Refactor message sending logic for better modularity

Extracted message sending functionality into a new helper function `sendSingleMsg`. This improves the code readability and maintainability by reducing the complexity of the main loop and encapsulating error handling per message.

client_120.go

@@ -24,96 +24,87 @@ func (c *Client) Send(messages ...*Msg) (returnErr error) {
 		returnErr = errors.Join(errs...)
 	}()
 
-	for msgid, message := range messages {
+	for _, message := range messages {
-		message.sendError = nil
+		if sendErr := c.sendSingleMsg(message); sendErr != nil {
-		if message.encoding == NoEncoding {
+			message.sendError = sendErr
-			if ok, _ := c.smtpClient.Extension("8BITMIME"); !ok {
+			errs = append(errs, sendErr)
-				message.sendError = &SendError{Reason: ErrNoUnencoded, isTemp: false}
-				errs = append(errs, message.sendError)
-				continue
-			}
-		}
-		from, err := message.GetSender(false)
-		if err != nil {
-			message.sendError = &SendError{Reason: ErrGetSender, errlist: []error{err}, isTemp: isTempError(err),
-				affectedMsg: messages[msgid]}
-			errs = append(errs, message.sendError)
-			continue
-		}
-		rcpts, err := message.GetRecipients()
-		if err != nil {
-			message.sendError = &SendError{Reason: ErrGetRcpts, errlist: []error{err}, isTemp: isTempError(err),
-				affectedMsg: messages[msgid]}
-			errs = append(errs, message.sendError)
-			continue
-		}
-
-		if c.dsn {
-			if c.dsnmrtype != "" {
-				c.smtpClient.SetDSNMailReturnOption(string(c.dsnmrtype))
-			}
-		}
-		if err = c.smtpClient.Mail(from); err != nil {
-			message.sendError = &SendError{Reason: ErrSMTPMailFrom, errlist: []error{err}, isTemp: isTempError(err)}
-			errs = append(errs, message.sendError)
-			if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
-				errs = append(errs, resetSendErr)
-			}
-			continue
-		}
-		failed := false
-		rcptSendErr := &SendError{}
-		rcptSendErr.errlist = make([]error, 0)
-		rcptSendErr.rcpt = make([]string, 0)
-		rcptNotifyOpt := strings.Join(c.dsnrntype, ",")
-		c.smtpClient.SetDSNRcptNotifyOption(rcptNotifyOpt)
-		for _, rcpt := range rcpts {
-			if err = c.smtpClient.Rcpt(rcpt); err != nil {
-				rcptSendErr.Reason = ErrSMTPRcptTo
-				rcptSendErr.errlist = append(rcptSendErr.errlist, err)
-				rcptSendErr.rcpt = append(rcptSendErr.rcpt, rcpt)
-				rcptSendErr.isTemp = isTempError(err)
-				failed = true
-			}
-		}
-		if failed {
-			if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
-				errs = append(errs, resetSendErr)
-			}
-			message.sendError = rcptSendErr
-			errs = append(errs, message.sendError)
-			continue
-		}
-		writer, err := c.smtpClient.Data()
-		if err != nil {
-			message.sendError = &SendError{Reason: ErrSMTPData, errlist: []error{err}, isTemp: isTempError(err)}
-			errs = append(errs, message.sendError)
-			continue
-		}
-		_, err = message.WriteTo(writer)
-		if err != nil {
-			message.sendError = &SendError{Reason: ErrWriteContent, errlist: []error{err}, isTemp: isTempError(err)}
-			errs = append(errs, message.sendError)
-			continue
-		}
-		message.isDelivered = true
-
-		if err = writer.Close(); err != nil {
-			message.sendError = &SendError{Reason: ErrSMTPDataClose, errlist: []error{err}, isTemp: isTempError(err)}
-			errs = append(errs, message.sendError)
-			continue
-		}
-
-		if err = c.Reset(); err != nil {
-			message.sendError = &SendError{Reason: ErrSMTPReset, errlist: []error{err}, isTemp: isTempError(err)}
-			errs = append(errs, message.sendError)
-			continue
-		}
-		if err = c.checkConn(); err != nil {
-			message.sendError = &SendError{Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err)}
-			errs = append(errs, message.sendError)
 		}
 	}
 
 	return
 }
+
+// sendSingleMsg sends out a single message and returns an error if the transmission/delivery fails.
+// It is invoked by the public Send methods
+func (c *Client) sendSingleMsg(message *Msg) error {
+	if message.encoding == NoEncoding {
+		if ok, _ := c.smtpClient.Extension("8BITMIME"); !ok {
+			return &SendError{Reason: ErrNoUnencoded, isTemp: false}
+		}
+	}
+	from, err := message.GetSender(false)
+	if err != nil {
+		return &SendError{Reason: ErrGetSender, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message}
+	}
+	rcpts, err := message.GetRecipients()
+	if err != nil {
+		return &SendError{Reason: ErrGetRcpts, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message}
+	}
+
+	if c.dsn {
+		if c.dsnmrtype != "" {
+			c.smtpClient.SetDSNMailReturnOption(string(c.dsnmrtype))
+		}
+	}
+	if err = c.smtpClient.Mail(from); err != nil {
+		retError := &SendError{Reason: ErrSMTPMailFrom, errlist: []error{err}, isTemp: isTempError(err)}
+		if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
+			retError.errlist = append(retError.errlist, resetSendErr)
+		}
+		return retError
+	}
+	failed := false
+	rcptSendErr := &SendError{}
+	rcptSendErr.errlist = make([]error, 0)
+	rcptSendErr.rcpt = make([]string, 0)
+	rcptNotifyOpt := strings.Join(c.dsnrntype, ",")
+	c.smtpClient.SetDSNRcptNotifyOption(rcptNotifyOpt)
+	for _, rcpt := range rcpts {
+		if err = c.smtpClient.Rcpt(rcpt); err != nil {
+			rcptSendErr.Reason = ErrSMTPRcptTo
+			rcptSendErr.errlist = append(rcptSendErr.errlist, err)
+			rcptSendErr.rcpt = append(rcptSendErr.rcpt, rcpt)
+			rcptSendErr.isTemp = isTempError(err)
+			failed = true
+		}
+	}
+	if failed {
+		if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
+			rcptSendErr.errlist = append(rcptSendErr.errlist, resetSendErr)
+		}
+		return rcptSendErr
+	}
+	writer, err := c.smtpClient.Data()
+	if err != nil {
+		return &SendError{Reason: ErrSMTPData, errlist: []error{err}, isTemp: isTempError(err)}
+	}
+	_, err = message.WriteTo(writer)
+	if err != nil {
+		return &SendError{Reason: ErrWriteContent, errlist: []error{err}, isTemp: isTempError(err)}
+	}
+	message.isDelivered = true
+
+	if err = writer.Close(); err != nil {
+		return &SendError{Reason: ErrSMTPDataClose, errlist: []error{err}, isTemp: isTempError(err)}
+	}
+
+	if err = c.Reset(); err != nil {
+		return &SendError{Reason: ErrSMTPReset, errlist: []error{err}, isTemp: isTempError(err)}
+	}
+	if err = c.checkConn(); err != nil {
+		return &SendError{Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err)}
+	}
+	return nil
+}