Generate Random Strings in Go

package main

import (
    "crypto/rand"
    "fmt"
    "math/big"
)

const (
    alphanumeric = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
    hexChars     = "0123456789abcdef"
)

func generateRandomString(length int, customChars string) (string, error) {
    if customChars == "" {
        customChars = alphanumeric
    }

    result := make([]byte, length)
    charsLen := big.NewInt(int64(len(customChars)))

    for i := 0; i < length; i++ {
        num, err := rand.Int(rand.Reader, charsLen)
        if err != nil {
            return "", err
        }
        result[i] = customChars[num.Int64()]
    }

    return string(result), nil
}

func main() {
    // Generate a 16-character alphanumeric string
    randomString, _ := generateRandomString(16, "")
    fmt.Println(randomString)  // Example: aB3xY7mN2pQ9zR5t

    // Generate a 12-character hex string
    hexString, _ := generateRandomString(12, hexChars)
    fmt.Println(hexString)  // Example: a3f7b2e9c4d1

    // Generate a 10-character lowercase string
    lowercaseString, _ := generateRandomString(10, "abcdefghijklmnopqrstuvwxyz")
    fmt.Println(lowercaseString)  // Example: xmkpqrstuv
}