GODT-1044: lite parser

pkg/message/scanner.go

@@ -0,0 +1,96 @@
+// Copyright (c) 2021 Proton Technologies AG
+//
+// This file is part of ProtonMail Bridge.
+//
+// ProtonMail 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.
+//
+// ProtonMail 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 ProtonMail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package message
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"io"
+)
+
+type partScanner struct {
+	r *bufio.Reader
+
+	boundary string
+	progress int
+}
+
+type part struct {
+	b      []byte
+	offset int
+}
+
+func newPartScanner(r io.Reader, boundary string) (*partScanner, error) {
+	scanner := &partScanner{r: bufio.NewReader(r), boundary: boundary}
+
+	if _, _, err := scanner.readToBoundary(); err != nil {
+		return nil, err
+	}
+
+	return scanner, nil
+}
+
+func (s *partScanner) scanAll() ([]part, error) {
+	var parts []part
+
+	for {
+		offset := s.progress
+
+		b, more, err := s.readToBoundary()
+		if err != nil {
+			return nil, err
+		}
+
+		if !more {
+			return parts, nil
+		}
+
+		parts = append(parts, part{b: b, offset: offset})
+	}
+}
+
+func (s *partScanner) readToBoundary() ([]byte, bool, error) {
+	var res []byte
+
+	for {
+		line, err := s.r.ReadBytes('\n')
+		if err != nil {
+			if !errors.Is(err, io.EOF) {
+				return nil, false, err
+			}
+
+			if len(line) == 0 {
+				return nil, false, nil
+			}
+		}
+
+		s.progress += len(line)
+
+		switch {
+		case bytes.HasPrefix(bytes.TrimSpace(line), []byte("--"+s.boundary)):
+			return bytes.TrimSuffix(bytes.TrimSuffix(res, []byte("\n")), []byte("\r")), true, nil
+
+		case bytes.HasSuffix(bytes.TrimSpace(line), []byte(s.boundary+"--")):
+			return bytes.TrimSuffix(bytes.TrimSuffix(res, []byte("\n")), []byte("\r")), false, nil
+
+		default:
+			res = append(res, line...)
+		}
+	}
+}