ganache extract logs from reverted transaction?

Question

Is it possible to extract logs from reverted transactions in Ganache?

Of course, the public blockchain won't keep logs for reverted transactions.

However, I'm wondering is there a way in ganache (local blockchain) to find out what the logs would have been for a transaction if it hadn't reverted it, that is, the logs that occurred up until the point of reverting?

I am using a ganache fork and simulating some transactions locally and would like to extract such data even for reverted transactions.

Answer 1

Yes, you can achieve it by debugging the failed transaction.

From ganache-cli, get the required transaction hash.
In a new terminal window, run npx truffle debug <YOUR_TXN_HASH>
You can then step over to the next line with o, till the point transaction was reverted.

A detailed list of commands is available here: https://trufflesuite.com/docs/truffle/getting-started/using-the-truffle-debugger.html

Answer 2

Another way would be to use ganache-cli with the verbose flag:

--verbose

This would log the requests and responses.

Now, after you send your request, you will in the logs the response. This latter would contain the following information:

{
  "id": 17,
  "jsonrpc": "2.0",
  "result": "...",
  "error": {
    "message": "VM Exception while processing transaction: revert",
    "code": -32000,
    "data": {
      "...": {
        "error": "revert",
        "program_counter": 2145,
        "return": "0x8baa579f"
      },
      "stack": "o: VM Exception while processing transaction: revert\n    at Function.o.fromResults (/app/ganache-core.docker.cli.js:4:297036)\n    at w.processBlock (/app/ganache-core.docker.cli.js:42:106258)\n    at processTicksAndRejections (internal/process/task_queues.js:93:5)",
      "name": "o"
    }
  }
}

The return would contain the revert error.

In this case, it is 0x8baa579f. To know which error is it, you will need to know which encoded function/error signature matches the above.

You can use this online encoder. First, put your ABI there. Then, compare the encoded output with 0x8baa579f.

For more details on how the encoding works, checkout this article.