Pad a function with random bytes

Question

I'm writing a function to append 5-10 bytes (count is random) at the beginning of a byte array, and 5-10 random bytes at the end:

func padWithRandomBytes(b []byte) []byte {
 startBytes := make([]byte, 10-rand.Intn(5))
 endBytes := make([]byte, 10-rand.Intn(5))
 newSlice := make([]byte, len(startBytes)+len(b)+len(endBytes))
 copy(newSlice[:len(startBytes)], startBytes)
 copy(newSlice[len(startBytes):len(startBytes)+len(b)], b)
 copy(newSlice[len(startBytes)+len(b):], endBytes)
 return newSlice
}

This feels pretty inefficient. Is there a more intuitive way to write this in Go?

Answer 1

For example,

package main
import (
 "fmt"
 "math/rand"
 "time"
)
func padWithRandomBytes(b []byte) []byte {
 s := 5 + rand.Intn(5+1)
 e := 5 + rand.Intn(5+1)
 r := make([]byte, s+len(b)+e)
 copy(r[s:], b)
 return r
}
func main() {
 rand.Seed(time.Now().UnixNano())
 b := []byte{1, 2, 3}
 fmt.Println(len(b), b)
 r := padWithRandomBytes(b)
 fmt.Println(len(r), r)
}

Output (random):

3 [1 2 3]
20 [0 0 0 0 0 0 0 0 1 2 3 0 0 0 0 0 0 0 0 0]
3 [1 2 3]
15 [0 0 0 0 0 0 1 2 3 0 0 0 0 0 0]