fix(smartproxy): Correct NFTables forwarding handling to avoid premature connection termination and add comprehensive tests

test/test.forwarding-regression.ts

@@ -0,0 +1,105 @@
+import { expect, tap } from '@git.zone/tapbundle';
+import * as net from 'net';
+import { SmartProxy } from '../ts/proxies/smart-proxy/smart-proxy.js';
+
+// Test to verify port forwarding works correctly
+tap.test('forward connections should not be immediately closed', async (t) => {
+  // Create a backend server that accepts connections
+  const testServer = net.createServer((socket) => {
+    console.log('Client connected to test server');
+    socket.write('Welcome from test server\n');
+    
+    socket.on('data', (data) => {
+      console.log('Test server received:', data.toString());
+      socket.write(`Echo: ${data}`);
+    });
+    
+    socket.on('error', (err) => {
+      console.error('Test server socket error:', err);
+    });
+  });
+
+  // Listen on a non-privileged port
+  await new Promise<void>((resolve) => {
+    testServer.listen(9090, '127.0.0.1', () => {
+      console.log('Test server listening on port 9090');
+      resolve();
+    });
+  });
+
+  // Create SmartProxy with a forward route
+  const smartProxy = new SmartProxy({
+    enableDetailedLogging: true,
+    routes: [
+      {
+        id: 'forward-test',
+        name: 'Forward Test Route',
+        match: {
+          port: 8080,
+        },
+        action: {
+          type: 'forward',
+          target: {
+            host: '127.0.0.1',
+            port: 9090,
+          },
+        },
+      },
+    ],
+  });
+
+  await smartProxy.start();
+
+  // Create a client connection through the proxy
+  const client = net.createConnection({
+    port: 8080,
+    host: '127.0.0.1',
+  });
+
+  let connectionClosed = false;
+  let dataReceived = false;
+  let welcomeMessage = '';
+
+  client.on('connect', () => {
+    console.log('Client connected to proxy');
+  });
+
+  client.on('data', (data) => {
+    console.log('Client received:', data.toString());
+    dataReceived = true;
+    welcomeMessage = data.toString();
+  });
+
+  client.on('close', () => {
+    console.log('Client connection closed');
+    connectionClosed = true;
+  });
+
+  client.on('error', (err) => {
+    console.error('Client error:', err);
+  });
+
+  // Wait for the welcome message
+  await t.waitForExpect(() => {
+    return dataReceived;
+  }, 'Data should be received from the server', 2000);
+
+  // Verify we got the welcome message
+  expect(welcomeMessage).toContain('Welcome from test server');
+  
+  // Send some data
+  client.write('Hello from client');
+  
+  // Wait a bit to make sure connection isn't immediately closed
+  await new Promise(resolve => setTimeout(resolve, 100));
+  
+  // Connection should still be open
+  expect(connectionClosed).toBe(false);
+  
+  // Clean up
+  client.end();
+  await smartProxy.stop();
+  testServer.close();
+});
+
+export default tap.start();