Introduce RcptOptions

Some SMTP extensions add new RCPT parameters. Add a struct to be
able to support these.

backend.go

@@ -43,7 +43,7 @@ type Session interface {
 	// Set return path for currently processed message.
 	Mail(from string, opts *MailOptions) error
 	// Add recipient for currently processed message.
-	Rcpt(to string) error
+	Rcpt(to string, opts *RcptOptions) error
 	// Set currently processed message contents and send it.
 	//
 	// r must be consumed before Data returns.

backendutil/transform.go

@@ -48,15 +48,15 @@ func (s *transformSession) Mail(from string, opts *smtp.MailOptions) error {
 	return s.Session.Mail(from, opts)
 }
 
-func (s *transformSession) Rcpt(to string) error {
+func (s *transformSession) Rcpt(to string, opts *smtp.RcptOptions) error {
 	if s.be.TransformRcpt != nil {
 		var err error
 		to, err = s.be.TransformRcpt(to)
 		if err != nil {
 			return err
 		}
 	}
-	return s.Session.Rcpt(to)
+	return s.Session.Rcpt(to, opts)
 }
 
 func (s *transformSession) Data(r io.Reader) error {

backendutil/transform_test.go

@@ -65,7 +65,7 @@ func (s *session) Mail(from string, opts *smtp.MailOptions) error {
 	return nil
 }
 
-func (s *session) Rcpt(to string) error {
+func (s *session) Rcpt(to string, opts *smtp.RcptOptions) error {
 	s.msg.To = append(s.msg.To, to)
 	return nil
 }

client.go

@@ -414,8 +414,11 @@ func (c *Client) Mail(from string, opts *MailOptions) error {
 // A call to Rcpt must be preceded by a call to Mail and may be followed by
 // a Data call or another Rcpt call.
 //
+// If opts is not nil, RCPT arguments provided in the structure will be added
+// to the command. Handling of unsupported options depends on the extension.
+//
 // If server returns an error, it will be of type *SMTPError.
-func (c *Client) Rcpt(to string) error {
+func (c *Client) Rcpt(to string, opts *RcptOptions) error {
 	if err := validateLine(to); err != nil {
 		return err
 	}
@@ -531,7 +534,7 @@ func (c *Client) SendMail(from string, to []string, r io.Reader) error {
 		return err
 	}
 	for _, addr := range to {
-		if err = c.Rcpt(addr); err != nil {
+		if err = c.Rcpt(addr, nil); err != nil {
 			return err
 		}
 	}

client_test.go

@@ -120,7 +120,7 @@ func TestBasic(t *testing.T) {
 		t.Fatalf("AUTH failed: %s", err)
 	}
 
-	if err := c.Rcpt("[email protected]>\r\nDATA\r\nInjected message body\r\n.\r\nQUIT\r\n"); err == nil {
+	if err := c.Rcpt("[email protected]>\r\nDATA\r\nInjected message body\r\n.\r\nQUIT\r\n", nil); err == nil {
 		t.Fatalf("RCPT should have failed due to a message injection attempt")
 	}
 	if err := c.Mail("[email protected]>\r\nDATA\r\nAnother injected message body\r\n.\r\nQUIT\r\n", nil); err == nil {
@@ -129,7 +129,7 @@ func TestBasic(t *testing.T) {
 	if err := c.Mail("[email protected]", nil); err != nil {
 		t.Fatalf("MAIL failed: %s", err)
 	}
-	if err := c.Rcpt("[email protected]"); err != nil {
+	if err := c.Rcpt("[email protected]", nil); err != nil {
 		t.Fatalf("RCPT failed: %s", err)
 	}
 	msg := `From: [email protected]
@@ -797,7 +797,7 @@ func TestLMTP(t *testing.T) {
 	if err := c.Mail("[email protected]", nil); err != nil {
 		t.Fatalf("MAIL failed: %s", err)
 	}
-	if err := c.Rcpt("[email protected]"); err != nil {
+	if err := c.Rcpt("[email protected]", nil); err != nil {
 		t.Fatalf("RCPT failed: %s", err)
 	}
 	msg := `From: [email protected]
@@ -882,10 +882,10 @@ func TestLMTPData(t *testing.T) {
 	if err := c.Mail("[email protected]", nil); err != nil {
 		t.Fatalf("MAIL failed: %s", err)
 	}
-	if err := c.Rcpt("[email protected]"); err != nil {
+	if err := c.Rcpt("[email protected]", nil); err != nil {
 		t.Fatalf("RCPT failed: %s", err)
 	}
-	if err := c.Rcpt("[email protected]"); err != nil {
+	if err := c.Rcpt("[email protected]", nil); err != nil {
 		t.Fatalf("RCPT failed: %s", err)
 	}
 	msg := `From: [email protected]

cmd/smtp-debug-server/main.go

@@ -31,7 +31,7 @@ func (s *session) Mail(from string, opts *smtp.MailOptions) error {
 	return nil
 }
 
-func (s *session) Rcpt(to string) error {
+func (s *session) Rcpt(to string, opts *smtp.RcptOptions) error {
 	return nil
 }
 

conn.go

@@ -473,7 +473,8 @@ func (c *Conn) handleRcpt(arg string) {
 		return
 	}
 
-	if err := c.Session().Rcpt(recipient); err != nil {
+	opts := &RcptOptions{}
+	if err := c.Session().Rcpt(recipient, opts); err != nil {
 		if smtpErr, ok := err.(*SMTPError); ok {
 			c.writeResponse(smtpErr.Code, smtpErr.EnhancedCode, smtpErr.Message)
 			return

example_test.go

@@ -28,7 +28,7 @@ func ExampleDial() {
 	if err := c.Mail("[email protected]", nil); err != nil {
 		log.Fatal(err)
 	}
-	if err := c.Rcpt("[email protected]"); err != nil {
+	if err := c.Rcpt("[email protected]", nil); err != nil {
 		log.Fatal(err)
 	}
 
@@ -113,7 +113,7 @@ func (s *Session) Mail(from string, opts *smtp.MailOptions) error {
 	return nil
 }
 
-func (s *Session) Rcpt(to string) error {
+func (s *Session) Rcpt(to string, opts *smtp.RcptOptions) error {
 	log.Println("Rcpt to:", to)
 	return nil
 }

server_test.go

@@ -94,7 +94,7 @@ func (s *session) Mail(from string, opts *smtp.MailOptions) error {
 	return nil
 }
 
-func (s *session) Rcpt(to string) error {
+func (s *session) Rcpt(to string, opts *smtp.RcptOptions) error {
 	s.msg.To = append(s.msg.To, to)
 	return nil
 }

smtp.go

@@ -24,8 +24,7 @@ const (
 	BodyBinaryMIME BodyType = "BINARYMIME"
 )
 
-// MailOptions contains custom arguments that were
-// passed as an argument to the MAIL command.
+// MailOptions contains parameters for the MAIL command.
 type MailOptions struct {
 	// Value of BODY= argument, 7BIT, 8BITMIME or BINARYMIME.
 	Body BodyType
@@ -52,3 +51,6 @@ type MailOptions struct {
 	// Defined in RFC 4954.
 	Auth *string
 }
+
+// RcptOptions contains parameters for the RCPT command.
+type RcptOptions struct{}