mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-12-05 01:52:46 +00:00
336 lines
9.5 KiB
Go
336 lines
9.5 KiB
Go
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// 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 encoding defines an interface for character encodings, such as Shift
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// JIS and Windows 1252, that can convert to and from UTF-8.
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//
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// Encoding implementations are provided in other packages, such as
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// golang.org/x/text/encoding/charmap and
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// golang.org/x/text/encoding/japanese.
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package encoding // import "golang.org/x/text/encoding"
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import (
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"errors"
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"io"
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"strconv"
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"unicode/utf8"
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"golang.org/x/text/encoding/internal/identifier"
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"golang.org/x/text/transform"
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)
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// TODO:
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// - There seems to be some inconsistency in when decoders return errors
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// and when not. Also documentation seems to suggest they shouldn't return
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// errors at all (except for UTF-16).
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// - Encoders seem to rely on or at least benefit from the input being in NFC
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// normal form. Perhaps add an example how users could prepare their output.
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// Encoding is a character set encoding that can be transformed to and from
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// UTF-8.
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type Encoding interface {
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// NewDecoder returns a Decoder.
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NewDecoder() *Decoder
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// NewEncoder returns an Encoder.
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NewEncoder() *Encoder
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}
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// A Decoder converts bytes to UTF-8. It implements transform.Transformer.
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//
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// Transforming source bytes that are not of that encoding will not result in an
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// error per se. Each byte that cannot be transcoded will be represented in the
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// output by the UTF-8 encoding of '\uFFFD', the replacement rune.
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type Decoder struct {
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transform.Transformer
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// This forces external creators of Decoders to use names in struct
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// initializers, allowing for future extendibility without having to break
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// code.
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_ struct{}
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}
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// Bytes converts the given encoded bytes to UTF-8. It returns the converted
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// bytes or nil, err if any error occurred.
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func (d *Decoder) Bytes(b []byte) ([]byte, error) {
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b, _, err := transform.Bytes(d, b)
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if err != nil {
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return nil, err
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}
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return b, nil
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}
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// String converts the given encoded string to UTF-8. It returns the converted
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// string or "", err if any error occurred.
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func (d *Decoder) String(s string) (string, error) {
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s, _, err := transform.String(d, s)
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if err != nil {
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return "", err
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}
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return s, nil
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}
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// Reader wraps another Reader to decode its bytes.
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//
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// The Decoder may not be used for any other operation as long as the returned
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// Reader is in use.
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func (d *Decoder) Reader(r io.Reader) io.Reader {
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return transform.NewReader(r, d)
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}
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// An Encoder converts bytes from UTF-8. It implements transform.Transformer.
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//
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// Each rune that cannot be transcoded will result in an error. In this case,
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// the transform will consume all source byte up to, not including the offending
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// rune. Transforming source bytes that are not valid UTF-8 will be replaced by
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// `\uFFFD`. To return early with an error instead, use transform.Chain to
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// preprocess the data with a UTF8Validator.
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type Encoder struct {
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transform.Transformer
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// This forces external creators of Encoders to use names in struct
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// initializers, allowing for future extendibility without having to break
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// code.
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_ struct{}
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}
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// Bytes converts bytes from UTF-8. It returns the converted bytes or nil, err if
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// any error occurred.
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func (e *Encoder) Bytes(b []byte) ([]byte, error) {
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b, _, err := transform.Bytes(e, b)
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if err != nil {
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return nil, err
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}
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return b, nil
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}
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// String converts a string from UTF-8. It returns the converted string or
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// "", err if any error occurred.
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func (e *Encoder) String(s string) (string, error) {
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s, _, err := transform.String(e, s)
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if err != nil {
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return "", err
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}
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return s, nil
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}
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// Writer wraps another Writer to encode its UTF-8 output.
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//
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// The Encoder may not be used for any other operation as long as the returned
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// Writer is in use.
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func (e *Encoder) Writer(w io.Writer) io.Writer {
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return transform.NewWriter(w, e)
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}
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// ASCIISub is the ASCII substitute character, as recommended by
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// https://unicode.org/reports/tr36/#Text_Comparison
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const ASCIISub = '\x1a'
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// Nop is the nop encoding. Its transformed bytes are the same as the source
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// bytes; it does not replace invalid UTF-8 sequences.
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var Nop Encoding = nop{}
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type nop struct{}
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func (nop) NewDecoder() *Decoder {
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return &Decoder{Transformer: transform.Nop}
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}
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func (nop) NewEncoder() *Encoder {
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return &Encoder{Transformer: transform.Nop}
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}
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// Replacement is the replacement encoding. Decoding from the replacement
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// encoding yields a single '\uFFFD' replacement rune. Encoding from UTF-8 to
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// the replacement encoding yields the same as the source bytes except that
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// invalid UTF-8 is converted to '\uFFFD'.
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//
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// It is defined at http://encoding.spec.whatwg.org/#replacement
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var Replacement Encoding = replacement{}
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type replacement struct{}
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func (replacement) NewDecoder() *Decoder {
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return &Decoder{Transformer: replacementDecoder{}}
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}
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func (replacement) NewEncoder() *Encoder {
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return &Encoder{Transformer: replacementEncoder{}}
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}
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func (replacement) ID() (mib identifier.MIB, other string) {
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return identifier.Replacement, ""
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}
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type replacementDecoder struct{ transform.NopResetter }
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func (replacementDecoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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if len(dst) < 3 {
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return 0, 0, transform.ErrShortDst
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}
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if atEOF {
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const fffd = "\ufffd"
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dst[0] = fffd[0]
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dst[1] = fffd[1]
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dst[2] = fffd[2]
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nDst = 3
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}
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return nDst, len(src), nil
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}
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type replacementEncoder struct{ transform.NopResetter }
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func (replacementEncoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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r, size := rune(0), 0
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for ; nSrc < len(src); nSrc += size {
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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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r = '\ufffd'
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}
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}
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if nDst+utf8.RuneLen(r) > 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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}
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return nDst, nSrc, err
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}
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// HTMLEscapeUnsupported wraps encoders to replace source runes outside the
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// repertoire of the destination encoding with HTML escape sequences.
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//
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// This wrapper exists to comply to URL and HTML forms requiring a
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// non-terminating legacy encoder. The produced sequences may lead to data
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// loss as they are indistinguishable from legitimate input. To avoid this
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// issue, use UTF-8 encodings whenever possible.
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func HTMLEscapeUnsupported(e *Encoder) *Encoder {
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return &Encoder{Transformer: &errorHandler{e, errorToHTML}}
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}
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// ReplaceUnsupported wraps encoders to replace source runes outside the
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// repertoire of the destination encoding with an encoding-specific
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// replacement.
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//
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// This wrapper is only provided for backwards compatibility and legacy
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// handling. Its use is strongly discouraged. Use UTF-8 whenever possible.
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func ReplaceUnsupported(e *Encoder) *Encoder {
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return &Encoder{Transformer: &errorHandler{e, errorToReplacement}}
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}
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type errorHandler struct {
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*Encoder
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handler func(dst []byte, r rune, err repertoireError) (n int, ok bool)
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}
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// TODO: consider making this error public in some form.
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type repertoireError interface {
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Replacement() byte
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}
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func (h errorHandler) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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nDst, nSrc, err = h.Transformer.Transform(dst, src, atEOF)
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for err != nil {
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rerr, ok := err.(repertoireError)
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if !ok {
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return nDst, nSrc, err
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}
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r, sz := utf8.DecodeRune(src[nSrc:])
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n, ok := h.handler(dst[nDst:], r, rerr)
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if !ok {
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return nDst, nSrc, transform.ErrShortDst
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}
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err = nil
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nDst += n
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if nSrc += sz; nSrc < len(src) {
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var dn, sn int
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dn, sn, err = h.Transformer.Transform(dst[nDst:], src[nSrc:], atEOF)
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nDst += dn
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nSrc += sn
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}
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}
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return nDst, nSrc, err
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}
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func errorToHTML(dst []byte, r rune, err repertoireError) (n int, ok bool) {
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buf := [8]byte{}
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b := strconv.AppendUint(buf[:0], uint64(r), 10)
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if n = len(b) + len("&#;"); n >= len(dst) {
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return 0, false
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}
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dst[0] = '&'
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dst[1] = '#'
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dst[copy(dst[2:], b)+2] = ';'
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return n, true
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}
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func errorToReplacement(dst []byte, r rune, err repertoireError) (n int, ok bool) {
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if len(dst) == 0 {
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return 0, false
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}
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dst[0] = err.Replacement()
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return 1, true
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}
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// ErrInvalidUTF8 means that a transformer encountered invalid UTF-8.
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var ErrInvalidUTF8 = errors.New("encoding: invalid UTF-8")
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// UTF8Validator is a transformer that returns ErrInvalidUTF8 on the first
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// input byte that is not valid UTF-8.
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var UTF8Validator transform.Transformer = utf8Validator{}
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type utf8Validator struct{ transform.NopResetter }
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func (utf8Validator) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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n := len(src)
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if n > len(dst) {
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n = len(dst)
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}
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for i := 0; i < n; {
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if c := src[i]; c < utf8.RuneSelf {
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dst[i] = c
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i++
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continue
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}
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_, size := utf8.DecodeRune(src[i:])
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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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err = ErrInvalidUTF8
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if !atEOF && !utf8.FullRune(src[i:]) {
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err = transform.ErrShortSrc
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}
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return i, i, err
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}
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if i+size > len(dst) {
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return i, i, transform.ErrShortDst
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}
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for ; size > 0; size-- {
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dst[i] = src[i]
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i++
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}
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}
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if len(src) > len(dst) {
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err = transform.ErrShortDst
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}
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return n, n, err
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}
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