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forgejo/vendor/github.com/blevesearch/vellum/regexp/regexp.go
2021-02-28 18:08:33 -05:00

119 lines
3.4 KiB
Go
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// Copyright (c) 2017 Couchbase, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package regexp
import (
"fmt"
"regexp/syntax"
)
// ErrNoEmpty returned when "zero width assertions" are used
var ErrNoEmpty = fmt.Errorf("zero width assertions not allowed")
// ErrNoWordBoundary returned when word boundaries are used
var ErrNoWordBoundary = fmt.Errorf("word boundaries are not allowed")
// ErrNoBytes returned when byte literals are used
var ErrNoBytes = fmt.Errorf("byte literals are not allowed")
// ErrNoLazy returned when lazy quantifiers are used
var ErrNoLazy = fmt.Errorf("lazy quantifiers are not allowed")
// ErrCompiledTooBig returned when regular expression parses into
// too many instructions
var ErrCompiledTooBig = fmt.Errorf("too many instructions")
var DefaultLimit = uint(10 * (1 << 20))
// Regexp implements the vellum.Automaton interface for matcing a user
// specified regular expression.
type Regexp struct {
orig string
dfa *dfa
}
// NewRegexp creates a new Regular Expression automaton with the specified
// expression. By default it is limited to approximately 10MB for the
// compiled finite state automaton. If this size is exceeded,
// ErrCompiledTooBig will be returned.
func New(expr string) (*Regexp, error) {
return NewWithLimit(expr, DefaultLimit)
}
// NewRegexpWithLimit creates a new Regular Expression automaton with
// the specified expression. The size of the compiled finite state
// automaton exceeds the user specified size, ErrCompiledTooBig will be
// returned.
func NewWithLimit(expr string, size uint) (*Regexp, error) {
parsed, err := syntax.Parse(expr, syntax.Perl)
if err != nil {
return nil, err
}
return NewParsedWithLimit(expr, parsed, size)
}
func NewParsedWithLimit(expr string, parsed *syntax.Regexp, size uint) (*Regexp, error) {
compiler := newCompiler(size)
insts, err := compiler.compile(parsed)
if err != nil {
return nil, err
}
dfaBuilder := newDfaBuilder(insts)
dfa, err := dfaBuilder.build()
if err != nil {
return nil, err
}
return &Regexp{
orig: expr,
dfa: dfa,
}, nil
}
// Start returns the start state of this automaton.
func (r *Regexp) Start() int {
return 1
}
// IsMatch returns if the specified state is a matching state.
func (r *Regexp) IsMatch(s int) bool {
if s < len(r.dfa.states) {
return r.dfa.states[s].match
}
return false
}
// CanMatch returns if the specified state can ever transition to a matching
// state.
func (r *Regexp) CanMatch(s int) bool {
if s < len(r.dfa.states) && s > 0 {
return true
}
return false
}
// WillAlwaysMatch returns if the specified state will always end in a
// matching state.
func (r *Regexp) WillAlwaysMatch(int) bool {
return false
}
// Accept returns the new state, resulting from the transition byte b
// when currently in the state s.
func (r *Regexp) Accept(s int, b byte) int {
if s < len(r.dfa.states) {
return r.dfa.states[s].next[b]
}
return 0
}