GODT-1044: lite parser

pkg/message/header.go

@@ -0,0 +1,123 @@
+// 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"
+	"io"
+	"io/ioutil"
+
+	"github.com/emersion/go-message/textproto"
+	"github.com/pkg/errors"
+)
+
+// HeaderLines returns each line in the given header.
+func HeaderLines(header []byte) [][]byte {
+	var (
+		lines [][]byte
+		quote int
+	)
+
+	forEachLine(bufio.NewReader(bytes.NewReader(header)), func(line []byte) {
+		switch {
+		case len(bytes.TrimSpace(line)) == 0:
+			lines = append(lines, line)
+
+		case quote%2 != 0, len(bytes.SplitN(line, []byte(`: `), 2)) != 2:
+			if len(lines) > 0 {
+				lines[len(lines)-1] = append(lines[len(lines)-1], line...)
+			} else {
+				lines = append(lines, line)
+			}
+
+		default:
+			lines = append(lines, line)
+		}
+
+		quote += bytes.Count(line, []byte(`"`))
+	})
+
+	return lines
+}
+
+func forEachLine(br *bufio.Reader, fn func([]byte)) {
+	for {
+		b, err := br.ReadBytes('\n')
+		if err != nil {
+			if !errors.Is(err, io.EOF) {
+				panic(err)
+			}
+
+			if len(b) > 0 {
+				fn(b)
+			}
+
+			return
+		}
+
+		fn(b)
+	}
+}
+
+func readHeaderBody(b []byte) (*textproto.Header, []byte, error) {
+	rawHeader, body, err := splitHeaderBody(b)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	var header textproto.Header
+
+	for _, line := range HeaderLines(rawHeader) {
+		if len(bytes.TrimSpace(line)) > 0 {
+			header.AddRaw(line)
+		}
+	}
+
+	return &header, body, nil
+}
+
+func splitHeaderBody(b []byte) ([]byte, []byte, error) {
+	br := bufio.NewReader(bytes.NewReader(b))
+
+	var header []byte
+
+	for {
+		b, err := br.ReadBytes('\n')
+		if err != nil {
+			if !errors.Is(err, io.EOF) {
+				panic(err)
+			}
+
+			break
+		}
+
+		header = append(header, b...)
+
+		if len(bytes.TrimSpace(b)) == 0 {
+			break
+		}
+	}
+
+	body, err := ioutil.ReadAll(br)
+	if err != nil && !errors.Is(err, io.EOF) {
+		return nil, nil, err
+	}
+
+	return header, body, nil
+}