gtsocial-umbx

bidirule.go (9558B)

---

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