Go random
last modified April 11, 2024
In this article we show how to generate random values in Golang.
$ go version go version go1.22.2 linux/amd64
We use Go version 1.22.2.
Random number generator
Random number generator (RNG) generates a set of values that do not display any distinguishable patterns in their appearance. The random number generators are divided into two categories: hardware random-number generators and pseudo-random number generators. Hardware random-number generators are believed to produce genuine random numbers. Pseudo-random number generators generate values based on software algorithms. They produce values that look random. But these values are deterministic and can be reproduced, if the algorithm is known.
In computing, random generators are used in gambling, gaming, simulations, or cryptography.
To increase the quality of the pseudo random-number generators, operating systems use environmental noise collected from device drivers, user input latency, or jitter from one or more hardware components. This is the core of the cryptographically secure pseudo-random number generators.
Go contains the math/random package which implements pseudo-random
number generators, and the crypto/rand package which implements a
cryptographically secure random number generator.
The seed
The seed is a value which initializes the random number generator. Random number generators produce values by performing some operation on a previous value. When the algorithm starts, the seed is the initial value on which the generator operates. The most important and difficult part of the generators is to provide a seed that is close to a truly random number.
In Go, the seed value is provided with the rand.Seed
function. If Seed is not called, the generator behaves as if seeded
by Seed(1).
Go random same seed
In the following example, we use the same seed.
package main
import (
"fmt"
"math/rand"
)
func main() {
rand.Seed(20)
fmt.Printf("%d ", rand.Intn(100))
fmt.Printf("%d ", rand.Intn(100))
fmt.Printf("%d \n", rand.Intn(100))
rand.Seed(20)
fmt.Printf("%d ", rand.Intn(100))
fmt.Printf("%d ", rand.Intn(100))
fmt.Printf("%d \n", rand.Intn(100))
fmt.Println()
}
The same seed value produces the same pseudo-random values.
$ go run same_seed.go 30 48 40 30 48 40
Go rand.Intn
The rand.Intn function returns, as an int, a non-negative
pseudo-random number in [0,n) from the default source.
package main
import (
"fmt"
"math/rand"
"time"
)
func init() {
rand.Seed(time.Now().UnixNano())
}
func main() {
for i := 0; i < 5; i++ {
fmt.Printf("%d ", rand.Intn(20))
}
fmt.Println()
}
The example prints five random integers.
rand.Seed(time.Now().UnixNano())
To get different pseudo random values, we seed the random generator with
time.Now().UnixNano().
Go random string
The following example generates random strings.
package main
import (
"fmt"
"math/rand"
"time"
)
func main() {
rand.Seed(time.Now().UTC().UnixNano())
fmt.Println(randomString(12))
}
func randomString(len int) string {
bytes := make([]byte, len)
for i := 0; i < len; i++ {
bytes[i] = byte(randInt(97, 122))
}
return string(bytes)
}
func randInt(min int, max int) int {
return min + rand.Intn(max-min)
}
The example creates a random string having twelve characters.
$ go run random_string.go gqvqyybfuhxl $ go run random_string.go rrwmqaqkrslu $ go run random_string.go axhhrkwyhnxm
We run the example three times.
Go random array of integers
The following example creates an array of random integer values.
package main
import (
"fmt"
"math/rand"
"time"
)
func randArray(len int) []int {
a := make([]int, len)
for i := 0; i <= len-1; i++ {
a[i] = rand.Intn(len)
}
return a
}
func main() {
rand.Seed(time.Now().UnixNano())
len := 12
fmt.Println(randArray(len))
}
The example creates an array of twelve integer values.
$ go run rand_array.go [5 6 3 5 3 4 7 3 5 6 5 0] $ go run rand_array.go [2 5 10 9 1 5 1 4 11 7 6 3]
Go random element
The following example picks a random element.
package main
import (
"fmt"
"math/rand"
"time"
)
func init() {
rand.Seed(time.Now().UnixNano())
}
func main() {
runes := []rune("červená čiara")
myrune := runes[rand.Intn(len(runes))]
fmt.Println(string(myrune))
}
We have a slice of runes. From this slice, we randomly pick a value.
$ go run random_element.go č $ go run random_element.go á
We ran the example twice and get these characters.
Go random string from a pool
The following example picks letters randomly from a pool of characters.
package main
import (
"fmt"
"math/rand"
"time"
)
var pool = "abcdefghijklmnopqrstuvwxyzABCEFGHIJKLMNOPQRSTUVWXYZ:|?$%@][{}#&/()*"
func randomString(l int) string {
bytes := make([]byte, l)
for i := 0; i < l; i++ {
bytes[i] = pool[rand.Intn(len(pool))]
}
return string(bytes)
}
func main() {
rand.Seed(time.Now().UnixNano())
fmt.Println(randomString(12))
}
The example prints random strings from the predefined pool of various characters.
var pool = "abcdefghijklmnopqrstuvwxyzABCEFGHIJKLMNOPQRSTUVWXYZ:|?$%@][{}#&/()*"
This is the set of predefined characters.
for i := 0; i < l; i++ {
bytes[i] = pool[rand.Intn(len(pool))]
}
We pick a random letter by generating a random index of the string.
$ go run rand_pool.go
FFFZW(sHvE:a
$ go run rand_pool.go
(my%Tmf&qOVs
$ go run rand_pool.go
/{GqgkhRVOfi
We run the example three times.
Go crypto-secure random values
Go provides cryptographically secure pseudorandom number generator in the
standard library package crypto/rand. While math/random
is much faster, crypto/rand is suited for programs where security
is paramount. For instance, when generating strong passwords, CSRF tokens,
or session keys.
On Linux and FreeBSD, crypto/rand uses getrandom
if available, /dev/urandom otherwise. On OpenBSD, it uses
getentropy. Unix-likesystems, it reads from
/dev/urandom. On Windows systems, it uses the CryptGenRandom
function. On Wasm, it uses the Web Crypto API.
package main
import (
"crypto/rand"
"fmt"
"log"
)
func main() {
data, err := generateRandomBytes(16)
if err != nil {
log.Fatal(err)
}
fmt.Println(data)
}
func generateRandomBytes(n int) ([]byte, error) {
b := make([]byte, n)
_, err := rand.Read(b)
if err != nil {
return nil, err
}
return b, nil
}
In the code example, we create 16 securely generated random bytes.
b := make([]byte, n) _, err := rand.Read(b)
We read n cryptographically secure pseudorandom numbers and write
them into a byte slice.
$ go run crypto_rand.go [151 0 67 88 199 60 220 50 34 198 169 158 18 162 85 61]
Source
Go math/rand package - reference
In this article we have worked with random values in Golang.
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