114 lines
3.2 KiB
Go
114 lines
3.2 KiB
Go
// Copyright (c) 2017 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 regexp
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import (
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"fmt"
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"regexp/syntax"
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)
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// ErrNoEmpty returned when "zero width assertions" are used
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var ErrNoEmpty = fmt.Errorf("zero width assertions not allowed")
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// ErrNoWordBoundary returned when word boundaries are used
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var ErrNoWordBoundary = fmt.Errorf("word boundaries are not allowed")
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// ErrNoBytes returned when byte literals are used
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var ErrNoBytes = fmt.Errorf("byte literals are not allowed")
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// ErrNoLazy returned when lazy quantifiers are used
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var ErrNoLazy = fmt.Errorf("lazy quantifiers are not allowed")
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// ErrCompiledTooBig returned when regular expression parses into
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// too many instructions
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var ErrCompiledTooBig = fmt.Errorf("too many instructions")
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// Regexp implements the vellum.Automaton interface for matcing a user
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// specified regular expression.
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type Regexp struct {
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orig string
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dfa *dfa
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}
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// NewRegexp creates a new Regular Expression automaton with the specified
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// expression. By default it is limited to approximately 10MB for the
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// compiled finite state automaton. If this size is exceeded,
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// ErrCompiledTooBig will be returned.
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func New(expr string) (*Regexp, error) {
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return NewWithLimit(expr, 10*(1<<20))
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}
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// NewRegexpWithLimit creates a new Regular Expression automaton with
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// the specified expression. The size of the compiled finite state
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// automaton exceeds the user specified size, ErrCompiledTooBig will be
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// returned.
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func NewWithLimit(expr string, size uint) (*Regexp, error) {
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parsed, err := syntax.Parse(expr, syntax.Perl)
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if err != nil {
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return nil, err
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}
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compiler := newCompiler(size)
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insts, err := compiler.compile(parsed)
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if err != nil {
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return nil, err
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}
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dfaBuilder := newDfaBuilder(insts)
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dfa, err := dfaBuilder.build()
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if err != nil {
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return nil, err
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}
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return &Regexp{
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orig: expr,
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dfa: dfa,
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}, nil
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}
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// Start returns the start state of this automaton.
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func (r *Regexp) Start() int {
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return 1
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}
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// IsMatch returns if the specified state is a matching state.
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func (r *Regexp) IsMatch(s int) bool {
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if s < len(r.dfa.states) {
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return r.dfa.states[s].match
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}
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return false
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}
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// CanMatch returns if the specified state can ever transition to a matching
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// state.
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func (r *Regexp) CanMatch(s int) bool {
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if s < len(r.dfa.states) && s > 0 {
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return true
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}
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return false
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}
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// WillAlwaysMatch returns if the specified state will always end in a
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// matching state.
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func (r *Regexp) WillAlwaysMatch(int) bool {
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return false
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}
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// Accept returns the new state, resulting from the transite byte b
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// when currently in the state s.
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func (r *Regexp) Accept(s int, b byte) int {
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if s < len(r.dfa.states) {
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return r.dfa.states[s].next[b]
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}
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return 0
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}
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