Generating a random, fixed-length byte array in Go

Package rand

import "math/rand" 

func Read

func Read(p []byte) (n int, err error)

Read generates len(p) random bytes from the default Source and writes
them into p. It always returns len(p) and a nil error.

func (*Rand) Read

func (r *Rand) Read(p []byte) (n int, err error)

Read generates len(p) random bytes and writes them into p. It always
returns len(p) and a nil error.

For example,

package main

import (
    "math/rand"
    "fmt"
)

func main() {
    token := make([]byte, 4)
    rand.Read(token)
    fmt.Println(token)
}

Output:

[187 163 35 30]