mirror of https://github.com/go-gitea/gitea.git
76 lines
1.9 KiB
Go
76 lines
1.9 KiB
Go
// Copyright (c) 2018 Couchbase, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package segment
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import (
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"regexp/syntax"
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"github.com/couchbase/vellum/regexp"
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)
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func ParseRegexp(pattern string) (a *regexp.Regexp, prefixBeg, prefixEnd []byte, err error) {
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// TODO: potential optimization where syntax.Regexp supports a Simplify() API?
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parsed, err := syntax.Parse(pattern, syntax.Perl)
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if err != nil {
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return nil, nil, nil, err
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}
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re, err := regexp.NewParsedWithLimit(pattern, parsed, regexp.DefaultLimit)
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if err != nil {
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return nil, nil, nil, err
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}
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prefix := LiteralPrefix(parsed)
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if prefix != "" {
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prefixBeg := []byte(prefix)
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prefixEnd := IncrementBytes(prefixBeg)
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return re, prefixBeg, prefixEnd, nil
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}
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return re, nil, nil, nil
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}
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// Returns the literal prefix given the parse tree for a regexp
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func LiteralPrefix(s *syntax.Regexp) string {
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// traverse the left-most branch in the parse tree as long as the
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// node represents a concatenation
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for s != nil && s.Op == syntax.OpConcat {
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if len(s.Sub) < 1 {
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return ""
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}
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s = s.Sub[0]
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}
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if s.Op == syntax.OpLiteral && (s.Flags&syntax.FoldCase == 0) {
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return string(s.Rune)
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}
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return "" // no literal prefix
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}
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func IncrementBytes(in []byte) []byte {
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rv := make([]byte, len(in))
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copy(rv, in)
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for i := len(rv) - 1; i >= 0; i-- {
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rv[i] = rv[i] + 1
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if rv[i] != 0 {
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return rv // didn't overflow, so stop
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}
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}
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return nil // overflowed
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}
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