dcrouter/test/suite/smtpserver_security/test.sec-11.bounce-management.ts

import { tap, expect } from '@git.zone/tstest/tapbundle';
import * as plugins from '../../../ts/plugins.js';
import * as net from 'net';
import { startTestServer, stopTestServer } from '../../helpers/server.loader.js'
import type { ITestServer } from '../../helpers/server.loader.js';

const TEST_PORT = 2525;
let testServer: ITestServer;

// Helper to wait for SMTP response
const waitForResponse = (socket: net.Socket, expectedCode?: string, timeout = 5000): Promise<string> => {
  return new Promise((resolve, reject) => {
    let buffer = '';
    const timer = setTimeout(() => {
      socket.removeListener('data', handler);
      reject(new Error(`Timeout waiting for ${expectedCode || 'any'} response`));
    }, timeout);
    
    const handler = (data: Buffer) => {
      buffer += data.toString();
      const lines = buffer.split('\r\n');
      
      for (const line of lines) {
        if (expectedCode) {
          if (line.startsWith(expectedCode + ' ')) {
            clearTimeout(timer);
            socket.removeListener('data', handler);
            resolve(buffer);
            return;
          }
        } else {
          // Look for any complete response
          if (line.match(/^\d{3} /)) {
            clearTimeout(timer);
            socket.removeListener('data', handler);
            resolve(buffer);
            return;
          }
        }
      }
    };
    
    socket.on('data', handler);
  });
};

tap.test('setup - start test server', async (toolsArg) => {
  testServer = await startTestServer({ port: TEST_PORT });
  await toolsArg.delayFor(1000);
});

tap.test('Bounce Management - Invalid recipient domain', async (tools) => {
  const socket = net.createConnection({
    host: 'localhost',
    port: TEST_PORT,
    timeout: 30000
  });
  
  try {
    // Wait for greeting
    await waitForResponse(socket, '220');
    
    // Send EHLO
    socket.write('EHLO testclient\r\n');
    await waitForResponse(socket, '250');
    
    // Send MAIL FROM
    socket.write('MAIL FROM:<sender@example.com>\r\n');
    await waitForResponse(socket, '250');
    
    // Send to non-existent domain
    socket.write('RCPT TO:<nonexistent@invalid-domain-that-does-not-exist.com>\r\n');
    const rcptResponse = await waitForResponse(socket);
    
    if (rcptResponse.startsWith('550') || rcptResponse.startsWith('551') || rcptResponse.startsWith('553')) {
      console.log('Bounce management active - invalid recipient properly rejected');
      expect(true).toEqual(true);
    } else if (rcptResponse.startsWith('250')) {
      // Server accepted, may generate bounce later
      console.log('Invalid recipient accepted - bounce may be generated later');
      
      // Send DATA
      socket.write('DATA\r\n');
      await waitForResponse(socket, '354');
      
      const email = [
        `From: sender@example.com`,
        `To: nonexistent@invalid-domain-that-does-not-exist.com`,
        `Subject: Bounce Management Test`,
        `Return-Path: <bounce@example.com>`,
        `Date: ${new Date().toUTCString()}`,
        `Message-ID: <bounce-test-${Date.now()}@example.com>`,
        '',
        'This email is designed to test bounce management functionality.',
        '.',
        ''
      ].join('\r\n');
      
      socket.write(email);
      const dataResponse = await waitForResponse(socket, '250');
      
      console.log('Email accepted for processing - bounce will be generated');
      expect(dataResponse.startsWith('250')).toEqual(true);
    }
    
    socket.write('QUIT\r\n');
    await waitForResponse(socket, '221').catch(() => {});
  } finally {
    socket.destroy();
  }
});

tap.test('Bounce Management - Empty return path (null sender)', async (tools) => {
  const socket = net.createConnection({
    host: 'localhost',
    port: TEST_PORT,
    timeout: 30000
  });
  
  try {
    // Wait for greeting
    await waitForResponse(socket, '220');
    
    // Send EHLO
    socket.write('EHLO testclient\r\n');
    await waitForResponse(socket, '250');
    
    // Empty return path (null sender) - used for bounce messages
    socket.write('MAIL FROM:<>\r\n');
    const mailResponse = await waitForResponse(socket);
    
    if (mailResponse.startsWith('250')) {
      console.log('Null sender accepted (for bounce messages)');
      
      // Send RCPT TO
      socket.write('RCPT TO:<recipient@example.com>\r\n');
      await waitForResponse(socket, '250');
      
      // Send DATA
      socket.write('DATA\r\n');
      const dataCommandResponse = await waitForResponse(socket);
      
      if (dataCommandResponse.startsWith('354')) {
        // Bounce message format
        const email = [
          `From: MAILER-DAEMON@example.com`,
          `To: recipient@example.com`,
          `Subject: Mail delivery failed: returning message to sender`,
          `Date: ${new Date().toUTCString()}`,
          `Message-ID: <bounce-${Date.now()}@example.com>`,
          `Auto-Submitted: auto-replied`,
          '',
          'This message was created automatically by mail delivery software.',
          '',
          'A message that you sent could not be delivered to one or more recipients.',
          '.',
          ''
        ].join('\r\n');
        
        socket.write(email);
        const dataResponse = await waitForResponse(socket, '250');
        
        console.log('Bounce message with null sender accepted');
        expect(dataResponse.startsWith('250')).toEqual(true);
      } else if (dataCommandResponse.startsWith('503')) {
        // Server rejects DATA for null sender
        console.log('Server rejects DATA command for null sender (strict policy)');
        expect(dataCommandResponse.startsWith('503')).toEqual(true);
      }
    } else {
      console.log('Null sender rejected');
      expect(true).toEqual(true);
    }
    
    socket.write('QUIT\r\n');
    await waitForResponse(socket, '221').catch(() => {});
  } finally {
    socket.destroy();
  }
});

tap.test('Bounce Management - DSN headers', async (tools) => {
  const socket = net.createConnection({
    host: 'localhost',
    port: TEST_PORT,
    timeout: 30000
  });
  
  try {
    // Wait for greeting
    await waitForResponse(socket, '220');
    
    // Send EHLO
    socket.write('EHLO testclient\r\n');
    await waitForResponse(socket, '250');
    
    // Send MAIL FROM
    socket.write('MAIL FROM:<sender@example.com>\r\n');
    await waitForResponse(socket, '250');
    
    // Send RCPT TO
    socket.write('RCPT TO:<recipient@example.com>\r\n');
    await waitForResponse(socket, '250');
    
    // Send DATA
    socket.write('DATA\r\n');
    await waitForResponse(socket, '354');
    
    // Email with DSN request headers
    const email = [
      `From: sender@example.com`,
      `To: recipient@example.com`,
      `Subject: DSN Test`,
      `Return-Path: <bounce-handler@example.com>`,
      `Disposition-Notification-To: sender@example.com`,
      `Return-Receipt-To: sender@example.com`,
      `Date: ${new Date().toUTCString()}`,
      `Message-ID: <dsn-test-${Date.now()}@example.com>`,
      '',
      'This email requests delivery status notifications.',
      '.',
      ''
    ].join('\r\n');
    
    socket.write(email);
    const dataResponse = await waitForResponse(socket, '250');
    
    console.log('Email with DSN headers accepted');
    expect(dataResponse.startsWith('250')).toEqual(true);
    
    socket.write('QUIT\r\n');
    await waitForResponse(socket, '221').catch(() => {});
  } finally {
    socket.destroy();
  }
});

tap.test('Bounce Management - Bounce loop prevention', async (tools) => {
  const socket = net.createConnection({
    host: 'localhost',
    port: TEST_PORT,
    timeout: 30000
  });
  
  try {
    // Wait for greeting
    await waitForResponse(socket, '220');
    
    // Send EHLO
    socket.write('EHLO testclient\r\n');
    await waitForResponse(socket, '250');
    
    // Null sender (bounce message)
    socket.write('MAIL FROM:<>\r\n');
    await waitForResponse(socket, '250');
    
    // To another mailer-daemon (potential loop)
    socket.write('RCPT TO:<mailer-daemon@another-server.com>\r\n');
    const rcptResponse = await waitForResponse(socket);
    
    if (rcptResponse.startsWith('550') || rcptResponse.startsWith('553')) {
      console.log('Bounce loop prevented - mailer-daemon recipient rejected');
      expect(true).toEqual(true);
    } else if (rcptResponse.startsWith('250')) {
      console.log('Mailer-daemon recipient accepted - check for loop prevention');
      
      // Send DATA
      socket.write('DATA\r\n');
      const dataCommandResponse = await waitForResponse(socket);
      
      if (dataCommandResponse.startsWith('354')) {
        const email = [
          `From: MAILER-DAEMON@example.com`,
          `To: mailer-daemon@another-server.com`,
          `Subject: Delivery Status Notification (Failure)`,
          `Date: ${new Date().toUTCString()}`,
          `Message-ID: <bounce-loop-${Date.now()}@example.com>`,
          `Auto-Submitted: auto-replied`,
          `X-Loop: example.com`,
          '',
          'This is a bounce of a bounce - potential loop.',
          '.',
          ''
        ].join('\r\n');
        
        socket.write(email);
        const dataResponse = await waitForResponse(socket);
        
        const result = dataResponse.startsWith('250') ? 'accepted' : 'rejected';
        console.log(`Bounce loop test: ${result}`);
        expect(true).toEqual(true);
      } else if (dataCommandResponse.startsWith('503')) {
        // Server rejects DATA for null sender
        console.log('Bounce loop prevented at DATA stage (null sender rejection)');
        expect(dataCommandResponse.startsWith('503')).toEqual(true);
      }
    }
    
    socket.write('QUIT\r\n');
    await waitForResponse(socket, '221').catch(() => {});
  } finally {
    socket.destroy();
  }
});

tap.test('Bounce Management - Valid email (control test)', async (tools) => {
  const socket = net.createConnection({
    host: 'localhost',
    port: TEST_PORT,
    timeout: 30000
  });
  
  try {
    // Wait for greeting
    await waitForResponse(socket, '220');
    
    // Send EHLO
    socket.write('EHLO testclient\r\n');
    await waitForResponse(socket, '250');
    
    // Send MAIL FROM
    socket.write('MAIL FROM:<sender@example.com>\r\n');
    await waitForResponse(socket, '250');
    
    // Send RCPT TO
    socket.write('RCPT TO:<valid@example.com>\r\n');
    await waitForResponse(socket, '250');
    
    // Send DATA
    socket.write('DATA\r\n');
    await waitForResponse(socket, '354');
    
    const email = [
      `From: sender@example.com`,
      `To: valid@example.com`,
      `Subject: Valid Email Test`,
      `Return-Path: <sender@example.com>`,
      `Date: ${new Date().toUTCString()}`,
      `Message-ID: <valid-email-${Date.now()}@example.com>`,
      '',
      'This is a valid email that should not trigger bounce.',
      '.',
      ''
    ].join('\r\n');
    
    socket.write(email);
    const dataResponse = await waitForResponse(socket, '250');
    
    console.log('Valid email accepted - no bounce expected');
    expect(dataResponse.startsWith('250')).toEqual(true);
    
    socket.write('QUIT\r\n');
    await waitForResponse(socket, '221').catch(() => {});
  } finally {
    socket.destroy();
  }
});

tap.test('cleanup - stop test server', async () => {
  await stopTestServer(testServer);
});

tap.start();