smtp_client.js

'use strict';
// SMTP client object and class. This allows every part of the client
// protocol to be hooked for different levels of control, such as
// smtp_forward and smtp_proxy queue plugins.
// It can use HostPool to get a connection to a pool of
// possible hosts in the configuration value "forwarding_host_pool", rather
// than a bunch of connections to a single host from the configuration values
// in "host" and "port" (see host_pool.js).

const events = require('node:events');

const ipaddr    = require('ipaddr.js');
const net_utils = require('haraka-net-utils');
const utils     = require('haraka-utils');

const tls_socket = require('./tls_socket')
const logger     = require('./logger');
const HostPool   = require('./host_pool');

const smtp_regexp = /^(\d{3})([ -])(.*)/;
const STATE = {
    IDLE: 1,
    ACTIVE: 2,
    RELEASED: 3,
    DESTROYED: 4,
}

class SMTPClient extends events.EventEmitter {
    constructor (opts = {}) {
        super();
        this.uuid = utils.uuid();
        this.connect_timeout = parseInt(opts.connect_timeout) || 30;
        this.socket = opts.socket || this.get_socket(opts)
        this.socket.setTimeout(this.connect_timeout * 1000);
        this.socket.setKeepAlive(true);
        this.state = STATE.IDLE;
        this.command = 'greeting';
        this.response = [];
        this.connected = false;
        this.authenticating= false;
        this.authenticated = false;
        this.auth_capabilities = [];
        this.host = opts.host;
        this.port = opts.port;
        this.smtputf8 = false;

        const client = this;

        client.socket.on('line', (line) => {
            client.emit('server_protocol', line);
            const matches = smtp_regexp.exec(line);
            if (!matches) {
                client.emit('error', `${client.uuid}: Unrecognized response from upstream server: ${line}`);
                client.destroy();
                return;
            }

            const code = matches[1];
            const cont = matches[2];
            const msg = matches[3];

            client.response.push(msg);
            if (cont !== ' ') return;

            if (client.command === 'auth' || client.authenticating) {
                logger.info(`SERVER RESPONSE, CLIENT ${client.command}, authenticating=${client.authenticating},code=${code},cont=${cont},msg=${msg}`);
                if (/^3/.test(code) && (
                    msg === 'VXNlcm5hbWU6' ||
                    msg === 'dXNlcm5hbWU6' // Workaround ill-mannered SMTP servers (namely smtp.163.com)
                )) {
                    client.emit('auth_username');
                    return;
                }
                if (/^3/.test(code) && msg === 'UGFzc3dvcmQ6') {
                    client.emit('auth_password');
                    return;
                }
                if (/^2/.test(code) && client.authenticating) {
                    logger.info('AUTHENTICATED');
                    client.authenticating = false;
                    client.authenticated = true;
                    client.emit('auth');
                    return;
                }
            }

            if (client.command === 'ehlo') {
                if (code.match(/^5/)) {
                    // Handle fallback to HELO if EHLO is rejected
                    client.emit('greeting', 'HELO');
                    return;
                }
                client.emit('capabilities');
                if (client.command !== 'ehlo') {
                    return;
                }
            }

            if (client.command === 'xclient' && /^5/.test(code)) {
                // XCLIENT command was rejected (no permission?)
                // Carry on without XCLIENT
                client.command = 'helo';
            }
            else if (/^[45]/.test(code)) {
                client.emit('bad_code', code, client.response.join(' '));
                if (client.state !== STATE.ACTIVE) {
                    return;
                }
            }

            if (/^441/.test(code)) {
                if (/Connection timed out/i.test(msg)) {
                    client.destroy();
                }
            }

            switch (client.command) {
                case 'xclient':
                    client.xclient = true;
                    client.emit('xclient', 'EHLO');
                    break;
                case 'starttls':
                    client.upgrade(client.tls_options);
                    break;
                case 'greeting':
                    client.connected = true;
                    client.emit('greeting', 'EHLO');
                    break;
                case 'ehlo':
                    client.emit('helo');
                    break;
                case 'helo':
                case 'mail':
                case 'rcpt':
                case 'data':
                case 'dot':
                case 'rset':
                case 'auth':
                    client.emit(client.command);
                    break;
                case 'quit':
                    client.emit('quit');
                    client.destroy();
                    break;
                default:
                    throw new Error(`Unknown command: ${client.command}`);
            }
        });

        client.socket.on('connect', () => {
            // Replace connection timeout with idle timeout
            client.socket.setTimeout((opts.idle_timeout || 300) * 1000);
            if (!client.socket.remoteAddress) {
                // "Value may be undefined if the socket is destroyed"
                logger.debug('socket.remoteAddress undefined');
                return;
            }
            client.remote_ip = ipaddr.process(client.socket.remoteAddress).toString();
        })

        function closed (msg) {
            return error => {
                if (!error) error = '';

                // error is e.g. "Error: connect ECONNREFUSED"
                const errMsg = `${client.uuid}: [${client.host}:${client.port}] SMTP connection ${msg} ${error}`;

                /* eslint-disable no-fallthrough */
                switch (client.state) {
                    case STATE.ACTIVE:
                        client.emit('error', errMsg);
                    case STATE.IDLE:
                    case STATE.RELEASED:
                        client.destroy();
                        break;
                    case STATE.DESTROYED:
                        if (msg === 'errored' || msg === 'timed out') {
                            client.emit('connection-error', errMsg);
                        }
                        break
                    default:
                }

                logger.debug(`[smtp_client] ${errMsg} (state=${client.state})`);
            }
        }

        client.socket.on('error',   closed('errored'));
        client.socket.on('timeout', closed('timed out'));
        client.socket.on('close',   closed('closed'));
        client.socket.on('end',     closed('ended'));
    }

    load_tls_config (opts) {

        const tls_options = { servername: this.host };
        if (opts) {
            Object.assign(tls_options, opts);
        }

        this.tls_options = tls_options;
    }

    send_command (command, data) {
        const line = (command === 'dot') ? '.' : command + (data ? (` ${data}`) : '');
        this.emit('client_protocol', line);
        this.command = command.toLowerCase();
        this.response = [];
        this.socket.write(`${line}\r\n`);
    }

    start_data (data) {
        this.response = [];
        this.command = 'dot';
        data.pipe(this.socket, { dot_stuffing: true, ending_dot: true, end: false });
    }

    release () {
        if (this.state === STATE.DESTROYED) return;
        logger.debug(`[smtp_client] ${this.uuid} releasing, state=${this.state}`);

        [
            'auth',   'bad_code', 'capabilities', 'client_protocol', 'connection-error',
            'data',   'dot',      'error',        'greeting',        'helo',
            'mail',   'rcpt',     'rset',         'server_protocol', 'xclient',
        ].forEach(l => {
            this.removeAllListeners(l);
        })

        if (this.connected) this.send_command('QUIT');
        this.destroy()
    }

    destroy () {
        if (this.state === STATE.DESTROYED) return
        this.state = STATE.DESTROYED;
        this.socket.destroy();
    }

    upgrade (tls_options) {

        this.socket.upgrade(tls_options, (verified, verifyError, cert, cipher) => {
            logger.info(`secured:${

                (cipher) ? ` cipher=${cipher.name} version=${cipher.version}` : ''
            } verified=${verified}${
                (verifyError) ? ` error="${verifyError}"` : ''
            }${(cert?.subject) ? ` cn="${cert.subject.CN}" organization="${cert.subject.O}"` : ''
            }${(cert?.issuer) ? ` issuer="${cert.issuer.O}"` : ''
            }${(cert?.valid_to) ? ` expires="${cert.valid_to}"` : ''
            }${(cert?.fingerprint) ? ` fingerprint=${cert.fingerprint}` : ''}`);
        });
    }

    is_dead_sender (plugin, connection) {
        if (connection?.transaction) return false;

        // This likely means the sender went away on us, cleanup.
        connection.logwarn(plugin, "transaction went away, releasing smtp_client");
        this.release();
        return true;
    }

    get_socket(opts) {
        const socket = tls_socket.connect({
            host: opts.host,
            port: opts.port,
            timeout: this.connect_timeout,
        })
        net_utils.add_line_processor(socket)
        return socket
    }
}

exports.smtp_client = SMTPClient;

// Get a smtp_client for the given attributes.
// used only in testing
exports.get_client = (server, callback, opts = {}) => {
    const smtp_client = new SMTPClient(opts)
    logger.debug(`[smtp_client] uuid=${smtp_client.uuid} host=${opts.host} port=${opts.port} created`)
    callback(smtp_client)
}

exports.onCapabilitiesOutbound = (smtp_client, secured, connection, config, on_secured) => {
    for (const line in smtp_client.response) {
        if (/^XCLIENT/.test(smtp_client.response[line])) {
            if (!smtp_client.xclient) {
                smtp_client.send_command('XCLIENT', `ADDR=${connection.remote.ip}`);
                return;
            }
        }

        if (/^SMTPUTF8/.test(smtp_client.response[line])) {
            smtp_client.smtputf8 = true;
        }

        if (/^STARTTLS/.test(smtp_client.response[line]) && !secured) {

            let hostBanned = false
            let serverBanned = false

            // Check if there are any banned TLS hosts
            if (smtp_client.tls_options.no_tls_hosts) {
                // If there are check if these hosts are in the blacklist
                hostBanned = net_utils.ip_in_list(smtp_client.tls_config.no_tls_hosts, config.host);
                serverBanned = net_utils.ip_in_list(smtp_client.tls_config.no_tls_hosts, smtp_client.remote_ip);
            }

            if (!hostBanned && !serverBanned && config.enable_tls) {
                smtp_client.socket.on('secure', on_secured);
                smtp_client.secured = false;  // have to wait in forward plugin before we can do auth, even if capabilities are there on first EHLO
                smtp_client.send_command('STARTTLS');
                return;
            }
        }

        let auth_matches = smtp_client.response[line].match(/^AUTH (.*)$/);
        if (auth_matches) {
            smtp_client.auth_capabilities = [];
            auth_matches = auth_matches[1].split(' ');
            for (const authMatch of auth_matches) {
                smtp_client.auth_capabilities.push(authMatch.toLowerCase());
            }
        }
    }
}

// Get a smtp_client for the given attributes and set up the common
// config and listeners for plugins. This is what smtp_proxy and
// smtp_forward have in common.
exports.get_client_plugin = (plugin, connection, c, callback) => {
    // c = config
    // Merge in authentication settings from smtp_forward/proxy.ini if present
    // FIXME: config.auth could be changed when API isn't frozen
    if (c.auth_type || c.auth_user || c.auth_pass) {
        c.auth = {
            type: c.auth_type,
            user: c.auth_user,
            pass: c.auth_pass
        }
    }

    const hostport = get_hostport(connection, connection.server, c);
    const smtp_client = new SMTPClient(hostport)
    logger.info(`[smtp_client] uuid=${smtp_client.uuid} host=${hostport.host} port=${hostport.port} created`);

    connection.logdebug(plugin, `Got smtp_client: ${smtp_client.uuid}`);

    let secured = false;

    smtp_client.load_tls_config(plugin.tls_options);

    smtp_client.call_next = function (retval, msg) {
        if (this.next) {
            const { next } = this;
            delete this.next;
            next(retval, msg);
        }
    }

    smtp_client.on('client_protocol', (line) => {
        connection.logprotocol(plugin, `C: ${line}`);
    })

    smtp_client.on('server_protocol', (line) => {
        connection.logprotocol(plugin, `S: ${line}`);
    })

    function helo (command) {
        if (smtp_client.xclient) {
            smtp_client.send_command(command, connection.hello.host);
        }
        else {
            smtp_client.send_command(command, connection.local.host);
        }
    }
    smtp_client.on('greeting', helo);
    smtp_client.on('xclient', helo);

    function on_secured () {
        if (secured) return;
        secured = true;
        smtp_client.secured = true;
        smtp_client.emit('greeting', 'EHLO');
    }

    smtp_client.on('capabilities', () => {
        exports.onCapabilitiesOutbound(smtp_client, secured, connection, c, on_secured);
    });

    smtp_client.on('helo', () => {
        if (!c.auth || smtp_client.authenticated) {
            if (smtp_client.is_dead_sender(plugin, connection)) return;

            smtp_client.send_command('MAIL', `FROM:${connection.transaction.mail_from.format(!smtp_client.smtp_utf8)}`);
            return;
        }

        if (c.auth.type === null || typeof (c.auth.type) === 'undefined') return; // Ignore blank
        const auth_type = c.auth.type.toLowerCase();
        if (!smtp_client.auth_capabilities.includes(auth_type)) {
            throw new Error(`Auth type "${auth_type}" not supported by server (supports: ${smtp_client.auth_capabilities.join(',')})`);
        }
        switch (auth_type) {
            case 'plain':
                if (!c.auth.user || !c.auth.pass) {
                    throw new Error("Must include auth.user and auth.pass for PLAIN auth.");
                }
                logger.debug(`[smtp_client] uuid=${smtp_client.uuid} authenticating as "${c.auth.user}"`);
                smtp_client.send_command('AUTH', `PLAIN ${utils.base64(`${c.auth.user}\0${c.auth.user}\0${c.auth.pass}`)}`);
                break;
            case 'cram-md5':
                throw new Error("Not implemented");
            default:
                throw new Error(`Unknown AUTH type: ${auth_type}`);
        }
    });

    smtp_client.on('auth', () => {
        // if authentication has been handled by plugin(s)
        if (smtp_client.authenticating) return;

        if (smtp_client.is_dead_sender(plugin, connection)) return;

        smtp_client.authenticated = true;
        smtp_client.send_command('MAIL', `FROM:${connection.transaction.mail_from.format(!smtp_client.smtp_utf8)}`);
    });

    // these errors only get thrown when the connection is still active
    smtp_client.on('error', (msg) => {
        connection.logwarn(plugin, msg);
        smtp_client.call_next();
    });

    // these are the errors thrown when the connection is dead
    smtp_client.on('connection-error', (error) => {
        // error contains e.g. "Error: connect ECONNREFUSE"
        logger.error(`backend failure: ${smtp_client.host}:${smtp_client.port} - ${error}`);
        const { host_pool } = connection.server.notes;
        // only exists for if forwarding_host_pool is set in the config
        if (host_pool) {
            host_pool.failed(smtp_client.host, smtp_client.port);
        }
        smtp_client.call_next();
    });

    if (smtp_client.connected) {
        if (smtp_client.xclient) {
            smtp_client.send_command('XCLIENT', `ADDR=${connection.remote.ip}`);
        }
        else {
            smtp_client.emit('helo');
        }
    }

    callback(null, smtp_client);
}

function get_hostport (connection, server, cfg) {

    if (cfg.forwarding_host_pool) {
        if (! server.notes.host_pool) {
            connection.logwarn(`creating host_pool from ${cfg.forwarding_host_pool}`);
            server.notes.host_pool =
                new HostPool(
                    cfg.forwarding_host_pool, // 1.2.3.4:420, 5.6.7.8:420
                    cfg.dead_forwarding_host_retry_secs
                );
        }

        const host = server.notes.host_pool.get_host();
        if (host) return host; // { host: 1.2.3.4, port: 567 }

        logger.error('[smtp_client] no backend hosts in pool!');
        throw new Error("no backend hosts found in pool!");
    }

    if (cfg.host && cfg.port) return { host: cfg.host, port: cfg.port };

    logger.warn("[smtp_client] forwarding_host_pool or host and port were not found in config file");
    throw new Error("You must specify either forwarding_host_pool or host and port");
}