extract_revert_data

Documentation for eth_defi.revert_reason.extract_revert_data function.

extract_revert_data(error)

Extract ABI-encoded custom-error data from a failed eth_call.

Use this after catching a simulation exception when the caller needs to distinguish an expected, typed contract decision from an unexpected execution failure. Solidity custom errors encode a four-byte selector followed by ABI-encoded arguments. Web3 and JSON-RPC providers do not use one common exception shape: the same bytes may appear in error.data, a nested data/result mapping, or an exception argument string.

This is useful for preflight simulations such as GuardV0 settlement. A gross-flow cap breach and an active cooldown are valid contract outcomes that a caller may turn into a deferred action; insufficient liquidity, access-control failures and unknown selectors must remain failures. Recovering raw data lets protocol code decode only its explicitly supported selectors instead of matching provider-specific error text.

Do not use this helper to suppress arbitrary exceptions. If it returns None, or if the selector is not one the caller explicitly supports, re-raise the original exception. This helper only extracts transport data; the calling protocol owns selector matching and ABI argument decoding.

Example custom-error handling:

try:
    web3.eth.call(transaction)
except Exception as exc:
    revert_data = extract_revert_data(exc)
    if revert_data is None:
        raise

    selector = revert_data[:4]
    if selector == expected_error_selector:
        value = abi_decode(["uint256"], revert_data[4:])[0]
        handle_expected_contract_decision(value)
    else:
        raise

Parameters

error (Exception) – Exception raised by a reverted eth_call or contract call().

Returns

Raw Solidity revert bytes, including the four-byte selector, or None when no usable ABI payload is present.

Return type

Optional[bytes]