Wow it forwards mail :D

cmd/server/main.go

@@ -25,7 +25,11 @@ import (
 )
 
 func main() {
-	err := smtp.Run(":4650", false)
+	err := smtp.Run(
+		"localhost",
+		"4650",
+		false,
+	)
 	if err != nil {
 		log.Fatal(err)
 	}

smtp/commands.go

@@ -25,10 +25,10 @@ import (
 
 type Command struct {
 	name string
-	Exec func(SMTPSession, string)(bool, error)
+	Exec func(*SMTPSession, string)(bool, error)
 }
 
-func (self Command) Name() string {
+func (self Command) GetName() string {
 	return self.name
 }
 
@@ -36,9 +36,12 @@ func (self Command) Check(message string) bool {
 	return strings.HasPrefix(message, self.name)
 }
 
-func Greet(smtp_session SMTPSession) error {
+func Greet(smtp_session *SMTPSession) error {
 	err := smtp_session.Write(
-		"220 localhost ESMTPSession diodemail -- Service ready" + "\n",
+		fmt.Sprintf(
+			"220 %v ESMTP diodemail -- Service ready" + "\n",
+			smtp_session.GetHost(),
+		),
 	)
 	if err != nil {
 		return err
@@ -47,93 +50,111 @@ func Greet(smtp_session SMTPSession) error {
 	return nil
 }
 
-func Helo(smtp_session SMTPSession, message string) (bool, error) {
+func Helo(smtp_session *SMTPSession, message string) (bool, error) {
 	err := smtp_session.Write(
 		fmt.Sprintf(
 			"250 %v is shy" + "\r\n",
-			smtp_session.GetAddress(),
+			smtp_session.GetHost(),
 		),
 	)
 	if err != nil {
-		return false, err
+		return true, err
 	}
 
 	return false, nil
 }
 
-func Ehlo(smtp_session SMTPSession, message string) (bool, error) {
+func Ehlo(smtp_session *SMTPSession, message string) (bool, error) {
 	err := smtp_session.Write(
 		fmt.Sprintf(
 			"250 %v is shy" + "\r\n",
-			smtp_session.GetAddress(),
+			smtp_session.GetHost(),
 		),
 	)
 	if err != nil {
-		return false, err
+		return true, err
 	}
 
 	return false, nil
 }
 
-func MailFrom(smtp_session SMTPSession, message string) (bool, error) {
+func MailFrom(smtp_session *SMTPSession, message string) (bool, error) {
 	match := ReversePath.FindStringSubmatch(message)
 	if match == nil {
-		smtp_session.Write(
-			"501 Could not parse reverse-path",
+		err := smtp_session.Write(
+			"501 Could not parse reverse-path\n",
 		)
+		if err != nil {
+			return true, err
+		}
 	} else if len(match) > 1 {
 		smtp_session.MailFrom(match[1])
 		err := smtp_session.Write(
 			"250 OK\n",
 		)
 		if err != nil {
-			return false, err
+			return true, err
 		}
 	}
 
 	return false, nil
 }
 
-func RcptTo(smtp_session SMTPSession, message string) (bool, error) {
+func RcptTo(smtp_session *SMTPSession, message string) (bool, error) {
 	match := ForwardPath.FindStringSubmatch(message)
 	if match == nil {
-		smtp_session.Write(
-			"501 Could not parse forward-path",
+		err := smtp_session.Write(
+			"501 Could not parse forward-path\n",
 		)
+		if err != nil {
+			return true, err
+		}
 	} else {
 		smtp_session.AddRecipient(match[1])
 		err := smtp_session.Write(
 			"250 OK\n",
 		)
 		if err != nil {
-			return false, err
+			return true, err
 		}
 	}
 
 	return false, nil
 }
 
-func Data(smtp_session SMTPSession, message string) (bool, error) {
+func Data(smtp_session *SMTPSession, message string) (bool, error) {
 	err := smtp_session.Write(
 		"354 Start Input\n",
 	)
 	if err != nil {
-		return false, err
+		return true, err
 	}
 	data, err := smtp_session.Read("\r\n.\r\n")
-	smtp_session.SetMailBuffer(data)
+	if err != nil {
+		smtp_session.Write(
+			"550 Action not taken\n",
+		)
+		return false, err
+	}
+	err = smtp_session.SendMail(data)
+	if err != nil {
+		smtp_session.Write(
+			"550 Action not taken\n",
+		)
+		return false, err
+	}
+	smtp_session.Reset()
 	err = smtp_session.Write(
 		"250 OK\n",
 	)
-	smtp_session.Reset()
 	if err != nil {
-		return false, err
+		return true, err
 	}
 
 	return false, nil
 }
 
-func Quit(smtp_session SMTPSession, message string) (bool, error) {
+func Quit(smtp_session *SMTPSession, message string) (bool, error) {
 	err := smtp_session.Write(
 		"221 Goodbye :)\n",
 	)
@@ -144,24 +165,24 @@ func Quit(smtp_session SMTPSession, message string) (bool, error) {
 	return true, nil
 }
 
-func Noop(smtp_session SMTPSession, message string) (bool, error) {
+func Noop(smtp_session *SMTPSession, message string) (bool, error) {
 	err := smtp_session.Write(
 		"250 OK\n",
 	)
 	if err != nil {
-		return false, err
+		return true, err
 	}
 
 	return false, nil
 }
 
-func Rset(smtp_session SMTPSession, message string) (bool, error) {
+func Rset(smtp_session *SMTPSession, message string) (bool, error) {
+	smtp_session.Reset()
 	err := smtp_session.Write(
 		"250 Reset\n",
 	)
-	smtp_session.Reset()
 	if err != nil {
-		return false, err
+		return true, err
 	}
 
 	return false, nil

smtp/parsers.go

@@ -25,6 +25,7 @@ import (
 
 var ReversePath = regexp.MustCompile(fmt.Sprintf("(?:%v)|<>", path))
 var ForwardPath = regexp.MustCompile(path)
+var Domain      = regexp.MustCompile("\\w+@(\\w+(?:\\.\\w+)*)")
 
 // https://datatracker.ietf.org/doc/html/rfc5321#page-41
 // Is this...legal, m'lord? (no, but ¯\_(ツ)_/¯)

smtp/server.go

@@ -19,6 +19,7 @@
 package smtp
 
 import (
+	"fmt"
 	"net"
 	"os"
 
@@ -30,14 +31,14 @@ type PlainListener struct {
 	listener net.Listener
 }
 
-func handle(connection net.Conn) {
+func handle(connection net.Conn, host string) {
 	log.Info().Msgf(
 		"New connection %v. Starting session.",
 		connection.RemoteAddr(),
 	)
 	defer connection.Close()
 
-	session := MakeSMTPSession(connection)
+	session := MakeSMTPSession(connection, host)
 	err := session.Run()
 	if err != nil {
 		log.Error().Msgf(
@@ -53,7 +54,7 @@ func handle(connection net.Conn) {
 	}
 }
 
-func Run(host string, implicit_tls bool) error {
+func Run(host string, port string, implicit_tls bool) error {
 	log.Logger = zerolog.
 		New(zerolog.ConsoleWriter{Out: os.Stderr}).
 		With().
@@ -61,18 +62,19 @@ func Run(host string, implicit_tls bool) error {
 		Logger().
 		Level(zerolog.TraceLevel)
 	
-	listener, err := net.Listen("tcp", host)
+	listener, err := net.Listen("tcp", fmt.Sprintf("%v:%v", host, port))
 	if err != nil {
 		return err
 	}
 
+	log.Info().Msgf("Server started on port %v for host %v", port, host)
 	for {
 		connection, err := listener.Accept()
 		if err != nil {
 			return err
 		}
 
-		go handle(connection)
+		go handle(connection, host)
 	}
 }
 

smtp/session.go

@@ -20,30 +20,32 @@ package smtp
 
 import (
 	"net"
+	"net/smtp"
 	"fmt"
 	"strings"
+	"crypto/tls"
 
 	"github.com/rs/zerolog/log"
 )
 
 type SMTPSession struct {
 	connection net.Conn
+	host       string
 
 	ReversePathBuffer *string
 	ForwardPathBuffer []string
-	MailBuffer        *string
 }
 
-func MakeSMTPSession(connection net.Conn) SMTPSession {
+func MakeSMTPSession(connection net.Conn, host string) SMTPSession {
 	return SMTPSession{
 		connection,
+		host,
 		nil,
 		[]string{},
-		nil,
 	}
 }
 
-func (self SMTPSession) Run() error {
+func (self *SMTPSession) Run() error {
 	err := Greet(self)
 	if err != nil {
 		return err
@@ -69,9 +71,13 @@ func (self SMTPSession) Run() error {
 		for _, command := range COMMANDS {
 			if command.Check(message) {
 				command_found = true
-				quit, err = command.Exec(self, message[len(command.Name()):])
+				quit, err = command.Exec(self, message[len(command.GetName()):])
 				if err != nil {
+					if quit {
 						return err
+					} else {
+						log.Error().Msgf("%v: %v", self.connection.RemoteAddr(), err)
+					}
 				}
 				break
 			}
@@ -83,7 +89,7 @@ func (self SMTPSession) Run() error {
 	return nil
 }
 
-func (self SMTPSession) TraceSession(direction string, message string) {
+func (self *SMTPSession) TraceSession(direction string, message string) {
 	lines := strings.Split(message, "\n")
 	for index, line := range lines {
 		if index != len(lines) - 1 || line != "" {
@@ -98,7 +104,7 @@ func (self SMTPSession) TraceSession(direction string, message string) {
 }
 
 var buffer = [1024]byte{}
-func (self SMTPSession) Read(delimiter string) (string, error) {
+func (self *SMTPSession) Read(delimiter string) (string, error) {
 	var message string
 	for !strings.Contains(message, delimiter) {
 		num_read, err := self.connection.Read(buffer[:])
@@ -112,31 +118,80 @@ func (self SMTPSession) Read(delimiter string) (string, error) {
 	return message[:len(message) - len(delimiter)], nil
 }
 
-func (self SMTPSession) Write(message string) error {
+func (self *SMTPSession) Write(message string) error {
 	self.TraceSession("<- ", message)
 	_, err := self.connection.Write([]byte(message))
 	return err
 }
 
-func (self SMTPSession) GetAddress() string {
-	return fmt.Sprint(self.connection.LocalAddr())
+func (self *SMTPSession) GetHost() string {
+	return self.host
 }
 
-func (self SMTPSession) MailFrom(from string) {
+func (self *SMTPSession) MailFrom(from string) {
 	self.Reset()
 	self.ReversePathBuffer = &from
 }
 
-func (self SMTPSession) AddRecipient(recipient string) {
+func (self *SMTPSession) AddRecipient(recipient string) {
 	self.ForwardPathBuffer = append(self.ForwardPathBuffer, recipient)
 }
 
-func (self SMTPSession) SetMailBuffer(data string) {
-	self.MailBuffer = &data
+func (self *SMTPSession) SendMail(data string) error {
+	mx_hostname := Domain.FindStringSubmatch(self.ForwardPathBuffer[0])[1]
+	mx, err := net.LookupMX(mx_hostname)
+	if err != nil {
+		return err
+	}
+	var smtp_hostname string
+	if len(mx) == 0 {
+		smtp_hostname = self.host
+	} else {
+		smtp_hostname = mx[0].Host
+	}
+	tls_connection, err := tls.Dial("tcp", fmt.Sprintf("%v:4560", smtp_hostname), nil)
+	if err != nil {
+		return err
+	}
+	smtp_client, err := smtp.NewClient(tls_connection, "")
+	if err != nil {
+		return err
+	}
+	defer smtp_client.Close()
+
+	err = smtp_client.Hello(self.host)
+	if err != nil {
+		return err
+	}
+	err = smtp_client.Mail(*self.ReversePathBuffer)
+	if err != nil {
+		return err
+	}
+	err = smtp_client.Rcpt(self.ForwardPathBuffer[0])
+	if err != nil {
+		return err
+	}
+	writer, err := smtp_client.Data()
+	if err != nil {
+		return err
+	}
+	_, err = writer.Write([]byte(data))
+	if err != nil {
+		return err
+	}
+	err = writer.Close()
+	if err != nil {
+		return err
+	}
+	err = smtp_client.Quit()
+	if err != nil {
+		return err
+	}
+
+	return nil
 }
 
-func (self SMTPSession) Reset() {
+func (self *SMTPSession) Reset() {
 	self.ReversePathBuffer = nil
 	self.ForwardPathBuffer = []string{}
-	self.MailBuffer        = nil
 }