move MTA SMTP connection to external lib

go.mod

@@ -18,6 +18,7 @@ require (
 	gitlab.com/etke.cc/go/logger v1.1.0
 	gitlab.com/etke.cc/go/mxidwc v1.0.0
 	gitlab.com/etke.cc/go/secgen v1.1.1
+	gitlab.com/etke.cc/go/trysmtp v1.0.0
 	gitlab.com/etke.cc/linkpearl v0.0.0-20221002171411-bb783f7e50f0
 	golang.org/x/net v0.0.0-20221002022538-bcab6841153b
 	maunium.net/go/mautrix v0.12.1

go.sum

@@ -95,6 +95,8 @@ gitlab.com/etke.cc/go/mxidwc v1.0.0 h1:6EAlJXvs3nU4RaMegYq6iFlyVvLw7JZYnZmNCGMYQ
 gitlab.com/etke.cc/go/mxidwc v1.0.0/go.mod h1:E/0kh45SAN9+ntTG0cwkAEKdaPxzvxVmnjwivm9nmz8=
 gitlab.com/etke.cc/go/secgen v1.1.1 h1:RmKOki725HIhWJHzPtAc9X4YvBneczndchpMgoDkE8w=
 gitlab.com/etke.cc/go/secgen v1.1.1/go.mod h1:3pJqRGeWApzx7qXjABqz2o2SMCNpKSZao/gXVdasqE8=
+gitlab.com/etke.cc/go/trysmtp v1.0.0 h1:f/7gSmzohKniVeLSLevI+ZsySYcPUGkT9cRlOTwjOr8=
+gitlab.com/etke.cc/go/trysmtp v1.0.0/go.mod h1:KqRuIB2IPElEEbAxXmFyKtm7S5YiuEb4lxwWthccqyE=
 gitlab.com/etke.cc/linkpearl v0.0.0-20221002171411-bb783f7e50f0 h1:B5YV62XKsLb9sCu9jW4Pnc5HDNRzdR1FswtRBMw1sR0=
 gitlab.com/etke.cc/linkpearl v0.0.0-20221002171411-bb783f7e50f0/go.mod h1:hjn0SVswej+Jo3+MycLm+lTsAVFy047Df+adX6MoXoE=
 golang.org/x/crypto v0.0.0-20220518034528-6f7dac969898/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=

smtp/mta.go

@@ -2,14 +2,11 @@ package smtp
 
 import (
 	"context"
-	"crypto/tls"
-	"fmt"
 	"io"
-	"net"
-	"net/smtp"
 	"strings"
 
 	"gitlab.com/etke.cc/go/logger"
+	"gitlab.com/etke.cc/go/trysmtp"
 	"maunium.net/go/mautrix/id"
 
 	"gitlab.com/etke.cc/postmoogle/utils"
@@ -28,9 +25,6 @@ type mta struct {
 	log *logger.Logger
 }
 
-// SMTPAddrs priority list
-var SMTPAddrs = []string{":25", ":587", ":465"}
-
 func NewMTA(loglevel string) utils.MTA {
 	return &mta{
 		log: logger.New("smtp/mta.", loglevel),
@@ -39,22 +33,12 @@ func NewMTA(loglevel string) utils.MTA {
 
 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)
+	conn, err := trysmtp.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()
@@ -73,61 +57,3 @@ func (m *mta) Send(from, to, data string) error {
 	m.log.Debug("email has been sent")
 	return nil
 }
-
-func (m *mta) tryServer(localname, mxhost, addr string) *smtp.Client {
-	m.log.Debug("trying SMTP connection to %s%s", mxhost, addr)
-	conn, err := smtp.Dial(mxhost + addr)
-	if err != nil {
-		m.log.Warn("cannot connect to the %s%s: %v", mxhost, addr, err)
-		return nil
-	}
-	err = conn.Hello(localname)
-	if err != nil {
-		m.log.Warn("cannot call HELLO command of the %s%s: %v", mxhost, addr, 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 {
-		for _, addr := range SMTPAddrs {
-			client := m.tryServer(localname, strings.TrimSuffix(mx.Host, "."), addr)
-			if client != nil {
-				return client, nil
-			}
-		}
-	}
-
-	// If there are no MX records, according to https://datatracker.ietf.org/doc/html/rfc5321#section-5.1,
-	// we're supposed to try talking directly to the host.
-	if len(mxs) == 0 {
-		for _, addr := range SMTPAddrs {
-			client := m.tryServer(localname, hostname, addr)
-			if client != nil {
-				return client, nil
-			}
-		}
-	}
-
-	return nil, fmt.Errorf("target SMTP server not found")
-}