[Question] PublicKey as_bytes and from_bytes

[roynalnaruto]

Hello, thank you for the wonderful work that has been put into building this library!

As I understand, a PublicKey by default is stored in the compressed form (33 bytes).

On obtaining a byte array for the public key, I get an array of length 33

let mut rng = rand::thread_rng();
let secret_key = SecretKey::generate(rng);
let public_key = PublicKey::from_secret_key(&secret_key, true)
    .expect("invalid secret key");

// length 33 (compressed form)
let public_key_bytes = public_key.as_bytes()

When I try to construct the publicKey back from these bytes:

let public_key = PublicKey::from_bytes(&public_key_bytes);

I get an error:

error[E0277]: arrays only have std trait implementations for lengths 0..=32
   --> ethers-core/src/types/crypto/keys.rs:308:60
    |
308 |                 let public_key = PublicKey::from_bytes(&public_key_bytes)
    |                                                            ^^^^^^ the trait `std::array::LengthAtMost32` is not implemented for `[u8; 33]`
    |
    = note: required because of the requirements on the impl of `std::convert::AsRef<[u8]>` for `[u8; 33]`
    = note: required because of the requirements on the impl of `std::convert::AsRef<[u8]>` for `&[u8; 33]`
    = note: required by `elliptic_curve::weierstrass::public_key::PublicKey::<C>::from_bytes`

Basically, the from_bytes expects a byte array of length 32.

What am I missing here? Any help would be appreciated.

[tarcieri]

This is a (recently removed) limitation of the Rust standard library: common trait impls used to be special cased for [T; 0] -> [T; 32] because Rust's type system didn't used to support const generics. But now it does and this restriction was recently removed in the nightly compiler.

In the meantime you'll need to explicitly slice the array to get &[u8]:

let public_key = PublicKey::from_bytes(&public_key_bytes[..]);