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)(bool, 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 {
	err := Greet(self)
	if err != nil {
		return err
	}
	COMMANDS := []Command{
		Command{ "HELO",       Helo     },
		Command{ "EHLO",       Ehlo     },
		Command{ "MAIL FROM:", MailFrom },
		Command{ "RCPT TO:",   RcptTo   },
		Command{ "DATA",       Data     },
		Command{ "QUIT",       Quit     },
		Command{ "NOOP",       Noop     },
		Command{ "RSET",       Rset     },
	}
	quit := false
	for !quit {
		message, err := self.Read("\n")
		if err != nil {
			return err
		}

		command_found := false
		for _, command := range COMMANDS {
			if command.Check(message) {
				command_found = true
				quit, err = command.Exec(self, message[len(command.Name()):])
				if err != nil {
					return err
				}
				break
			}
		}
		if !command_found {
			self.Write("500 Unrecognized Command\n")
		}
	}
	return nil
}

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

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

	return nil
}

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

func Helo(connection Connection, message string) (bool, error) {
	err := connection.Write(
		fmt.Sprintf(
			"250 %v is shy" + "\r\n",
			connection.connection.LocalAddr(),
		),
	)
	if err != nil {
		return false, err
	}

	return false, nil
}

func Ehlo(connection Connection, message string) (bool, error) {
	err := connection.Write(
		fmt.Sprintf(
			"250 %v is shy" + "\r\n",
			connection.connection.LocalAddr(),
		),
	)
	if err != nil {
		return false, err
	}

	return false, nil
}

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

func MailFrom(connection Connection, message string) (bool, error) {
	match := ReversePath.FindStringSubmatch(message)
	if match == nil {
		connection.Write(
			"501 Could not parse reverse-path",
		)
	} else if len(match) > 1 {
		connection.ReversePathBuffer = &match[1]
		err := connection.Write(
			"250 OK\n",
		)
		if err != nil {
			return false, err
		}
	}

	return false, nil
}

func RcptTo(connection Connection, message string) (bool, error) {
	match := ForwardPath.FindStringSubmatch(message)
	if match == nil {
		connection.Write(
			"501 Could not parse forward-path",
		)
	} else {
		connection.AddRecipient(match[1])
		err := connection.Write(
			"250 OK\n",
		)
		if err != nil {
			return false, err
		}
	}

	return false, nil
}

func Data(connection Connection, message string) (bool, error) {
	err := connection.Write(
		"354 Start Input\n",
	)
	if err != nil {
		return false, err
	}
	data, err := connection.Read("\r\n.\r\n")
	connection.MailBuffer = &data
	err = connection.Write(
		"250 OK\n",
	)
	connection.Reset()
	if err != nil {
		return false, err
	}

	return false, nil
}

func Quit(connection Connection, message string) (bool, error) {
	err := connection.Write(
		"221 Goodbye :)\n",
	)
	if err != nil {
		return true, err
	}

	return true, nil
}

func Noop(connection Connection, message string) (bool, error) {
	err := connection.Write(
		"250 OK\n",
	)
	if err != nil {
		return false, err
	}

	return false, nil
}

func Rset(connection Connection, message string) (bool, error) {
	err := connection.Write(
		"250 Reset\n",
	)
	connection.Reset()
	if err != nil {
		return false, err
	}

	return false, nil
}