Updated on April 4, 2020

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.

Example

pragma solidity >=0.5.0 <0.7.0;

contract VendingMachine {
    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.
    }
}

Enabling revert reason

Use the --revert-reason-enabled command line option to include the revert reason in the transaction receipt in Hyperledger 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 is the revert reason included

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

Important

The revert reason is not included in the transactions receipts root hash. Not including the revert reason in the transactions receipts 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

{
  "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"
   }
}

Revert reason format

As described in the Solidity documentation, the transaction receipt includes the revert reason as an ABI-encoded string consisting of:

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

Example

"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.