Issue with latest_block_based_cache_middleware

[Meemaw]

• Version: 5.24.0
• Python: 3.9.5
• OS: osx

What was wrong?

Please include any of the following that are applicable:

There seems to be an issue with the latest_block_based_cache_middleware implementation. Given the following config:

w3 = Web3(HTTPProvider(settings.ETHEREUM_NODE_URL, request_kwargs={"timeout": 8}))

# Set the gas price strategy
# https://web3py.readthedocs.io/en/stable/gas_price.html#selecting-the-gas-price-strategy
# NOTE - It's recommended to add a cache solution because of how inneficient this gas strategy is
w3.eth.setGasPriceStrategy(fast_gas_price_strategy)

w3.middleware_onion.add(middleware.time_based_cache_middleware)
w3.middleware_onion.add(middleware.latest_block_based_cache_middleware)
w3.middleware_onion.add(middleware.simple_cache_middleware)

I'm observing w3.eth.get_block('latest') to always be cached even though it should never be cached.

Digging into the code a bit more, I suspect the issue in in _is_latest_block_number_request fn,

web3.py/web3/middleware/cache.py

Line 317 in 4893947

def _is_latest_block_number_request(method: RPCEndpoint, params: Any) -> bool:

, specifically the part where params are compared:

web3.py/web3/middleware/cache.py

Line 320 in 4893947

elif params[:1] == ['latest']:

I've printed params locally, and it seems that params[:1] evaluates to ('latest',) (tuple) and thus the comparison with list fails.

How can it be fixed?

Convert params slice to list before comparing?

[kclowes]

Thanks for raising this! This does look like a bug, will fix!

[B3nac]

Dibs! If nobody is working on this already. 😄

[pacrob]

Fixed in #2346