bounded_vec: Avoid unnecessary allocation when decoding

[mrcnski]

Needed for https://github.com/paritytech/polkadot/pull/6603. See https://github.com/paritytech/polkadot/pull/6603#discussion_r1083461147:

You want to ensure that you don't even start try decoding/allocating when the length of the vector is more than the allowed maximum.

You first decode length of the vector and then early reject if that is too long.

[mrcnski]

Also probably requires a version bump for substrate to pick up the changes.

Should I do that in this PR?

Also, I'll try to get to BoundedBTreeMap and BoundedBTreeSet soon, haven't had a chance yet.

[bkchr]

As the crate is currently lacking test, I would be happy if this pr could start with this ;) We could ensure that we don't consume more data than the compact length.

[mrcnski]

@bkchr There are tests, including for that case -- see too_big_vec_fail_to_decode and too_big_fail_to_decode. Or do you mean we should check whether unnecessary memory is consumed (allocated)? I wasn't sure how to do that, or if such a test was necessary.

[mrcnski]

This PR is already approved, but would like a quick re-approval from someone (to sanity check the last two commits). :)

[ggwpez]

I wasn't sure how to do that, or if such a test was necessary.

Dump idea: Just use u32::MAX as Bound and 1MiB as value, then try to decode that. Should fail to allocate if the implementation is wrong.

[bkchr]

I wasn't sure how to do that, or if such a test was necessary.

let data = something.encode();
let data_input = &mut &data[..];

Something::decode(data_input).unwrap_err();
assert_eq!(data_input.len(), data.len() - Compact::<u32>(data.len() as u32).compact_len());

This should do it. Also some easy tests ensuring that Vec etc encodings are the same as the bounded impls.

There are tests, including for that case -- see too_big_vec_fail_to_decode and too_big_fail_to_decode

Sorry :see_no_evil:

[mrcnski]

@KiChjang Looks like I'm not able to publish 0.1.4, you're the only listed owner. Possible to add paritytech/Core devs as an owner?

[KiChjang]

I've added the core-devs team as the owner for the crate on crates.io.