django-ethereum-events 1.0.4

Django Ethereum Events

######################
django-ethereum-events
######################

Ethereum Contract Event Log monitoring in Django

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********
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.


.. _`Contract Events`: http://solidity.readthedocs.io/en/develop/contracts.html#events

************
Installation
************

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 manage.py migrate django_ethereum_events


*****
Usage
*****

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

::

ETHEREUM_NODE_HOST = 'localhost'
ETHEREUM_NODE_PORT = 8545
ETHEREUM_NODE_SSL = False


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

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

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 `web3.utils.events.get_event_data`_ method.

.. _`web3.utils.events.get_event_data`: https://github.com/pipermerriam/web3.py/blob/master/web3/utils/events.py#L143

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

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``.