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Is there any way to recognize if a log contains an anonymous topic? From what I can tell is that anonymous events are represented in a log without the signature on the first index. Giving the option to include 4 instead of 3 topics. That would be a way to recognize them, however what if an anonymous event generates a log with less than 4 topics?

I need to find a couple of logs with anonymous events so that I can study them.

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In a non-anonymous event, topics[0] will be the signature of the event name. In an anonymous event, the signature of the event name is not a topic.

If you have access to the ABI or the source code of the contract, here is what you could do:

  1. Find the signature hash of the event name.
  2. Check if topics[0] is equal to this signature. If not, you have an anonymous event.

If you don't have access to the ABI or the source code, I don't think that it is possible because there is no way to know if topics[0] is the event name signature or a bytes32 indexed argument.

On a side-note, the JSON ABI would indicate if an event is anonymous (see the docs).

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  • Ok so if I understand correctly. A log can therefore always have a max of 4 topics. When the event is anonymous it has a max of 4 topics. When the event isn't anonymous it has a signature on topic[0] and 3 topics. Only if I have the ABI, I can say for sure that the signature is on topic[0].
    – user1213904
    Commented Dec 16, 2021 at 20:35
  • That's my understanding, yes. Unless someone can think of another way...
    – Undead8
    Commented Dec 16, 2021 at 20:36

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