Add AsyncBufRead

[ishitatsuyuki]

std::io::BufRead being a trait allows zero-copy reading on already on-memory buffers. I propose here to add the similar thing in tokio-io. Adapters should also be added, either separated, or specialized (I haven't think into the detail).

One usecase of the async version is that adding additional transform on half-decoded byte buffers. In hyper, the response body is decoded into chunk, then we're going to apply gzip decoding on it (planned to be implemented in reqwest).

This should benefit tokio-tls as well.

[alexcrichton]

I've been using AsyncRead + std::io::BufRead for this, but what would you think AsyncBufRead would do differently?

[ishitatsuyuki]

Well, I still haven't found a usecase, but if there's something missing, it's the way to wait for fill_buf.

[alexcrichton]

Ok, in that case I believe this is solved with AsyncRead + BufRead. Waiting for fill_buf to succeed is the same as waiting for read to succeed.