dcrouter/test/suite/smtpserver_reliability/test.rel-05.dns-resolution-failure.ts

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

const TEST_PORT = 2525;

let testServer;

interface DnsTestResult {
  scenario: string;
  domain: string;
  expectedBehavior: string;
  mailFromSuccess: boolean;
  rcptToSuccess: boolean;
  mailFromResponse: string;
  rcptToResponse: string;
  handledGracefully: boolean;
}

// Helper function 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');
      
      // Check if we have a complete response
      for (const line of lines) {
        if (expectedCode) {
          if (line.startsWith(expectedCode + ' ')) {
            clearTimeout(timer);
            socket.removeListener('data', handler);
            resolve(buffer);
            return;
          }
        } else {
          // Any complete response line
          if (line.match(/^\d{3} /)) {
            clearTimeout(timer);
            socket.removeListener('data', handler);
            resolve(buffer);
            return;
          }
        }
      }
    };
    
    socket.on('data', handler);
  });
};

tap.test('prepare server', async () => {
  testServer = await startTestServer({ port: TEST_PORT });
  await new Promise(resolve => setTimeout(resolve, 100));
});

tap.test('REL-05: DNS resolution failure handling - Non-existent domains', async (tools) => {
  const done = tools.defer();

  try {
    const socket = net.createConnection({
      host: 'localhost',
      port: TEST_PORT,
      timeout: 30000
    });

    await new Promise<void>((resolve, reject) => {
      socket.once('connect', resolve);
      socket.once('error', reject);
    });

    // Read greeting
    await waitForResponse(socket, '220');

    // Send EHLO
    socket.write('EHLO dns-test\r\n');
    await waitForResponse(socket, '250');

    console.log('Testing DNS resolution for non-existent domains...');

    // Test 1: Non-existent domain in MAIL FROM
    socket.write('MAIL FROM:<sender@non-existent-domain-12345.invalid>\r\n');
    const mailResponse = await waitForResponse(socket);

    console.log('  MAIL FROM response:', mailResponse.trim());
    
    // Server should either accept (and defer later) or reject immediately
    const mailFromHandled = mailResponse.includes('250') || 
                           mailResponse.includes('450') || 
                           mailResponse.includes('550');
    expect(mailFromHandled).toEqual(true);

    // Reset if needed
    if (mailResponse.includes('250')) {
      socket.write('RSET\r\n');
      await waitForResponse(socket, '250');
    }

    // Test 2: Non-existent domain in RCPT TO
    socket.write('MAIL FROM:<sender@example.com>\r\n');
    const mailFromResp = await waitForResponse(socket, '250');
    expect(mailFromResp).toInclude('250');

    socket.write('RCPT TO:<recipient@non-existent-domain-xyz.invalid>\r\n');
    const rcptResponse = await waitForResponse(socket);

    console.log('  RCPT TO response:', rcptResponse.trim());
    
    // Server may accept (and defer validation) or reject immediately
    const rcptToHandled = rcptResponse.includes('250') || // Accepted (for later validation)
                         rcptResponse.includes('450') || // Temporary failure
                         rcptResponse.includes('550') || // Permanent failure
                         rcptResponse.includes('553');   // Address error
    expect(rcptToHandled).toEqual(true);

    socket.write('QUIT\r\n');
    socket.end();
    done.resolve();
  } catch (error) {
    done.reject(error);
  }
});

tap.test('REL-05: DNS resolution failure handling - Malformed domains', async (tools) => {
  const done = tools.defer();

  try {
    const socket = net.createConnection({
      host: 'localhost',
      port: TEST_PORT,
      timeout: 30000
    });

    await new Promise<void>((resolve, reject) => {
      socket.once('connect', resolve);
      socket.once('error', reject);
    });

    // Read greeting
    await waitForResponse(socket, '220');

    // Send EHLO
    socket.write('EHLO malformed-test\r\n');
    await waitForResponse(socket, '250');

    console.log('\nTesting malformed domain handling...');

    const malformedDomains = [
      'malformed..domain..test',
      'invalid-.domain.com',
      'domain.with.spaces .com',
      '.leading-dot.com',
      'trailing-dot.com.',
      'domain@with@at.com',
      'a'.repeat(255) + '.toolong.com' // Domain too long
    ];

    for (const domain of malformedDomains) {
      console.log(`  Testing: ${domain.substring(0, 50)}${domain.length > 50 ? '...' : ''}`);

      socket.write(`MAIL FROM:<test@${domain}>\r\n`);
      const response = await waitForResponse(socket);

      // Server should reject malformed domains or accept for later validation
      const properlyHandled = response.includes('250') || // Accepted (may validate later)
                             response.includes('501') || // Syntax error
                             response.includes('550') || // Rejected
                             response.includes('553');   // Address error
      
      console.log(`    Response: ${response.trim().substring(0, 50)}`);
      expect(properlyHandled).toEqual(true);

      // Reset if needed
      if (!response.includes('5')) {
        socket.write('RSET\r\n');
        await waitForResponse(socket, '250');
      }
    }

    socket.write('QUIT\r\n');
    socket.end();
    done.resolve();
  } catch (error) {
    done.reject(error);
  }
});

tap.test('REL-05: DNS resolution failure handling - Special cases', async (tools) => {
  const done = tools.defer();

  try {
    const socket = net.createConnection({
      host: 'localhost',
      port: TEST_PORT,
      timeout: 30000
    });

    await new Promise<void>((resolve, reject) => {
      socket.once('connect', resolve);
      socket.once('error', reject);
    });

    // Read greeting
    await waitForResponse(socket, '220');

    // Send EHLO
    socket.write('EHLO special-test\r\n');
    await waitForResponse(socket, '250');

    console.log('\nTesting special DNS cases...');

    // Test 1: Localhost (may be accepted or rejected)
    socket.write('MAIL FROM:<sender@localhost>\r\n');
    const localhostResponse = await waitForResponse(socket);

    console.log('  Localhost response:', localhostResponse.trim());
    const localhostHandled = localhostResponse.includes('250') || localhostResponse.includes('501');
    expect(localhostHandled).toEqual(true);

    // Only reset if transaction was started
    if (localhostResponse.includes('250')) {
      socket.write('RSET\r\n');
      await waitForResponse(socket, '250');
    }

    // Test 2: IP address (should work)
    socket.write('MAIL FROM:<sender@[127.0.0.1]>\r\n');
    const ipResponse = await waitForResponse(socket);

    console.log('  IP address response:', ipResponse.trim());
    const ipHandled = ipResponse.includes('250') || ipResponse.includes('501');
    expect(ipHandled).toEqual(true);

    // Only reset if transaction was started
    if (ipResponse.includes('250')) {
      socket.write('RSET\r\n');
      await waitForResponse(socket, '250');
    }

    // Test 3: Empty domain
    socket.write('MAIL FROM:<sender@>\r\n');
    const emptyResponse = await waitForResponse(socket);

    console.log('  Empty domain response:', emptyResponse.trim());
    expect(emptyResponse).toMatch(/50[1-3]/); // Should reject

    socket.write('QUIT\r\n');
    socket.end();
    done.resolve();
  } catch (error) {
    done.reject(error);
  }
});

tap.test('REL-05: DNS resolution failure handling - Mixed valid/invalid recipients', async (tools) => {
  const done = tools.defer();

  try {
    const socket = net.createConnection({
      host: 'localhost',
      port: TEST_PORT,
      timeout: 30000
    });

    await new Promise<void>((resolve, reject) => {
      socket.once('connect', resolve);
      socket.once('error', reject);
    });

    // Read greeting
    await waitForResponse(socket, '220');

    // Send EHLO
    socket.write('EHLO mixed-test\r\n');
    await waitForResponse(socket, '250');

    console.log('\nTesting mixed valid/invalid recipients...');

    // Start transaction
    socket.write('MAIL FROM:<sender@example.com>\r\n');
    const mailFromResp = await waitForResponse(socket, '250');
    expect(mailFromResp).toInclude('250');

    // Add valid recipient
    socket.write('RCPT TO:<valid@example.com>\r\n');
    const validRcptResponse = await waitForResponse(socket, '250');

    console.log('  Valid recipient:', validRcptResponse.trim());
    expect(validRcptResponse).toInclude('250');

    // Add invalid recipient
    socket.write('RCPT TO:<invalid@non-existent-domain-abc.invalid>\r\n');
    const invalidRcptResponse = await waitForResponse(socket);

    console.log('  Invalid recipient:', invalidRcptResponse.trim());
    
    // Server may accept (for later validation) or reject invalid domain
    const invalidHandled = invalidRcptResponse.includes('250') || // Accepted (for later validation)
                          invalidRcptResponse.includes('450') || 
                          invalidRcptResponse.includes('550') ||
                          invalidRcptResponse.includes('553');
    expect(invalidHandled).toEqual(true);

    // Try to send data (should work if at least one valid recipient)
    socket.write('DATA\r\n');
    const dataResponse = await waitForResponse(socket);

    if (dataResponse.includes('354')) {
      socket.write('Subject: Mixed recipient test\r\n\r\nTest\r\n.\r\n');
      await waitForResponse(socket, '250');
      console.log('  Message accepted with valid recipient');
    } else {
      console.log('  Server rejected DATA (acceptable behavior)');
    }

    socket.write('QUIT\r\n');
    socket.end();
    done.resolve();
  } catch (error) {
    done.reject(error);
  }
});

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

export default tap.start();