Adds Buf impl for VecDeque<impl Buf>

[b01o]

This PR adds an implementation of the Buf trait for VecDeque<impl Buf>.

Sometimes we need to store multiple non-contiguous Bytes at runtime. Using Chain can be limiting because it doesn't provide a concrete type for a collection of buffers. Implementing Buf for VecDeque<impl Buf> gives a handy way to view these disjoint chunks as a single logical buffer.

Update:

• Buf is implemented for VecDeque<impl Buf> instead of VecDeque<Bytes>.
• implements chunks_vectored for VecDeque<impl Buf>
• only return empty chunks if remaining() is 0
• adds a test for chunks_vectored()

[paolobarbolini]

Now that I think of it more, this violates the implementer notes on chunk(). Since we accept any VecDeque, there could be empty elements within it, something that common BufList implementations prevent ^{1 2}

chunk() should return an empty slice if and only if remaining() returns 0

Footnotes

1. https://docs.rs/crate/hyper/1.8.1/source/src/common/buf.rs#17-21 ↩

2. https://docs.rs/crate/watermelon-proto/0.1.8/source/src/util/buf_list.rs#22-27 ↩

[b01o]

I see what you mean, let me try to make it follow the contract.

[Darksonn]

If we need a bugfix to existing code, it should be a separate PR.

[Darksonn]

This loop must exit if the chunks written by buf have a combined length smaller than buf.remaining(), because you must read everything from the first buffer before you start reading from the second buffer. Please add a test that would have caught this.

[b01o]

The access issue should be fixed now. Let me know if I missed anything.

[Darksonn]

Tests go in tests/ directory outside of src/ unless they have to be here.

[b01o]

Now under tests/test_buf.rs.