Refactor SMTP mail sending code using gomail package

The gomail package is now used to handle the generation  of emails in the SMTP client code. This refactoring simplifies and standardizes the mail sending code. The necessary dependencies have also been added to go.mod and vendor/modules.txt.

Signed-off-by: Christian Roessner <[email protected]>

go.mod

@@ -38,6 +38,7 @@ require (
 	golang.org/x/net v0.24.0
 	golang.org/x/oauth2 v0.19.0
 	golang.org/x/text v0.14.0
+	gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
 )
 
 require (
@@ -113,6 +114,7 @@ require (
 	golang.org/x/exp v0.0.0-20240416160154-fe59bbe5cc7f // indirect
 	golang.org/x/sys v0.19.0 // indirect
 	google.golang.org/protobuf v1.34.0 // indirect
+	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc // indirect
 	gopkg.in/ini.v1 v1.67.0 // indirect
 	gopkg.in/xmlpath.v2 v2.0.0-20150820204837-860cbeca3ebc // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect

go.sum

@@ -500,12 +500,16 @@ google.golang.org/protobuf v1.28.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqw
 google.golang.org/protobuf v1.34.0 h1:Qo/qEd2RZPCf2nKuorzksSknv0d3ERwp1vFG38gSmH4=
 google.golang.org/protobuf v1.34.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
 gopkg.in/alecthomas/kingpin.v2 v2.2.6/go.mod h1:FMv+mEhP44yOT+4EoQTLFTRgOQ1FBLkstjWtayDeSgw=
+gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc h1:2gGKlE2+asNV9m7xrywl36YYNnBG5ZQ0r/BOOxqPpmk=
+gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc/go.mod h1:m7x9LTH6d71AHyAX77c9yqWCCa3UKHcVEj9y7hAtKDk=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
+gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df h1:n7WqCuqOuCbNr617RXOY0AWRXxgwEyPp2z+p0+hgMuE=
+gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df/go.mod h1:LRQQ+SO6ZHR7tOkpBDuZnXENFzX8qRjMDMyPD6BRkCw=
 gopkg.in/ini.v1 v1.67.0 h1:Dgnx+6+nfE+IfzjUEISNeydPJh9AXNNsWbGP9KzCsOA=
 gopkg.in/ini.v1 v1.67.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
 gopkg.in/xmlpath.v2 v2.0.0-20150820204837-860cbeca3ebc h1:LMEBgNcZUqXaP7evD1PZcL6EcDVa2QOFuI+cqM3+AJM=

server/lualib/smtp/client.go

@@ -1,6 +1,7 @@
 package smtp
 
 import (
+	"bytes"
 	"crypto/tls"
 	"fmt"
 	"io"
@@ -11,6 +12,8 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	"gopkg.in/gomail.v2"
 )
 
 // GenericClient is an interface that defines the methods required for sending emails using an SMTP or LMTP server.
@@ -278,6 +281,7 @@ type Client interface {
 // Otherwise, it uses the smtp.SendMail function to send the email without encryption.
 func SendMail(options *MailOptions) error {
 	var (
+		buf  bytes.Buffer
 		auth smtp.Auth
 		err  error
 	)
@@ -311,22 +315,21 @@ func SendMail(options *MailOptions) error {
 		}
 	}
 
-	// Connect to the server, authenticate, set the sender and recipient,
-	// and send the email all in one step.
-	toConcatenated := strings.Join(options.To, ",")
-	msg := []byte(
-		"Date: " + time.Now().Format(time.RFC1123Z) + "\r\n" +
-			"Message-ID: <" + strconv.FormatInt(time.Now().UnixNano(), 10) + "@" + msgIDDomain + ">\r\n" +
-			"From: " + options.From + "\r\n" +
-			"To: " + toConcatenated + "\r\n" +
-			"Subject: " + options.Subject + "\r\n" +
-			"Content-Type: text/plain; charset=utf-8\r\n" +
-			"MIME-Version: 1.0\r\n" +
-			"\r\n" +
-			options.Body +
-			"\r\n")
-
-	err = sendMail(options.Server+fmt.Sprintf(":%d", options.Port), options.HeloName, auth, options.From, options.To, msg, options.TLS, options.StartTLS, options.LMTP)
+	msg := gomail.NewMessage()
+
+	msg.SetHeader("Date", msg.FormatDate(time.Now()))
+	msg.SetHeader("Message-ID", strconv.FormatInt(time.Now().UnixNano(), 10)+"@"+msgIDDomain)
+	msg.SetHeader("From", options.From)
+	msg.SetHeader("To", options.To...)
+	msg.SetHeader("Subject", options.Subject)
+	msg.SetBody("text/plain; charset=UTF-8", options.Body)
+
+	_, err = msg.WriteTo(&buf)
+	if err != nil {
+		return err
+	}
+
+	err = sendMail(options.Server+fmt.Sprintf(":%d", options.Port), options.HeloName, auth, options.From, options.To, buf.Bytes(), options.TLS, options.StartTLS, options.LMTP)
 
 	return err
 }