434 lines
13 KiB
Go
434 lines
13 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package unicode provides Unicode encodings such as UTF-16.
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package unicode // import "golang.org/x/text/encoding/unicode"
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import (
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"errors"
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"unicode/utf16"
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"unicode/utf8"
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"golang.org/x/text/encoding"
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"golang.org/x/text/encoding/internal"
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"golang.org/x/text/encoding/internal/identifier"
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"golang.org/x/text/internal/utf8internal"
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"golang.org/x/text/runes"
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"golang.org/x/text/transform"
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)
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// TODO: I think the Transformers really should return errors on unmatched
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// surrogate pairs and odd numbers of bytes. This is not required by RFC 2781,
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// which leaves it open, but is suggested by WhatWG. It will allow for all error
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// modes as defined by WhatWG: fatal, HTML and Replacement. This would require
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// the introduction of some kind of error type for conveying the erroneous code
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// point.
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// UTF8 is the UTF-8 encoding.
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var UTF8 encoding.Encoding = utf8enc
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var utf8enc = &internal.Encoding{
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&internal.SimpleEncoding{utf8Decoder{}, runes.ReplaceIllFormed()},
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"UTF-8",
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identifier.UTF8,
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}
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type utf8Decoder struct{ transform.NopResetter }
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func (utf8Decoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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var pSrc int // point from which to start copy in src
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var accept utf8internal.AcceptRange
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// The decoder can only make the input larger, not smaller.
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n := len(src)
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if len(dst) < n {
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err = transform.ErrShortDst
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n = len(dst)
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atEOF = false
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}
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for nSrc < n {
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c := src[nSrc]
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if c < utf8.RuneSelf {
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nSrc++
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continue
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}
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first := utf8internal.First[c]
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size := int(first & utf8internal.SizeMask)
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if first == utf8internal.FirstInvalid {
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goto handleInvalid // invalid starter byte
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}
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accept = utf8internal.AcceptRanges[first>>utf8internal.AcceptShift]
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if nSrc+size > n {
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if !atEOF {
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// We may stop earlier than necessary here if the short sequence
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// has invalid bytes. Not checking for this simplifies the code
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// and may avoid duplicate computations in certain conditions.
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if err == nil {
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err = transform.ErrShortSrc
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}
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break
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}
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// Determine the maximal subpart of an ill-formed subsequence.
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switch {
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case nSrc+1 >= n || src[nSrc+1] < accept.Lo || accept.Hi < src[nSrc+1]:
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size = 1
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case nSrc+2 >= n || src[nSrc+2] < utf8internal.LoCB || utf8internal.HiCB < src[nSrc+2]:
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size = 2
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default:
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size = 3 // As we are short, the maximum is 3.
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}
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goto handleInvalid
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}
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if c = src[nSrc+1]; c < accept.Lo || accept.Hi < c {
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size = 1
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goto handleInvalid // invalid continuation byte
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} else if size == 2 {
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} else if c = src[nSrc+2]; c < utf8internal.LoCB || utf8internal.HiCB < c {
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size = 2
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goto handleInvalid // invalid continuation byte
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} else if size == 3 {
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} else if c = src[nSrc+3]; c < utf8internal.LoCB || utf8internal.HiCB < c {
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size = 3
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goto handleInvalid // invalid continuation byte
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}
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nSrc += size
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continue
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handleInvalid:
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// Copy the scanned input so far.
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nDst += copy(dst[nDst:], src[pSrc:nSrc])
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// Append RuneError to the destination.
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const runeError = "\ufffd"
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if nDst+len(runeError) > len(dst) {
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return nDst, nSrc, transform.ErrShortDst
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}
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nDst += copy(dst[nDst:], runeError)
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// Skip the maximal subpart of an ill-formed subsequence according to
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// the W3C standard way instead of the Go way. This Transform is
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// probably the only place in the text repo where it is warranted.
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nSrc += size
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pSrc = nSrc
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// Recompute the maximum source length.
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if sz := len(dst) - nDst; sz < len(src)-nSrc {
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err = transform.ErrShortDst
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n = nSrc + sz
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atEOF = false
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}
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}
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return nDst + copy(dst[nDst:], src[pSrc:nSrc]), nSrc, err
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}
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// UTF16 returns a UTF-16 Encoding for the given default endianness and byte
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// order mark (BOM) policy.
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//
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// When decoding from UTF-16 to UTF-8, if the BOMPolicy is IgnoreBOM then
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// neither BOMs U+FEFF nor noncharacters U+FFFE in the input stream will affect
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// the endianness used for decoding, and will instead be output as their
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// standard UTF-8 encodings: "\xef\xbb\xbf" and "\xef\xbf\xbe". If the BOMPolicy
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// is UseBOM or ExpectBOM a staring BOM is not written to the UTF-8 output.
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// Instead, it overrides the default endianness e for the remainder of the
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// transformation. Any subsequent BOMs U+FEFF or noncharacters U+FFFE will not
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// affect the endianness used, and will instead be output as their standard
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// UTF-8 encodings. For UseBOM, if there is no starting BOM, it will proceed
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// with the default Endianness. For ExpectBOM, in that case, the transformation
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// will return early with an ErrMissingBOM error.
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//
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// When encoding from UTF-8 to UTF-16, a BOM will be inserted at the start of
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// the output if the BOMPolicy is UseBOM or ExpectBOM. Otherwise, a BOM will not
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// be inserted. The UTF-8 input does not need to contain a BOM.
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//
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// There is no concept of a 'native' endianness. If the UTF-16 data is produced
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// and consumed in a greater context that implies a certain endianness, use
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// IgnoreBOM. Otherwise, use ExpectBOM and always produce and consume a BOM.
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//
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// In the language of https://www.unicode.org/faq/utf_bom.html#bom10, IgnoreBOM
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// corresponds to "Where the precise type of the data stream is known... the
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// BOM should not be used" and ExpectBOM corresponds to "A particular
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// protocol... may require use of the BOM".
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func UTF16(e Endianness, b BOMPolicy) encoding.Encoding {
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return utf16Encoding{config{e, b}, mibValue[e][b&bomMask]}
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}
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// mibValue maps Endianness and BOMPolicy settings to MIB constants. Note that
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// some configurations map to the same MIB identifier. RFC 2781 has requirements
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// and recommendations. Some of the "configurations" are merely recommendations,
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// so multiple configurations could match.
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var mibValue = map[Endianness][numBOMValues]identifier.MIB{
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BigEndian: [numBOMValues]identifier.MIB{
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IgnoreBOM: identifier.UTF16BE,
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UseBOM: identifier.UTF16, // BigEnding default is preferred by RFC 2781.
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// TODO: acceptBOM | strictBOM would map to UTF16BE as well.
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},
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LittleEndian: [numBOMValues]identifier.MIB{
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IgnoreBOM: identifier.UTF16LE,
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UseBOM: identifier.UTF16, // LittleEndian default is allowed and preferred on Windows.
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// TODO: acceptBOM | strictBOM would map to UTF16LE as well.
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},
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// ExpectBOM is not widely used and has no valid MIB identifier.
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}
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// All lists a configuration for each IANA-defined UTF-16 variant.
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var All = []encoding.Encoding{
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UTF8,
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UTF16(BigEndian, UseBOM),
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UTF16(BigEndian, IgnoreBOM),
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UTF16(LittleEndian, IgnoreBOM),
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}
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// BOMPolicy is a UTF-16 encoding's byte order mark policy.
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type BOMPolicy uint8
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const (
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writeBOM BOMPolicy = 0x01
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acceptBOM BOMPolicy = 0x02
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requireBOM BOMPolicy = 0x04
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bomMask BOMPolicy = 0x07
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// HACK: numBOMValues == 8 triggers a bug in the 1.4 compiler (cannot have a
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// map of an array of length 8 of a type that is also used as a key or value
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// in another map). See golang.org/issue/11354.
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// TODO: consider changing this value back to 8 if the use of 1.4.* has
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// been minimized.
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numBOMValues = 8 + 1
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// IgnoreBOM means to ignore any byte order marks.
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IgnoreBOM BOMPolicy = 0
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// Common and RFC 2781-compliant interpretation for UTF-16BE/LE.
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// UseBOM means that the UTF-16 form may start with a byte order mark, which
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// will be used to override the default encoding.
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UseBOM BOMPolicy = writeBOM | acceptBOM
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// Common and RFC 2781-compliant interpretation for UTF-16.
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// ExpectBOM means that the UTF-16 form must start with a byte order mark,
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// which will be used to override the default encoding.
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ExpectBOM BOMPolicy = writeBOM | acceptBOM | requireBOM
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// Used in Java as Unicode (not to be confused with Java's UTF-16) and
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// ICU's UTF-16,version=1. Not compliant with RFC 2781.
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// TODO (maybe): strictBOM: BOM must match Endianness. This would allow:
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// - UTF-16(B|L)E,version=1: writeBOM | acceptBOM | requireBOM | strictBOM
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// (UnicodeBig and UnicodeLittle in Java)
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// - RFC 2781-compliant, but less common interpretation for UTF-16(B|L)E:
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// acceptBOM | strictBOM (e.g. assigned to CheckBOM).
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// This addition would be consistent with supporting ExpectBOM.
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)
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// Endianness is a UTF-16 encoding's default endianness.
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type Endianness bool
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const (
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// BigEndian is UTF-16BE.
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BigEndian Endianness = false
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// LittleEndian is UTF-16LE.
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LittleEndian Endianness = true
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)
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// ErrMissingBOM means that decoding UTF-16 input with ExpectBOM did not find a
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// starting byte order mark.
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var ErrMissingBOM = errors.New("encoding: missing byte order mark")
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type utf16Encoding struct {
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config
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mib identifier.MIB
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}
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type config struct {
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endianness Endianness
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bomPolicy BOMPolicy
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}
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func (u utf16Encoding) NewDecoder() *encoding.Decoder {
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return &encoding.Decoder{Transformer: &utf16Decoder{
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initial: u.config,
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current: u.config,
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}}
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}
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func (u utf16Encoding) NewEncoder() *encoding.Encoder {
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return &encoding.Encoder{Transformer: &utf16Encoder{
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endianness: u.endianness,
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initialBOMPolicy: u.bomPolicy,
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currentBOMPolicy: u.bomPolicy,
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}}
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}
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func (u utf16Encoding) ID() (mib identifier.MIB, other string) {
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return u.mib, ""
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}
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func (u utf16Encoding) String() string {
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e, b := "B", ""
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if u.endianness == LittleEndian {
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e = "L"
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}
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switch u.bomPolicy {
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case ExpectBOM:
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b = "Expect"
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case UseBOM:
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b = "Use"
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case IgnoreBOM:
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b = "Ignore"
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}
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return "UTF-16" + e + "E (" + b + " BOM)"
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}
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type utf16Decoder struct {
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initial config
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current config
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}
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func (u *utf16Decoder) Reset() {
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u.current = u.initial
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}
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func (u *utf16Decoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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if len(src) == 0 {
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if atEOF && u.current.bomPolicy&requireBOM != 0 {
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return 0, 0, ErrMissingBOM
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}
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return 0, 0, nil
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}
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if u.current.bomPolicy&acceptBOM != 0 {
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if len(src) < 2 {
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return 0, 0, transform.ErrShortSrc
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}
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switch {
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case src[0] == 0xfe && src[1] == 0xff:
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u.current.endianness = BigEndian
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nSrc = 2
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case src[0] == 0xff && src[1] == 0xfe:
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u.current.endianness = LittleEndian
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nSrc = 2
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default:
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if u.current.bomPolicy&requireBOM != 0 {
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return 0, 0, ErrMissingBOM
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}
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}
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u.current.bomPolicy = IgnoreBOM
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}
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var r rune
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var dSize, sSize int
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for nSrc < len(src) {
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if nSrc+1 < len(src) {
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x := uint16(src[nSrc+0])<<8 | uint16(src[nSrc+1])
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if u.current.endianness == LittleEndian {
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x = x>>8 | x<<8
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}
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r, sSize = rune(x), 2
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if utf16.IsSurrogate(r) {
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if nSrc+3 < len(src) {
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x = uint16(src[nSrc+2])<<8 | uint16(src[nSrc+3])
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if u.current.endianness == LittleEndian {
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x = x>>8 | x<<8
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}
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// Save for next iteration if it is not a high surrogate.
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if isHighSurrogate(rune(x)) {
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r, sSize = utf16.DecodeRune(r, rune(x)), 4
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}
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} else if !atEOF {
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err = transform.ErrShortSrc
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break
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}
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}
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if dSize = utf8.RuneLen(r); dSize < 0 {
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r, dSize = utf8.RuneError, 3
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}
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} else if atEOF {
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// Single trailing byte.
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r, dSize, sSize = utf8.RuneError, 3, 1
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} else {
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err = transform.ErrShortSrc
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break
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}
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if nDst+dSize > len(dst) {
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err = transform.ErrShortDst
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break
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}
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nDst += utf8.EncodeRune(dst[nDst:], r)
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nSrc += sSize
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}
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return nDst, nSrc, err
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}
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func isHighSurrogate(r rune) bool {
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return 0xDC00 <= r && r <= 0xDFFF
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}
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type utf16Encoder struct {
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endianness Endianness
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initialBOMPolicy BOMPolicy
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currentBOMPolicy BOMPolicy
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}
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func (u *utf16Encoder) Reset() {
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u.currentBOMPolicy = u.initialBOMPolicy
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}
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func (u *utf16Encoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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if u.currentBOMPolicy&writeBOM != 0 {
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if len(dst) < 2 {
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return 0, 0, transform.ErrShortDst
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}
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dst[0], dst[1] = 0xfe, 0xff
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u.currentBOMPolicy = IgnoreBOM
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nDst = 2
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}
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r, size := rune(0), 0
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for nSrc < len(src) {
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r = rune(src[nSrc])
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// Decode a 1-byte rune.
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if r < utf8.RuneSelf {
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size = 1
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} else {
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// Decode a multi-byte rune.
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r, size = utf8.DecodeRune(src[nSrc:])
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if size == 1 {
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// All valid runes of size 1 (those below utf8.RuneSelf) were
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// handled above. We have invalid UTF-8 or we haven't seen the
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// full character yet.
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if !atEOF && !utf8.FullRune(src[nSrc:]) {
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err = transform.ErrShortSrc
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break
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}
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}
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}
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if r <= 0xffff {
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if nDst+2 > len(dst) {
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err = transform.ErrShortDst
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break
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}
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dst[nDst+0] = uint8(r >> 8)
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dst[nDst+1] = uint8(r)
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nDst += 2
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} else {
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if nDst+4 > len(dst) {
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err = transform.ErrShortDst
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break
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}
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r1, r2 := utf16.EncodeRune(r)
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dst[nDst+0] = uint8(r1 >> 8)
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dst[nDst+1] = uint8(r1)
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dst[nDst+2] = uint8(r2 >> 8)
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dst[nDst+3] = uint8(r2)
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nDst += 4
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}
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nSrc += size
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}
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if u.endianness == LittleEndian {
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for i := 0; i < nDst; i += 2 {
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dst[i], dst[i+1] = dst[i+1], dst[i]
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}
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}
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return nDst, nSrc, err
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}
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