RLP decoding woes

[holiman]

We now have rlp encoding, and can encode RLP. However, RLP decoding requires to implement this interface: https://github.com/ethereum/go-ethereum/blob/44b41641f8220fe79e43461356c147cc3cc72380/rlp/decode.go#L64

I.e,

type Decoder interface {
	DecodeRLP(*Stream) error
}

Where *Stream is this struct from the same package.

If we want uint256.Int to implement that, it would require adding rlp as a dependency :( .

@fjl any ideas to get us out of this? Seems quirky, from API-perspective, to have Encoder interface be implementable without rlp-dependency, but have the Decoder interface depend on package rlp.

[fjl]

The Decoder taking stream is an unfortunate design decision, but it does make the decoder work a bit faster because you have direct access to the underlying parser state in your custom decoder.

[holiman]

Yeah.. I'm thinking that maybe we'll add DecodeRLPBytes([]byte) error, and then the a 'custom' decoder can just do a.DecodeRLPBytes(stream.Bytes()).

[holiman]

I was thinking something like this:

func (z *Int) DecodeRLPBytes(b []byte) error {
	// Check length
	if len(b) > 32 {
		return errors.New("rlp: uint overflow")
	}
	if len(b) == 0 {
		z.Clear()
		return nil
	}
	// Check leading zero-bytes
	if b[0] == 0 {
		return errors.New("rlp: non-canonical integer format")
	}
	z.SetBytes(b)
}

But I don't know -- perhaps not worth it, since we will have to have a custom uint256-decoder inside rlp anyway.

[fjl]

I think we can agree to just add special support for uint256 in package rlp.