prometheus/pkg/labels/regexp.go

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// Copyright 2020 The Prometheus Authors
// 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 labels
import (
"regexp"
"regexp/syntax"
"strings"
)
type FastRegexMatcher struct {
re *regexp.Regexp
prefix string
suffix string
contains string
}
func NewFastRegexMatcher(v string) (*FastRegexMatcher, error) {
re, err := regexp.Compile("^(?:" + v + ")$")
if err != nil {
return nil, err
}
parsed, err := syntax.Parse(v, syntax.Perl)
if err != nil {
return nil, err
}
m := &FastRegexMatcher{
re: re,
}
if parsed.Op == syntax.OpConcat {
m.prefix, m.suffix, m.contains = optimizeConcatRegex(parsed)
}
return m, nil
}
func (m *FastRegexMatcher) MatchString(s string) bool {
if m.prefix != "" && !strings.HasPrefix(s, m.prefix) {
return false
}
if m.suffix != "" && !strings.HasSuffix(s, m.suffix) {
return false
}
if m.contains != "" && !strings.Contains(s, m.contains) {
return false
}
return m.re.MatchString(s)
}
func (m *FastRegexMatcher) GetRegexString() string {
return m.re.String()
}
// optimizeConcatRegex returns literal prefix/suffix text that can be safely
// checked against the label value before running the regexp matcher.
func optimizeConcatRegex(r *syntax.Regexp) (prefix, suffix, contains string) {
sub := r.Sub
// We can safely remove begin and end text matchers respectively
// at the beginning and end of the regexp.
if len(sub) > 0 && sub[0].Op == syntax.OpBeginText {
sub = sub[1:]
}
if len(sub) > 0 && sub[len(sub)-1].Op == syntax.OpEndText {
sub = sub[:len(sub)-1]
}
if len(sub) == 0 {
return
}
// Given Prometheus regex matchers are always anchored to the begin/end
// of the text, if the first/last operations are literals, we can safely
// treat them as prefix/suffix.
if sub[0].Op == syntax.OpLiteral {
prefix = string(sub[0].Rune)
}
if last := len(sub) - 1; sub[last].Op == syntax.OpLiteral {
suffix = string(sub[last].Rune)
}
// If contains any literal which is not a prefix/suffix, we keep the
// 1st one. We do not keep the whole list of literals to simplify the
// fast path.
for i := 1; i < len(sub)-1; i++ {
if sub[i].Op == syntax.OpLiteral {
contains = string(sub[i].Rune)
break
}
}
return
}