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The following regex patterns are optimized: - literal string match, e.g. "foo" - prefix match, e.g. "foo.*" and "foo.+" - substring match, e.g. ".*foo.*" and ".+foo.+" - alternate values match, e.g. "foo|bar|baz"
119 lines
3.2 KiB
Go
119 lines
3.2 KiB
Go
package regexutil
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import (
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"regexp"
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"strings"
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)
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// PromRegex implements an optimized string matching for Prometheus-like regex.
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//
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// The following regexs are optimized:
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//
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// - plain string such as "foobar"
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// - alternate strings such as "foo|bar|baz"
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// - prefix match such as "foo.*" or "foo.+"
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// - substring match such as ".*foo.*" or ".+bar.+"
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type PromRegex struct {
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// prefix contains literal prefix for regex.
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// For example, prefix="foo" for regex="foo(a|b)"
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prefix string
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// Suffix contains regex suffix left after removing the prefix.
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// For example, suffix="a|b" for regex="foo(a|b)"
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suffix string
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// substrDotStar contains literal string for regex suffix=".*string.*"
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substrDotStar string
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// substrDotPlus contains literal string for regex suffix=".+string.+"
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substrDotPlus string
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// orValues contains or values for the suffix regex.
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// For example, orValues contain ["foo","bar","baz"] for regex suffix="foo|bar|baz"
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orValues []string
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// reSuffix contains an anchored regexp built from suffix:
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// "^(?:suffix)$"
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reSuffix *regexp.Regexp
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}
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// NewPromRegex returns PromRegex for the given expr.
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func NewPromRegex(expr string) (*PromRegex, error) {
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if _, err := regexp.Compile(expr); err != nil {
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return nil, err
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}
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prefix, suffix := Simplify(expr)
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orValues := GetOrValues(suffix)
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substrDotStar := getSubstringLiteral(suffix, ".*")
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substrDotPlus := getSubstringLiteral(suffix, ".+")
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// It is expected that Optimize returns valid regexp in suffix, so use MustCompile here.
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// Anchor suffix to the beginning and the end of the matching string.
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suffixExpr := "^(?:" + suffix + ")$"
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reSuffix := regexp.MustCompile(suffixExpr)
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pr := &PromRegex{
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prefix: prefix,
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suffix: suffix,
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substrDotStar: substrDotStar,
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substrDotPlus: substrDotPlus,
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orValues: orValues,
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reSuffix: reSuffix,
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}
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return pr, nil
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}
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// MatchString retruns true if s matches pr.
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//
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// The pr is automatically anchored to the beginning and to the end
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// of the matching string with '^' and '$'.
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func (pr *PromRegex) MatchString(s string) bool {
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if !strings.HasPrefix(s, pr.prefix) {
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// Fast path - s has another prefix than pr.
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return false
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}
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s = s[len(pr.prefix):]
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if len(pr.orValues) > 0 {
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// Fast path - pr contains only alternate strings such as 'foo|bar|baz'
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for _, v := range pr.orValues {
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if s == v {
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return true
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}
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}
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return false
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}
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if pr.substrDotStar != "" {
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// Fast path - pr contains ".*someText.*"
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return strings.Contains(s, pr.substrDotStar)
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}
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if pr.substrDotPlus != "" {
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// Fast path - pr contains ".+someText.+"
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n := strings.Index(s, pr.substrDotPlus)
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return n > 0 && n + len(pr.substrDotPlus) < len(s)
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}
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switch pr.suffix {
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case ".*":
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// Fast path - the pr contains "prefix.*"
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return true
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case ".+":
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// Fast path - the pr contains "prefix.+"
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return len(s) > 0
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}
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// Fall back to slow path by matching the original regexp.
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return pr.reSuffix.MatchString(s)
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}
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func getSubstringLiteral(expr, prefixSuffix string) string {
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if !strings.HasPrefix(expr, prefixSuffix) {
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return ""
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}
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expr = expr[len(prefixSuffix):]
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if !strings.HasSuffix(expr, prefixSuffix) {
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return ""
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}
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expr = expr[:len(expr)-len(prefixSuffix)]
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prefix, suffix := Simplify(expr)
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if suffix != "" {
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return ""
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}
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return prefix
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}
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