Extend `Digest` trait to support inputting data from a `Read`-able object about hashes HOT 5 CLOSED

You are right that such method is nice to have. Initially I thought about implementing Write trait, but I was hesitant to add it, as it would be incompatible with no_std and I didn't want to add std feature to every digest crate. But thanks to your issue it seems I found a good way to do it.

I've added DigestReader trait to the digest crate behind std feature gate. In contrast to your proposal it's an additive feature, so while digest crates do not use std feature your can enable it in Cargo.toml:

[dependencies]
blake2 = "0.5.1"
digest = {version="0.5.1", features=["std"]}

And then use DigestReader in your code:

let mut hash = Blake2b::default();
hash.read_from(&mut file).unwrap();
let result = hash.result();
println!("{:x}\t{}", result, path);

As afterthought I am thinking it's also worth to add a convenience function which will look like this:

pub fn digest_reader<D>(source: &mut io::Read)
    -> io::Result<GenericArray<u8, D::OutputSize>>
    where D: Default + DigestReader + FixedOutput
{
    let mut digest: D = Default::default();
    digest.read_from(source)?;
    Ok(digest.fixed_result())
}

UPD: I've added it in the digest v0.5.2.

from hashes.

I guess this method would actually go under the Input trait in the digest crate - not Digest. In any case, I see the Crates.io links are outdated & digest is hosted at https://github.com/RustCrypto/traits now. Should I move the issue there?

from hashes.

Ok, I'm using the digest_reader function in my own crate now. I don't have any tests for this portion yet, but it's compiling alright!

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BTW you can write your code shorter without unnecessary copy:

&Some(hash) => {
    let mut file = File::open(path).expect("Failed to open file");
    let result = digest_reader::<Sha256>(&mut file).expect("Failed to read data from file");
    hash == result.as_slice()
}

Also in the next version of digest I will add digest_reader to the trait, so we could use Sha256::digest_reader(..) without turbofish operator. Should've done it initially, but forgot about it for some reason...

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@newpavlov Thanks for the tip. FWIW, this portion of the code is tested now, so the DigestReader trait seems to be working as expected.

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