Merging topic lists when creating filters not possible in current api. Yields unexpected results.

[dylanjw]

What was wrong?

The contract.events.myEvent.createFilter and contract.eventFilter both allow entering topics directly along with "argument filters" via filter param dict. The implementation is built on a false assumption about the topic list. The constructed topics are merged with the raw topics in a simple list addition:

    if topics is None:
        topic_set = construct_event_topic_set(event_abi, argument_filters)
    else:
        topic_set = [topics] + construct_event_topic_set(event_abi, argument_filters)

Merging two topic lists with additive results is impossible with a single filter. Merging two topic lists by using the available OR logic within single topic positions would yield all topic combinations.

Example:
Given the following "logs": AA BB AB
Topic list 1 ["A", "A"] would match AA
Topic list 2 ["B", "B"] would match BB
merged list [["A", "B"], ["A","B"]] would match AA BB AB

How can it be fixed?

Option 1. Remove option of entering raw topics along with argument filters that generate topics.
Option 2. Provide the functionality of merging topic lists, by extending the Filter object to manage multiple node filters.

something like:

FilterAggregator(Filter):
    def __init__(self, web3, filter_ids):
        self.web3 = web3
        self.filter_ids = filter_ids
    
    def get_new_entries(self):
        log_entries = mapcat(
            compose(self._filter_valid_entries, self.web3.eth.getFilterChanges),
            filter_ids)
        return self._format_log_entries(log_entries)

    def get_all_entries(self):
            log_entries = mapcat(
                compose(self._filter_valid_entries, self.web3.eth.getFilterLogs),
                self.filter_ids)
        return self._format_log_entries(log_entries)

[dylanjw]

There isnt a test that proves this, but Im 99% sure that this is broken. I'll write the broken test before starting on either option to fix.

[carver]

I think Option 1 is better. Clearly it's subtle enough that reasonable people can get confused by what merging is supposed to do. So let's just remove the opportunity for mistake. People can still manually merge topics themselves first, if they like.