337 lines
9.3 KiB
Go
337 lines
9.3 KiB
Go
// Copyright 2016 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 bidirule implements the Bidi Rule defined by RFC 5893.
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//
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// This package is under development. The API may change without notice and
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// without preserving backward compatibility.
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package bidirule
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import (
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"errors"
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"unicode/utf8"
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"golang.org/x/text/transform"
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"golang.org/x/text/unicode/bidi"
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)
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// This file contains an implementation of RFC 5893: Right-to-Left Scripts for
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// Internationalized Domain Names for Applications (IDNA)
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//
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// A label is an individual component of a domain name. Labels are usually
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// shown separated by dots; for example, the domain name "www.example.com" is
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// composed of three labels: "www", "example", and "com".
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//
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// An RTL label is a label that contains at least one character of class R, AL,
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// or AN. An LTR label is any label that is not an RTL label.
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//
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// A "Bidi domain name" is a domain name that contains at least one RTL label.
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//
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// The following guarantees can be made based on the above:
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//
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// o In a domain name consisting of only labels that satisfy the rule,
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// the requirements of Section 3 are satisfied. Note that even LTR
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// labels and pure ASCII labels have to be tested.
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//
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// o In a domain name consisting of only LDH labels (as defined in the
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// Definitions document [RFC5890]) and labels that satisfy the rule,
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// the requirements of Section 3 are satisfied as long as a label
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// that starts with an ASCII digit does not come after a
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// right-to-left label.
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//
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// No guarantee is given for other combinations.
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// ErrInvalid indicates a label is invalid according to the Bidi Rule.
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var ErrInvalid = errors.New("bidirule: failed Bidi Rule")
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type ruleState uint8
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const (
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ruleInitial ruleState = iota
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ruleLTR
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ruleLTRFinal
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ruleRTL
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ruleRTLFinal
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ruleInvalid
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)
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type ruleTransition struct {
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next ruleState
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mask uint16
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}
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var transitions = [...][2]ruleTransition{
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// [2.1] The first character must be a character with Bidi property L, R, or
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// AL. If it has the R or AL property, it is an RTL label; if it has the L
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// property, it is an LTR label.
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ruleInitial: {
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{ruleLTRFinal, 1 << bidi.L},
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{ruleRTLFinal, 1<<bidi.R | 1<<bidi.AL},
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},
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ruleRTL: {
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// [2.3] In an RTL label, the end of the label must be a character with
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// Bidi property R, AL, EN, or AN, followed by zero or more characters
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// with Bidi property NSM.
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{ruleRTLFinal, 1<<bidi.R | 1<<bidi.AL | 1<<bidi.EN | 1<<bidi.AN},
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// [2.2] In an RTL label, only characters with the Bidi properties R,
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// AL, AN, EN, ES, CS, ET, ON, BN, or NSM are allowed.
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// We exclude the entries from [2.3]
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{ruleRTL, 1<<bidi.ES | 1<<bidi.CS | 1<<bidi.ET | 1<<bidi.ON | 1<<bidi.BN | 1<<bidi.NSM},
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},
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ruleRTLFinal: {
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// [2.3] In an RTL label, the end of the label must be a character with
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// Bidi property R, AL, EN, or AN, followed by zero or more characters
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// with Bidi property NSM.
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{ruleRTLFinal, 1<<bidi.R | 1<<bidi.AL | 1<<bidi.EN | 1<<bidi.AN | 1<<bidi.NSM},
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// [2.2] In an RTL label, only characters with the Bidi properties R,
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// AL, AN, EN, ES, CS, ET, ON, BN, or NSM are allowed.
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// We exclude the entries from [2.3] and NSM.
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{ruleRTL, 1<<bidi.ES | 1<<bidi.CS | 1<<bidi.ET | 1<<bidi.ON | 1<<bidi.BN},
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},
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ruleLTR: {
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// [2.6] In an LTR label, the end of the label must be a character with
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// Bidi property L or EN, followed by zero or more characters with Bidi
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// property NSM.
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{ruleLTRFinal, 1<<bidi.L | 1<<bidi.EN},
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// [2.5] In an LTR label, only characters with the Bidi properties L,
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// EN, ES, CS, ET, ON, BN, or NSM are allowed.
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// We exclude the entries from [2.6].
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{ruleLTR, 1<<bidi.ES | 1<<bidi.CS | 1<<bidi.ET | 1<<bidi.ON | 1<<bidi.BN | 1<<bidi.NSM},
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},
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ruleLTRFinal: {
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// [2.6] In an LTR label, the end of the label must be a character with
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// Bidi property L or EN, followed by zero or more characters with Bidi
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// property NSM.
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{ruleLTRFinal, 1<<bidi.L | 1<<bidi.EN | 1<<bidi.NSM},
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// [2.5] In an LTR label, only characters with the Bidi properties L,
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// EN, ES, CS, ET, ON, BN, or NSM are allowed.
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// We exclude the entries from [2.6].
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{ruleLTR, 1<<bidi.ES | 1<<bidi.CS | 1<<bidi.ET | 1<<bidi.ON | 1<<bidi.BN},
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},
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ruleInvalid: {
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{ruleInvalid, 0},
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{ruleInvalid, 0},
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},
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}
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// [2.4] In an RTL label, if an EN is present, no AN may be present, and
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// vice versa.
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const exclusiveRTL = uint16(1<<bidi.EN | 1<<bidi.AN)
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// From RFC 5893
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// An RTL label is a label that contains at least one character of type
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// R, AL, or AN.
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//
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// An LTR label is any label that is not an RTL label.
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// Direction reports the direction of the given label as defined by RFC 5893.
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// The Bidi Rule does not have to be applied to labels of the category
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// LeftToRight.
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func Direction(b []byte) bidi.Direction {
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for i := 0; i < len(b); {
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e, sz := bidi.Lookup(b[i:])
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if sz == 0 {
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i++
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}
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c := e.Class()
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if c == bidi.R || c == bidi.AL || c == bidi.AN {
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return bidi.RightToLeft
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}
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i += sz
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}
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return bidi.LeftToRight
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}
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// DirectionString reports the direction of the given label as defined by RFC
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// 5893. The Bidi Rule does not have to be applied to labels of the category
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// LeftToRight.
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func DirectionString(s string) bidi.Direction {
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for i := 0; i < len(s); {
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e, sz := bidi.LookupString(s[i:])
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if sz == 0 {
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i++
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continue
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}
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c := e.Class()
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if c == bidi.R || c == bidi.AL || c == bidi.AN {
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return bidi.RightToLeft
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}
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i += sz
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}
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return bidi.LeftToRight
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}
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// Valid reports whether b conforms to the BiDi rule.
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func Valid(b []byte) bool {
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var t Transformer
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if n, ok := t.advance(b); !ok || n < len(b) {
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return false
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}
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return t.isFinal()
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}
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// ValidString reports whether s conforms to the BiDi rule.
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func ValidString(s string) bool {
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var t Transformer
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if n, ok := t.advanceString(s); !ok || n < len(s) {
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return false
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}
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return t.isFinal()
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}
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// New returns a Transformer that verifies that input adheres to the Bidi Rule.
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func New() *Transformer {
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return &Transformer{}
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}
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// Transformer implements transform.Transform.
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type Transformer struct {
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state ruleState
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hasRTL bool
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seen uint16
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}
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// A rule can only be violated for "Bidi Domain names", meaning if one of the
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// following categories has been observed.
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func (t *Transformer) isRTL() bool {
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const isRTL = 1<<bidi.R | 1<<bidi.AL | 1<<bidi.AN
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return t.seen&isRTL != 0
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}
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// Reset implements transform.Transformer.
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func (t *Transformer) Reset() { *t = Transformer{} }
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// Transform implements transform.Transformer. This Transformer has state and
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// needs to be reset between uses.
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func (t *Transformer) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
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if len(dst) < len(src) {
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src = src[:len(dst)]
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atEOF = false
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err = transform.ErrShortDst
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}
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n, err1 := t.Span(src, atEOF)
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copy(dst, src[:n])
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if err == nil || err1 != nil && err1 != transform.ErrShortSrc {
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err = err1
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}
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return n, n, err
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}
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// Span returns the first n bytes of src that conform to the Bidi rule.
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func (t *Transformer) Span(src []byte, atEOF bool) (n int, err error) {
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if t.state == ruleInvalid && t.isRTL() {
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return 0, ErrInvalid
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}
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n, ok := t.advance(src)
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switch {
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case !ok:
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err = ErrInvalid
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case n < len(src):
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if !atEOF {
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err = transform.ErrShortSrc
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break
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}
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err = ErrInvalid
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case !t.isFinal():
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err = ErrInvalid
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}
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return n, err
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}
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// Precomputing the ASCII values decreases running time for the ASCII fast path
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// by about 30%.
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var asciiTable [128]bidi.Properties
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func init() {
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for i := range asciiTable {
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p, _ := bidi.LookupRune(rune(i))
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asciiTable[i] = p
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}
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}
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func (t *Transformer) advance(s []byte) (n int, ok bool) {
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var e bidi.Properties
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var sz int
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for n < len(s) {
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if s[n] < utf8.RuneSelf {
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e, sz = asciiTable[s[n]], 1
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} else {
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e, sz = bidi.Lookup(s[n:])
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if sz <= 1 {
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if sz == 1 {
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// We always consider invalid UTF-8 to be invalid, even if
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// the string has not yet been determined to be RTL.
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// TODO: is this correct?
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return n, false
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}
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return n, true // incomplete UTF-8 encoding
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}
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}
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// TODO: using CompactClass would result in noticeable speedup.
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// See unicode/bidi/prop.go:Properties.CompactClass.
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c := uint16(1 << e.Class())
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t.seen |= c
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if t.seen&exclusiveRTL == exclusiveRTL {
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t.state = ruleInvalid
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return n, false
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}
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switch tr := transitions[t.state]; {
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case tr[0].mask&c != 0:
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t.state = tr[0].next
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case tr[1].mask&c != 0:
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t.state = tr[1].next
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default:
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t.state = ruleInvalid
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if t.isRTL() {
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return n, false
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}
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}
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n += sz
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}
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return n, true
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}
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func (t *Transformer) advanceString(s string) (n int, ok bool) {
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var e bidi.Properties
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var sz int
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for n < len(s) {
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if s[n] < utf8.RuneSelf {
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e, sz = asciiTable[s[n]], 1
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} else {
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e, sz = bidi.LookupString(s[n:])
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if sz <= 1 {
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if sz == 1 {
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return n, false // invalid UTF-8
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}
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return n, true // incomplete UTF-8 encoding
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}
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}
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// TODO: using CompactClass results in noticeable speedup.
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// See unicode/bidi/prop.go:Properties.CompactClass.
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c := uint16(1 << e.Class())
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t.seen |= c
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if t.seen&exclusiveRTL == exclusiveRTL {
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t.state = ruleInvalid
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return n, false
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}
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switch tr := transitions[t.state]; {
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case tr[0].mask&c != 0:
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t.state = tr[0].next
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case tr[1].mask&c != 0:
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t.state = tr[1].next
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default:
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t.state = ruleInvalid
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if t.isRTL() {
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return n, false
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}
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}
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n += sz
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}
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return n, true
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}
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