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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 unicode provides Unicode encodings such as UTF-16.
package unicode // import "golang.org/x/text/encoding/unicode"
import (
"errors"
"unicode/utf16"
"unicode/utf8"
"golang.org/x/text/encoding"
"golang.org/x/text/encoding/internal"
"golang.org/x/text/encoding/internal/identifier"
"golang.org/x/text/internal/utf8internal"
"golang.org/x/text/runes"
"golang.org/x/text/transform"
)
// TODO: I think the Transformers really should return errors on unmatched
// surrogate pairs and odd numbers of bytes. This is not required by RFC 2781,
// which leaves it open, but is suggested by WhatWG. It will allow for all error
// modes as defined by WhatWG: fatal, HTML and Replacement. This would require
// the introduction of some kind of error type for conveying the erroneous code
// point.
// UTF8 is the UTF-8 encoding.
var UTF8 encoding.Encoding = utf8enc
var utf8enc = &internal.Encoding{
&internal.SimpleEncoding{utf8Decoder{}, runes.ReplaceIllFormed()},
"UTF-8",
identifier.UTF8,
}
type utf8Decoder struct{ transform.NopResetter }
func (utf8Decoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
var pSrc int // point from which to start copy in src
var accept utf8internal.AcceptRange
// The decoder can only make the input larger, not smaller.
n := len(src)
if len(dst) < n {
err = transform.ErrShortDst
n = len(dst)
atEOF = false
}
for nSrc < n {
c := src[nSrc]
if c < utf8.RuneSelf {
nSrc++
continue
}
first := utf8internal.First[c]
size := int(first & utf8internal.SizeMask)
if first == utf8internal.FirstInvalid {
goto handleInvalid // invalid starter byte
}
accept = utf8internal.AcceptRanges[first>>utf8internal.AcceptShift]
if nSrc+size > n {
if !atEOF {
// We may stop earlier than necessary here if the short sequence
// has invalid bytes. Not checking for this simplifies the code
// and may avoid duplicate computations in certain conditions.
if err == nil {
err = transform.ErrShortSrc
}
break
}
// Determine the maximal subpart of an ill-formed subsequence.
switch {
case nSrc+1 >= n || src[nSrc+1] < accept.Lo || accept.Hi < src[nSrc+1]:
size = 1
case nSrc+2 >= n || src[nSrc+2] < utf8internal.LoCB || utf8internal.HiCB < src[nSrc+2]:
size = 2
default:
size = 3 // As we are short, the maximum is 3.
}
goto handleInvalid
}
if c = src[nSrc+1]; c < accept.Lo || accept.Hi < c {
size = 1
goto handleInvalid // invalid continuation byte
} else if size == 2 {
} else if c = src[nSrc+2]; c < utf8internal.LoCB || utf8internal.HiCB < c {
size = 2
goto handleInvalid // invalid continuation byte
} else if size == 3 {
} else if c = src[nSrc+3]; c < utf8internal.LoCB || utf8internal.HiCB < c {
size = 3
goto handleInvalid // invalid continuation byte
}
nSrc += size
continue
handleInvalid:
// Copy the scanned input so far.
nDst += copy(dst[nDst:], src[pSrc:nSrc])
// Append RuneError to the destination.
const runeError = "\ufffd"
if nDst+len(runeError) > len(dst) {
return nDst, nSrc, transform.ErrShortDst
}
nDst += copy(dst[nDst:], runeError)
// Skip the maximal subpart of an ill-formed subsequence according to
// the W3C standard way instead of the Go way. This Transform is
// probably the only place in the text repo where it is warranted.
nSrc += size
pSrc = nSrc
// Recompute the maximum source length.
if sz := len(dst) - nDst; sz < len(src)-nSrc {
err = transform.ErrShortDst
n = nSrc + sz
atEOF = false
}
}
return nDst + copy(dst[nDst:], src[pSrc:nSrc]), nSrc, err
}
// UTF16 returns a UTF-16 Encoding for the given default endianness and byte
// order mark (BOM) policy.
//
// When decoding from UTF-16 to UTF-8, if the BOMPolicy is IgnoreBOM then
// neither BOMs U+FEFF nor noncharacters U+FFFE in the input stream will affect
// the endianness used for decoding, and will instead be output as their
// standard UTF-8 encodings: "\xef\xbb\xbf" and "\xef\xbf\xbe". If the BOMPolicy
// is UseBOM or ExpectBOM a staring BOM is not written to the UTF-8 output.
// Instead, it overrides the default endianness e for the remainder of the
// transformation. Any subsequent BOMs U+FEFF or noncharacters U+FFFE will not
// affect the endianness used, and will instead be output as their standard
// UTF-8 encodings. For UseBOM, if there is no starting BOM, it will proceed
// with the default Endianness. For ExpectBOM, in that case, the transformation
// will return early with an ErrMissingBOM error.
//
// When encoding from UTF-8 to UTF-16, a BOM will be inserted at the start of
// the output if the BOMPolicy is UseBOM or ExpectBOM. Otherwise, a BOM will not
// be inserted. The UTF-8 input does not need to contain a BOM.
//
// There is no concept of a 'native' endianness. If the UTF-16 data is produced
// and consumed in a greater context that implies a certain endianness, use
// IgnoreBOM. Otherwise, use ExpectBOM and always produce and consume a BOM.
//
// In the language of https://www.unicode.org/faq/utf_bom.html#bom10, IgnoreBOM
// corresponds to "Where the precise type of the data stream is known... the
// BOM should not be used" and ExpectBOM corresponds to "A particular
// protocol... may require use of the BOM".
func UTF16(e Endianness, b BOMPolicy) encoding.Encoding {
return utf16Encoding{config{e, b}, mibValue[e][b&bomMask]}
}
// mibValue maps Endianness and BOMPolicy settings to MIB constants. Note that
// some configurations map to the same MIB identifier. RFC 2781 has requirements
// and recommendations. Some of the "configurations" are merely recommendations,
// so multiple configurations could match.
var mibValue = map[Endianness][numBOMValues]identifier.MIB{
BigEndian: [numBOMValues]identifier.MIB{
IgnoreBOM: identifier.UTF16BE,
UseBOM: identifier.UTF16, // BigEnding default is preferred by RFC 2781.
// TODO: acceptBOM | strictBOM would map to UTF16BE as well.
},
LittleEndian: [numBOMValues]identifier.MIB{
IgnoreBOM: identifier.UTF16LE,
UseBOM: identifier.UTF16, // LittleEndian default is allowed and preferred on Windows.
// TODO: acceptBOM | strictBOM would map to UTF16LE as well.
},
// ExpectBOM is not widely used and has no valid MIB identifier.
}
// All lists a configuration for each IANA-defined UTF-16 variant.
var All = []encoding.Encoding{
UTF8,
UTF16(BigEndian, UseBOM),
UTF16(BigEndian, IgnoreBOM),
UTF16(LittleEndian, IgnoreBOM),
}
// BOMPolicy is a UTF-16 encoding's byte order mark policy.
type BOMPolicy uint8
const (
writeBOM BOMPolicy = 0x01
acceptBOM BOMPolicy = 0x02
requireBOM BOMPolicy = 0x04
bomMask BOMPolicy = 0x07
// HACK: numBOMValues == 8 triggers a bug in the 1.4 compiler (cannot have a
// map of an array of length 8 of a type that is also used as a key or value
// in another map). See golang.org/issue/11354.
// TODO: consider changing this value back to 8 if the use of 1.4.* has
// been minimized.
numBOMValues = 8 + 1
// IgnoreBOM means to ignore any byte order marks.
IgnoreBOM BOMPolicy = 0
// Common and RFC 2781-compliant interpretation for UTF-16BE/LE.
// UseBOM means that the UTF-16 form may start with a byte order mark, which
// will be used to override the default encoding.
UseBOM BOMPolicy = writeBOM | acceptBOM
// Common and RFC 2781-compliant interpretation for UTF-16.
// ExpectBOM means that the UTF-16 form must start with a byte order mark,
// which will be used to override the default encoding.
ExpectBOM BOMPolicy = writeBOM | acceptBOM | requireBOM
// Used in Java as Unicode (not to be confused with Java's UTF-16) and
// ICU's UTF-16,version=1. Not compliant with RFC 2781.
// TODO (maybe): strictBOM: BOM must match Endianness. This would allow:
// - UTF-16(B|L)E,version=1: writeBOM | acceptBOM | requireBOM | strictBOM
// (UnicodeBig and UnicodeLittle in Java)
// - RFC 2781-compliant, but less common interpretation for UTF-16(B|L)E:
// acceptBOM | strictBOM (e.g. assigned to CheckBOM).
// This addition would be consistent with supporting ExpectBOM.
)
// Endianness is a UTF-16 encoding's default endianness.
type Endianness bool
const (
// BigEndian is UTF-16BE.
BigEndian Endianness = false
// LittleEndian is UTF-16LE.
LittleEndian Endianness = true
)
// ErrMissingBOM means that decoding UTF-16 input with ExpectBOM did not find a
// starting byte order mark.
var ErrMissingBOM = errors.New("encoding: missing byte order mark")
type utf16Encoding struct {
config
mib identifier.MIB
}
type config struct {
endianness Endianness
bomPolicy BOMPolicy
}
func (u utf16Encoding) NewDecoder() *encoding.Decoder {
return &encoding.Decoder{Transformer: &utf16Decoder{
initial: u.config,
current: u.config,
}}
}
func (u utf16Encoding) NewEncoder() *encoding.Encoder {
return &encoding.Encoder{Transformer: &utf16Encoder{
endianness: u.endianness,
initialBOMPolicy: u.bomPolicy,
currentBOMPolicy: u.bomPolicy,
}}
}
func (u utf16Encoding) ID() (mib identifier.MIB, other string) {
return u.mib, ""
}
func (u utf16Encoding) String() string {
e, b := "B", ""
if u.endianness == LittleEndian {
e = "L"
}
switch u.bomPolicy {
case ExpectBOM:
b = "Expect"
case UseBOM:
b = "Use"
case IgnoreBOM:
b = "Ignore"
}
return "UTF-16" + e + "E (" + b + " BOM)"
}
type utf16Decoder struct {
initial config
current config
}
func (u *utf16Decoder) Reset() {
u.current = u.initial
}
func (u *utf16Decoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
if len(src) == 0 {
if atEOF && u.current.bomPolicy&requireBOM != 0 {
return 0, 0, ErrMissingBOM
}
return 0, 0, nil
}
if u.current.bomPolicy&acceptBOM != 0 {
if len(src) < 2 {
return 0, 0, transform.ErrShortSrc
}
switch {
case src[0] == 0xfe && src[1] == 0xff:
u.current.endianness = BigEndian
nSrc = 2
case src[0] == 0xff && src[1] == 0xfe:
u.current.endianness = LittleEndian
nSrc = 2
default:
if u.current.bomPolicy&requireBOM != 0 {
return 0, 0, ErrMissingBOM
}
}
u.current.bomPolicy = IgnoreBOM
}
var r rune
var dSize, sSize int
for nSrc < len(src) {
if nSrc+1 < len(src) {
x := uint16(src[nSrc+0])<<8 | uint16(src[nSrc+1])
if u.current.endianness == LittleEndian {
x = x>>8 | x<<8
}
r, sSize = rune(x), 2
if utf16.IsSurrogate(r) {
if nSrc+3 < len(src) {
x = uint16(src[nSrc+2])<<8 | uint16(src[nSrc+3])
if u.current.endianness == LittleEndian {
x = x>>8 | x<<8
}
// Save for next iteration if it is not a high surrogate.
if isHighSurrogate(rune(x)) {
r, sSize = utf16.DecodeRune(r, rune(x)), 4
}
} else if !atEOF {
err = transform.ErrShortSrc
break
}
}
if dSize = utf8.RuneLen(r); dSize < 0 {
r, dSize = utf8.RuneError, 3
}
} else if atEOF {
// Single trailing byte.
r, dSize, sSize = utf8.RuneError, 3, 1
} else {
err = transform.ErrShortSrc
break
}
if nDst+dSize > len(dst) {
err = transform.ErrShortDst
break
}
nDst += utf8.EncodeRune(dst[nDst:], r)
nSrc += sSize
}
return nDst, nSrc, err
}
func isHighSurrogate(r rune) bool {
return 0xDC00 <= r && r <= 0xDFFF
}
type utf16Encoder struct {
endianness Endianness
initialBOMPolicy BOMPolicy
currentBOMPolicy BOMPolicy
}
func (u *utf16Encoder) Reset() {
u.currentBOMPolicy = u.initialBOMPolicy
}
func (u *utf16Encoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
if u.currentBOMPolicy&writeBOM != 0 {
if len(dst) < 2 {
return 0, 0, transform.ErrShortDst
}
dst[0], dst[1] = 0xfe, 0xff
u.currentBOMPolicy = IgnoreBOM
nDst = 2
}
r, size := rune(0), 0
for nSrc < len(src) {
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
}
}
}
if r <= 0xffff {
if nDst+2 > len(dst) {
err = transform.ErrShortDst
break
}
dst[nDst+0] = uint8(r >> 8)
dst[nDst+1] = uint8(r)
nDst += 2
} else {
if nDst+4 > len(dst) {
err = transform.ErrShortDst
break
}
r1, r2 := utf16.EncodeRune(r)
dst[nDst+0] = uint8(r1 >> 8)
dst[nDst+1] = uint8(r1)
dst[nDst+2] = uint8(r2 >> 8)
dst[nDst+3] = uint8(r2)
nDst += 4
}
nSrc += size
}
if u.endianness == LittleEndian {
for i := 0; i < nDst; i += 2 {
dst[i], dst[i+1] = dst[i+1], dst[i]
}
}
return nDst, nSrc, err
}
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