block-padding: remove unsafe code

[newpavlov]

The only piece of unsafe code in the crate resides in the blanket implementation of the Padding::unpad_blocks method. It would be nice to remove it, but we need something like slice_as_flattened to be added into hybrid-array (i.e. equivalent of slice::as_flattened).

[newpavlov]

I tried to use Array::cast_slice_to_core(blocks).as_flattened(), but it has failed with the following error:

error[E0271]: type mismatch resolving `<BlockSize as ArraySize>::ArrayType<u8> == [u8; _]`
   --> block-padding/src/lib.rs:82:53
    |
 82 |         let data: &[u8] = Array::cast_slice_to_core(blocks).as_flattened();
    |                           ------------------------- ^^^^^^ expected `[u8; _]`, found associated type
    |                           |
    |                           required by a bound introduced by this call
    |
    = note:        expected array `[u8; _]`
            found associated type `<BlockSize as hybrid_array::ArraySize>::ArrayType<u8>`

[tarcieri]

@newpavlov this should do it: RustCrypto/hybrid-array#142

[newpavlov]

@tarcieri Could you publish v0.4.2 with the addition or do you plan to add something else?

[tarcieri]

sure

[tarcieri]

it's published