teleport/lib/utils/replace.go

// Copyright 2021 Gravitational, 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 utils

import (
	"regexp"
	"strings"

	"github.com/gravitational/trace"
)

// ContainsExpansion returns true if value contains
// expansion syntax, e.g. $1 or ${10}
func ContainsExpansion(val string) bool {
	return reExpansion.FindStringIndex(val) != nil
}

// GlobToRegexp replaces glob-style standalone wildcard values
// with real .* regexp-friendly values, does not modify regexp-compatible values,
// quotes non-wildcard values
func GlobToRegexp(in string) string {
	return replaceWildcard.ReplaceAllString(regexp.QuoteMeta(in), "(.*)")
}

// ReplaceRegexp replaces value in string, accepts regular expression and simplified
// wildcard syntax, it has several important differences with standard lib
// regexp replacer:
// * Wildcard globs '*' are treated as regular expression .* expression
// * Expression is treated as regular expression if it starts with ^ and ends with $
// * Full match is expected, partial replacements ignored
// * If there is no match, returns a NotFound error
func ReplaceRegexp(expression string, replaceWith string, input string) (string, error) {
	expr, err := RegexpWithConfig(expression, RegexpConfig{})
	if err != nil {
		return "", trace.Wrap(err)
	}
	return ReplaceRegexpWith(expr, replaceWith, input)
}

// RegexpWithConfig compiles a regular expression given some configuration.
// There are several important differences with standard lib (see ReplaceRegexp).
func RegexpWithConfig(expression string, config RegexpConfig) (*regexp.Regexp, error) {
	if !strings.HasPrefix(expression, "^") || !strings.HasSuffix(expression, "$") {
		// replace glob-style wildcards with regexp wildcards
		// for plain strings, and quote all characters that could
		// be interpreted in regular expression
		expression = "^" + GlobToRegexp(expression) + "$"
	}
	if config.IgnoreCase {
		expression = "(?i)" + expression
	}
	expr, err := regexp.Compile(expression)
	if err != nil {
		return nil, trace.BadParameter(err.Error())
	}
	return expr, nil
}

// ReplaceRegexp replaces string in a given regexp.
func ReplaceRegexpWith(expr *regexp.Regexp, replaceWith string, input string) (string, error) {
	// if there is no match, return NotFound error
	index := expr.FindStringIndex(input)
	if index == nil {
		return "", trace.NotFound("no match found")
	}
	return expr.ReplaceAllString(input, replaceWith), nil
}

// RegexpConfig defines the configuration of the regular expression matcher
type RegexpConfig struct {
	// IgnoreCase specifies whether matching is case-insensitive
	IgnoreCase bool
}

// SliceMatchesRegex checks if input matches any of the expressions. The
// match is always evaluated as a regex either an exact match or regexp.
func SliceMatchesRegex(input string, expressions []string) (bool, error) {
	for _, expression := range expressions {
		if !strings.HasPrefix(expression, "^") || !strings.HasSuffix(expression, "$") {
			// replace glob-style wildcards with regexp wildcards
			// for plain strings, and quote all characters that could
			// be interpreted in regular expression
			expression = "^" + GlobToRegexp(expression) + "$"
		}

		expr, err := regexp.Compile(expression)
		if err != nil {
			return false, trace.BadParameter(err.Error())
		}

		// Since the expression is always surrounded by ^ and $ this is an exact
		// match for either a a plain string (for example ^hello$) or for a regexp
		// (for example ^hel*o$).
		if expr.MatchString(input) {
			return true, nil
		}
	}

	return false, nil
}

var replaceWildcard = regexp.MustCompile(`(\\\*)`)
var reExpansion = regexp.MustCompile(`\$[^\$]+`)