Initial server setup and performs initial greeting and hello

smtp/connection.go

@@ -0,0 +1,57 @@
+/* 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"
+
+	"github.com/rs/zerolog/log"
+)
+
+type Connection struct {
+	connection net.Conn
+}
+
+func (self Connection) Read() (string, error) {
+	buffer := [64]byte{}
+	read, err := self.connection.Read(buffer[:])
+	if err != nil {
+		return "", err
+	}
+
+	message := string(buffer[:read - 2])
+
+	log.Trace().Msgf("%v  -> %v", self.RemoteAddr(), message)
+
+	return message, nil
+}
+
+func (self Connection) Write(message string) error {
+	log.Trace().Msgf("%v <-  %v", self.RemoteAddr(), message[:len(message) - 1])
+	_, err := self.connection.Write([]byte(message))
+	return err
+}
+
+func (self Connection) Close() {
+	self.connection.Close()
+}
+
+func (self Connection) RemoteAddr() net.Addr {
+	return self.connection.RemoteAddr()
+}

smtp/handlers.go

@@ -0,0 +1,103 @@
+/* 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)([]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()
+		if err != nil {
+			return err
+		}
+
+		command_found := false
+		for _, command := range commands {
+			if command.Check(message) {
+				commands, err = command.Exec(self)
+				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 nil, err
+	}
+
+	return []Command{
+		Command{ "HELO", Hello },
+		Command{ "EHLO", Hello },
+	}, nil
+}
+
+/* --- HELO/EHLO RESPONSE --- */
+
+func Hello(connection Connection) ([]Command, error) {
+	err := connection.Write(
+		fmt.Sprintf("250 %v is shy", connection.connection.LocalAddr()) + "\n",
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return []Command{}, nil
+}

smtp/server.go

@@ -0,0 +1,69 @@
+/* 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"
+	"os"
+
+	"github.com/rs/zerolog"
+	"github.com/rs/zerolog/log"
+)
+
+type PlainListener struct {
+	listener net.Listener
+}
+
+func handle(connection Connection) {
+	log.Info().Msgf("New connection %v", connection.RemoteAddr())
+	defer connection.Close()
+	err := connection.Chain()
+	if err != nil {
+		log.Error().Msgf("Failed to serve %v: %v", connection.RemoteAddr(), err)
+	} else {
+		log.Info().Msgf("Successfully served %v", connection.RemoteAddr())
+	}
+}
+
+func Run(host string, implicit_tls bool) error {
+	log.Logger = zerolog.
+		New(zerolog.ConsoleWriter{Out: os.Stderr}).
+		With().
+		Timestamp().
+		Logger().
+		Level(zerolog.TraceLevel)
+	
+	listener, err := net.Listen("tcp", host)
+	if err != nil {
+		return err
+	}
+
+	for {
+		connection, err := listener.Accept()
+		if err != nil {
+			return err
+		}
+
+		go handle(Connection{connection})
+	}
+}
+
+func (self PlainListener) Close() error {
+	return self.listener.Close()
+}