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ethereum / web3.py

A python interface for interacting with the Ethereum blockchain and ecosystem.
http://web3py.readthedocs.io
MIT License
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web3.eth.getBlock is broken with PyEVMBackend #1213

Closed njgheorghita closed 5 years ago

njgheorghita commented 5 years ago 
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What was wrong?

Using web3.eth.getBlock() method is broken in v5 alpha - when using a PyEVMBackend - the same code works fine when using MockBackend.

from web3 import Web3
from eth_tester import PyEVMBackend

w3 = Web3(Web3.EthereumTesterProvider(PyEVMBackend()))
w3.testing.mine()
>>> '0x123....'
w3.eth.getBlock('0x123....')

The final line breaks with the following error

~/ethereum/py-ethpm/trash-venv/lib/python3.6/site-packages/eth/validation.py in validate_word(value, title)
    162             "{title} is not a valid word. Must be of bytes type: Got: {0}".format(
    163                 type(value),
--> 164                 title=title,
    165             )
    166         )

ValidationError: Block Hash is not a valid word. Must be of bytes type: Got: <class 'str'>

How can it be fixed?

Not sure, I spent some time digging around eth-tester/py-evm to try and find a solution, but no luck. Though, this is most likely related to update in those dependencies in v5.

pipermerriam commented 5 years ago

This is almost certainly related to #1212

Likely candidate for when/how this got introduced is to look at https://github.com/ethereum/web3.py/pull/1188 since it touched the middlewares in web3.py that handled some of the normalization steps.

njgheorghita commented 5 years ago

@pipermerriam The problem was with how I was instantiating my class using the PyEVMBackend.

This is what was broken...

from web3 import Web3
from eth_tester import PyEVMBackend

w3 = Web3(Web3.EthereumTesterProvider(PyEVMBackend()))

This is what I should have been doing / What works fine.

from web3 import Web3
from eth_tester import PyEVMBackend, EthereumTester

w3 = Web3(Web3.EthereumTesterProvider(EthereumTester(PyEVMBackend())))

Basically, the inbound tx normalization happens in the EthereumTester class and not in PyEVMBackend - but they share the same methods, so web3's delegator was calling the PyEVMBackend.estimate_gas() directly instead of EthereumTester.estimate_gas() which would normalize and then subsequently pass on the normalized tx to PyEVMBackend.estimate_gas()

I'm unsure as to exactly where I saw the first (aka broken) pattern, but it seems to me that maybe the best fix is something in the docs explaining how to instantiate w/ PyEVMBackend directly - as I think this'll be common now that you can adjust genesis-params in eth-tester.

pipermerriam commented 5 years ago

When @kclowes and I looked over this today I had the thought that we could add a check to EthereumTesterProvider.__init__ which checked if the provided value was an instance of EthereumTester and errors out if it isn't. Additionally, if the value is a backend it could lazily wrap it in the EthereumTester class. Either way we can prevent this mistake with some simple value checks.