MailSend/src/mailer.js

import net from 'node:net';
import tls from 'node:tls';
import crypto from 'node:crypto';
import { signDkim } from './dkim.js';

export function parseAddressList(value) {
  return String(value || '')
    .split(',')
    .map((item) => item.trim())
    .filter(Boolean)
    .map(extractAddress)
    .filter(Boolean);
}

export function extractAddress(value) {
  const match = String(value || '').match(/<([^<>@\s]+@[^<>@\s]+)>/);
  const address = match ? match[1] : String(value || '').trim();
  if (!/^[^@\s<>]+@[^@\s<>]+\.[^@\s<>]+$/.test(address)) return '';
  return address.toLowerCase();
}

export function domainFromAddress(value) {
  const address = extractAddress(value);
  return address.split('@')[1] || '';
}

export function buildMessage({ from, to, subject, text, html, baseUrl }) {
  const recipients = Array.isArray(to) ? to : parseAddressList(to);
  if (!recipients.length) throw new Error('At least one recipient is required.');
  const messageIdHost = domainFromAddress(from) || 'localhost';
  const messageId = `<${crypto.randomUUID()}@${messageIdHost}>`;
  const commonHeaders = [
    ['From', sanitizeHeader(from)],
    ['To', recipients.join(', ')],
    ['Subject', encodeHeader(subject || '(no subject)')],
    ['Date', new Date().toUTCString()],
    ['Message-ID', messageId],
    ['MIME-Version', '1.0'],
    ['X-MailHub', baseUrl || 'mailhub']
  ];

  if (html) {
    const boundary = `mailhub-${crypto.randomBytes(12).toString('hex')}`;
    const headers = [
      ...commonHeaders,
      ['Content-Type', `multipart/alternative; boundary="${boundary}"`]
    ];
    const body = [
      `--${boundary}`,
      'Content-Type: text/plain; charset=UTF-8',
      'Content-Transfer-Encoding: base64',
      '',
      encodeBase64Body(text || stripHtml(html)),
      `--${boundary}`,
      'Content-Type: text/html; charset=UTF-8',
      'Content-Transfer-Encoding: base64',
      '',
      encodeBase64Body(html),
      `--${boundary}--`,
      ''
    ].join('\r\n');
    return `${formatHeaders(headers)}\r\n\r\n${body}`;
  }

  const headers = [
    ...commonHeaders,
    ['Content-Type', 'text/plain; charset=UTF-8'],
    ['Content-Transfer-Encoding', 'base64']
  ];
  return `${formatHeaders(headers)}\r\n\r\n${encodeBase64Body(text || '')}\r\n`;
}

export function signMessageForDomain(rawMessage, domain) {
  if (!domain?.dkimPrivate || !domain?.selector) return rawMessage;
  return signDkim(rawMessage, {
    domain: domain.domain,
    selector: domain.selector,
    privateKey: domain.dkimPrivate
  });
}

export async function sendViaSmtp({ host, port, secure, username, password, helo, mailFrom, recipients, rawMessage }) {
  if (!host) throw new Error('SMTP_HOST is not configured.');
  const client = await SmtpClient.connect({ host, port, secure });
  try {
    await client.expect([220]);
    let response = await client.command(`EHLO ${helo || 'mailhub.local'}`, [250, 502, 500]);
    if (![250].includes(response.code)) {
      await client.command(`HELO ${helo || 'mailhub.local'}`, [250]);
    }
    if (username || password) {
      const auth = Buffer.from(`\u0000${username || ''}\u0000${password || ''}`).toString('base64');
      await client.command(`AUTH PLAIN ${auth}`, [235]);
    }
    await client.command(`MAIL FROM:<${extractAddress(mailFrom)}>`, [250]);
    for (const recipient of recipients) {
      await client.command(`RCPT TO:<${recipient}>`, [250, 251]);
    }
    await client.command('DATA', [354]);
    await client.writeData(dotStuff(rawMessage));
    const dataResponse = await client.expect([250]);
    await client.command('QUIT', [221]).catch(() => null);
    return dataResponse;
  } finally {
    client.close();
  }
}

function sanitizeHeader(value) {
  return String(value || '').replace(/[\r\n]+/g, ' ').trim();
}

function encodeHeader(value) {
  const clean = sanitizeHeader(value);
  if (/^[\x20-\x7e]*$/.test(clean)) return clean;
  return `=?UTF-8?B?${Buffer.from(clean).toString('base64')}?=`;
}

function formatHeaders(headers) {
  return headers
    .filter(([, value]) => value !== undefined && value !== null && value !== '')
    .map(([name, value]) => `${name}: ${value}`)
    .join('\r\n');
}

function normalizeBody(value) {
  return String(value || '').replace(/\r?\n/g, '\r\n');
}

function encodeBase64Body(value) {
  const encoded = Buffer.from(normalizeBody(value), 'utf8').toString('base64');
  return encoded.replace(/.{1,76}/g, '$&\r\n').trimEnd();
}

function stripHtml(value) {
  return String(value || '')
    .replace(/<style[\s\S]*?<\/style>/gi, '')
    .replace(/<script[\s\S]*?<\/script>/gi, '')
    .replace(/<[^>]+>/g, ' ')
    .replace(/\s+/g, ' ')
    .trim();
}

function dotStuff(rawMessage) {
  const normalized = rawMessage.replace(/\r?\n/g, '\r\n');
  return `${normalized.replace(/^\./gm, '..')}\r\n.`;
}

class SmtpClient {
  static connect({ host, port = 25, secure = false }) {
    return new Promise((resolve, reject) => {
      const socket = secure
        ? tls.connect({ host, port: Number(port), servername: host })
        : net.createConnection({ host, port: Number(port) });
      const client = new SmtpClient(socket);
      socket.once('connect', () => resolve(client));
      socket.once('secureConnect', () => resolve(client));
      socket.once('error', reject);
      setTimeout(() => reject(new Error('SMTP connection timeout.')), 15000).unref();
    });
  }

  constructor(socket) {
    this.socket = socket;
    this.buffer = '';
    this.pending = [];
    this.currentLines = [];
    socket.setEncoding('utf8');
    socket.on('data', (chunk) => this.onData(chunk));
    socket.on('error', (error) => this.rejectPending(error));
    socket.on('close', () => this.rejectPending(new Error('SMTP connection closed.')));
  }

  command(command, expectedCodes) {
    this.socket.write(`${command}\r\n`);
    return this.expect(expectedCodes);
  }

  writeData(data) {
    this.socket.write(`${data}\r\n`);
    return Promise.resolve();
  }

  expect(expectedCodes) {
    return new Promise((resolve, reject) => {
      this.pending.push({ expectedCodes, resolve, reject });
      this.flushResponses();
    });
  }

  close() {
    this.socket.destroy();
  }

  onData(chunk) {
    this.buffer += chunk;
    let index;
    while ((index = this.buffer.indexOf('\n')) !== -1) {
      const rawLine = this.buffer.slice(0, index).replace(/\r$/, '');
      this.buffer = this.buffer.slice(index + 1);
      this.currentLines.push(rawLine);
      if (/^\d{3} /.test(rawLine)) {
        this.flushResponses();
      }
    }
  }

  flushResponses() {
    while (this.pending.length && this.currentLines.length) {
      const lastLine = this.currentLines[this.currentLines.length - 1];
      if (!/^\d{3} /.test(lastLine)) return;
      const responseLines = this.currentLines.splice(0);
      const code = Number(lastLine.slice(0, 3));
      const response = {
        code,
        message: responseLines.join('\n')
      };
      const pending = this.pending.shift();
      if (pending.expectedCodes.includes(code)) {
        pending.resolve(response);
      } else {
        pending.reject(new Error(`Unexpected SMTP response ${response.message}`));
      }
    }
  }

  rejectPending(error) {
    while (this.pending.length) {
      this.pending.shift().reject(error);
    }
  }
}