[Bug-Candidate]: `Cannot decode byte '\xe4': Data.Text.Encoding: Invalid UTF-8 stream`

[pcaversaccio]

[Bug-Candidate]: `Cannot decode byte '\xe4': Data.Text.Encoding: Invalid UTF-8 stream`

[pcaversaccio]

I think I found partially the issue: Vyper adds the following signature to the init code which I use in the ffi command:

sig = b"\xa1\x65vyper\x83".hex()

See my comment here: vyperlang/vyper#2860 (comment). And \xa1 and \x83 are common decoding errors I see in that context. There might be some further method Ids that might not be decoded properly as well.

[ggrieco-tob]

Sounds like a plan!

[ggrieco-tob]

Hey, this looks very cool. Do you know if the bug is related to hevm code or echidna?

[pcaversaccio]

Hey, this looks very cool. Do you know if the bug is related to hevm code or echidna?

I'm really not sure tbh - didn't have time to investigate properly.

[pcaversaccio]

and btw the decode error is also in the CI https://github.com/pcaversaccio/snekmate/actions/runs/8803366873/job/24161302034#step:19:21

[elopez]

On an initial triage, it seems this happens due to Echidna calling VyperDeployer.deploy(....) with non-utf8-valid strings. The config has allContracts: true. valsArr in hevm ends up having invalid utf8 which then fails to decode.
https://github.com/ethereum/hevm/blob/release/0.53.0/src/EVM.hs#L1564

Filtering the affected functions so echidna does not try to fuzz them seems to work around the issue:

filterFunctions: ["VyperDeployer.deployContract(string,string)", "VyperDeployer.deployContract(string,string,bytes)", "VyperDeployer.deployContract(string,string,bytes,string,bool)", "VyperDeployer.deployContract(string,string,string,bool)"]

This is a smaller repro of this issue:

interface Hevm {
  function ffi(string[] calldata) external returns (bytes memory);
}

contract TestFFI {
  address constant HEVM_ADDRESS = 0x7109709ECfa91a80626fF3989D68f67F5b1DD12D;

  function foo() public {
    bytes memory w = hex"c328"; // invalid utf-8

    string[] memory inputs = new string[](2);
    inputs[0] = "echo";
    inputs[1] = string(w);

    bytes memory res = Hevm(HEVM_ADDRESS).ffi(inputs);
  }
}

$ echo allowFFI: true > config.yml
$ echidna foo.sol --test-mode assertion --format text --contract TestFFI --config config.yml
[2024-04-23 18:04:34.90] Compiling foo.sol... Done! (0.775142s)
Analyzing contract: .../foo.sol:TestFFI
[2024-04-23 18:04:35.70] Running slither on foo.sol... Done! (0.81568s)
[2024-04-23 18:04:36.52] [Worker 0] Crashed:

Cannot decode byte '\xc3': Data.Text.Encoding: Invalid UTF-8 stream

Please report it to https://github.com/crytic/echidna/issues
[2024-04-23 18:04:36.52] [status] tests: 0/2, fuzzing: 0/50000, values: [], cov: 481, corpus: 0
foo(): passing
AssertionFailed(..): passing
...

[pcaversaccio]

@elopez confirmed, this was the issue. Thanks a lot! Fixed via pcaversaccio/snekmate@0d6889f. Will close the issue accordingly.

[ggrieco-tob]

Uhm, is there something we should recommend to hevm to avoid this decoding error?

[pcaversaccio]

Uhm, is there something we should recommend to hevm to avoid this decoding error?

maybe raise this issue to them at least and get their thoughts on it?