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package main
import (
"bufio"
"bytes"
"net"
"os"
"slices"
"strings"
"go.lindenii.runxiyu.org/lindenii-common/clog"
"go.lindenii.runxiyu.org/lindenii-common/scfg"
)
const VERSION = "lindenii-maild v0.0.0"
func main() {
config_file, err := os.Open("maild.scfg")
if err != nil {
panic(err)
}
err = scfg.NewDecoder(bufio.NewReader(config_file)).Decode(&config)
if err != nil {
panic(err)
}
listener, err := net.Listen("tcp", ":25")
if err != nil {
panic(err)
}
defer listener.Close()
for {
conn, err := listener.Accept()
if err != nil {
panic(err)
}
go func() {
err := handle_connection(bufio.NewReader(conn), bufio.NewWriter(conn))
if err != nil {
clog.Error("connection handler returned error", "err", err)
}
}()
}
}
type server_state_t uint
const (
server_state_begin server_state_t = iota
server_state_helo
server_state_mail
server_state_rcpt
)
func handle_connection(reader *bufio.Reader, writer *bufio.Writer) error {
_, _ = writer.WriteString("220 " + config.Server_name + " " + VERSION + "\r\n")
_ = writer.Flush()
server_state := server_state_begin
var remote_server_name string
var current_mail_from string
var current_rcpt_to []string
for {
line, err := reader.ReadString('\n')
if err != nil {
return err
}
line = strings.TrimSuffix(line, "\n")
line = strings.TrimSuffix(line, "\r")
cmd_end := strings.IndexByte(line, ' ')
var param_start int
if cmd_end == -1 {
cmd_end = len(line)
param_start = len(line)
} else {
param_start = cmd_end + 1
}
cmd := strings.ToUpper(line[:cmd_end])
param := line[param_start:]
switch_cmd:
switch cmd {
case "HELO":
if param == "" { // TODO: actually validate the hostname
_, _ = writer.WriteString("501 Syntax: HELO hostname\r\n")
_ = writer.Flush()
break
}
remote_server_name = param
_ = remote_server_name // TODO
server_state = server_state_helo
_, _ = writer.WriteString("250 " + config.Server_name + "\r\n")
_ = writer.Flush()
case "MAIL":
switch server_state {
case server_state_begin:
_, _ = writer.WriteString("503 5.5.1 Error: send HELO/EHLO first\r\n")
_ = writer.Flush()
break switch_cmd
case server_state_helo:
break
case server_state_mail:
_, _ = writer.WriteString("503 5.5.1 Error: nested MAIL command\r\n")
_ = writer.Flush()
break switch_cmd
}
if len(param) <= len("FROM:") || strings.ToUpper(param[:len("FROM:")]) != "FROM:" {
_, _ = writer.WriteString("501 5.5.4 Syntax: MAIL FROM:<address>\r\n")
_ = writer.Flush()
break
}
current_mail_from = param[len("FROM:"):]
current_rcpt_to = []string{}
server_state = server_state_mail
_, _ = writer.WriteString("250 2.1.0 Ok\r\n")
_ = writer.Flush()
// TODO: Address validation
case "RCPT":
if server_state != server_state_mail && server_state != server_state_rcpt {
_, _ = writer.WriteString("503 5.5.1 Error: need MAIL command\r\n")
_ = writer.Flush()
break
}
if len(param) <= len("TO:") || strings.ToUpper(param[:len("TO:")]) != "TO:" {
_, _ = writer.WriteString("501 5.5.4 Syntax: RCPT TO:<address>\r\n")
_ = writer.Flush()
break
}
current_rcpt_to = append(current_rcpt_to, param[len("TO:"):])
server_state = server_state_rcpt
_, _ = writer.WriteString("250 2.1.5 Ok\r\n")
_ = writer.Flush()
case "DATA":
if server_state != server_state_rcpt {
_, _ = writer.WriteString("503 5.5.1 Error: need RCPT command\r\n")
_ = writer.Flush()
break
}
_, _ = writer.WriteString("354 End data with <CR><LF>.<CR><LF>\r\n")
_ = writer.Flush()
var current_data []byte
for {
tmp, err := reader.ReadSlice('\r')
if err != nil {
return err
}
// reader.ReadSlice returns an internal buffer that gets
// overwritten on the next reader operation. So we must
// make a copy; also we have to allocate data_part to
// the correct length because [[builtin.copy]] copies
// min(len(dst), len(src)) items.
data_part := make([]byte, len(tmp))
copy(data_part, tmp)
clog.Debug("e", "e", string(data_part))
next_four, err := reader.Peek(4)
if err != nil {
return err
}
if bytes.Equal(next_four, []byte{'\n', '.', '\r', '\n'}) {
current_data = slices.Concat(current_data, data_part[:len(data_part)-1])
clog.Debug("eee", string(next_four)) // shut up go
break
}
clog.Debug("pre concat", "current_data", string(current_data), "data_part", string(data_part))
current_data = slices.Concat(current_data, data_part)
clog.Debug("post concat", "current_data", string(current_data), "data_part", string(data_part))
}
_, err := reader.Discard(4)
if err != nil {
return err
}
deliver_incoming(current_mail_from, current_rcpt_to, current_data)
server_state = server_state_helo
_, _ = writer.WriteString("250 2.0.0 Ok: Accepted\r\n")
_ = writer.Flush()
default:
_, _ = writer.WriteString("500 5.5.2 Error: command not recognized\r\n")
_ = writer.Flush()
}
}
}
func deliver_incoming(envelope_from string, envelope_recipients []string, data []byte) {
clog.Debug(
"incoming_mail",
"envelope_from", envelope_from,
"envelope_recipients", envelope_recipients,
"data", string(data),
)
}
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