chore(GODT-2799): Move SMTP backend to SMTP service module

internal/services/smtp/smtp_backend.go

@@ -0,0 +1,115 @@
+// Copyright (c) 2023 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge 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.
+//
+// Proton Mail Bridge 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 Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package smtp
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/ProtonMail/proton-bridge/v3/internal/identifier"
+	"github.com/ProtonMail/proton-bridge/v3/internal/useragent"
+	"github.com/emersion/go-smtp"
+	"github.com/sirupsen/logrus"
+)
+
+type Backend struct {
+	accounts  *Accounts
+	userAgent identifier.UserAgentUpdater
+}
+
+func NewBackend(accounts *Accounts, userAgent identifier.UserAgentUpdater) *Backend {
+	return &Backend{
+		accounts:  accounts,
+		userAgent: userAgent,
+	}
+}
+
+type smtpSession struct {
+	accounts  *Accounts
+	userAgent identifier.UserAgentUpdater
+
+	userID string
+	authID string
+
+	from string
+	to   []string
+}
+
+func (be *Backend) NewSession(*smtp.Conn) (smtp.Session, error) {
+	return &smtpSession{accounts: be.accounts, userAgent: be.userAgent}, nil
+}
+
+func (s *smtpSession) AuthPlain(username, password string) error {
+	userID, authID, err := s.accounts.CheckAuth(username, []byte(password))
+	if err != nil {
+		if !errors.Is(err, ErrNoSuchUser) {
+			return fmt.Errorf("unknown error")
+		}
+		logrus.WithFields(logrus.Fields{
+			"username": username,
+			"pkg":      "smtp",
+		}).Error("Incorrect login credentials.")
+
+		return fmt.Errorf("invalid username or password")
+	}
+
+	s.userID = userID
+	s.authID = authID
+
+	if strings.Contains(s.userAgent.GetUserAgent(), useragent.DefaultUserAgent) {
+		s.userAgent.SetUserAgent(useragent.UnknownClient, useragent.DefaultVersion)
+	}
+
+	return nil
+}
+
+func (s *smtpSession) Reset() {
+	s.from = ""
+	s.to = nil
+}
+
+func (s *smtpSession) Logout() error {
+	s.Reset()
+	return nil
+}
+
+func (s *smtpSession) Mail(from string, _ *smtp.MailOptions) error {
+	s.from = from
+	return nil
+}
+
+func (s *smtpSession) Rcpt(to string) error {
+	if len(to) > 0 {
+		s.to = append(s.to, to)
+	}
+
+	return nil
+}
+
+func (s *smtpSession) Data(r io.Reader) error {
+	err := s.accounts.SendMail(context.Background(), s.userID, s.authID, s.from, s.to, r)
+
+	if err != nil {
+		logrus.WithField("pkg", "smtp").WithError(err).Error("Send mail failed.")
+	}
+
+	return err
+}