors.Wrap(err, "provided multiple network flags")
+	}
+
 	return cmd.ValidateNoArgs(ctx)
 }
 

cmd/prysmctl/validator/cmd.go

@@ -175,6 +175,9 @@ var Commands = []*cli.Command{
 					if err := cmd.LoadFlagsFromConfig(cliCtx, cliCtx.Command.Flags); err != nil {
 						return err
 					}
+					if err := features.ValidateNetworkFlags(cliCtx); err != nil {
+						return err
+					}
 					if err := tos.VerifyTosAcceptedOrPrompt(cliCtx); err != nil {
 						return err
 					}

cmd/validator/main.go

@@ -193,6 +193,10 @@ func main() {
 				return errors.Wrap(err, "failed to setup debug")
 			}
 
+			if err := features.ValidateNetworkFlags(ctx); err != nil {
+				return errors.Wrap(err, "provided multiple network flags")
+			}
+
 			return cmd.ValidateNoArgs(ctx)
 		},
 		After: func(ctx *cli.Context) error {

config/features/config.go

@@ -20,6 +20,8 @@ The process for implementing new features using this package is as follows:
 package features
 
 import (
+	"fmt"
+	"strings"
 	"sync"
 	"time"
 
@@ -337,3 +339,25 @@ func logDisabled(flag cli.DocGenerationFlag) {
 	}
 	log.WithField(name, flag.GetUsage()).Warn(disabledFeatureFlag)
 }
+
+// ValidateNetworkFlags validates provided flags and
+// prevents beacon node or validator to start
+// if more than one network flag is provided
+func ValidateNetworkFlags(ctx *cli.Context) error {
+	networkFlagsCount := 0
+	for _, flag := range NetworkFlags {
+		if ctx.IsSet(flag.Names()[0]) {
+			networkFlagsCount++
+			if networkFlagsCount > 1 {
+				// using a forLoop so future addition
+				// doesn't require changes in this function
+				var flagNames []string
+				for _, flag := range NetworkFlags {
+					flagNames = append(flagNames, "--"+flag.Names()[0])
+				}
+				return fmt.Errorf("cannot use more than one network flag at the same time. Possible network flags are: %s", strings.Join(flagNames, ", "))
+			}
+		}
+	}
+	return nil
+}

config/features/config_test.go

@@ -46,3 +46,50 @@ func TestConfigureBeaconConfig(t *testing.T) {
 	c := Get()
 	assert.Equal(t, true, c.EnableSlasher)
 }
+
+func TestValidateNetworkFlags(t *testing.T) {
+	// Define the test cases
+	tests := []struct {
+		name    string
+		args    []string
+		wantErr bool
+	}{
+		{
+			name:    "No network flags",
+			args:    []string{"command"},
+			wantErr: false,
+		},
+		{
+			name:    "One network flag",
+			args:    []string{"command", "--sepolia"},
+			wantErr: false,
+		},
+		{
+			name:    "Two network flags",
+			args:    []string{"command", "--sepolia", "--holesky"},
+			wantErr: true,
+		},
+		{
+			name:    "All network flags",
+			args:    []string{"command", "--sepolia", "--holesky", "--mainnet"},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Create a new CLI app with the ValidateNetworkFlags function as the Before action
+			app := &cli.App{
+				Before: ValidateNetworkFlags,
+				Action: func(c *cli.Context) error {
+					return nil
+				},
+				// Set the network flags for the app
+				Flags: NetworkFlags,
+			}
+			err := app.Run(tt.args)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ValidateNetworkFlags() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}