encoding/unicode/utf32/utf32.go - text - Git at Google

 // Copyright 2016 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 utf32 provides the UTF-32 Unicode encoding.
 //
 // Please note that support for UTF-32 is discouraged as it is a rare and
 // inefficient encoding, unfit for use as an interchange format. For use
 // on the web, the W3C strongly discourages its use
 // (https://www.w3.org/TR/html5/document-metadata.html#charset)
 // while WHATWG directly prohibits supporting it
 // (https://html.spec.whatwg.org/multipage/syntax.html#character-encodings).
 package utf32 // import "golang.org/x/text/encoding/unicode/utf32"

 import (
 	"errors"
 	"unicode/utf8"

 	"golang.org/x/text/encoding"
 	"golang.org/x/text/encoding/internal/identifier"
 	"golang.org/x/text/transform"
 )

 // All lists a configuration for each IANA-defined UTF-32 variant.
 var All = []encoding.Encoding{
 	UTF32(BigEndian, UseBOM),
 	UTF32(BigEndian, IgnoreBOM),
 	UTF32(LittleEndian, IgnoreBOM),
 }

 // ErrMissingBOM means that decoding UTF-32 input with ExpectBOM did not
 // find a starting byte order mark.
 var ErrMissingBOM = errors.New("encoding: missing byte order mark")

 // UTF32 returns a UTF-32 Encoding for the given default endianness and
 // byte order mark (BOM) policy.
 //
 // When decoding from UTF-32 to UTF-8, if the BOMPolicy is IgnoreBOM then
 // neither BOMs U+FEFF nor ill-formed code units 0xFFFE0000 in the input
 // stream will affect the endianness used for decoding. Instead BOMs will
 // be output as their standard UTF-8 encoding "\xef\xbb\xbf" while
 // 0xFFFE0000 code units will be output as "\xef\xbf\xbd", the standard
 // UTF-8 encoding for the Unicode replacement character. If the BOMPolicy
 // is UseBOM or ExpectBOM a starting 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 ill-formed code
 // units 0xFFFE0000 will not affect the endianness used, and will instead
 // be output as their standard UTF-8 (replacement) 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-32, 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-32 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 UTF32(e Endianness, b BOMPolicy) encoding.Encoding {
 	return utf32Encoding{config{e, b}, mibValue[e][b&bomMask]}
 }

 // mibValue maps Endianness and BOMPolicy settings to MIB constants for UTF-32.
 // Note that some configurations map to the same MIB identifier.
 var mibValue = map[Endianness][numBOMValues]identifier.MIB{
 	BigEndian: [numBOMValues]identifier.MIB{
 		IgnoreBOM: identifier.UTF32BE,
 		UseBOM:    identifier.UTF32,
 	},
 	LittleEndian: [numBOMValues]identifier.MIB{
 		IgnoreBOM: identifier.UTF32LE,
 		UseBOM:    identifier.UTF32,
 	},
 	// ExpectBOM is not widely used and has no valid MIB identifier.
 }

 // BOMPolicy is a UTF-32 encodings'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
 	// Unicode-compliant interpretation for UTF-32BE/LE.

 	// UseBOM means that the UTF-32 form may start with a byte order mark,
 	// which will be used to override the default encoding.
 	UseBOM BOMPolicy = writeBOM | acceptBOM
 	// Unicode-compliant interpretation for UTF-32.

 	// ExpectBOM means that the UTF-32 form must start with a byte order mark,
 	// which will be used to override the default encoding.
 	ExpectBOM BOMPolicy = writeBOM | acceptBOM | requireBOM
 	// Consistent with BOMPolicy definition in golang.org/x/text/encoding/unicode
 )

 // Endianness is a UTF-32 encoding's default endianness.
 type Endianness bool

 const (
 	// BigEndian is UTF-32BE.
 	BigEndian Endianness = false
 	// LittleEndian is UTF-32LE.
 	LittleEndian Endianness = true
 )

 type config struct {
 	endianness Endianness
 	bomPolicy  BOMPolicy
 }

 type utf32Encoding struct {
 	config
 	mib identifier.MIB
 }

 func (u utf32Encoding) NewDecoder() *encoding.Decoder {
 	return &encoding.Decoder{Transformer: &utf32Decoder{
 		initial: u.config,
 		current: u.config,
 	}}
 }

 func (u utf32Encoding) NewEncoder() *encoding.Encoder {
 	return &encoding.Encoder{Transformer: &utf32Encoder{
 		endianness:       u.endianness,
 		initialBOMPolicy: u.bomPolicy,
 		currentBOMPolicy: u.bomPolicy,
 	}}
 }

 func (u utf32Encoding) ID() (mib identifier.MIB, other string) {
 	return u.mib, ""
 }

 func (u utf32Encoding) 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-32" + e + "E (" + b + " BOM)"
 }

 type utf32Decoder struct {
 	initial config
 	current config
 }

 func (u *utf32Decoder) Reset() {
 	u.current = u.initial
 }

 func (u *utf32Decoder) 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) < 4 {
 			return 0, 0, transform.ErrShortSrc
 		}
 		switch {
 		case src[0] == 0x00 && src[1] == 0x00 && src[2] == 0xfe && src[3] == 0xff:
 			u.current.endianness = BigEndian
 			nSrc = 4
 		case src[0] == 0xff && src[1] == 0xfe && src[2] == 0x00 && src[3] == 0x00:
 			u.current.endianness = LittleEndian
 			nSrc = 4
 		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+3 < len(src) {
 			x := uint32(src[nSrc+0])<<24 | uint32(src[nSrc+1])<<16 |
 				uint32(src[nSrc+2])<<8 | uint32(src[nSrc+3])
 			if u.current.endianness == LittleEndian {
 				x = x>>24 | (x >> 8 & 0x0000FF00) | (x << 8 & 0x00FF0000) | x<<24
 			}
 			r, sSize = rune(x), 4
 			if dSize = utf8.RuneLen(r); dSize < 0 {
 				r, dSize = utf8.RuneError, 3
 			}
 		} else if atEOF {
 			// 1..3 trailing bytes.
 			r, dSize, sSize = utf8.RuneError, 3, len(src)-nSrc
 		} 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
 }

 type utf32Encoder struct {
 	endianness       Endianness
 	initialBOMPolicy BOMPolicy
 	currentBOMPolicy BOMPolicy
 }

 func (u *utf32Encoder) Reset() {
 	u.currentBOMPolicy = u.initialBOMPolicy
 }

 func (u *utf32Encoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
 	if u.currentBOMPolicy&writeBOM != 0 {
 		if len(dst) < 4 {
 			return 0, 0, transform.ErrShortDst
 		}
 		dst[0], dst[1], dst[2], dst[3] = 0x00, 0x00, 0xfe, 0xff
 		u.currentBOMPolicy = IgnoreBOM
 		nDst = 4
 	}

 	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 nDst+4 > len(dst) {
 			err = transform.ErrShortDst
 			break
 		}

 		dst[nDst+0] = uint8(r >> 24)
 		dst[nDst+1] = uint8(r >> 16)
 		dst[nDst+2] = uint8(r >> 8)
 		dst[nDst+3] = uint8(r)
 		nDst += 4
 		nSrc += size
 	}

 	if u.endianness == LittleEndian {
 		for i := 0; i < nDst; i += 4 {
 			dst[i], dst[i+1], dst[i+2], dst[i+3] = dst[i+3], dst[i+2], dst[i+1], dst[i]
 		}
 	}
 	return nDst, nSrc, err
 }
	// Copyright 2016 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 utf32 provides the UTF-32 Unicode encoding.
	//
	// Please note that support for UTF-32 is discouraged as it is a rare and
	// inefficient encoding, unfit for use as an interchange format. For use
	// on the web, the W3C strongly discourages its use
	// (https://www.w3.org/TR/html5/document-metadata.html#charset)
	// while WHATWG directly prohibits supporting it
	// (https://html.spec.whatwg.org/multipage/syntax.html#character-encodings).
	package utf32 // import "golang.org/x/text/encoding/unicode/utf32"

	import (
	"errors"
	"unicode/utf8"

	"golang.org/x/text/encoding"
	"golang.org/x/text/encoding/internal/identifier"
	"golang.org/x/text/transform"
	)

	// All lists a configuration for each IANA-defined UTF-32 variant.
	var All = []encoding.Encoding{
	UTF32(BigEndian, UseBOM),
	UTF32(BigEndian, IgnoreBOM),
	UTF32(LittleEndian, IgnoreBOM),
	}

	// ErrMissingBOM means that decoding UTF-32 input with ExpectBOM did not
	// find a starting byte order mark.
	var ErrMissingBOM = errors.New("encoding: missing byte order mark")

	// UTF32 returns a UTF-32 Encoding for the given default endianness and
	// byte order mark (BOM) policy.
	//
	// When decoding from UTF-32 to UTF-8, if the BOMPolicy is IgnoreBOM then
	// neither BOMs U+FEFF nor ill-formed code units 0xFFFE0000 in the input
	// stream will affect the endianness used for decoding. Instead BOMs will
	// be output as their standard UTF-8 encoding "\xef\xbb\xbf" while
	// 0xFFFE0000 code units will be output as "\xef\xbf\xbd", the standard
	// UTF-8 encoding for the Unicode replacement character. If the BOMPolicy
	// is UseBOM or ExpectBOM a starting 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 ill-formed code
	// units 0xFFFE0000 will not affect the endianness used, and will instead
	// be output as their standard UTF-8 (replacement) 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-32, 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-32 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 UTF32(e Endianness, b BOMPolicy) encoding.Encoding {
	return utf32Encoding{config{e, b}, mibValue[e][b&bomMask]}
	}

	// mibValue maps Endianness and BOMPolicy settings to MIB constants for UTF-32.
	// Note that some configurations map to the same MIB identifier.
	var mibValue = map[Endianness][numBOMValues]identifier.MIB{
	BigEndian: [numBOMValues]identifier.MIB{
	IgnoreBOM: identifier.UTF32BE,
	UseBOM: identifier.UTF32,
	},
	LittleEndian: [numBOMValues]identifier.MIB{
	IgnoreBOM: identifier.UTF32LE,
	UseBOM: identifier.UTF32,
	},
	// ExpectBOM is not widely used and has no valid MIB identifier.
	}

	// BOMPolicy is a UTF-32 encodings'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
	// Unicode-compliant interpretation for UTF-32BE/LE.

	// UseBOM means that the UTF-32 form may start with a byte order mark,
	// which will be used to override the default encoding.
	UseBOM BOMPolicy = writeBOM \| acceptBOM
	// Unicode-compliant interpretation for UTF-32.

	// ExpectBOM means that the UTF-32 form must start with a byte order mark,
	// which will be used to override the default encoding.
	ExpectBOM BOMPolicy = writeBOM \| acceptBOM \| requireBOM
	// Consistent with BOMPolicy definition in golang.org/x/text/encoding/unicode
	)

	// Endianness is a UTF-32 encoding's default endianness.
	type Endianness bool

	const (
	// BigEndian is UTF-32BE.
	BigEndian Endianness = false
	// LittleEndian is UTF-32LE.
	LittleEndian Endianness = true
	)

	type config struct {
	endianness Endianness
	bomPolicy BOMPolicy
	}

	type utf32Encoding struct {
	config
	mib identifier.MIB
	}

	func (u utf32Encoding) NewDecoder() *encoding.Decoder {
	return &encoding.Decoder{Transformer: &utf32Decoder{
	initial: u.config,
	current: u.config,
	}}
	}

	func (u utf32Encoding) NewEncoder() *encoding.Encoder {
	return &encoding.Encoder{Transformer: &utf32Encoder{
	endianness: u.endianness,
	initialBOMPolicy: u.bomPolicy,
	currentBOMPolicy: u.bomPolicy,
	}}
	}

	func (u utf32Encoding) ID() (mib identifier.MIB, other string) {
	return u.mib, ""
	}

	func (u utf32Encoding) 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-32" + e + "E (" + b + " BOM)"
	}

	type utf32Decoder struct {
	initial config
	current config
	}

	func (u *utf32Decoder) Reset() {
	u.current = u.initial
	}

	func (u *utf32Decoder) 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) < 4 {
	return 0, 0, transform.ErrShortSrc
	}
	switch {
	case src[0] == 0x00 && src[1] == 0x00 && src[2] == 0xfe && src[3] == 0xff:
	u.current.endianness = BigEndian
	nSrc = 4
	case src[0] == 0xff && src[1] == 0xfe && src[2] == 0x00 && src[3] == 0x00:
	u.current.endianness = LittleEndian
	nSrc = 4
	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+3 < len(src) {
	x := uint32(src[nSrc+0])<<24 \| uint32(src[nSrc+1])<<16 \|
	uint32(src[nSrc+2])<<8 \| uint32(src[nSrc+3])
	if u.current.endianness == LittleEndian {
	x = x>>24 \| (x >> 8 & 0x0000FF00) \| (x << 8 & 0x00FF0000) \| x<<24
	}
	r, sSize = rune(x), 4
	if dSize = utf8.RuneLen(r); dSize < 0 {
	r, dSize = utf8.RuneError, 3
	}
	} else if atEOF {
	// 1..3 trailing bytes.
	r, dSize, sSize = utf8.RuneError, 3, len(src)-nSrc
	} 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
	}

	type utf32Encoder struct {
	endianness Endianness
	initialBOMPolicy BOMPolicy
	currentBOMPolicy BOMPolicy
	}

	func (u *utf32Encoder) Reset() {
	u.currentBOMPolicy = u.initialBOMPolicy
	}

	func (u *utf32Encoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
	if u.currentBOMPolicy&writeBOM != 0 {
	if len(dst) < 4 {
	return 0, 0, transform.ErrShortDst
	}
	dst[0], dst[1], dst[2], dst[3] = 0x00, 0x00, 0xfe, 0xff
	u.currentBOMPolicy = IgnoreBOM
	nDst = 4
	}

	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 nDst+4 > len(dst) {
	err = transform.ErrShortDst
	break
	}

	dst[nDst+0] = uint8(r >> 24)
	dst[nDst+1] = uint8(r >> 16)
	dst[nDst+2] = uint8(r >> 8)
	dst[nDst+3] = uint8(r)
	nDst += 4
	nSrc += size
	}

	if u.endianness == LittleEndian {
	for i := 0; i < nDst; i += 4 {
	dst[i], dst[i+1], dst[i+2], dst[i+3] = dst[i+3], dst[i+2], dst[i+1], dst[i]
	}
	}
	return nDst, nSrc, err
	}