diodemail/smtp/session.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 (
	"net"
	"net/smtp"
	"fmt"
	"strings"
	"crypto/tls"
	"crypto/sha256"

	"github.com/rs/zerolog/log"
)

type SMTPSession struct {
	connection    net.Conn
	host          string
	password_hash string
	buffer        [4096]byte

	ReversePathBuffer *string
	ForwardPathBuffer []string
}

func MakeSMTPSession(connection net.Conn, host string, password_hash string) SMTPSession {
	return SMTPSession{
		connection:    connection,
		host:          host,
		password_hash: password_hash,
	}
}

func (self *SMTPSession) Run() error {
	err := Greet(self)
	if err != nil {
		return err
	}
	COMMANDS := []Command{
		Command{ "HELO",       Helo     },
		Command{ "EHLO",       Ehlo     },
		Command{ "AUTH",       Auth     },
		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.ReadUntil("\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.GetName()):])
				if err != nil {
					if quit {
						return err
					} else {
						log.Error().Msgf("%v: %v", self.connection.RemoteAddr(), err)
					}
				}
				break
			}
		}
		if !command_found {
			self.Write("500 Unrecognized Command\n")
		}
	}
	return nil
}

func (self *SMTPSession) TraceSession(direction string, message string) {
	lines := strings.Split(message, "\n")
	for index, line := range lines {
		if index != len(lines) - 1 || line != "" {
			if index == 0 {
				log.Trace().Msgf("%v %v %v", self.connection.RemoteAddr(), direction, line)
			} else {
				log.Trace().Msgf("%v     %v", self.connection.RemoteAddr(), line)
			}
		}
	}

}

func (self *SMTPSession) ReadUntil(delimiter string) (string, error) {
	var message string
	for !strings.Contains(message, delimiter) {
		num_read, err := self.connection.Read(self.buffer[:])
		if err != nil {
			return "", err
		}
		message += string(self.buffer[:num_read])
	}
	self.TraceSession(" ->", message)

	return message[:len(message) - len(delimiter)], nil
}

func (self *SMTPSession) ReadCount(num_bytes int) ([]byte, error) {
	bytes := make([]byte, num_bytes)
	_, err := self.connection.Read(bytes[:])
	return bytes, err
}

func (self *SMTPSession) Write(message string) error {
	self.TraceSession("<- ", message)
	_, err := self.connection.Write([]byte(message))
	return err
}

func (self *SMTPSession) GetHost() string {
	return self.host
}

func (self *SMTPSession) ValidatePassword(password string) bool {
	return fmt.Sprintf("%x", sha256.Sum256([]byte(password))) == self.password_hash
}

func (self *SMTPSession) MailFrom(from string) {
	self.Reset()
	self.ReversePathBuffer = &from
}

func (self *SMTPSession) AddRecipient(recipient string) {
	self.ForwardPathBuffer = append(self.ForwardPathBuffer, recipient)
}

func (self *SMTPSession) SendMail(data string) error {
	mx_hostname := Domain.FindStringSubmatch(self.ForwardPathBuffer[0])[1]
	mx, err := net.LookupMX(mx_hostname)
	if err != nil {
		return err
	}
	var smtp_hostname string
	if len(mx) == 0 {
		smtp_hostname = self.host
	} else {
		smtp_hostname = mx[0].Host
	}
	tls_connection, err := tls.Dial("tcp", fmt.Sprintf("%v:465", smtp_hostname), nil)
	if err != nil {
		return err
	}
	smtp_client, err := smtp.NewClient(tls_connection, "")
	if err != nil {
		return err
	}
	defer smtp_client.Close()

	err = smtp_client.Hello(self.host)
	if err != nil {
		return err
	}
	err = smtp_client.Mail(*self.ReversePathBuffer)
	if err != nil {
		return err
	}
	err = smtp_client.Rcpt(self.ForwardPathBuffer[0])
	if err != nil {
		return err
	}
	writer, err := smtp_client.Data()
	if err != nil {
		return err
	}
	_, err = writer.Write([]byte(data))
	if err != nil {
		return err
	}
	err = writer.Close()
	if err != nil {
		return err
	}
	err = smtp_client.Quit()
	if err != nil {
		return err
	}

	return nil
}

func (self *SMTPSession) Reset() {
	self.ReversePathBuffer = nil
	self.ForwardPathBuffer = []string{}
}