I’m assuming you specifically want the result to be a 48 byte array.
stringBytes := []byte(siteName) // convert input string to slice of bytes
var result [48]byte
copy( result[:], stringBytes ) // copy expects slice parameters, but the [:] tricks it I guess
return result
I don’t use arrays much, but think this should work.
Keep in mind that this passes the 48 byte array by value. If you really do want an array instead of just a slice, you might want to pass a pointer instead.