Connection between tonic::codec and tokio_util::codec?

[themaxdavitt]

I see that tokio-util (specifically the "codec" feature) is a dependency of tonic, but running grep -R tokio_util . in the root of the repository yielded nothing. tokio-util's Decoder and Encoder traits are very similar to tonic's Decoder and Encoder, mainly differing in tokio-util's Encoder using a type parameter versus an associated type and tonic's traits preferring mutable references to DecodeBufs and EncodeBufs over BytesMuts.

Is there a specific reason why the codec design pattern was reimplemented here rather than reused? What benefit do DecodeBuf and EncodeBuf provide over BytesMut? Sorry if I would've been able to answer these myself by working with the code more, I just found this crate recently. Thanks in advance!