wildduck/lmtp.js

'use strict';

// Simple LMTP server that accepts all messages for valid recipients

const config = require('config');
const log = require('npmlog');
const SMTPServer = require('smtp-server').SMTPServer;
const tools = require('./lib/tools');
const MessageHandler = require('./lib/message-handler');
const db = require('./lib/db');
const forward = require('./lib/forward');
const autoreply = require('./lib/autoreply');

let messageHandler;

const serverOptions = {
    lmtp: true,

    // log to console
    logger: {
        info(...args) {
            args.shift();
            log.info('LMTP', ...args);
        },
        debug(...args) {
            args.shift();
            log.silly('LMTP', ...args);
        },
        error(...args) {
            args.shift();
            log.error('LMTP', ...args);
        }
    },

    name: false,

    // not required but nice-to-have
    banner: 'Welcome to Wild Duck Mail Server',

    disabledCommands: ['AUTH'],

    onMailFrom(address, session, callback) {
        // reset session entries
        session.users = [];

        // accept alls sender addresses
        return callback();
    },

    // Validate RCPT TO envelope address. Example allows all addresses that do not start with 'deny'
    // If this method is not set, all addresses are allowed
    onRcptTo(rcpt, session, callback) {
        let originalRecipient = tools.normalizeAddress(rcpt.address);
        let recipient = originalRecipient.replace(/\+[^@]*@/, '@');

        db.database.collection('addresses').findOne({
            address: recipient
        }, (err, address) => {
            if (err) {
                log.error('LMTP', err);
                return callback(new Error('Database error'));
            }
            if (!address) {
                return callback(new Error('Unknown recipient'));
            }

            db.database.collection('users').findOne({
                _id: address.user
            }, {
                fields: {
                    name: true,
                    filters: true,
                    forwards: true,
                    forward: true,
                    targetUrl: true,
                    autoreply: true
                }
            }, (err, user) => {
                if (err) {
                    log.error('LMTP', err);
                    return callback(new Error('Database error'));
                }
                if (!user) {
                    return callback(new Error('Unknown recipient'));
                }

                if (!session.users) {
                    session.users = [];
                }

                session.users.push({
                    recipient: originalRecipient,
                    user
                });

                callback();
            });
        });
    },

    // Handle message stream
    onData(stream, session, callback) {
        let chunks = [];
        let chunklen = 0;

        stream.on('readable', () => {
            let chunk;
            while ((chunk = stream.read()) !== null) {
                chunks.push(chunk);
                chunklen += chunk.length;
            }
        });

        stream.once('error', err => {
            log.error('LMTP', err);
            callback(new Error('Error reading from stream'));
        });

        stream.once('end', () => {
            let spamHeader = config.spamHeader && config.spamHeader.toLowerCase();
            let sender = tools.normalizeAddress((session.envelope.mailFrom && session.envelope.mailFrom.address) || '');
            let responses = [];
            let users = session.users;
            let stored = 0;

            let storeNext = () => {
                if (stored >= users.length) {
                    return callback(null, responses.map(r => r.response));
                }

                let rcptData = users[stored++];
                let recipient = rcptData.recipient;
                let user = rcptData.user;

                let response = responses.filter(r => r.user === user);
                if (response.length) {
                    responses.push(response[0]);
                    return storeNext();
                }

                // create Delivered-To and Received headers
                let header = Buffer.from(
                    'Delivered-To: ' + recipient + '\r\n'
                    //+ 'Received: ' + generateReceivedHeader(session, queueId, os.hostname().toLowerCase(), recipient) + '\r\n'
                );

                chunks.unshift(header);
                chunklen += header.length;

                let raw = Buffer.concat(chunks, chunklen);
                let prepared = messageHandler.prepareMessage({
                    raw
                });
                let maildata = messageHandler.indexer.getMaildata(prepared.id, prepared.mimeTree);

                // default flags are empty
                let flags = [];

                // default mailbox target is INBOX
                let mailboxQueryKey = 'path';
                let mailboxQueryValue = 'INBOX';

                let filters = (user.filters || []).concat(
                    spamHeader
                        ? {
                            id: 'SPAM',
                            query: {
                                headers: {
                                    [spamHeader]: 'Yes'
                                }
                            },
                            action: {
                                // only applies if any other filter does not already mark message as spam or ham
                                spam: true
                            }
                        }
                        : []
                );

                let forwardTargets = new Set();
                let forwardTargetUrls = new Set();
                let matchingFilters = [];
                let filterActions = new Map();

                filters
                    // apply all filters to the message
                    .map(filter => checkFilter(filter, prepared, maildata))
                    // remove all unmatched filers
                    .filter(filter => filter)
                    // apply filter actions
                    .forEach(filter => {
                        matchingFilters.push(filter.id);

                        // apply matching filter
                        if (!filterActions) {
                            filterActions = filter.action;
                        } else {
                            Object.keys(filter.action).forEach(key => {
                                if (key === 'forward') {
                                    forwardTargets.add(filter.action[key]);
                                    return;
                                }

                                if (key === 'targetUrl') {
                                    forwardTargetUrls.add(filter.action[key]);
                                    return;
                                }

                                // if a previous filter already has set a value then do not touch it
                                if (!filterActions.has(key)) {
                                    filterActions.set(key, filter.action[key]);
                                }
                            });
                        }
                    });

                let forwardMessage = done => {
                    if (user.forward && !filterActions.get('delete')) {
                        // forward to default recipient only if the message is not deleted
                        forwardTargets.add(user.forward);
                    }

                    if (user.targetUrl && !filterActions.get('delete')) {
                        // forward to default URL only if the message is not deleted
                        forwardTargetUrls.add(user.targetUrl);
                    }

                    // never forward messages marked as spam
                    if ((!forwardTargets.size && !forwardTargetUrls.size) || filterActions.get('spam')) {
                        return setImmediate(done);
                    }

                    // check limiting counters
                    messageHandler.counters.ttlcounter(
                        'wdf:' + user._id.toString(),
                        forwardTargets.size + forwardTargetUrls.size,
                        user.forwards,
                        (err, result) => {
                            if (err) {
                                // failed checks
                                log.error('LMTP', 'FRWRDFAIL key=%s error=%s', 'wdf:' + user._id.toString(), err.message);
                            } else if (!result.success) {
                                log.silly('LMTP', 'FRWRDFAIL key=%s error=%s', 'wdf:' + user._id.toString(), 'Precondition failed');
                                return done();
                            }

                            forward(
                                {
                                    user,
                                    sender,
                                    recipient,

                                    forward: forwardTargets.size ? Array.from(forwardTargets) : false,
                                    targetUrl: forwardTargetUrls.size ? Array.from(forwardTargetUrls) : false,

                                    chunks
                                },
                                done
                            );
                        }
                    );
                };

                let sendAutoreply = done => {
                    // never reply to messages marked as spam
                    if (!sender || !user.autoreply || !user.autoreply.status || !user.autoreply.message || filterActions.get('spam')) {
                        return setImmediate(done);
                    }

                    autoreply(
                        {
                            user,
                            sender,
                            recipient,
                            chunks,
                            messageHandler
                        },
                        done
                    );
                };

                forwardMessage((err, id) => {
                    if (err) {
                        log.error(
                            'LMTP',
                            '%s FRWRDFAIL from=%s to=%s target=%s error=%s',
                            prepared.id.toString(),
                            sender,
                            recipient,
                            Array.from(forwardTargets).concat(forwardTargetUrls).join(','),
                            err.message
                        );
                    } else if (id) {
                        log.silly(
                            'LMTP',
                            '%s FRWRDOK id=%s from=%s to=%s target=%s',
                            prepared.id.toString(),
                            id,
                            sender,
                            recipient,
                            Array.from(forwardTargets).concat(forwardTargetUrls).join(',')
                        );
                    }

                    sendAutoreply((err, id) => {
                        if (err) {
                            log.error('LMTP', '%s AUTOREPLYFAIL from=%s to=%s error=%s', prepared.id.toString(), '<>', sender, err.message);
                        } else if (id) {
                            log.silly('LMTP', '%s AUTOREPLYOK id=%s from=%s to=%s', prepared.id.toString(), id, '<>', sender);
                        }

                        if (filterActions.get('delete')) {
                            // nothing to do with the message, just continue
                            responses.push({
                                user,
                                response: 'Message dropped by policy as ' + prepared.id.toString()
                            });
                            prepared = false;
                            maildata = false;
                            return storeNext();
                        }

                        // apply filter results to the message
                        filterActions.forEach((value, key) => {
                            switch (key) {
                                case 'spam':
                                    if (value > 0) {
                                        // positive value is spam
                                        mailboxQueryKey = 'specialUse';
                                        mailboxQueryValue = '\\Junk';
                                    }
                                    break;
                                case 'seen':
                                    if (value) {
                                        flags.push('\\Seen');
                                    }
                                    break;
                                case 'flag':
                                    if (value) {
                                        flags.push('\\Flagged');
                                    }
                                    break;
                                case 'mailbox':
                                    if (value) {
                                        // positive value is spam
                                        mailboxQueryKey = 'mailbox';
                                        mailboxQueryValue = value;
                                    }
                                    break;
                            }
                        });

                        let messageOptions = {
                            user: (user && user._id) || user,
                            [mailboxQueryKey]: mailboxQueryValue,

                            prepared,
                            maildata,

                            meta: {
                                source: 'LMTP',
                                from: sender,
                                to: recipient,
                                origin: session.remoteAddress,
                                originhost: session.clientHostname,
                                transhost: session.hostNameAppearsAs,
                                transtype: session.transmissionType,
                                time: Date.now()
                            },

                            filters: matchingFilters,

                            date: false,
                            flags,

                            // if similar message exists, then skip
                            skipExisting: true
                        };

                        messageHandler.add(messageOptions, (err, inserted, info) => {
                            // remove Delivered-To
                            chunks.shift();
                            chunklen -= header.length;

                            // push to response list
                            responses.push({
                                user,
                                response: err ? err : 'Message stored as ' + info.id.toString()
                            });

                            storeNext();
                        });
                    });
                });
            };

            storeNext();
        });
    }
};

if (config.lmtp.tls) {
    if (config.lmtp.tls.key) {
        serverOptions.key = config.lmtp.tls.key;

        if (config.lmtp.tls.ca) {
            serverOptions.ca = config.lmtp.tls.ca;
        }

        if (config.lmtp.tls.cert) {
            serverOptions.cert = config.lmtp.tls.cert;
        }
    } else if (config.tls.key) {
        serverOptions.key = config.tls.key;

        if (config.tls.ca) {
            serverOptions.ca = config.tls.ca;
        }

        if (config.tls.cert) {
            serverOptions.cert = config.tls.cert;
        }
    }
}

const server = new SMTPServer(serverOptions);

module.exports = done => {
    if (!config.lmtp.enabled) {
        return setImmediate(() => done(null, false));
    }

    messageHandler = new MessageHandler(db.database, db.redisConfig);

    let started = false;

    server.on('error', err => {
        if (!started) {
            started = true;
            return done(err);
        }
        log.error('LMTP', err);
    });

    server.listen(config.lmtp.port, config.lmtp.host, () => {
        if (started) {
            return server.close();
        }
        started = true;
        done(null, server);
    });
};

function checkFilter(filter, prepared, maildata) {
    if (!filter || !filter.query) {
        return false;
    }

    let query = filter.query;

    // prepare filter data
    let headerFilters = new Map();
    if (query.headers) {
        Object.keys(query.headers).forEach(key => {
            headerFilters.set(key, (query.headers[key] || '').toString().toLowerCase());
        });
    }

    // check headers
    if (headerFilters.size) {
        let headerMatches = new Set();
        for (let j = prepared.headers.length - 1; j >= 0; j--) {
            let header = prepared.headers[j];
            if (headerFilters.has(header.key) && header.value.indexOf(headerFilters.get(header.key)) >= 0) {
                headerMatches.add(header.key);
            }
        }
        if (headerMatches.size < headerFilters.size) {
            // not enough matches
            return false;
        }
    }

    if (query.ha) {
        let hasAttachments = maildata.attachments && maildata.attachments.length;
        // negative ha means no attachmens
        if (hasAttachments && query.ha < 0) {
            return false;
        }
        // positive ha means attachmens must exist
        if (!hasAttachments && query.ha > 0) {
            return false;
        }
    }

    if (query.size) {
        let messageSize = prepared.size;
        let filterSize = Math.abs(query.size);
        // negative value means "less than", positive means "more than"
        if (query.size < 0 && messageSize > filterSize) {
            return false;
        }
        if (query.size > 0 && messageSize < filterSize) {
            return false;
        }
    }

    if (query.text && maildata.text.toLowerCase().indexOf(query.text.toLowerCase()) < 0) {
        // message plaintext does not match the text field value
        return false;
    }

    log.silly('Filter', 'Filter %s matched message %s', filter.id, prepared.id);

    // we reached the end of the filter, so this means we have a match
    return filter;
}