279 lines
6.7 KiB
Go
279 lines
6.7 KiB
Go
// Copyright 2014 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 runes provide transforms for UTF-8 encoded text.
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package runes
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import (
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"unicode"
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"unicode/utf8"
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"golang.org/x/text/transform"
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)
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// A Set is a collection of runes.
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type Set interface {
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// Contains returns true if r is contained in the set.
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Contains(r rune) bool
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}
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type setFunc func(rune) bool
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func (s setFunc) Contains(r rune) bool {
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return s(r)
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}
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// Note: using funcs here instead of wrapping types result in cleaner
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// documentation and a smaller API.
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// In creates a Set with a Contains method that returns true for all runes in
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// the given RangeTable.
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func In(rt *unicode.RangeTable) Set {
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return setFunc(func(r rune) bool { return unicode.Is(rt, r) })
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}
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// In creates a Set with a Contains method that returns true for all runes not
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// in the given RangeTable.
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func NotIn(rt *unicode.RangeTable) Set {
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return setFunc(func(r rune) bool { return !unicode.Is(rt, r) })
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}
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// Predicate creates a Set with a Contains method that returns f(r).
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func Predicate(f func(rune) bool) Set {
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return setFunc(f)
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}
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// Transformer implements the transform.Transformer interface.
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type Transformer struct {
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transform.Transformer
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}
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// Bytes returns a new byte slice with the result of converting b using t. It
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// calls Reset on t. It returns nil if any error was found. This can only happen
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// if an error-producing Transformer is passed to If.
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func (t Transformer) Bytes(b []byte) []byte {
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b, _, err := transform.Bytes(t, b)
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if err != nil {
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return nil
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}
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return b
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}
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// String returns a string with the result of converting s using t. It calls
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// Reset on t. It returns the empty string if any error was found. This can only
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// happen if an error-producing Transformer is passed to If.
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func (t Transformer) String(s string) string {
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s, _, err := transform.String(t, s)
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if err != nil {
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return ""
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}
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return s
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}
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// TODO:
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// - Copy: copying strings and bytes in whole-rune units.
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// - Validation (maybe)
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// - Well-formed-ness (maybe)
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const runeErrorString = string(utf8.RuneError)
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// Remove returns a Transformer that removes runes r for which s.Contains(r).
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// Illegal input bytes are replaced by RuneError before being passed to f.
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func Remove(s Set) Transformer {
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if f, ok := s.(setFunc); ok {
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// This little trick cuts the running time of BenchmarkRemove for sets
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// created by Predicate roughly in half.
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// TODO: special-case RangeTables as well.
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return Transformer{remove(f)}
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}
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return Transformer{remove(s.Contains)}
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}
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// TODO: remove transform.RemoveFunc.
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type remove func(r rune) bool
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func (remove) Reset() {}
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// Transform implements transform.Transformer.
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func (t remove) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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for r, size := rune(0), 0; nSrc < len(src); {
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if r = rune(src[nSrc]); r < utf8.RuneSelf {
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size = 1
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} else {
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r, size = utf8.DecodeRune(src[nSrc:])
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if size == 1 {
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// Invalid rune.
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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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// We replace illegal bytes with RuneError. Not doing so might
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// otherwise turn a sequence of invalid UTF-8 into valid UTF-8.
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// The resulting byte sequence may subsequently contain runes
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// for which t(r) is true that were passed unnoticed.
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if !t(utf8.RuneError) {
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if nDst+3 > 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] = runeErrorString[0]
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dst[nDst+1] = runeErrorString[1]
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dst[nDst+2] = runeErrorString[2]
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nDst += 3
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}
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nSrc++
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continue
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}
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}
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if t(r) {
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nSrc += size
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continue
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}
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if nDst+size > len(dst) {
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err = transform.ErrShortDst
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break
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}
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for i := 0; i < size; i++ {
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dst[nDst] = src[nSrc]
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nDst++
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nSrc++
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}
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}
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return
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}
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// Map returns a Transformer that maps the runes in the input using the given
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// mapping. Illegal bytes in the input are converted to utf8.RuneError before
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// being passed to the mapping func.
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func Map(mapping func(rune) rune) Transformer {
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return Transformer{mapper(mapping)}
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}
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type mapper func(rune) rune
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func (mapper) Reset() {}
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// Transform implements transform.Transformer.
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func (t mapper) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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var replacement rune
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var b [utf8.UTFMax]byte
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for r, size := rune(0), 0; nSrc < len(src); {
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if r = rune(src[nSrc]); r < utf8.RuneSelf {
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if replacement = t(r); replacement < utf8.RuneSelf {
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if nDst == len(dst) {
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err = transform.ErrShortDst
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break
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}
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dst[nDst] = byte(replacement)
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nDst++
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nSrc++
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continue
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}
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size = 1
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} else if r, size = utf8.DecodeRune(src[nSrc:]); size == 1 {
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// Invalid rune.
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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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if replacement = t(utf8.RuneError); replacement == utf8.RuneError {
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if nDst+3 > 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] = runeErrorString[0]
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dst[nDst+1] = runeErrorString[1]
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dst[nDst+2] = runeErrorString[2]
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nDst += 3
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nSrc++
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continue
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}
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} else if replacement = t(r); replacement == r {
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if nDst+size > len(dst) {
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err = transform.ErrShortDst
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break
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}
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for i := 0; i < size; i++ {
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dst[nDst] = src[nSrc]
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nDst++
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nSrc++
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}
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continue
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}
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n := utf8.EncodeRune(b[:], replacement)
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if nDst+n > len(dst) {
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err = transform.ErrShortDst
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break
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}
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for i := 0; i < n; i++ {
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dst[nDst] = b[i]
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nDst++
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}
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nSrc += size
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}
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return
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}
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// ReplaceIllFormed returns a transformer that replaces all input bytes that are
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// not part of a well-formed UTF-8 code sequence with utf8.RuneError.
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func ReplaceIllFormed() Transformer {
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return Transformer{&replaceIllFormed{}}
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}
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type replaceIllFormed struct{ transform.NopResetter }
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func (t replaceIllFormed) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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for nSrc < len(src) {
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r, size := utf8.DecodeRune(src[nSrc:])
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// Look for an ASCII rune.
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if r < utf8.RuneSelf {
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if nDst == len(dst) {
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err = transform.ErrShortDst
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break
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}
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dst[nDst] = byte(r)
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nDst++
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nSrc++
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continue
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}
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// Look for a valid non-ASCII rune.
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if r != utf8.RuneError || size != 1 {
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if size != copy(dst[nDst:], src[nSrc:nSrc+size]) {
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err = transform.ErrShortDst
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break
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}
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nDst += size
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nSrc += size
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continue
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}
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// Look for short source data.
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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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// We have an invalid rune.
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if nDst+3 > 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] = runeErrorString[0]
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dst[nDst+1] = runeErrorString[1]
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dst[nDst+2] = runeErrorString[2]
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nDst += 3
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nSrc++
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}
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return nDst, nSrc, err
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}
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