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Django Ethereum Events

Project description


Ethereum Contract Event Log monitoring in Django

.. image::

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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:


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.

.. _`Contract Events`:


1. Install using pip:


pip install django-ethereum-events

2. 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``.

3. Make necessary migrations


python migrate django_ethereum_events


1. In your ``settings`` file, specify the following settings


ETHEREUM_NODE_HOST = 'localhost'

2. 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


3. 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 ``_ method.

.. _``:

4. 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

'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 method
from django_ethereum_events.utils import HexJsonEncoder
decoded_event_data = json.dumps(decoded_event, cls=HexJsonEncoder)

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``.

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