1// Copyright 2015 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5package runes 6 7import ( 8 "unicode/utf8" 9 10 "golang.org/x/text/transform" 11) 12 13// Note: below we pass invalid UTF-8 to the tIn and tNotIn transformers as is. 14// This is done for various reasons: 15// - To retain the semantics of the Nop transformer: if input is passed to a Nop 16// one would expect it to be unchanged. 17// - It would be very expensive to pass a converted RuneError to a transformer: 18// a transformer might need more source bytes after RuneError, meaning that 19// the only way to pass it safely is to create a new buffer and manage the 20// intermingling of RuneErrors and normal input. 21// - Many transformers leave ill-formed UTF-8 as is, so this is not 22// inconsistent. Generally ill-formed UTF-8 is only replaced if it is a 23// logical consequence of the operation (as for Map) or if it otherwise would 24// pose security concerns (as for Remove). 25// - An alternative would be to return an error on ill-formed UTF-8, but this 26// would be inconsistent with other operations. 27 28// If returns a transformer that applies tIn to consecutive runes for which 29// s.Contains(r) and tNotIn to consecutive runes for which !s.Contains(r). Reset 30// is called on tIn and tNotIn at the start of each run. A Nop transformer will 31// substitute a nil value passed to tIn or tNotIn. Invalid UTF-8 is translated 32// to RuneError to determine which transformer to apply, but is passed as is to 33// the respective transformer. 34func If(s Set, tIn, tNotIn transform.Transformer) Transformer { 35 if tIn == nil && tNotIn == nil { 36 return Transformer{transform.Nop} 37 } 38 if tIn == nil { 39 tIn = transform.Nop 40 } 41 if tNotIn == nil { 42 tNotIn = transform.Nop 43 } 44 sIn, ok := tIn.(transform.SpanningTransformer) 45 if !ok { 46 sIn = dummySpan{tIn} 47 } 48 sNotIn, ok := tNotIn.(transform.SpanningTransformer) 49 if !ok { 50 sNotIn = dummySpan{tNotIn} 51 } 52 53 a := &cond{ 54 tIn: sIn, 55 tNotIn: sNotIn, 56 f: s.Contains, 57 } 58 a.Reset() 59 return Transformer{a} 60} 61 62type dummySpan struct{ transform.Transformer } 63 64func (d dummySpan) Span(src []byte, atEOF bool) (n int, err error) { 65 return 0, transform.ErrEndOfSpan 66} 67 68type cond struct { 69 tIn, tNotIn transform.SpanningTransformer 70 f func(rune) bool 71 check func(rune) bool // current check to perform 72 t transform.SpanningTransformer // current transformer to use 73} 74 75// Reset implements transform.Transformer. 76func (t *cond) Reset() { 77 t.check = t.is 78 t.t = t.tIn 79 t.t.Reset() // notIn will be reset on first usage. 80} 81 82func (t *cond) is(r rune) bool { 83 if t.f(r) { 84 return true 85 } 86 t.check = t.isNot 87 t.t = t.tNotIn 88 t.tNotIn.Reset() 89 return false 90} 91 92func (t *cond) isNot(r rune) bool { 93 if !t.f(r) { 94 return true 95 } 96 t.check = t.is 97 t.t = t.tIn 98 t.tIn.Reset() 99 return false 100} 101 102// This implementation of Span doesn't help all too much, but it needs to be 103// there to satisfy this package's Transformer interface. 104// TODO: there are certainly room for improvements, though. For example, if 105// t.t == transform.Nop (which will a common occurrence) it will save a bundle 106// to special-case that loop. 107func (t *cond) Span(src []byte, atEOF bool) (n int, err error) { 108 p := 0 109 for n < len(src) && err == nil { 110 // Don't process too much at a time as the Spanner that will be 111 // called on this block may terminate early. 112 const maxChunk = 4096 113 max := len(src) 114 if v := n + maxChunk; v < max { 115 max = v 116 } 117 atEnd := false 118 size := 0 119 current := t.t 120 for ; p < max; p += size { 121 r := rune(src[p]) 122 if r < utf8.RuneSelf { 123 size = 1 124 } else if r, size = utf8.DecodeRune(src[p:]); size == 1 { 125 if !atEOF && !utf8.FullRune(src[p:]) { 126 err = transform.ErrShortSrc 127 break 128 } 129 } 130 if !t.check(r) { 131 // The next rune will be the start of a new run. 132 atEnd = true 133 break 134 } 135 } 136 n2, err2 := current.Span(src[n:p], atEnd || (atEOF && p == len(src))) 137 n += n2 138 if err2 != nil { 139 return n, err2 140 } 141 // At this point either err != nil or t.check will pass for the rune at p. 142 p = n + size 143 } 144 return n, err 145} 146 147func (t *cond) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) { 148 p := 0 149 for nSrc < len(src) && err == nil { 150 // Don't process too much at a time, as the work might be wasted if the 151 // destination buffer isn't large enough to hold the result or a 152 // transform returns an error early. 153 const maxChunk = 4096 154 max := len(src) 155 if n := nSrc + maxChunk; n < len(src) { 156 max = n 157 } 158 atEnd := false 159 size := 0 160 current := t.t 161 for ; p < max; p += size { 162 r := rune(src[p]) 163 if r < utf8.RuneSelf { 164 size = 1 165 } else if r, size = utf8.DecodeRune(src[p:]); size == 1 { 166 if !atEOF && !utf8.FullRune(src[p:]) { 167 err = transform.ErrShortSrc 168 break 169 } 170 } 171 if !t.check(r) { 172 // The next rune will be the start of a new run. 173 atEnd = true 174 break 175 } 176 } 177 nDst2, nSrc2, err2 := current.Transform(dst[nDst:], src[nSrc:p], atEnd || (atEOF && p == len(src))) 178 nDst += nDst2 179 nSrc += nSrc2 180 if err2 != nil { 181 return nDst, nSrc, err2 182 } 183 // At this point either err != nil or t.check will pass for the rune at p. 184 p = nSrc + size 185 } 186 return nDst, nSrc, err 187} 188