Basic debugging LMTP handler

1 files changed, 115 insertions, 2 deletions

diff --git a/lmtp_server.go b/lmtp_server.go
index 57f319a..8e574e4 100644
--- a/lmtp_server.go
+++ b/lmtp_server.go
@@ -1,10 +1,123 @@
 // 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 "net"
+import (
+	"bytes"
+	"errors"
+	"io"
+	"log/slog"
+	"net"
+	"strings"
 
-func serveLMTP(_ net.Listener) error {
+	"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
+}