[Ethereum] Error in EthereumMessageSigner for hex messages

[JaimeToca]

Describe the bug
Some dapps directly return message to sign as hexadecimal, when assembling the ethereum message, wallet core could check if it needs to be decoded or not, and do the formatting/size.

wallet-core/rust/tw_evm/src/message/eip191.rs

Line 25 in 406abe4

fn data_to_sign(&self) -> Vec<u8> {

Logic could be something like:

if string.isHex() -> hex::decode(s)
else -> s.as_bytes()

Problem
If client tries to decode hex string and transform to string, wallet core returns "invalid data when serializing a protocol buffer"

EthereumMessageSigner.signMessage(<PrivateKey>, <Message>)

To Reproduce
Message: "0xc0a96273d5c3fbe4d4000491f08daef9c17f88df846c1d6f57eb5f33c1fbd035"

[satoshiotomakan]

Hi @JaimeToca, thank you for the suggestion! I think we can do that. The only note is that we should check if the provided data contains expected "Ethereum Signed Message" EIP191 prefix, otherwise I think we shouldn't allow to sign such a message.