Revert reason

In smart contracts, the revert operation triggers an exception to flag an error and revert the current call. The EVM passes back to the client an optional string message containing information about the error.

pragma solidity ^0.8.4;

contract VendingMachine {
    address owner;
    constructor() {
        owner = msg.sender;
    }
    error Unauthorized();
    function buy(uint amount) public payable {
        if (amount > msg.value / 2 ether)
            revert("Not enough Ether provided.");
        // Alternative way to do it:
        require(
            amount <= msg.value / 2 ether,
            "Not enough Ether provided."
        );
        // Perform the purchase.
    }
    function withdraw() public {
        if (msg.sender != owner)
            revert Unauthorized();

        payable(msg.sender).transfer(address(this).balance);
    }
}

Enable revert reason

Use the --revert-reason-enabled command line option to include the revert reason in the transaction receipt and the trace response in Besu.

caution

Enabling revert reason may use a significant amount of memory. We do not recommend enabling revert reason when connected to public Ethereum networks.

Where the revert reason is included

With revert reason enabled, the transaction receipt returned by eth_getTransactionReceipt includes the revert reason as an ABI-encoded string.

info

The revert reason is not included in the transaction receipt's root hash. Not including the revert reason in the transactions receipt's root hash means the revert reason is only available to nodes that execute the transaction when importing the block. That is, the revert reason is not available if using fast synchronization (--sync-mode=FAST).

Example of transaction receipt

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "blockHash": "0xe7212a92cfb9b06addc80dec2a0dfae9ea94fd344efeb157c41e12994fcad60a",
    "blockNumber": "0x50",
    "contractAddress": null,
    "cumulativeGasUsed": "0x5208",
    "from": "0x627306090abab3a6e1400e9345bc60c78a8bef57",
    "gasUsed": "0x5208",
    "logs": [],
    "logsBloom": "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
    "status": "0x1",
    "to": "0xf17f52151ebef6c7334fad080c5704d77216b732",
    "transactionHash": "0xc00e97af59c6f88de163306935f7682af1a34c67245e414537d02e422815efc3",
    "transactionIndex": "0x0",
    "revertReason": "0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001a4e6f7420656e6f7567682045746865722070726f76696465642e000000000000"
  }
}

With revert reason enabled, the list items in the trace response returned by trace_replayBlockTransactions, trace_block, and trace_transaction include the revert reason as an ABI-encoded string.

Example of trace response list item

{
  "jsonrpc": "2.0",
  "id": 415,
  "result": [
    {
      "action": {
        "callType": "call",
        "from": "0xfe3b557e8fb62b89f4916b721be55ceb828dbd73",
        "gas": "0xffadea",
        "input": "0x",
        "to": "0x0110000000000000000000000000000000000000",
        "value": "0x0"
      },
      "blockHash": "0x220bc13dc4f1ed38dcca927a5be15eca16497d279f4c40d7b8fe9704eadf1464",
      "blockNumber": 18,
      "error": "Reverted",
      "revertReason": "0x7d88c1856cc95352",
      "subtraces": 0,
      "traceAddress": [],
      "transactionHash": "0xc388baa0e55e6b73e850b22dc7e9853700f6b995fd55d95dd6ccd5a13d63c566",
      "transactionPosition": 1,
      "type": "call"
    }
  ]
}

By default, the error returned by eth_estimateGas and eth_call includes the revert reason as an ABI-encoded string in the data field.

Example of eth_estimateGas and eth_call error

{
  "jsonrpc": "2.0",
  "id": 3,
  "error": {
    "code": -32000,
    "message": "Execution reverted: ERC20: transfer amount exceeds balance",
    "data": "0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001a4e6f7420656e6f7567682045746865722070726f76696465642e000000000000"
  }
}

Revert reason format

As described in the Solidity documentation, the revert reason is an ABI-encoded string consisting of:

0x08c379a0                                                         // Function selector for Error(string)
0x0000000000000000000000000000000000000000000000000000000000000020 // Data offset
0x000000000000000000000000000000000000000000000000000000000000001a // String length
0x4e6f7420656e6f7567682045746865722070726f76696465642e000000000000 // String data

Example of revert reason string for 'Not enough Ether provided'

"0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001a4e6f7420656e6f7567682045746865722070726f76696465642e000000000000"

Dapp support

Client libraries, such as web3j, do not support extracting the revert reason from the transaction receipt. To extract the revert reason your dapp must interact directly with Besu using a custom JSON -> Object converter.