Ethereum utility codes
ctx = EthLogSubscriber(wss_provider_url, address, event_abi, callback, fromDate=datetime.datetime, dateTolerance=60)
ctx.start()
ctx.stop()
Neither web3.js nor web3.py have a convenient way to get historical logs and
then stay subscribed to async capture new ones. At least web3.js has an
implementation of eth_subscribe; web3.py doesn't even have that.
EthLogSubscriber combines historial lookup and ongoing subscription into a
tidy package that hides thread, async, and ethereum encode/decode details.
The built-in main() offers a example of how to use it. Features:
- Logic properly sets up async notification before looking up historical information. This ensures seamless transition from vending historic logs to real-time subscription without danger of creating a gap between processing the last historic log and the setup of the websocket listener.
- An event ABI is used to facilitate decoding the pile of bytes in the
dataportion of the log into a well-structured dictionary of names and real types. - The web3 JSON-RPC has no facility to lookup a block by timestamp. As this
is a frequent use case, it is implemented in EthLogSubscriber and further
simplified by using a
datetime.datetimetype in the method. The closest block after the givenfromDatewill be used as a starting point. - Nothing happens until
start()is called. This permits separation of the locus of initialization from the logic where the callback will be active.start()returns after the historic lookup and processing are complete and the websocket listener has been established, leaving a subthread running. - Subscription can be formally shut down with the
stop()method. Currently there is no use case to restart the subscription other than creating a new EthLogSubscriber instance.