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// Copyright 2010 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 textproto
import (
"bufio"
"fmt"
"io"
)
// A Writer implements convenience methods for writing
// requests or responses to a text protocol network connection.
type Writer struct {
W *bufio.Writer
dot *dotWriter
}
// NewWriter returns a new [Writer] writing to w.
func NewWriter(w *bufio.Writer) *Writer {
return &Writer{W: w}
}
var crnl = []byte{'\r', '\n'}
var dotcrnl = []byte{'.', '\r', '\n'}
// PrintfLine writes the formatted output followed by \r\n.
func (w *Writer) PrintfLine(format string, args ...any) error {
w.closeDot()
fmt.Fprintf(w.W, format, args...)
w.W.Write(crnl)
return w.W.Flush()
}
// DotWriter returns a writer that can be used to write a dot-encoding to w.
// It takes care of inserting leading dots when necessary,
// translating line-ending \n into \r\n, and adding the final .\r\n line
// when the DotWriter is closed. The caller should close the
// DotWriter before the next call to a method on w.
//
// See the documentation for the [Reader.DotReader] method for details about dot-encoding.
func (w *Writer) DotWriter() io.WriteCloser {
w.closeDot()
w.dot = &dotWriter{w: w}
return w.dot
}
func (w *Writer) closeDot() {
if w.dot != nil {
w.dot.Close() // sets w.dot = nil
}
}
type dotWriter struct {
w *Writer
state int
}
const (
wstateBegin = iota // initial state; must be zero
wstateBeginLine // beginning of line
wstateCR // wrote \r (possibly at end of line)
wstateData // writing data in middle of line
)
func (d *dotWriter) Write(b []byte) (n int, err error) {
bw := d.w.W
for n < len(b) {
c := b[n]
switch d.state {
case wstateBegin, wstateBeginLine:
d.state = wstateData
if c == '.' {
// escape leading dot
bw.WriteByte('.')
}
fallthrough
case wstateData:
if c == '\r' {
d.state = wstateCR
}
if c == '\n' {
bw.WriteByte('\r')
d.state = wstateBeginLine
}
case wstateCR:
d.state = wstateData
if c == '\n' {
d.state = wstateBeginLine
}
}
if err = bw.WriteByte(c); err != nil {
break
}
n++
}
return
}
func (d *dotWriter) Close() error {
if d.w.dot == d {
d.w.dot = nil
}
bw := d.w.W
switch d.state {
default:
bw.WriteByte('\r')
fallthrough
case wstateCR:
bw.WriteByte('\n')
fallthrough
case wstateBeginLine:
bw.Write(dotcrnl)
}
return bw.Flush()
}
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