Secure SMTP listener

smtp/server.go

@@ -0,0 +1,125 @@
+package smtp
+
+import (
+	"crypto/tls"
+	"net"
+	"os"
+	"time"
+
+	"github.com/emersion/go-smtp"
+	"gitlab.com/etke.cc/go/logger"
+)
+
+type Config struct {
+	Domain string
+	Port   string
+
+	TLSCert     string
+	TLSKey      string
+	TLSPort     string
+	TLSRequired bool
+
+	LogLevel string
+	MaxSize  int
+	Bot      Bot
+}
+
+type Server struct {
+	log  *logger.Logger
+	msa  *smtp.Server
+	errs chan error
+
+	port    string
+	tlsPort string
+	tlsCfg  *tls.Config
+}
+
+// NewServer creates new SMTP server
+func NewServer(cfg *Config) *Server {
+	log := logger.New("smtp/msa.", cfg.LogLevel)
+	sender := NewMTA(cfg.LogLevel)
+	receiver := &msa{
+		log:    log,
+		bot:    cfg.Bot,
+		domain: cfg.Domain,
+	}
+	receiver.bot.SetMTA(sender)
+
+	s := smtp.NewServer(receiver)
+	s.Domain = cfg.Domain
+	s.ReadTimeout = 10 * time.Second
+	s.WriteTimeout = 10 * time.Second
+	s.MaxMessageBytes = cfg.MaxSize * 1024 * 1024
+	s.EnableREQUIRETLS = cfg.TLSRequired
+	if log.GetLevel() == "DEBUG" || log.GetLevel() == "TRACE" {
+		s.Debug = os.Stdout
+	}
+
+	server := &Server{
+		msa:     s,
+		log:     log,
+		port:    cfg.Port,
+		tlsPort: cfg.TLSPort,
+	}
+	server.loadTLSConfig(cfg.TLSCert, cfg.TLSKey)
+	return server
+}
+
+// Start SMTP server
+func (s *Server) Start() error {
+	s.errs = make(chan error, 1)
+	go s.listen(s.port, nil)
+	if s.tlsCfg != nil {
+		go s.listen(s.tlsPort, s.tlsCfg)
+	}
+
+	return <-s.errs
+}
+
+// Stop SMTP server
+func (s *Server) Stop() {
+	err := s.msa.Close()
+	if err != nil {
+		s.log.Error("cannot stop SMTP server properly: %v", err)
+	}
+	s.log.Info("SMTP server has been stopped")
+}
+
+func (s *Server) listen(port string, tlsCfg *tls.Config) {
+	var l net.Listener
+	var err error
+	if tlsCfg != nil {
+		l, err = tls.Listen("tcp", ":"+port, tlsCfg)
+	} else {
+		l, err = net.Listen("tcp", ":"+port)
+	}
+	if err != nil {
+		s.log.Error("cannot start listener on %s: %v", port, err)
+		s.errs <- err
+		close(s.errs)
+		return
+	}
+
+	s.log.Info("Starting SMTP server on port %s", port)
+
+	err = s.msa.Serve(l)
+	if err != nil {
+		s.log.Error("cannot start SMTP server on %s: %v", port, err)
+		s.errs <- err
+		close(s.errs)
+	}
+}
+
+func (s *Server) loadTLSConfig(cert, key string) {
+	if cert == "" || key == "" {
+		s.log.Warn("SSL certificate is not provided")
+		return
+	}
+
+	tlsCert, err := tls.LoadX509KeyPair(cert, key)
+	if err != nil {
+		s.log.Error("cannot load SSL certificate: %v", err)
+		return
+	}
+	s.tlsCfg = &tls.Config{Certificates: []tls.Certificate{tlsCert}}
+}