Show u8 slice in hex representation

Question

I need to convert &[u8] to a hex representation. For example [ A9, 45, FF, 00 ... ].

The trait std::fmt::UpperHex is not implemented for slices (so I can't use std::fmt::format). Rust has the serialize::hex::ToHex trait, which converts &[u8] to a hex String, but I need a representation with separate bytes.

I can implement trait UpperHex for &[u8] myself, but I'm not sure how canonical this would be. What is the most canonical way to do this?

Answer 1

Since the accepted answer doesn't work on Rust 1.0 stable, here's my attempt. Should be allocationless and thus reasonably fast. This is basically a formatter for [u8], but because of the coherence rules, we must wrap [u8] to a self-defined type ByteBuf(&[u8]) to use it:

struct ByteBuf<'a>(&'a [u8]);

impl<'a> std::fmt::LowerHex for ByteBuf<'a> {
    fn fmt(&self, fmtr: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
        for byte in self.0 {
            try!( fmtr.write_fmt(format_args!("{:02x}", byte)));
        }
        Ok(())
    }
}

Usage:

let buff = [0_u8; 24];
println!("{:x}", ByteBuf(&buff));

Answer 2

There's a crate for this: hex-slice.

For example:

extern crate hex_slice;
use hex_slice::AsHex;

fn main() {
    let foo = vec![0u32, 1, 2 ,3];
    println!("{:02x}", foo.as_hex());
}

Answer 3

use hex::encode:

let a: [u8;4] = [1, 3, 3, 7];
assert_eq!(hex::encode(&a), "01030307");

[dependencies]
hex = "0.4"