// Copyright 2015 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 precis
import (
"bytes"
"errors"
"unicode/utf8"
"golang.org/x/text/cases"
"golang.org/x/text/language"
"golang.org/x/text/runes"
"golang.org/x/text/secure/bidirule"
"golang.org/x/text/transform"
"golang.org/x/text/width"
)
var (
errDisallowedRune = errors.New("precis: disallowed rune encountered")
)
var dpTrie = newDerivedPropertiesTrie(0)
// A Profile represents a set of rules for normalizing and validating strings in
// the PRECIS framework.
type Profile struct {
options
class *class
}
// NewIdentifier creates a new PRECIS profile based on the Identifier string
// class. Profiles created from this class are suitable for use where safety is
// prioritized over expressiveness like network identifiers, user accounts, chat
// rooms, and file names.
func NewIdentifier(opts ...Option) *Profile {
return &Profile{
options: getOpts(opts...),
class: identifier,
}
}
// NewFreeform creates a new PRECIS profile based on the Freeform string class.
// Profiles created from this class are suitable for use where expressiveness is
// prioritized over safety like passwords, and display-elements such as
// nicknames in a chat room.
func NewFreeform(opts ...Option) *Profile {
return &Profile{
options: getOpts(opts...),
class: freeform,
}
}
// NewRestrictedProfile creates a new PRECIS profile based on an existing
// profile.
// If the parent profile already had the Disallow option set, the new rule
// overrides the parents rule.
func NewRestrictedProfile(parent *Profile, disallow runes.Set) *Profile {
p := *parent
Disallow(disallow)(&p.options)
return &p
}
// NewTransformer creates a new transform.Transformer that performs the PRECIS
// preparation and enforcement steps on the given UTF-8 encoded bytes.
func (p *Profile) NewTransformer() *Transformer {
var ts []transform.Transformer
// These transforms are applied in the order defined in
// https://tools.ietf.org/html/rfc7564#section-7
// RFC 8266 §2.1:
//
// Implementation experience has shown that applying the rules for the
// Nickname profile is not an idempotent procedure for all code points.
// Therefore, an implementation SHOULD apply the rules repeatedly until
// the output string is stable; if the output string does not stabilize
// after reapplying the rules three (3) additional times after the first
// application, the implementation SHOULD terminate application of the
// rules and reject the input string as invalid.
//
// There is no known string that will change indefinitely, so repeat 4 times
// and rely on the Span method to keep things relatively performant.
r := 1
if p.options.repeat {
r = 4
}
for ; r > 0; r-- {
if p.options.foldWidth {
ts = append(ts, width.Fold)
}
for _, f := range p.options.additional {
ts = append(ts, f())
}
if p.options.cases != nil {
ts = append(ts, p.options.cases)
}
ts = append(ts, p.options.norm)
if p.options.bidiRule {
ts = append(ts, bidirule.New())
}
ts = append(ts, &checker{p: p, allowed: p.Allowed()})
}
// TODO: Add the disallow empty rule with a dummy transformer?
return &Transformer{transform.Chain(ts...)}
}
var errEmptyString = errors.New("precis: transformation resulted in empty string")
type buffers struct {
src []byte
buf [2][]byte
next int
}
func (b *buffers) apply(t transform.SpanningTransformer) (err error) {
n, err := t.Span(b.src, true)
if err != transform.ErrEndOfSpan {
return err
}
x := b.next & 1
if b.buf[x] == nil {
b.buf[x] = make([]byte, 0, 8+len(b.src)+len(b.src)>>2)
}
span := append(b.buf[x][:0], b.src[:n]...)
b.src, _, err = transform.Append(t, span, b.src[n:])
b.buf[x] = b.src
b.next++
return err
}
// Pre-allocate transformers when possible. In some cases this avoids allocation.
var (
foldWidthT transform.SpanningTransformer = width.Fold
lowerCaseT transform.SpanningTransformer = cases.Lower(language.Und, cases.HandleFinalSigma(false))
)
// TODO: make this a method on profile.
func (b *buffers) enforce(p *Profile, src []byte, comparing bool) (str []byte, err error) {
b.src = src
ascii := true
for _, c := range src {
if c >= utf8.RuneSelf {
ascii = false
break
}
}
// ASCII fast path.
if ascii {
for _, f := range p.options.additional {
if err = b.apply(f()); err != nil {
return nil, err
}
}
switch {
case p.options.asciiLower || (comparing && p.options.ignorecase):
for i, c := range b.src {
if 'A' <= c && c <= 'Z' {
b.src[i] = c ^ 1<<5
}
}
case p.options.cases != nil:
b.apply(p.options.cases)
}
c := checker{p: p}
if _, err := c.span(b.src, true); err != nil {
return nil, err
}
if p.disallow != nil {
for _, c := range b.src {
if p.disallow.Contains(rune(c)) {
return nil, errDisallowedRune
}
}
}
if p.options.disallowEmpty && len(b.src) == 0 {
return nil, errEmptyString
}
return b.src, nil
}
// These transforms are applied in the order defined in
// https://tools.ietf.org/html/rfc8264#section-7
r := 1
if p.options.repeat {
r = 4
}
for ; r > 0; r-- {
// TODO: allow different width transforms options.
if p.options.foldWidth || (p.options.ignorecase && comparing) {
b.apply(foldWidthT)
}
for _, f := range p.options.additional {
if err = b.apply(f()); err != nil {
return nil, err
}
}
if p.options.cases != nil {
b.apply(p.options.cases)
}
if comparing && p.options.ignorecase {
b.apply(lowerCaseT)
}
b.apply(p.norm)
if p.options.bidiRule && !bidirule.Valid(b.src) {
return nil, bidirule.ErrInvalid
}
c := checker{p: p}
if _, err := c.span(b.src, true); err != nil {
return nil, err
}
if p.disallow != nil {
for i := 0; i < len(b.src); {
r, size := utf8.DecodeRune(b.src[i:])
if p.disallow.Contains(r) {
return nil, errDisallowedRune
}
i += size
}
}
if p.options.disallowEmpty && len(b.src) == 0 {
return nil, errEmptyString
}
}
return b.src, nil
}
// Append appends the result of applying p to src writing the result to dst.
// It returns an error if the input string is invalid.
func (p *Profile) Append(dst, src []byte) ([]byte, error) {
var buf buffers
b, err := buf.enforce(p, src, false)
if err != nil {
return nil, err
}
return append(dst, b...), nil
}
func processBytes(p *Profile, b []byte, key bool) ([]byte, error) {
var buf buffers
b, err := buf.enforce(p, b, key)
if err != nil {
return nil, err
}
if buf.next == 0 {
c := make([]byte, len(b))
copy(c, b)
return c, nil
}
return b, nil
}
// Bytes returns a new byte slice with the result of applying the profile to b.
func (p *Profile) Bytes(b []byte) ([]byte, error) {
return processBytes(p, b, false)
}
// AppendCompareKey appends the result of applying p to src (including any
// optional rules to make strings comparable or useful in a map key such as
// applying lowercasing) writing the result to dst. It returns an error if the
// input string is invalid.
func (p *Profile) AppendCompareKey(dst, src []byte) ([]byte, error) {
var buf buffers
b, err := buf.enforce(p, src, true)
if err != nil {
return nil, err
}
return append(dst, b...), nil
}
func processString(p *Profile, s string, key bool) (string, error) {
var buf buffers
b, err := buf.enforce(p, []byte(s), key)
if err != nil {
return "", err
}
return string(b), nil
}
// String returns a string with the result of applying the profile to s.
func (p *Profile) String(s string) (string, error) {
return processString(p, s, false)
}
// CompareKey returns a string that can be used for comparison, hashing, or
// collation.
func (p *Profile) CompareKey(s string) (string, error) {
return processString(p, s, true)
}
// Compare enforces both strings, and then compares them for bit-string identity
// (byte-for-byte equality). If either string cannot be enforced, the comparison
// is false.
func (p *Profile) Compare(a, b string) bool {
var buf buffers
akey, err := buf.enforce(p, []byte(a), true)
if err != nil {
return false
}
buf = buffers{}
bkey, err := buf.enforce(p, []byte(b), true)
if err != nil {
return false
}
return bytes.Equal(akey, bkey)
}
// Allowed returns a runes.Set containing every rune that is a member of the
// underlying profile's string class and not disallowed by any profile specific
// rules.
func (p *Profile) Allowed() runes.Set {
if p.options.disallow != nil {
return runes.Predicate(func(r rune) bool {
return p.class.Contains(r) && !p.options.disallow.Contains(r)
})
}
return p.class
}
type checker struct {
p *Profile
allowed runes.Set
beforeBits catBitmap
termBits catBitmap
acceptBits catBitmap
}
func (c *checker) Reset() {
c.beforeBits = 0
c.termBits = 0
c.acceptBits = 0
}
func (c *checker) span(src []byte, atEOF bool) (n int, err error) {
for n < len(src) {
e, sz := dpTrie.lookup(src[n:])
d := categoryTransitions[category(e&catMask)]
if sz == 0 {
if !atEOF {
return n, transform.ErrShortSrc
}
return n, errDisallowedRune
}
doLookAhead := false
if property(e) < c.p.class.validFrom {
if d.rule == nil {
return n, errDisallowedRune
}
doLookAhead, err = d.rule(c.beforeBits)
if err != nil {
return n, err
}
}
c.beforeBits &= d.keep
c.beforeBits |= d.set
if c.termBits != 0 {
// We are currently in an unterminated lookahead.
if c.beforeBits&c.termBits != 0 {
c.termBits = 0
c.acceptBits = 0
} else if c.beforeBits&c.acceptBits == 0 {
// Invalid continuation of the unterminated lookahead sequence.
return n, errContext
}
}
if doLookAhead {
if c.termBits != 0 {
// A previous lookahead run has not been terminated yet.
return n, errContext
}
c.termBits = d.term
c.acceptBits = d.accept
}
n += sz
}
if m := c.beforeBits >> finalShift; c.beforeBits&m != m || c.termBits != 0 {
err = errContext
}
return n, err
}
// TODO: we may get rid of this transform if transform.Chain understands
// something like a Spanner interface.
func (c checker) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
short := false
if len(dst) < len(src) {
src = src[:len(dst)]
atEOF = false
short = true
}
nSrc, err = c.span(src, atEOF)
nDst = copy(dst, src[:nSrc])
if short && (err == transform.ErrShortSrc || err == nil) {
err = transform.ErrShortDst
}
return nDst, nSrc, err
}
