Function buffer_bytes 

pub fn buffer_bytes<'b, S, E>(
    stream: S,
    size: usize,
) -> impl Stream<Item = Result<Bytes, E>> + Send + 'b
where
    S: Stream<Item = Result<Bytes, E>> + Send + 'b,
    E: Send + 'b,

Coalesce output into chunks of at least size bytes.

The final chunk is whatever is left over, and may be shorter.