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|
// Package match provides a simple pattern matcher with unicode support.
package match
import (
"unicode/utf8"
)
// Match returns true if str matches pattern. This is a very
// simple wildcard match where '*' matches on any number characters
// and '?' matches on any one character.
//
// pattern:
// { term }
// term:
// '*' matches any sequence of non-Separator characters
// '?' matches any single non-Separator character
// c matches character c (c != '*', '?', '\\')
// '\\' c matches character c
//
func Match(str, pattern string) bool {
if pattern == "*" {
return true
}
return match(str, pattern, 0, nil, -1) == rMatch
}
// MatchLimit is the same as Match but will limit the complexity of the match
// operation. This is to avoid long running matches, specifically to avoid ReDos
// attacks from arbritary inputs.
//
// How it works:
// The underlying match routine is recursive and may call itself when it
// encounters a sandwiched wildcard pattern, such as: `user:*:name`.
// Everytime it calls itself a counter is incremented.
// The operation is stopped when counter > maxcomp*len(str).
func MatchLimit(str, pattern string, maxcomp int) (matched, stopped bool) {
if pattern == "*" {
return true, false
}
counter := 0
r := match(str, pattern, len(str), &counter, maxcomp)
if r == rStop {
return false, true
}
return r == rMatch, false
}
type result int
const (
rNoMatch result = iota
rMatch
rStop
)
func match(str, pat string, slen int, counter *int, maxcomp int) result {
// check complexity limit
if maxcomp > -1 {
if *counter > slen*maxcomp {
return rStop
}
*counter++
}
for len(pat) > 0 {
var wild bool
pc, ps := rune(pat[0]), 1
if pc > 0x7f {
pc, ps = utf8.DecodeRuneInString(pat)
}
var sc rune
var ss int
if len(str) > 0 {
sc, ss = rune(str[0]), 1
if sc > 0x7f {
sc, ss = utf8.DecodeRuneInString(str)
}
}
switch pc {
case '?':
if ss == 0 {
return rNoMatch
}
case '*':
// Ignore repeating stars.
for len(pat) > 1 && pat[1] == '*' {
pat = pat[1:]
}
// If this star is the last character then it must be a match.
if len(pat) == 1 {
return rMatch
}
// Match and trim any non-wildcard suffix characters.
var ok bool
str, pat, ok = matchTrimSuffix(str, pat)
if !ok {
return rNoMatch
}
// Check for single star again.
if len(pat) == 1 {
return rMatch
}
// Perform recursive wildcard search.
r := match(str, pat[1:], slen, counter, maxcomp)
if r != rNoMatch {
return r
}
if len(str) == 0 {
return rNoMatch
}
wild = true
default:
if ss == 0 {
return rNoMatch
}
if pc == '\\' {
pat = pat[ps:]
pc, ps = utf8.DecodeRuneInString(pat)
if ps == 0 {
return rNoMatch
}
}
if sc != pc {
return rNoMatch
}
}
str = str[ss:]
if !wild {
pat = pat[ps:]
}
}
if len(str) == 0 {
return rMatch
}
return rNoMatch
}
// matchTrimSuffix matches and trims any non-wildcard suffix characters.
// Returns the trimed string and pattern.
//
// This is called because the pattern contains extra data after the wildcard
// star. Here we compare any suffix characters in the pattern to the suffix of
// the target string. Basically a reverse match that stops when a wildcard
// character is reached. This is a little trickier than a forward match because
// we need to evaluate an escaped character in reverse.
//
// Any matched characters will be trimmed from both the target
// string and the pattern.
func matchTrimSuffix(str, pat string) (string, string, bool) {
// It's expected that the pattern has at least two bytes and the first byte
// is a wildcard star '*'
match := true
for len(str) > 0 && len(pat) > 1 {
pc, ps := utf8.DecodeLastRuneInString(pat)
var esc bool
for i := 0; ; i++ {
if pat[len(pat)-ps-i-1] != '\\' {
if i&1 == 1 {
esc = true
ps++
}
break
}
}
if pc == '*' && !esc {
match = true
break
}
sc, ss := utf8.DecodeLastRuneInString(str)
if !((pc == '?' && !esc) || pc == sc) {
match = false
break
}
str = str[:len(str)-ss]
pat = pat[:len(pat)-ps]
}
return str, pat, match
}
var maxRuneBytes = [...]byte{244, 143, 191, 191}
// Allowable parses the pattern and determines the minimum and maximum allowable
// values that the pattern can represent.
// When the max cannot be determined, 'true' will be returned
// for infinite.
func Allowable(pattern string) (min, max string) {
if pattern == "" || pattern[0] == '*' {
return "", ""
}
minb := make([]byte, 0, len(pattern))
maxb := make([]byte, 0, len(pattern))
var wild bool
for i := 0; i < len(pattern); i++ {
if pattern[i] == '*' {
wild = true
break
}
if pattern[i] == '?' {
minb = append(minb, 0)
maxb = append(maxb, maxRuneBytes[:]...)
} else {
minb = append(minb, pattern[i])
maxb = append(maxb, pattern[i])
}
}
if wild {
r, n := utf8.DecodeLastRune(maxb)
if r != utf8.RuneError {
if r < utf8.MaxRune {
r++
if r > 0x7f {
b := make([]byte, 4)
nn := utf8.EncodeRune(b, r)
maxb = append(maxb[:len(maxb)-n], b[:nn]...)
} else {
maxb = append(maxb[:len(maxb)-n], byte(r))
}
}
}
}
return string(minb), string(maxb)
}
// IsPattern returns true if the string is a pattern.
func IsPattern(str string) bool {
for i := 0; i < len(str); i++ {
if str[i] == '*' || str[i] == '?' {
return true
}
}
return false
}
|
