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// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0
package random
import (
// Rule to assert on string values.
type Rule interface {
// Pass should return true if the provided value passes any assertions this Rule is making.
Pass(value []rune) bool
// Type returns the name of the rule as associated in the registry
Type() string
// CharsetRule requires a certain number of characters from the specified charset.
type CharsetRule struct {
// CharsetRule is the list of rules that candidate strings must contain a minimum number of.
Charset runes `mapstructure:"charset" json:"charset"`
// MinChars indicates the minimum (inclusive) number of characters from the charset that should appear in the string.
MinChars int `mapstructure:"min-chars" json:"min-chars"`
// ParseCharset from the provided data map. The data map is expected to be parsed from HCL.
func ParseCharset(data map[string]interface{}) (rule Rule, err error) {
cr := &CharsetRule{}
decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
Metadata: nil,
Result: cr,
DecodeHook: stringToRunesFunc,
if err != nil {
return nil, fmt.Errorf("unable to decode charset restriction: %w", err)
err = decoder.Decode(data)
if err != nil {
return nil, fmt.Errorf("failed to parse charset restriction: %w", err)
return *cr, nil
func (c CharsetRule) Type() string {
return "charset"
// Chars returns the charset that this rule is looking for.
func (c CharsetRule) Chars() []rune {
return c.Charset
func (c CharsetRule) MinLength() int {
return c.MinChars
// Pass returns true if the provided candidate string has a minimum number of chars in it.
// This adheres to the Rule interface
func (c CharsetRule) Pass(value []rune) bool {
if c.MinChars <= 0 {
return true
count := 0
for _, r := range value {
// charIn is sometimes faster than a map lookup because the data is so small
// This is being kept rather than converted to a map to keep the code cleaner,
// otherwise there would need to be additional parsing logic.
if charIn(r, c.Charset) {
if count >= c.MinChars {
return true
return false
func charIn(search rune, charset []rune) bool {
for _, r := range charset {
if search == r {
return true
return false