Problem: inefficient transaction format

[yihuang]

the MsgEthereumTx protobuf message is quite inefficient because we do lots of conventions with the go-ethereum types to reuse the code there. Since ethereum tx already has a solid binary format, with the custom type feature in gogoproto, we can embed the ethereum binary format within the protobuf message.

[yihuang]

message MsgEthereumTx {
  option (cosmos.msg.v1.signer) = "from";
  option (gogoproto.goproto_getters) = false;

  reserved 1, 2, 3, 4;

  // from is the bytes of ethereum signer address. This address value is checked
  // against the address derived from the signature (V, R, S) using the
  // secp256k1 elliptic curve
  bytes from = 5;
  // raw is the raw ethereum transaction
  bytes raw = 6 [(gogoproto.customtype) = "EthereumTx"];
}

type EthereumTx struct {
	ethtypes.Transaction
}

func NewEthereumTx(tx *ethtypes.Transaction) *EthereumTx {
	return &EthereumTx{*tx}
}

func (tx *EthereumTx) Size() int {
	return tx.Size()
}

func (tx *EthereumTx) MarshalTo(dst []byte) (int, error) {
	bz, err := tx.MarshalBinary()
	if err != nil {
		return 0, err
	}
	copy(dst, bz)
	return len(bz), nil
}

func (tx *EthereumTx) Unmarshal(dst []byte) error {
	return tx.UnmarshalBinary(dst)
}