Other refactor: clean old builder

pkg/message/boundary_reader.go

@@ -0,0 +1,130 @@
+// 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"
+)
+
+type boundaryReader struct {
+	reader *bufio.Reader
+
+	closed, first bool
+	skipped       int
+
+	nl               []byte // "\r\n" or "\n" (set after seeing first boundary line)
+	nlDashBoundary   []byte // nl + "--boundary"
+	dashBoundaryDash []byte // "--boundary--"
+	dashBoundary     []byte // "--boundary"
+}
+
+func newBoundaryReader(r *bufio.Reader, boundary string) (br *boundaryReader, err error) {
+	b := []byte("\r\n--" + boundary + "--")
+	br = &boundaryReader{
+		reader:           r,
+		closed:           false,
+		first:            true,
+		nl:               b[:2],
+		nlDashBoundary:   b[:len(b)-2],
+		dashBoundaryDash: b[2:],
+		dashBoundary:     b[2 : len(b)-2],
+	}
+	err = br.writeNextPartTo(nil)
+	return
+}
+
+// writeNextPartTo will copy the the bytes of next part and write them to
+// writer. Will return EOF if the underlying reader is empty.
+func (br *boundaryReader) writeNextPartTo(part io.Writer) (err error) {
+	if br.closed {
+		return io.EOF
+	}
+
+	var line, slice []byte
+	br.skipped = 0
+
+	for {
+		slice, err = br.reader.ReadSlice('\n')
+		line = append(line, slice...)
+		if err == bufio.ErrBufferFull {
+			continue
+		}
+
+		br.skipped += len(line)
+
+		if err == io.EOF && br.isFinalBoundary(line) {
+			err = nil
+			br.closed = true
+			return
+		}
+
+		if err != nil {
+			return
+		}
+
+		if br.isBoundaryDelimiterLine(line) {
+			br.first = false
+			return
+		}
+
+		if br.isFinalBoundary(line) {
+			br.closed = true
+			return
+		}
+
+		if part != nil {
+			if _, err = part.Write(line); err != nil {
+				return
+			}
+		}
+
+		line = []byte{}
+	}
+}
+
+func (br *boundaryReader) isFinalBoundary(line []byte) bool {
+	if !bytes.HasPrefix(line, br.dashBoundaryDash) {
+		return false
+	}
+	rest := line[len(br.dashBoundaryDash):]
+	rest = skipLWSPChar(rest)
+	return len(rest) == 0 || bytes.Equal(rest, br.nl)
+}
+
+func (br *boundaryReader) isBoundaryDelimiterLine(line []byte) (ret bool) {
+	if !bytes.HasPrefix(line, br.dashBoundary) {
+		return false
+	}
+	rest := line[len(br.dashBoundary):]
+	rest = skipLWSPChar(rest)
+
+	if br.first && len(rest) == 1 && rest[0] == '\n' {
+		br.nl = br.nl[1:]
+		br.nlDashBoundary = br.nlDashBoundary[1:]
+	}
+	return bytes.Equal(rest, br.nl)
+}
+
+func skipLWSPChar(b []byte) []byte {
+	for len(b) > 0 && (b[0] == ' ' || b[0] == '\t') {
+		b = b[1:]
+	}
+	return b
+}