check for iptables before enabling the firewall and inform the user if

it is missing

src/nuxt.config.ts

@@ -147,6 +147,7 @@ export default defineNuxtConfig({
     },
     alias: {
       '#db': fileURLToPath(new URL('./server/database/', import.meta.url)),
+      '#utils': fileURLToPath(new URL('./server/utils/', import.meta.url)),
     },
     externals: {
       traceInclude: [fileURLToPath(new URL('./cli/index.ts', import.meta.url))],
@@ -155,5 +156,6 @@ export default defineNuxtConfig({
   alias: {
     // for typecheck reasons (https://github.com/nuxt/cli/issues/323)
     '#db': fileURLToPath(new URL('./server/database/', import.meta.url)),
+    '#utils': fileURLToPath(new URL('./server/utils/', import.meta.url)),
   },
 });

src/server/api/admin/interface/index.post.ts

@@ -1,4 +1,5 @@
 import { InterfaceUpdateSchema } from '#db/repositories/interface/types';
+import { firewall } from '#utils/firewall';
 
 export default definePermissionEventHandler(
   'admin',
@@ -8,6 +9,24 @@ export default definePermissionEventHandler(
       event,
       validateZod(InterfaceUpdateSchema, event)
     );
+
+    // If enabling firewall, check if iptables is available
+    if (data.firewallEnabled) {
+      // Clear cache to force fresh check
+      firewall.clearAvailabilityCache();
+
+      const iptablesAvailable = await firewall.isAvailable(!WG_ENV.DISABLE_IPV6);
+      if (!iptablesAvailable) {
+        const requiredTools = WG_ENV.DISABLE_IPV6
+          ? 'iptables'
+          : 'iptables and ip6tables';
+        throw createError({
+          statusCode: 400,
+          statusMessage: `Per-Client Firewall requires ${requiredTools} to be installed on the host system. Please install ${requiredTools} before enabling this feature.`,
+        });
+      }
+    }
+
     await Database.interfaces.update(data);
     await WireGuard.saveConfig();
     return { success: true };

src/server/utils/WireGuard.ts

@@ -266,6 +266,22 @@ class WireGuard {
     await this.#syncWireguardConfig(wgInterface);
     WG_DEBUG(`Wireguard Interface ${wgInterface.name} started successfully.`);
 
+    // Check if firewall was enabled but iptables isn't available
+    if (wgInterface.firewallEnabled) {
+      const enableIpv6 = !WG_ENV.DISABLE_IPV6;
+      const iptablesAvailable = await firewall.isAvailable(enableIpv6);
+      if (!iptablesAvailable) {
+        const requiredTools = enableIpv6
+          ? 'iptables/ip6tables'
+          : 'iptables';
+        console.warn(
+          `WARNING: Per-Client Firewall is enabled but ${requiredTools} is not available. Disabling firewall feature. Please install ${requiredTools} to use this feature.`
+        );
+        await Database.interfaces.update({ firewallEnabled: false });
+        wgInterface.firewallEnabled = false; // Update local copy
+      }
+    }
+
     WG_DEBUG('Applying firewall rules...');
     await this.#applyFirewallRules(wgInterface);
     WG_DEBUG('Firewall rules applied successfully.');

src/server/utils/firewall.ts

@@ -13,6 +13,9 @@ const CHAIN_NAME = 'WG_CLIENTS';
 let rebuildInProgress = false;
 let rebuildQueued = false;
 
+// Cache iptables availability check result
+let iptablesAvailable: boolean | null = null;
+
 type ParsedEntry = {
   ip: string;
   port?: number;
@@ -249,4 +252,43 @@ export const firewall = {
     await exec(`iptables -X ${CHAIN_NAME} 2>/dev/null || true`);
     await exec(`ip6tables -X ${CHAIN_NAME} 2>/dev/null || true`);
   },
+
+  /**
+   * Check if iptables (and optionally ip6tables) are available on the system.
+   * @param enableIpv6 - If true, also check for ip6tables. Defaults to true.
+   */
+  async isAvailable(enableIpv6: boolean = true): Promise<boolean> {
+    // Return cached result if we've already checked
+    if (iptablesAvailable !== null) {
+      return iptablesAvailable;
+    }
+
+    try {
+      // Check for iptables (always required)
+      await exec('iptables --version');
+      FW_DEBUG('iptables is available');
+
+      // Check for ip6tables (only if IPv6 is enabled)
+      if (enableIpv6) {
+        await exec('ip6tables --version');
+        FW_DEBUG('ip6tables is available');
+      } else {
+        FW_DEBUG('IPv6 disabled, skipping ip6tables check');
+      }
+
+      iptablesAvailable = true;
+      return true;
+    } catch (error) {
+      iptablesAvailable = false;
+      FW_DEBUG('iptables/ip6tables is not available:', error);
+      return false;
+    }
+  },
+
+  /**
+   * Clear the availability cache to force a re-check
+   */
+  clearAvailabilityCache(): void {
+    iptablesAvailable = null;
+  },
 };