1 files changed, 204 insertions, 0 deletions
diff --git a/forged/internal/unsorted/lmtp_server.go b/forged/internal/unsorted/lmtp_server.go
new file mode 100644
index 0000000..1e94894
--- /dev/null
+++ b/forged/internal/unsorted/lmtp_server.go
@@ -0,0 +1,204 @@
+// 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 unsorted
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"log/slog"
+	"net"
+	"strings"
+	"time"
+
+	"github.com/emersion/go-message"
+	"github.com/emersion/go-smtp"
+	"go.lindenii.runxiyu.org/forge/forged/internal/misc"
+)
+
+type lmtpHandler struct{}
+
+type lmtpSession struct {
+	from   string
+	to     []string
+	ctx    context.Context
+	cancel context.CancelFunc
+	s      Server
+}
+
+func (session *lmtpSession) Reset() {
+	session.from = ""
+	session.to = nil
+}
+
+func (session *lmtpSession) Logout() error {
+	session.cancel()
+	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) {
+	ctx, cancel := context.WithCancel(context.Background())
+	session := &lmtpSession{
+		ctx:    ctx,
+		cancel: cancel,
+	}
+	return session, nil
+}
+
+func (s *Server) serveLMTP(listener net.Listener) error {
+	smtpServer := smtp.NewServer(&lmtpHandler{})
+	smtpServer.LMTP = true
+	smtpServer.Domain = s.config.LMTP.Domain
+	smtpServer.Addr = s.config.LMTP.Socket
+	smtpServer.WriteTimeout = time.Duration(s.config.LMTP.WriteTimeout) * time.Second
+	smtpServer.ReadTimeout = time.Duration(s.config.LMTP.ReadTimeout) * time.Second
+	smtpServer.EnableSMTPUTF8 = true
+	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, session.s.config.LMTP.MaxSize)
+	switch {
+	case n == session.s.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 task is run.
+	from = session.from
+	to = session.to
+
+	_ = from
+
+	for _, to := range to {
+		if !strings.HasSuffix(to, "@"+session.s.config.LMTP.Domain) {
+			continue
+		}
+		localPart := to[:len(to)-len("@"+session.s.config.LMTP.Domain)]
+		var segments []string
+		segments, err = misc.PathToSegments(localPart)
+		if err != nil {
+			// TODO: Should the entire email fail or should we just
+			// notify them out of band?
+			err = fmt.Errorf("cannot parse path: %w", err)
+			goto end
+		}
+		sepIndex := -1
+		for i, part := range segments {
+			if part == "-" {
+				sepIndex = i
+				break
+			}
+		}
+		if segments[len(segments)-1] == "" {
+			segments = segments[:len(segments)-1] // We don't care about dir or not.
+		}
+		if sepIndex == -1 || len(segments) <= sepIndex+2 {
+			err = errors.New("illegal path")
+			goto end
+		}
+
+		mbox := bytes.Buffer{}
+		if _, err = fmt.Fprint(&mbox, "From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001\r\n"); err != nil {
+			slog.Error("error handling patch... malloc???", "error", err)
+			goto end
+		}
+		data = bytes.ReplaceAll(data, []byte("\r\n"), []byte("\n"))
+		if _, err = mbox.Write(data); err != nil {
+			slog.Error("error handling patch... malloc???", "error", err)
+			goto end
+		}
+		// TODO: Is mbox's From escaping necessary here?
+
+		groupPath := segments[:sepIndex]
+		moduleType := segments[sepIndex+1]
+		moduleName := segments[sepIndex+2]
+		switch moduleType {
+		case "repos":
+			err = session.s.lmtpHandlePatch(session, groupPath, moduleName, &mbox)
+			if err != nil {
+				slog.Error("error handling patch", "error", err)
+				goto end
+			}
+		default:
+			err = errors.New("Emailing any endpoint other than repositories, is not supported yet.") // TODO
+			goto end
+		}
+	}
+
+end:
+	session.to = nil
+	session.from = ""
+	switch err {
+	case nil:
+		return nil
+	default:
+		return &smtp.SMTPError{
+			Code:         550,
+			Message:      "Permanent failure: " + err.Error(),
+			EnhancedCode: [3]int{5, 7, 1},
+		}
+	}
+}