Matteo Scandolo | a428586 | 2020-12-01 18:10:10 -0800 | [diff] [blame^] | 1 | // Copyright 2016 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 | |
| 5 | // Package bidirule implements the Bidi Rule defined by RFC 5893. |
| 6 | // |
| 7 | // This package is under development. The API may change without notice and |
| 8 | // without preserving backward compatibility. |
| 9 | package bidirule |
| 10 | |
| 11 | import ( |
| 12 | "errors" |
| 13 | "unicode/utf8" |
| 14 | |
| 15 | "golang.org/x/text/transform" |
| 16 | "golang.org/x/text/unicode/bidi" |
| 17 | ) |
| 18 | |
| 19 | // This file contains an implementation of RFC 5893: Right-to-Left Scripts for |
| 20 | // Internationalized Domain Names for Applications (IDNA) |
| 21 | // |
| 22 | // A label is an individual component of a domain name. Labels are usually |
| 23 | // shown separated by dots; for example, the domain name "www.example.com" is |
| 24 | // composed of three labels: "www", "example", and "com". |
| 25 | // |
| 26 | // An RTL label is a label that contains at least one character of class R, AL, |
| 27 | // or AN. An LTR label is any label that is not an RTL label. |
| 28 | // |
| 29 | // A "Bidi domain name" is a domain name that contains at least one RTL label. |
| 30 | // |
| 31 | // The following guarantees can be made based on the above: |
| 32 | // |
| 33 | // o In a domain name consisting of only labels that satisfy the rule, |
| 34 | // the requirements of Section 3 are satisfied. Note that even LTR |
| 35 | // labels and pure ASCII labels have to be tested. |
| 36 | // |
| 37 | // o In a domain name consisting of only LDH labels (as defined in the |
| 38 | // Definitions document [RFC5890]) and labels that satisfy the rule, |
| 39 | // the requirements of Section 3 are satisfied as long as a label |
| 40 | // that starts with an ASCII digit does not come after a |
| 41 | // right-to-left label. |
| 42 | // |
| 43 | // No guarantee is given for other combinations. |
| 44 | |
| 45 | // ErrInvalid indicates a label is invalid according to the Bidi Rule. |
| 46 | var ErrInvalid = errors.New("bidirule: failed Bidi Rule") |
| 47 | |
| 48 | type ruleState uint8 |
| 49 | |
| 50 | const ( |
| 51 | ruleInitial ruleState = iota |
| 52 | ruleLTR |
| 53 | ruleLTRFinal |
| 54 | ruleRTL |
| 55 | ruleRTLFinal |
| 56 | ruleInvalid |
| 57 | ) |
| 58 | |
| 59 | type ruleTransition struct { |
| 60 | next ruleState |
| 61 | mask uint16 |
| 62 | } |
| 63 | |
| 64 | var transitions = [...][2]ruleTransition{ |
| 65 | // [2.1] The first character must be a character with Bidi property L, R, or |
| 66 | // AL. If it has the R or AL property, it is an RTL label; if it has the L |
| 67 | // property, it is an LTR label. |
| 68 | ruleInitial: { |
| 69 | {ruleLTRFinal, 1 << bidi.L}, |
| 70 | {ruleRTLFinal, 1<<bidi.R | 1<<bidi.AL}, |
| 71 | }, |
| 72 | ruleRTL: { |
| 73 | // [2.3] In an RTL label, the end of the label must be a character with |
| 74 | // Bidi property R, AL, EN, or AN, followed by zero or more characters |
| 75 | // with Bidi property NSM. |
| 76 | {ruleRTLFinal, 1<<bidi.R | 1<<bidi.AL | 1<<bidi.EN | 1<<bidi.AN}, |
| 77 | |
| 78 | // [2.2] In an RTL label, only characters with the Bidi properties R, |
| 79 | // AL, AN, EN, ES, CS, ET, ON, BN, or NSM are allowed. |
| 80 | // We exclude the entries from [2.3] |
| 81 | {ruleRTL, 1<<bidi.ES | 1<<bidi.CS | 1<<bidi.ET | 1<<bidi.ON | 1<<bidi.BN | 1<<bidi.NSM}, |
| 82 | }, |
| 83 | ruleRTLFinal: { |
| 84 | // [2.3] In an RTL label, the end of the label must be a character with |
| 85 | // Bidi property R, AL, EN, or AN, followed by zero or more characters |
| 86 | // with Bidi property NSM. |
| 87 | {ruleRTLFinal, 1<<bidi.R | 1<<bidi.AL | 1<<bidi.EN | 1<<bidi.AN | 1<<bidi.NSM}, |
| 88 | |
| 89 | // [2.2] In an RTL label, only characters with the Bidi properties R, |
| 90 | // AL, AN, EN, ES, CS, ET, ON, BN, or NSM are allowed. |
| 91 | // We exclude the entries from [2.3] and NSM. |
| 92 | {ruleRTL, 1<<bidi.ES | 1<<bidi.CS | 1<<bidi.ET | 1<<bidi.ON | 1<<bidi.BN}, |
| 93 | }, |
| 94 | ruleLTR: { |
| 95 | // [2.6] In an LTR label, the end of the label must be a character with |
| 96 | // Bidi property L or EN, followed by zero or more characters with Bidi |
| 97 | // property NSM. |
| 98 | {ruleLTRFinal, 1<<bidi.L | 1<<bidi.EN}, |
| 99 | |
| 100 | // [2.5] In an LTR label, only characters with the Bidi properties L, |
| 101 | // EN, ES, CS, ET, ON, BN, or NSM are allowed. |
| 102 | // We exclude the entries from [2.6]. |
| 103 | {ruleLTR, 1<<bidi.ES | 1<<bidi.CS | 1<<bidi.ET | 1<<bidi.ON | 1<<bidi.BN | 1<<bidi.NSM}, |
| 104 | }, |
| 105 | ruleLTRFinal: { |
| 106 | // [2.6] In an LTR label, the end of the label must be a character with |
| 107 | // Bidi property L or EN, followed by zero or more characters with Bidi |
| 108 | // property NSM. |
| 109 | {ruleLTRFinal, 1<<bidi.L | 1<<bidi.EN | 1<<bidi.NSM}, |
| 110 | |
| 111 | // [2.5] In an LTR label, only characters with the Bidi properties L, |
| 112 | // EN, ES, CS, ET, ON, BN, or NSM are allowed. |
| 113 | // We exclude the entries from [2.6]. |
| 114 | {ruleLTR, 1<<bidi.ES | 1<<bidi.CS | 1<<bidi.ET | 1<<bidi.ON | 1<<bidi.BN}, |
| 115 | }, |
| 116 | ruleInvalid: { |
| 117 | {ruleInvalid, 0}, |
| 118 | {ruleInvalid, 0}, |
| 119 | }, |
| 120 | } |
| 121 | |
| 122 | // [2.4] In an RTL label, if an EN is present, no AN may be present, and |
| 123 | // vice versa. |
| 124 | const exclusiveRTL = uint16(1<<bidi.EN | 1<<bidi.AN) |
| 125 | |
| 126 | // From RFC 5893 |
| 127 | // An RTL label is a label that contains at least one character of type |
| 128 | // R, AL, or AN. |
| 129 | // |
| 130 | // An LTR label is any label that is not an RTL label. |
| 131 | |
| 132 | // Direction reports the direction of the given label as defined by RFC 5893. |
| 133 | // The Bidi Rule does not have to be applied to labels of the category |
| 134 | // LeftToRight. |
| 135 | func Direction(b []byte) bidi.Direction { |
| 136 | for i := 0; i < len(b); { |
| 137 | e, sz := bidi.Lookup(b[i:]) |
| 138 | if sz == 0 { |
| 139 | i++ |
| 140 | } |
| 141 | c := e.Class() |
| 142 | if c == bidi.R || c == bidi.AL || c == bidi.AN { |
| 143 | return bidi.RightToLeft |
| 144 | } |
| 145 | i += sz |
| 146 | } |
| 147 | return bidi.LeftToRight |
| 148 | } |
| 149 | |
| 150 | // DirectionString reports the direction of the given label as defined by RFC |
| 151 | // 5893. The Bidi Rule does not have to be applied to labels of the category |
| 152 | // LeftToRight. |
| 153 | func DirectionString(s string) bidi.Direction { |
| 154 | for i := 0; i < len(s); { |
| 155 | e, sz := bidi.LookupString(s[i:]) |
| 156 | if sz == 0 { |
| 157 | i++ |
| 158 | continue |
| 159 | } |
| 160 | c := e.Class() |
| 161 | if c == bidi.R || c == bidi.AL || c == bidi.AN { |
| 162 | return bidi.RightToLeft |
| 163 | } |
| 164 | i += sz |
| 165 | } |
| 166 | return bidi.LeftToRight |
| 167 | } |
| 168 | |
| 169 | // Valid reports whether b conforms to the BiDi rule. |
| 170 | func Valid(b []byte) bool { |
| 171 | var t Transformer |
| 172 | if n, ok := t.advance(b); !ok || n < len(b) { |
| 173 | return false |
| 174 | } |
| 175 | return t.isFinal() |
| 176 | } |
| 177 | |
| 178 | // ValidString reports whether s conforms to the BiDi rule. |
| 179 | func ValidString(s string) bool { |
| 180 | var t Transformer |
| 181 | if n, ok := t.advanceString(s); !ok || n < len(s) { |
| 182 | return false |
| 183 | } |
| 184 | return t.isFinal() |
| 185 | } |
| 186 | |
| 187 | // New returns a Transformer that verifies that input adheres to the Bidi Rule. |
| 188 | func New() *Transformer { |
| 189 | return &Transformer{} |
| 190 | } |
| 191 | |
| 192 | // Transformer implements transform.Transform. |
| 193 | type Transformer struct { |
| 194 | state ruleState |
| 195 | hasRTL bool |
| 196 | seen uint16 |
| 197 | } |
| 198 | |
| 199 | // A rule can only be violated for "Bidi Domain names", meaning if one of the |
| 200 | // following categories has been observed. |
| 201 | func (t *Transformer) isRTL() bool { |
| 202 | const isRTL = 1<<bidi.R | 1<<bidi.AL | 1<<bidi.AN |
| 203 | return t.seen&isRTL != 0 |
| 204 | } |
| 205 | |
| 206 | // Reset implements transform.Transformer. |
| 207 | func (t *Transformer) Reset() { *t = Transformer{} } |
| 208 | |
| 209 | // Transform implements transform.Transformer. This Transformer has state and |
| 210 | // needs to be reset between uses. |
| 211 | func (t *Transformer) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) { |
| 212 | if len(dst) < len(src) { |
| 213 | src = src[:len(dst)] |
| 214 | atEOF = false |
| 215 | err = transform.ErrShortDst |
| 216 | } |
| 217 | n, err1 := t.Span(src, atEOF) |
| 218 | copy(dst, src[:n]) |
| 219 | if err == nil || err1 != nil && err1 != transform.ErrShortSrc { |
| 220 | err = err1 |
| 221 | } |
| 222 | return n, n, err |
| 223 | } |
| 224 | |
| 225 | // Span returns the first n bytes of src that conform to the Bidi rule. |
| 226 | func (t *Transformer) Span(src []byte, atEOF bool) (n int, err error) { |
| 227 | if t.state == ruleInvalid && t.isRTL() { |
| 228 | return 0, ErrInvalid |
| 229 | } |
| 230 | n, ok := t.advance(src) |
| 231 | switch { |
| 232 | case !ok: |
| 233 | err = ErrInvalid |
| 234 | case n < len(src): |
| 235 | if !atEOF { |
| 236 | err = transform.ErrShortSrc |
| 237 | break |
| 238 | } |
| 239 | err = ErrInvalid |
| 240 | case !t.isFinal(): |
| 241 | err = ErrInvalid |
| 242 | } |
| 243 | return n, err |
| 244 | } |
| 245 | |
| 246 | // Precomputing the ASCII values decreases running time for the ASCII fast path |
| 247 | // by about 30%. |
| 248 | var asciiTable [128]bidi.Properties |
| 249 | |
| 250 | func init() { |
| 251 | for i := range asciiTable { |
| 252 | p, _ := bidi.LookupRune(rune(i)) |
| 253 | asciiTable[i] = p |
| 254 | } |
| 255 | } |
| 256 | |
| 257 | func (t *Transformer) advance(s []byte) (n int, ok bool) { |
| 258 | var e bidi.Properties |
| 259 | var sz int |
| 260 | for n < len(s) { |
| 261 | if s[n] < utf8.RuneSelf { |
| 262 | e, sz = asciiTable[s[n]], 1 |
| 263 | } else { |
| 264 | e, sz = bidi.Lookup(s[n:]) |
| 265 | if sz <= 1 { |
| 266 | if sz == 1 { |
| 267 | // We always consider invalid UTF-8 to be invalid, even if |
| 268 | // the string has not yet been determined to be RTL. |
| 269 | // TODO: is this correct? |
| 270 | return n, false |
| 271 | } |
| 272 | return n, true // incomplete UTF-8 encoding |
| 273 | } |
| 274 | } |
| 275 | // TODO: using CompactClass would result in noticeable speedup. |
| 276 | // See unicode/bidi/prop.go:Properties.CompactClass. |
| 277 | c := uint16(1 << e.Class()) |
| 278 | t.seen |= c |
| 279 | if t.seen&exclusiveRTL == exclusiveRTL { |
| 280 | t.state = ruleInvalid |
| 281 | return n, false |
| 282 | } |
| 283 | switch tr := transitions[t.state]; { |
| 284 | case tr[0].mask&c != 0: |
| 285 | t.state = tr[0].next |
| 286 | case tr[1].mask&c != 0: |
| 287 | t.state = tr[1].next |
| 288 | default: |
| 289 | t.state = ruleInvalid |
| 290 | if t.isRTL() { |
| 291 | return n, false |
| 292 | } |
| 293 | } |
| 294 | n += sz |
| 295 | } |
| 296 | return n, true |
| 297 | } |
| 298 | |
| 299 | func (t *Transformer) advanceString(s string) (n int, ok bool) { |
| 300 | var e bidi.Properties |
| 301 | var sz int |
| 302 | for n < len(s) { |
| 303 | if s[n] < utf8.RuneSelf { |
| 304 | e, sz = asciiTable[s[n]], 1 |
| 305 | } else { |
| 306 | e, sz = bidi.LookupString(s[n:]) |
| 307 | if sz <= 1 { |
| 308 | if sz == 1 { |
| 309 | return n, false // invalid UTF-8 |
| 310 | } |
| 311 | return n, true // incomplete UTF-8 encoding |
| 312 | } |
| 313 | } |
| 314 | // TODO: using CompactClass results in noticeable speedup. |
| 315 | // See unicode/bidi/prop.go:Properties.CompactClass. |
| 316 | c := uint16(1 << e.Class()) |
| 317 | t.seen |= c |
| 318 | if t.seen&exclusiveRTL == exclusiveRTL { |
| 319 | t.state = ruleInvalid |
| 320 | return n, false |
| 321 | } |
| 322 | switch tr := transitions[t.state]; { |
| 323 | case tr[0].mask&c != 0: |
| 324 | t.state = tr[0].next |
| 325 | case tr[1].mask&c != 0: |
| 326 | t.state = tr[1].next |
| 327 | default: |
| 328 | t.state = ruleInvalid |
| 329 | if t.isRTL() { |
| 330 | return n, false |
| 331 | } |
| 332 | } |
| 333 | n += sz |
| 334 | } |
| 335 | return n, true |
| 336 | } |