send emails

smtp/mta.go

@@ -0,0 +1,116 @@
+package smtp
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"io"
+	"net"
+	"net/smtp"
+	"strings"
+
+	"gitlab.com/etke.cc/go/logger"
+	"maunium.net/go/mautrix/id"
+
+	"gitlab.com/etke.cc/postmoogle/utils"
+)
+
+// Client interface to send emails into matrix
+type Client interface {
+	GetMapping(string) (id.RoomID, bool)
+	Send2Matrix(ctx context.Context, email *utils.Email) error
+	SetMTA(mta utils.MTA)
+}
+
+// mta is Mail Transfer Agent
+type mta struct {
+	log *logger.Logger
+}
+
+func NewMTA(loglevel string) utils.MTA {
+	return &mta{
+		log: logger.New("smtp/mta.", loglevel),
+	}
+}
+
+func (m *mta) Send(from, to, data string) error {
+	m.log.Debug("Sending email from %s to %s", from, to)
+	conn, err := m.connect(from, to)
+	if err != nil {
+		m.log.Error("cannot connect to SMTP server of %s: %v", to, err)
+		return err
+	}
+	defer conn.Close()
+	err = conn.Mail(from)
+	if err != nil {
+		m.log.Error("cannot call MAIL command: %v", err)
+		return err
+	}
+	err = conn.Rcpt(to)
+	if err != nil {
+		m.log.Error("cannot send RCPT command: %v", err)
+		return err
+	}
+
+	var w io.WriteCloser
+	w, err = conn.Data()
+	if err != nil {
+		m.log.Error("cannot send DATA command: %v", err)
+		return err
+	}
+	defer w.Close()
+	m.log.Debug("sending DATA:\n%s", data)
+	_, err = strings.NewReader(data).WriteTo(w)
+	if err != nil {
+		m.log.Debug("cannot write DATA: %v", err)
+		return err
+	}
+
+	m.log.Debug("email has been sent")
+	return nil
+}
+
+func (m *mta) tryServer(localname, mxhost string) *smtp.Client {
+	m.log.Debug("trying SMTP connection to %s", mxhost)
+	conn, err := smtp.Dial(mxhost + ":smtp")
+	if err != nil {
+		m.log.Warn("cannot connect to the %s: %v", mxhost, err)
+		return nil
+	}
+	err = conn.Hello(localname)
+	if err != nil {
+		m.log.Warn("cannot call HELLO command of the %s: %v", mxhost, err)
+		return nil
+	}
+	if ok, _ := conn.Extension("STARTTLS"); ok {
+		m.log.Debug("%s supports STARTTLS", mxhost)
+		config := &tls.Config{ServerName: mxhost}
+		err = conn.StartTLS(config)
+		if err != nil {
+			m.log.Warn("STARTTLS connection to the %s failed: %v", mxhost, err)
+		}
+	}
+
+	return conn
+}
+
+func (m *mta) connect(from, to string) (*smtp.Client, error) {
+	localname := strings.SplitN(from, "@", 2)[1]
+	hostname := strings.SplitN(to, "@", 2)[1]
+
+	m.log.Debug("performing MX lookup of %s", hostname)
+	mxs, err := net.LookupMX(hostname)
+	if err != nil {
+		m.log.Error("cannot perform MX lookup: %v", err)
+		return nil, err
+	}
+
+	for _, mx := range mxs {
+		client := m.tryServer(localname, mx.Host)
+		if client != nil {
+			return client, nil
+		}
+	}
+
+	return nil, fmt.Errorf("target SMTP server not found")
+}