Add support for postfix XFORWARD command.

Author: Spiral90210

backend.go

@@ -63,6 +63,10 @@ type Session interface {
 	//
 	// r must be consumed before Data returns.
 	Data(r io.Reader) error
+
+	// XForward is called for any attribute name/value pair.
+	// See https://www.postfix.org/XFORWARD_README.html
+	XForward(attrName, attrValue string) error
 }
 
 // LMTPSession is an add-on interface for Session. It can be implemented by

cmd/smtp-debug-server/main.go

@@ -39,6 +39,10 @@ func (s *session) Data(r io.Reader) error {
 	return nil
 }
 
+func (s *session) XForward(attrName, attrValue string) error {
+	return nil
+}
+
 func (s *session) Reset() {}
 
 func (s *session) Logout() error {

conn.go

@@ -137,6 +137,8 @@ func (c *Conn) handle(cmd string, arg string) {
 		c.handleBdat(arg)
 	case "DATA":
 		c.handleData(arg)
+	case "XFORWARD":
+		c.handleXForward(arg)
 	case "QUIT":
 		c.writeResponse(221, EnhancedCode{2, 0, 0}, "Bye")
 		c.Close()
@@ -308,6 +310,9 @@ func (c *Conn) handleGreet(enhanced bool, arg string) {
 			caps = append(caps, fmt.Sprintf("MT-PRIORITY %s", c.server.MtPriorityProfile))
 		}
 	}
+	if c.server.EnableXFORWARD {
+		caps = append(caps, "XFORWARD NAME ADDR PROTO HELO")
+	}
 
 	args := []string{"Hello " + domain}
 	args = append(args, caps...)
@@ -990,6 +995,42 @@ func (c *Conn) handleData(arg string) {
 	c.writeResponse(code, enhancedCode, msg)
 }
 
+func (c *Conn) handleXForward(arg string) {
+	/*
+		Handling is according to https://www.postfix.org/XFORWARD_README.html
+			xforward-command = XFORWARD 1*( SP attribute-name"="attribute-value )
+			attribute-name = ( NAME | ADDR | PORT | PROTO | HELO | IDENT | SOURCE )
+			attribute-value = xtext
+			Attribute values are xtext encoded as per RFC 1891. https://datatracker.ietf.org/doc/html/rfc1891
+	*/
+
+	if c.bdatPipe != nil {
+		c.writeResponse(502, EnhancedCode{5, 5, 1}, "XFORWARD not allowed during message transfer")
+		return
+	}
+
+	attributes := strings.Split(arg, " ")
+	for _, attribute := range attributes {
+		if !strings.Contains(attribute, "=") {
+			c.writeResponse(501, EnhancedCode{5, 5, 1}, "Bad XFORWARD command.")
+			return
+		}
+		nameValue := strings.SplitN(attribute, "=", 2)
+		attrName := strings.ToUpper(nameValue[0]) // attr names are case insensitive, normalise
+		attrValue, err := decodeXtext(nameValue[1])
+		if err != nil {
+			c.writeResponse(501, EnhancedCode{5, 5, 1}, "Bad XFORWARD value.")
+			return
+		}
+		err = c.Session().XForward(attrName, attrValue)
+		if err != nil {
+			c.writeResponse(501, EnhancedCode{5, 0, 0}, "Error: transaction failed: "+err.Error())
+			return
+		}
+	}
+	c.writeResponse(250, EnhancedCode{2, 0, 0}, "OK")
+}
+
 func (c *Conn) handleBdat(arg string) {
 	args := strings.Fields(arg)
 	if len(args) == 0 {

example_server_test.go

@@ -68,6 +68,11 @@ func (s *Session) Data(r io.Reader) error {
 	return nil
 }
 
+func (s *Session) XForward(attrName, attrValue string) error {
+	log.Printf("XFORWARD %s=%s\n", attrName, attrValue)
+	return nil
+}
+
 func (s *Session) Reset() {}
 
 func (s *Session) Logout() error {
@@ -99,6 +104,7 @@ func ExampleServer() {
 	s.MaxMessageBytes = 1024 * 1024
 	s.MaxRecipients = 50
 	s.AllowInsecureAuth = true
+	s.EnableXFORWARD = true
 
 	log.Println("Starting server at", s.Addr)
 	if err := s.ListenAndServe(); err != nil {

parse.go

@@ -22,6 +22,8 @@ func parseCmd(line string) (cmd string, arg string, err error) {
 	switch {
 	case strings.HasPrefix(strings.ToUpper(line), "STARTTLS"):
 		return "STARTTLS", "", nil
+	case strings.HasPrefix(strings.ToUpper(line), "XFORWARD"):
+		return "XFORWARD", strings.TrimSpace(line[8:]), nil
 	case l == 0:
 		return "", "", nil
 	case l < 4:

server.go

@@ -73,6 +73,12 @@ type Server struct {
 	// Advertise MT-PRIORITY (RFC 6710) capability.
 	// Should only be used if backend supports it.
 	EnableMTPRIORITY bool
+
+	// Advertise XFORWARD NAME ADDR PROTO HELO
+	// (https://www.postfix.org/XFORWARD_README.html) capability.
+	// Should only be used if backend supports it.
+	EnableXFORWARD bool
+
 	// The priority profile mapping as defined
 	// in RFC 6710 section 10.2.
 	//

server_test.go

@@ -25,6 +25,7 @@ type message struct {
 	RcptOpts []*smtp.RcptOptions
 	Data     []byte
 	Opts     *smtp.MailOptions
+	XForward map[string]string
 }
 
 type backend struct {
@@ -98,7 +99,9 @@ func (s *session) Auth(mech string) (sasl.Server, error) {
 }
 
 func (s *session) Reset() {
-	s.msg = &message{}
+	s.msg = &message{
+		XForward: make(map[string]string),
+	}
 }
 
 func (s *session) Logout() error {
@@ -157,6 +160,11 @@ func (s *session) Data(r io.Reader) error {
 	return nil
 }
 
+func (s *session) XForward(attrName, attrValue string) error {
+	s.msg.XForward[attrName] = attrValue
+	return nil
+}
+
 func (s *session) LMTPData(r io.Reader, collector smtp.StatusCollector) error {
 	if err := s.Data(r); err != nil {
 		return err
@@ -1712,3 +1720,90 @@ func TestServerMTPRIORITY(t *testing.T) {
 		t.Fatal("Incorrect MtPriority parameter value:", fmt.Sprintf("expected %d, got %d", expectedPriority, *priority))
 	}
 }
+
+func TestServerXFORWARD(t *testing.T) {
+	be, s, c, scanner, caps := testServerEhlo(t,
+		func(s *smtp.Server) {
+			s.EnableXFORWARD = true
+		})
+	defer s.Close()
+	defer c.Close()
+
+	if _, ok := caps["XFORWARD NAME ADDR PROTO HELO"]; !ok {
+		t.Fatal("Missing capability: XFORWARD")
+	}
+
+	io.WriteString(c, "MAIL FROM:<root@nsa.gov>\r\n")
+	scanner.Scan()
+	if !strings.HasPrefix(scanner.Text(), "250 ") {
+		t.Fatal("Invalid MAIL response:", scanner.Text())
+	}
+
+	io.WriteString(c, "RCPT TO:<root@gchq.gov.uk>\r\n")
+	scanner.Scan()
+	if !strings.HasPrefix(scanner.Text(), "250 ") {
+		t.Fatal("Invalid RCPT response:", scanner.Text())
+	}
+
+	// Atrribute names are case insensitive, check we normalised them
+	io.WriteString(c, "XFORWARD NAME=spike.porcupine.org ADDR=168.100.189.2 proto=ESMTP\r\n")
+	scanner.Scan()
+	if !strings.HasPrefix(scanner.Text(), "250 ") {
+		t.Fatal("Invalid XFORWARD response:", scanner.Text())
+	}
+
+	io.WriteString(c, "DATA\r\n")
+	scanner.Scan()
+	if !strings.HasPrefix(scanner.Text(), "354 ") {
+		t.Fatal("Invalid DATA response:", scanner.Text())
+	}
+
+	io.WriteString(c, "From: root@nsa.gov\r\n")
+	io.WriteString(c, "\r\n")
+	io.WriteString(c, "Hey\r <3\r\n")
+	io.WriteString(c, "..this dot is fine\r\n")
+	io.WriteString(c, ".\r\n")
+	scanner.Scan()
+	if !strings.HasPrefix(scanner.Text(), "250 ") {
+		t.Fatal("Invalid DATA response:", scanner.Text())
+	}
+
+	if len(be.messages) != 0 || len(be.anonmsgs) != 1 {
+		t.Fatal("Invalid number of sent messages:", be.messages, be.anonmsgs)
+	}
+
+	msg := be.anonmsgs[0]
+
+	if len(msg.XForward) != 3 {
+		t.Fatal("Invalid XFORWARD data:", msg.XForward)
+	}
+
+	if got, ok := msg.XForward["NAME"]; !ok {
+		t.Fatal("Missing XFORWARD attribute NAME")
+	} else if got != "spike.porcupine.org" {
+		t.Fatal("Invalid XFORWARD attribute value for NAME", got)
+	}
+
+	if got, ok := msg.XForward["ADDR"]; !ok {
+		t.Fatal("Missing XFORWARD attribute ADDR")
+	} else if got != "168.100.189.2" {
+		t.Fatal("Invalid XFORWARD attribute value for ADDR", got)
+	}
+
+	if got, ok := msg.XForward["PROTO"]; !ok {
+		t.Fatal("Missing (normalised) XFORWARD attribute PROTO")
+	} else if got != "ESMTP" {
+		t.Fatal("Invalid (normalised) XFORWARD attribute value for PROTO", got)
+	}
+
+	// Sanity that the rest of the connection continued fine
+	if msg.From != "root@nsa.gov" {
+		t.Fatal("Invalid mail sender:", msg.From)
+	}
+	if len(msg.To) != 1 || msg.To[0] != "root@gchq.gov.uk" {
+		t.Fatal("Invalid mail recipients:", msg.To)
+	}
+	if string(msg.Data) != "From: root@nsa.gov\r\n\r\nHey\r <3\r\n.this dot is fine\r\n" {
+		t.Fatal("Invalid mail data:", string(msg.Data))
+	}
+}