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generate.go
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generate.go
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// Package password provides a library for generating high-entropy random
// password strings via the crypto/rand package.
//
// res, err := Generate(64, 10, 10, false, false)
// if err != nil {
// log.Fatal(err)
// }
// log.Printf(res)
//
// Most functions are safe for concurrent use.
package main
import (
"crypto/rand"
"errors"
"io"
"math/big"
"strings"
)
// Built-time checks that the generators implement the interface.
var _ PasswordGenerator = (*Generator)(nil)
// PasswordGenerator is an interface that implements the Generate function. This
// is useful for testing where you can pass this interface instead of a real
// password generator to mock responses for predicability.
type PasswordGenerator interface {
Generate(int, int, int, bool, bool) (string, error)
MustGenerate(int, int, int, bool, bool) string
}
const (
// LowerLetters is the list of lowercase letters.
LowerLetters = "abcdefghijklmnopqrstuvwxyz"
// UpperLetters is the list of uppercase letters.
UpperLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
// Digits is the list of permitted digits.
Digits = "0123456789"
// Symbols is the list of symbols.
Symbols = "~!@#$%^&*()_+`-={}|[]\\:\"<>?,./"
)
var (
// ErrExceedsTotalLength is the error returned with the number of digits and
// symbols is greater than the total length.
ErrExceedsTotalLength = errors.New("number of digits and symbols must be less than total length")
// ErrLettersExceedsAvailable is the error returned with the number of letters
// exceeds the number of available letters and repeats are not allowed.
ErrLettersExceedsAvailable = errors.New("number of letters exceeds available letters and repeats are not allowed")
// ErrDigitsExceedsAvailable is the error returned with the number of digits
// exceeds the number of available digits and repeats are not allowed.
ErrDigitsExceedsAvailable = errors.New("number of digits exceeds available digits and repeats are not allowed")
// ErrSymbolsExceedsAvailable is the error returned with the number of symbols
// exceeds the number of available symbols and repeats are not allowed.
ErrSymbolsExceedsAvailable = errors.New("number of symbols exceeds available symbols and repeats are not allowed")
)
// Generator is the stateful generator which can be used to customize the list
// of letters, digits, and/or symbols.
type Generator struct {
lowerLetters string
upperLetters string
digits string
symbols string
reader io.Reader
}
// GeneratorInput is used as input to the NewGenerator function.
type GeneratorInput struct {
LowerLetters string
UpperLetters string
Digits string
Symbols string
Reader io.Reader // rand.Reader by default
}
// NewGenerator creates a new Generator from the specified configuration. If no
// input is given, all the default values are used. This function is safe for
// concurrent use.
func NewGenerator(i *GeneratorInput) (*Generator, error) {
if i == nil {
i = new(GeneratorInput)
}
g := &Generator{
lowerLetters: i.LowerLetters,
upperLetters: i.UpperLetters,
digits: i.Digits,
symbols: i.Symbols,
reader: i.Reader,
}
if g.lowerLetters == "" {
g.lowerLetters = LowerLetters
}
if g.upperLetters == "" {
g.upperLetters = UpperLetters
}
if g.digits == "" {
g.digits = Digits
}
if g.symbols == "" {
g.symbols = Symbols
}
if g.reader == nil {
g.reader = rand.Reader
}
return g, nil
}
// Generate generates a password with the given requirements. length is the
// total number of characters in the password. numDigits is the number of digits
// to include in the result. numSymbols is the number of symbols to include in
// the result. noUpper excludes uppercase letters from the results. allowRepeat
// allows characters to repeat.
//
// The algorithm is fast, but it's not designed to be performant; it favors
// entropy over speed. This function is safe for concurrent use.
func (g *Generator) Generate(length, numDigits, numSymbols int, noUpper, allowRepeat bool) (string, error) {
letters := g.lowerLetters
if !noUpper {
letters += g.upperLetters
}
chars := length - numDigits - numSymbols
if chars < 0 {
return "", ErrExceedsTotalLength
}
if !allowRepeat && chars > len(letters) {
return "", ErrLettersExceedsAvailable
}
if !allowRepeat && numDigits > len(g.digits) {
return "", ErrDigitsExceedsAvailable
}
if !allowRepeat && numSymbols > len(g.symbols) {
return "", ErrSymbolsExceedsAvailable
}
var result string
// Characters
for i := 0; i < chars; i++ {
ch, err := randomElement(g.reader, letters)
if err != nil {
return "", err
}
if !allowRepeat && strings.Contains(result, ch) {
i--
continue
}
result, err = randomInsert(g.reader, result, ch)
if err != nil {
return "", err
}
}
// Digits
for i := 0; i < numDigits; i++ {
d, err := randomElement(g.reader, g.digits)
if err != nil {
return "", err
}
if !allowRepeat && strings.Contains(result, d) {
i--
continue
}
result, err = randomInsert(g.reader, result, d)
if err != nil {
return "", err
}
}
// Symbols
for i := 0; i < numSymbols; i++ {
sym, err := randomElement(g.reader, g.symbols)
if err != nil {
return "", err
}
if !allowRepeat && strings.Contains(result, sym) {
i--
continue
}
result, err = randomInsert(g.reader, result, sym)
if err != nil {
return "", err
}
}
return result, nil
}
// MustGenerate is the same as Generate, but panics on error.
func (g *Generator) MustGenerate(length, numDigits, numSymbols int, noUpper, allowRepeat bool) string {
res, err := g.Generate(length, numDigits, numSymbols, noUpper, allowRepeat)
if err != nil {
panic(err)
}
return res
}
// Generate is the package shortcut for Generator.Generate.
func Generate(length, numDigits, numSymbols int, noUpper, allowRepeat bool) (string, error) {
gen, err := NewGenerator(nil)
if err != nil {
return "", err
}
return gen.Generate(length, numDigits, numSymbols, noUpper, allowRepeat)
}
// MustGenerate is the package shortcut for Generator.MustGenerate.
func MustGenerate(length, numDigits, numSymbols int, noUpper, allowRepeat bool) string {
res, err := Generate(length, numDigits, numSymbols, noUpper, allowRepeat)
if err != nil {
panic(err)
}
return res
}
// randomInsert randomly inserts the given value into the given string.
func randomInsert(reader io.Reader, s, val string) (string, error) {
if s == "" {
return val, nil
}
n, err := rand.Int(reader, big.NewInt(int64(len(s)+1)))
if err != nil {
return "", err
}
i := n.Int64()
return s[0:i] + val + s[i:], nil
}
// randomElement extracts a random element from the given string.
func randomElement(reader io.Reader, s string) (string, error) {
n, err := rand.Int(reader, big.NewInt(int64(len(s))))
if err != nil {
return "", err
}
return string(s[n.Int64()]), nil
}