tokio_util::codec::FramedRead
→tokio_util::codec::Framed
FramedReadはStream (futures_core::Stream )を実装していて、poll_next で次のフレームがあれば返してくれる
Read data from underlying AsyncRead and append it to an internal buffer.
Pass the internal buffer to the Decoder. If it returns an item, the Stream impl on FramedRead returns that item.
https://users.rust-lang.org/t/understanding-framed-in-tokio/42449