chore(p2p/flags): Handle empty p2p.network flag. (celestiaorg#3004)

Fixes celestiaorg#3003. 
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---------

Co-authored-by: ramin <raminkeene@gmail.com>

nodebuilder/p2p/flags.go

@@ -32,10 +32,11 @@ Peers must bidirectionally point to each other. (Format: multiformats.io/multiad
 	)
 	flags.String(
 		networkFlag,
-		"",
-		"The name of the network to connect to, e.g. "+
-			listProvidedNetworks()+
-			". Must be passed on both init and start to take effect.",
+		DefaultNetwork.String(),
+		fmt.Sprintf("The name of the network to connect to, e.g. %s. Must be passed on "+
+			"both init and start to take effect. Assumes mainnet (%s) unless otherwise specified.",
+			listProvidedNetworks(),
+			DefaultNetwork.String()),
 	)
 
 	return flags
@@ -67,22 +68,23 @@ func ParseFlags(
 // ParseNetwork tries to parse the network from the flags and environment,
 // and returns either the parsed network or the build's default network
 func ParseNetwork(cmd *cobra.Command) (Network, error) {
-	parsed := cmd.Flag(networkFlag).Value.String()
-	// no network set through the flags, so check if there is an override in the env
-	if parsed == "" {
-		envNetwork, err := parseNetworkFromEnv()
-		// no network found in env, so use the default network
-		if envNetwork == "" {
-			return DefaultNetwork, err
-		}
+	if envNetwork, err := parseNetworkFromEnv(); envNetwork != "" {
 		return envNetwork, err
 	}
-	// check if user provided the actual network value
-	// or an alias
-	if net, err := Network(parsed).Validate(); err == nil {
-		return net, nil
+	parsed := cmd.Flag(networkFlag).Value.String()
+	switch parsed {
+	case "":
+		return "", fmt.Errorf("no network provided, allowed values: %s", listProvidedNetworks())
+
+	case DefaultNetwork.String():
+		return DefaultNetwork, nil
+
+	default:
+		if net, err := Network(parsed).Validate(); err == nil {
+			return net, nil
+		}
+		return "", fmt.Errorf("invalid network specified: %s, allowed values: %s", parsed, listProvidedNetworks())
 	}
-	return "", fmt.Errorf("invalid network specified: %s", parsed)
 }
 
 // parseNetworkFromEnv tries to parse the network from the environment.

nodebuilder/p2p/flags_test.go

@@ -69,3 +69,59 @@ func createCmdWithNetworkFlag() *cobra.Command {
 	cmd.Flags().AddFlagSet(flags)
 	return cmd
 }
+
+// Set empty network flag and ensure error returned
+func TestParseNetwork_emptyFlag(t *testing.T) {
+	cmd := createCmdWithNetworkFlag()
+
+	err := cmd.Flags().Set(networkFlag, "")
+	require.NoError(t, err)
+
+	_, err = ParseNetwork(cmd)
+	assert.Error(t, err)
+
+}
+
+// Set empty network flag and ensure error returned
+func TestParseNetwork_emptyEnvEmptyFlag(t *testing.T) {
+
+	t.Setenv(EnvCustomNetwork, "")
+
+	cmd := createCmdWithNetworkFlag()
+	err := cmd.Flags().Set(networkFlag, "")
+	require.NoError(t, err)
+
+	_, err = ParseNetwork(cmd)
+	require.Error(t, err)
+
+}
+
+// Env overrides empty flag to take precedence
+func TestParseNetwork_envOverridesEmptyFlag(t *testing.T) {
+
+	t.Setenv(EnvCustomNetwork, "custom-network")
+
+	cmd := createCmdWithNetworkFlag()
+	err := cmd.Flags().Set(networkFlag, "")
+	require.NoError(t, err)
+
+	network, err := ParseNetwork(cmd)
+	require.NoError(t, err)
+	assert.Equal(t, Network("custom-network"), network)
+
+}
+
+// Explicitly set flag but env should still override
+func TestParseNetwork_envOverridesFlag(t *testing.T) {
+
+	t.Setenv(EnvCustomNetwork, "custom-network")
+
+	cmd := createCmdWithNetworkFlag()
+	err := cmd.Flags().Set(networkFlag, string(Mocha))
+	require.NoError(t, err)
+
+	network, err := ParseNetwork(cmd)
+	require.NoError(t, err)
+	assert.Equal(t, Network("custom-network"), network)
+
+}