Rust cryptopal challenge

extern crate rustc_serialize;

use rustc_serialize::hex::{FromHex,ToHex};


fn main() {
   let hex_str = "1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736";
         let a = "88888888888888888888888888888888888888888888888888888888888888888888";
         let result = xor(hex_str,a);
   println!("{:?}",result);

}

/*
   This function does an exclusive or operation on two hexadecimal strings
   */
   pub fn xor(a: &str, b: &str) -> Vec<u8> {
      return a.from_hex().unwrap().iter().zip(b.from_hex().unwrap().iter()).map(|(&x,&y)|x^y).collect();

   }