Generating a random, fixed-length byte array in Go

Question

I have a byte array, with a fixed length of 4.

token := make([]byte, 4)

I need to set each byte to a random byte. How can I do so, in the most

Answer 1

Using math.Rand means that you are using the system CSPRNG that your operating system provides. This means using /dev/urandom/ and Windows’ CryptGenRandom API. Go’s crypto/rand package, thankfully, abstracts these implementation details away to minimise the risk of getting it wrong.

import(
   "crypto/rand"
   "encoding/base64"
 )

// GenerateRandomBytes returns securely generated random bytes. 
// It will return an error if the system's secure random
// number generator fails to function correctly, in which
// case the caller should not continue.
func GenerateRandomBytes(n int) ([]byte, error) {
     b := make([]byte, n)
    _, err := rand.Read(b)
    // Note that err == nil only if we read len(b) bytes.
    if err != nil {
       return nil, err
   }

   return b, nil
}