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// Copyright 2013 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 encoding defines an interface for character encodings, such as Shift
// JIS and Windows 1252, that can convert to and from UTF-8.
//
// To convert the bytes of an io.Reader r from the encoding e to UTF-8:
// rInUTF8 := transform.NewReader(r, e.NewDecoder())
// and to convert from UTF-8 to the encoding e:
// wInUTF8 := transform.NewWriter(w, e.NewEncoder())
// In both cases, import "golang.org/x/text/transform".
//
// Encoding implementations are provided in other packages, such as
// golang.org/x/text/encoding/charmap and
// golang.org/x/text/encoding/japanese.
package encoding
import (
"errors"
"unicode/utf8"
"golang.org/x/text/transform"
)
// Encoding is a character set encoding that can be transformed to and from
// UTF-8.
type Encoding interface {
// NewDecoder returns a transformer that converts to UTF-8.
//
// Transforming source bytes that are not of that encoding will not
// result in an error per se. Each byte that cannot be transcoded will
// be represented in the output by the UTF-8 encoding of '\uFFFD', the
// replacement rune.
NewDecoder() transform.Transformer
// NewEncoder returns a transformer that converts from UTF-8.
//
// Transforming source bytes that are not valid UTF-8 will not result in
// an error per se. Each rune that cannot be transcoded will be
// represented in the output by an encoding-specific replacement such as
// "\x1a" (the ASCII substitute character) or "\xff\xfd". To return
// early with error instead, use transform.Chain to preprocess the data
// with a UTF8Validator.
NewEncoder() transform.Transformer
}
// ASCIISub is the ASCII substitute character, as recommended by
// http://unicode.org/reports/tr36/#Text_Comparison
const ASCIISub = '\x1a'
// Nop is the nop encoding. Its transformed bytes are the same as the source
// bytes; it does not replace invalid UTF-8 sequences.
var Nop Encoding = nop{}
type nop struct{}
func (nop) NewDecoder() transform.Transformer {
return transform.Nop
}
func (nop) NewEncoder() transform.Transformer {
return transform.Nop
}
// Replacement is the replacement encoding. Decoding from the replacement
// encoding yields a single '\uFFFD' replacement rune. Encoding from UTF-8 to
// the replacement encoding yields the same as the source bytes except that
// invalid UTF-8 is converted to '\uFFFD'.
//
// It is defined at http://encoding.spec.whatwg.org/#replacement
var Replacement Encoding = replacement{}
type replacement struct{}
func (replacement) NewDecoder() transform.Transformer {
return replacementDecoder{}
}
func (replacement) NewEncoder() transform.Transformer {
return replacementEncoder{}
}
type replacementDecoder struct{ transform.NopResetter }
func (replacementDecoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
if len(dst) < 3 {
return 0, 0, transform.ErrShortDst
}
if atEOF {
const fffd = "\ufffd"
dst[0] = fffd[0]
dst[1] = fffd[1]
dst[2] = fffd[2]
nDst = 3
}
return nDst, len(src), nil
}
type replacementEncoder struct{ transform.NopResetter }
func (replacementEncoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
r, size := rune(0), 0
for ; nSrc < len(src); nSrc += size {
r = rune(src[nSrc])
// Decode a 1-byte rune.
if r < utf8.RuneSelf {
size = 1
} else {
// Decode a multi-byte rune.
r, size = utf8.DecodeRune(src[nSrc:])
if size == 1 {
// All valid runes of size 1 (those below utf8.RuneSelf) were
// handled above. We have invalid UTF-8 or we haven't seen the
// full character yet.
if !atEOF && !utf8.FullRune(src[nSrc:]) {
err = transform.ErrShortSrc
break
}
r = '\ufffd'
}
}
if nDst+utf8.RuneLen(r) > len(dst) {
err = transform.ErrShortDst
break
}
nDst += utf8.EncodeRune(dst[nDst:], r)
}
return nDst, nSrc, err
}
// ErrInvalidUTF8 means that a transformer encountered invalid UTF-8.
var ErrInvalidUTF8 = errors.New("encoding: invalid UTF-8")
// UTF8Validator is a transformer that returns ErrInvalidUTF8 on the first
// input byte that is not valid UTF-8.
var UTF8Validator transform.Transformer = utf8Validator{}
type utf8Validator struct{ transform.NopResetter }
func (utf8Validator) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
n := len(src)
if n > len(dst) {
n = len(dst)
}
for i := 0; i < n; {
if c := src[i]; c < utf8.RuneSelf {
dst[i] = c
i++
continue
}
_, size := utf8.DecodeRune(src[i:])
if size == 1 {
// All valid runes of size 1 (those below utf8.RuneSelf) were
// handled above. We have invalid UTF-8 or we haven't seen the
// full character yet.
err = ErrInvalidUTF8
if !atEOF && !utf8.FullRune(src[i:]) {
err = transform.ErrShortSrc
}
return i, i, err
}
if i+size > len(dst) {
return i, i, transform.ErrShortDst
}
for ; size > 0; size-- {
dst[i] = src[i]
i++
}
}
if len(src) > len(dst) {
err = transform.ErrShortDst
}
return n, n, err
}
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