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// SPDX-License-Identifier: AGPL-3.0-only
// SPDX-FileCopyrightText: Copyright (c) 2025 Runxi Yu <https://runxiyu.org>
// SPDX-FileCopyrightText: Copyright (c) 2024 Robin Jarry <robin@jarry.cc>
package main
import (
"bytes"
"errors"
"io"
"log/slog"
"net"
"strings"
"github.com/emersion/go-message"
"github.com/emersion/go-smtp"
)
type lmtpHandler struct{}
type lmtpSession struct {
from string
to []string
}
func (session *lmtpSession) Reset() {
session.from = ""
session.to = nil
}
func (session *lmtpSession) Logout() error {
return nil
}
func (session *lmtpSession) AuthPlain(_, _ string) error {
return nil
}
func (session *lmtpSession) Mail(from string, _ *smtp.MailOptions) error {
session.from = from
return nil
}
func (session *lmtpSession) Rcpt(to string, _ *smtp.RcptOptions) error {
session.to = append(session.to, to)
return nil
}
func (*lmtpHandler) NewSession(_ *smtp.Conn) (smtp.Session, error) {
// TODO
session := &lmtpSession{}
return session, nil
}
func serveLMTP(listener net.Listener) error {
smtpServer := smtp.NewServer(&lmtpHandler{})
return smtpServer.Serve(listener)
}
func (session *lmtpSession) Data(r io.Reader) error {
var (
email *message.Entity
from string
to []string
err error
buf bytes.Buffer
data []byte
n int64
)
n, err = io.CopyN(&buf, r, config.LMTP.MaxSize)
switch {
case n == config.LMTP.MaxSize:
err = errors.New("Message too big.")
// drain whatever is left in the pipe
_, _ = io.Copy(io.Discard, r)
goto end
case errors.Is(err, io.EOF):
// message was smaller than max size
break
case err != nil:
goto end
}
data = buf.Bytes()
email, err = message.Read(bytes.NewReader(data))
if err != nil && message.IsUnknownCharset(err) {
goto end
}
switch strings.ToLower(email.Header.Get("Auto-Submitted")) {
case "auto-generated", "auto-replied":
// disregard automatic emails like OOO replies
slog.Info("ignoring automatic message",
"from", session.from,
"to", strings.Join(session.to, ","),
"message-id", email.Header.Get("Message-Id"),
"subject", email.Header.Get("Subject"),
)
goto end
}
slog.Info("message received",
"from", session.from,
"to", strings.Join(session.to, ","),
"message-id", email.Header.Get("Message-Id"),
"subject", email.Header.Get("Subject"),
)
// Make local copies of the values before to ensure the references will
// still be valid when the queued task function is evaluated.
from = session.from
to = session.to
// TODO: Process the actual message contents
_, _ = from, to
end:
session.to = nil
session.from = ""
return err
}
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