Stop zeroing buffers in the local file storage.

[fulmicoton]

No description provided.

[rdettai]

If you want to avoid using unsafe, I think you can use .take(num_bytes).read_to_end(&mut vec)

[fulmicoton]

Oh? @rdettai does that do only one alloc?

[fulmicoton]

@rdettai this is a neat trick. Digging a little deeper.
Take does not pass a size hint to read_to_end(..).

This is not a problem per se. That means we would have to preallocate the vector, with with_capacity(..).
We would just have to be careful to allocate with a capacity of max(len, 8000), because read_to_end allocate such a buffer.

I however did not dig too deep into the implementation of default_read_to_end. I think we can stick with the unsafe code considering how contains it is.

[PSeitz]

@rdettai this is a neat trick. Digging a little deeper. Take does not pass a size hint to read_to_end(..).

This is not a problem per se. That means we would have to preallocate the vector, with with_capacity(..). We would just have to be careful to allocate with a capacity of max(len, 8000), because read_to_end allocate such a buffer.

I however did not dig too deep into the implementation of default_read_to_end. I think we can stick with the unsafe code considering how contains it is.

I think with take we end up in the non specialized read version for the Vec, which is much slower usually.