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// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package quotedprintable
import "io"
const lineMaxLen = 76
// A Writer is a quoted-printable writer that implements io.WriteCloser.
type Writer struct {
// Binary mode treats the writer's input as pure binary and processes end of
// line bytes as binary data.
Binary bool
w io.Writer
i int
line [78]byte
cr bool
}
// NewWriter returns a new Writer that writes to w.
func NewWriter(w io.Writer) *Writer {
return &Writer{w: w}
}
// Write encodes p using quoted-printable encoding and writes it to the
// underlying io.Writer. It limits line length to 76 characters. The encoded
// bytes are not necessarily flushed until the Writer is closed.
func (w *Writer) Write(p []byte) (n int, err error) {
for i, b := range p {
switch {
// Simple writes are done in batch.
case b >= '!' && b <= '~' && b != '=':
continue
case isWhitespace(b) || !w.Binary && (b == '\n' || b == '\r'):
continue
}
if i > n {
if err := w.write(p[n:i]); err != nil {
return n, err
}
n = i
}
if err := w.encode(b); err != nil {
return n, err
}
n++
}
if n == len(p) {
return n, nil
}
if err := w.write(p[n:]); err != nil {
return n, err
}
return len(p), nil
}
// Close closes the Writer, flushing any unwritten data to the underlying
// io.Writer, but does not close the underlying io.Writer.
func (w *Writer) Close() error {
if err := w.checkLastByte(); err != nil {
return err
}
return w.flush()
}
// write limits text encoded in quoted-printable to 76 characters per line.
func (w *Writer) write(p []byte) error {
for _, b := range p {
if b == '\n' || b == '\r' {
// If the previous byte was \r, the CRLF has already been inserted.
if w.cr && b == '\n' {
w.cr = false
continue
}
if b == '\r' {
w.cr = true
}
if err := w.checkLastByte(); err != nil {
return err
}
if err := w.insertCRLF(); err != nil {
return err
}
continue
}
if w.i == lineMaxLen-1 {
if err := w.insertSoftLineBreak(); err != nil {
return err
}
}
w.line[w.i] = b
w.i++
w.cr = false
}
return nil
}
func (w *Writer) encode(b byte) error {
if lineMaxLen-1-w.i < 3 {
if err := w.insertSoftLineBreak(); err != nil {
return err
}
}
w.line[w.i] = '='
w.line[w.i+1] = upperhex[b>>4]
w.line[w.i+2] = upperhex[b&0x0f]
w.i += 3
return nil
}
const upperhex = "0123456789ABCDEF"
// checkLastByte encodes the last buffered byte if it is a space or a tab.
func (w *Writer) checkLastByte() error {
if w.i == 0 {
return nil
}
b := w.line[w.i-1]
if isWhitespace(b) {
w.i--
if err := w.encode(b); err != nil {
return err
}
}
return nil
}
func (w *Writer) insertSoftLineBreak() error {
w.line[w.i] = '='
w.i++
return w.insertCRLF()
}
func (w *Writer) insertCRLF() error {
w.line[w.i] = '\r'
w.line[w.i+1] = '\n'
w.i += 2
return w.flush()
}
func (w *Writer) flush() error {
if _, err := w.w.Write(w.line[:w.i]); err != nil {
return err
}
w.i = 0
return nil
}
func isWhitespace(b byte) bool {
return b == ' ' || b == '\t'
}
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