django-ethereum-events

Ethereum Contract Event Log monitoring in Django

Overview

This package provides an easy way to monitor an ethereum blockchain for transactions that invoke Contract Events that are of particular interest.

The main concept was inspired by the following project:

https://github.com/gnosis/django-eth-events

Package versions 0.2.x+ support web3 v4.

If you want python 2.7 compatibility and/or web3 v3 support, use version 0.1.x of this package.

Installation

Install using pip:
```
pip install django-ethereum-events
```
Make sure to include 'django_ethereum_events' in your INSTALLED_APPS
```
INSTALLED_APPS += ('django_ethereum_events')
```
if you are using the admin backend, also include solo in your INSTALLED_APPS.

Make necessary migrations

python manage.py migrate django_ethereum_events

Usage

In your settings file, specify the following settings

ETHEREUM_NODE_HOST = 'localhost'
ETHEREUM_NODE_PORT = 8545
ETHEREUM_NODE_SSL = False

Create a new MonitoredEvent

contract_abi = """
The whole contract abi goes here
"""

event = "MyEvent"  # the emitted event name
event_receiver = "myapp.event_receivers.CustomEventReceiver"
contract_address = "0x10f683d9acc908cA6b7A34726271229B846b0292"  # the address of the contract emitting the event

MonitoredEvent.object.register_event(
    event_name=event,
    contract_address=contract_address,
    contract_abi=contract_abi,
    event_receiver=event_receiver
)

Create an appropriate event receiver

# inside myapp.event_receivers
from django_ethereum_events.chainevents import AbstractEventReceiver

class CustomEventReceiver(AbsractEventReceiver):
    def save(self, decoded_event):
        # custom logic goes here

The decoded_event parameter is the decoded log as provided from web3.utils.events.get_event_data method.

To start monitoring the blockchain, either run the celery task django_ethereum_events.tasks.event_listener or better, use celerybeat to run it as a periodical task
```
from celery.beat import crontab

CELERYBEAT_SCHEDULE = {
'ethereum_events': {
    'task': 'django_ethereum_events.tasks.event_listener',
    'schedule': crontab(minute='*/1')  # run every minute
    }
}
```
You can also set the optional ETHEREUM_LOGS_BATCH_SIZE setting which limits the maximum amount of the blocks that can be read at a time from the celery task.

More about the event receivers

It is advisable that the code inside the custom event receiver to be simple since it is run synchronously while the event_listener task is running. If that is not the case, pass the argument decoded_event to a celery task of your own:

# inside the CustomEventReceiver.save method
from django_ethereum_events.utils import HexJsonEncoder
decoded_event_data = json.dumps(decoded_event, cls=HexJsonEncoder)
my_custom_task.delay(decoded_event_data)

If an unhandled exception is raised inside the event receiver, the event_listener task logs the error and creates a new instance of the django_ethereum_events.models.FailedEventLog containing all the relevant event information.

The event listener does not attempt to rerun FailedEventLogs. That is up to the client implementation.

Resetting the internal state

Blocks are processed only once. The last block processed is stored in the .models.Daemon entry.

To reset the number of blocks processed, run the reset_block_daemon command optionally specifying the block number (-b, --block) to reset to (defaults to zero). If you reset it to zero, the next time the event_listener is fired, it will start processing blocks from the genesis block.

The Daemon entry can also be changed from the django admin backend.

Proof-of-Authority Networks

To use this package on Rinkeby or any other private network that uses the Proof-of-Authority consensus engine (also named clique), set the optional ETHEREUM_GETH_POA setting to True.