diodemail/smtp/handlers.go

/* diodemail - send-only smtp server
 * Copyright (c) 2024 Gnarwhal
 *
 * This file is part of SSHare.
 *
 * SSHare is free software: you can redistribute it and/or modify it under the terms of
 * the GNU General Public License as published by the Free Software Foundation,
 * either version 3 of the License, or (at your option) any later version.
 *
 * SSHare is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * SSHare. If not, see <https://www.gnu.org/licenses/>.
 */

package smtp

import (
	"fmt"
	"strings"
)

type Command struct {
	name string
	Exec func(Connection, string)([]Command, error)
}

func (self Command) Name() string {
	return self.name
}

func (self Command) Check(message string) bool {
	return strings.HasPrefix(message, self.name)
}

func (self Connection) Chain() error {
	commands, err := Greet(self)
	if err != nil {
		return err
	}
	for {
		message, err := self.Read("\r\n")
		if err != nil {
			return err
		}

		command_found := false
		for _, command := range commands {
			if command.Check(message) {
				commands, err = command.Exec(self, message[len(command.Name()):])
				if err != nil {
					return err
				}
				command_found = true
				break
			}
		}
		if !command_found {
			expected := make([]string, len(commands))
			for index, command := range commands {
				expected[index] = command.Name()
			}
			return fmt.Errorf("Expected one of %v, but got: %v", expected, message)
		}

		if len(commands) == 0 {
			break
		}
	}
	return nil
}

/* --- GREETING RESPONSE --- */

func Greet(connection Connection) ([]Command, error) {
	err := connection.Write(
		"220 localhost ESMTP diodemail -- Service ready" + "\n",
	)
	if err != nil {
		return []Command{}, err
	}

	return []Command{
		HELO,
		EHLO,
	}, nil
}

/* --- HELO/EHLO RESPONSE --- */

var HELO = Command{ "HELO", Hello }
var EHLO = Command{ "EHLO", Hello }
func Hello(connection Connection, message string) ([]Command, error) {
	err := connection.Write(
		fmt.Sprintf(
			"250 %v is shy" + "\r\n",
			connection.connection.LocalAddr(),
		),
	)
	if err != nil {
		return []Command{}, err
	}

	return []Command{
		MAIL_FROM,
	}, nil
}

/* --- MAIL FROM RESPONSE --- */

var MAIL_FROM = Command{ "MAIL FROM:", MailFrom }
func MailFrom(connection Connection, message string) ([]Command, error) {
	match := ReversePath.FindStringSubmatch(message)
	if match == nil {
		return []Command{}, fmt.Errorf("Invalid forward-path: %v", message)
	} else if len(match) > 1 {
		connection.ReversePathBuffer = &match[1]
	}
	err := connection.Write(
		"250 OK\n",
	)
	if err != nil {
		return []Command{}, err
	}

	return []Command{
		RCPT_TO,
	}, nil
}

var RCPT_TO = Command{ "RCPT TO:", RcptTo }
func RcptTo(connection Connection, message string) ([]Command, error) {
	match := ForwardPath.FindStringSubmatch(message)
	if match == nil {
		return []Command{}, fmt.Errorf("Invalid forward-path: %v", message)
	} else {
		connection.ForwardPathBuffer = &match[1]
	}
	err := connection.Write(
		"250 OK\n",
	)
	if err != nil {
		return []Command{}, err
	}

	return []Command{
		DATA,
	}, nil
}

var DATA = Command { "DATA", Data }
func Data(connection Connection, message string) ([]Command, error) {
	err := connection.Write(
		"354 Start Input\n",
	)
	if err != nil {
		return []Command{}, err
	}
	data, err := connection.Read("\r\n.\r\n")
	connection.MailBuffer = &data
	err = connection.Write(
		"250 OK\n",
	)
	if err != nil {
		return nil, err
	}
	return []Command{
		QUIT,
	}, nil
}

var QUIT = Command { "QUIT", Quit }
func Quit(connection Connection, message string) ([]Command, error) {
	err := connection.Write(
		"221 OK\n",
	)
	if err != nil {
		return nil, err
	}
	return []Command{}, nil
}