package server import ( "bytes" "errors" "github.com/emersion/go-smtp" "io" "mime" "mime/multipart" "net/mail" "strings" "sync" ) var ( errInvalidDomain = errors.New("invalid domain") errInvalidAddress = errors.New("invalid address") errInvalidTopic = errors.New("invalid topic") errTooManyRecipients = errors.New("too many recipients") errUnsupportedContentType = errors.New("unsupported content type") ) // smtpBackend implements SMTP server methods. type smtpBackend struct { config *Config sub subscriber success int64 failure int64 mu sync.Mutex } func newMailBackend(conf *Config, sub subscriber) *smtpBackend { return &smtpBackend{ config: conf, sub: sub, } } func (b *smtpBackend) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) { return &smtpSession{backend: b}, nil } func (b *smtpBackend) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) { return &smtpSession{backend: b}, nil } func (b *smtpBackend) Counts() (success int64, failure int64) { b.mu.Lock() defer b.mu.Unlock() return b.success, b.failure } // smtpSession is returned after EHLO. type smtpSession struct { backend *smtpBackend topic string mu sync.Mutex } func (s *smtpSession) AuthPlain(username, password string) error { return nil } func (s *smtpSession) Mail(from string, opts smtp.MailOptions) error { return nil } func (s *smtpSession) Rcpt(to string) error { return s.withFailCount(func() error { conf := s.backend.config addressList, err := mail.ParseAddressList(to) if err != nil { return err } else if len(addressList) != 1 { return errTooManyRecipients } to = addressList[0].Address if !strings.HasSuffix(to, "@"+conf.SMTPServerDomain) { return errInvalidDomain } to = strings.TrimSuffix(to, "@"+conf.SMTPServerDomain) if conf.SMTPServerAddrPrefix != "" { if !strings.HasPrefix(to, conf.SMTPServerAddrPrefix) { return errInvalidAddress } to = strings.TrimPrefix(to, conf.SMTPServerAddrPrefix) } if !topicRegex.MatchString(to) { return errInvalidTopic } s.mu.Lock() s.topic = to s.mu.Unlock() return nil }) } func (s *smtpSession) Data(r io.Reader) error { return s.withFailCount(func() error { conf := s.backend.config b, err := io.ReadAll(r) // Protected by MaxMessageBytes if err != nil { return err } msg, err := mail.ReadMessage(bytes.NewReader(b)) if err != nil { return err } body, err := readMailBody(msg) if err != nil { return err } body = strings.TrimSpace(body) if len(body) > conf.MessageLimit { body = body[:conf.MessageLimit] } m := newDefaultMessage(s.topic, body) subject := strings.TrimSpace(msg.Header.Get("Subject")) if subject != "" { dec := mime.WordDecoder{} subject, err := dec.DecodeHeader(subject) if err != nil { return err } m.Title = subject } if m.Title != "" && m.Message == "" { m.Message = m.Title // Flip them, this makes more sense m.Title = "" } if err := s.backend.sub(m); err != nil { return err } s.backend.mu.Lock() s.backend.success++ s.backend.mu.Unlock() return nil }) } func (s *smtpSession) Reset() { s.mu.Lock() s.topic = "" s.mu.Unlock() } func (s *smtpSession) Logout() error { return nil } func (s *smtpSession) withFailCount(fn func() error) error { err := fn() s.backend.mu.Lock() defer s.backend.mu.Unlock() if err != nil { s.backend.failure++ } return err } func readMailBody(msg *mail.Message) (string, error) { if msg.Header.Get("Content-Type") == "" { return readPlainTextMailBody(msg) } contentType, params, err := mime.ParseMediaType(msg.Header.Get("Content-Type")) if err != nil { return "", err } if contentType == "text/plain" { return readPlainTextMailBody(msg) } else if strings.HasPrefix(contentType, "multipart/") { return readMultipartMailBody(msg, params) } return "", errUnsupportedContentType } func readPlainTextMailBody(msg *mail.Message) (string, error) { body, err := io.ReadAll(msg.Body) if err != nil { return "", err } return string(body), nil } func readMultipartMailBody(msg *mail.Message, params map[string]string) (string, error) { mr := multipart.NewReader(msg.Body, params["boundary"]) for { part, err := mr.NextPart() if err != nil { // may be io.EOF return "", err } partContentType, _, err := mime.ParseMediaType(part.Header.Get("Content-Type")) if err != nil { return "", err } if partContentType != "text/plain" { continue } body, err := io.ReadAll(part) if err != nil { return "", err } return string(body), nil } }