Exonum Python Light Client

Python client for the Exonum Framework.

Overview

Exonum Light Client is a Python library for working with Exonum blockchain from the client side. It can be easily integrated to an existing application. Also, Exonum Light Client provides access to common utils toolkit which contains some helpful functions for hashing, cryptography, serialization, etc.

Capabilities

By using the client you are able to perform the following operations:

• Submit transactions to the node
• Receive information on transactions
• Receive information on blockchain blocks
• Receive information on the node system
• Receive information on the node status

Compatibility

The following table shows versions compatibility:

Light Client	Exonum
0.1	0.9.*
0.2	0.10.*
0.3.x	0.12.*
master	dynamic_services branch

System Dependencies

• Python 3.5 or above.
• Package installer for Python3 (pip3)

Examples

The following example shows how to create an instance of the Exonum client which will be able to work with an Exonum node with the Cryptocurrency Advanced service mounted on it, at http://localhost:8080 address:

Installing Python Light Client

First of all we need to install our client library:

git clone git@github.com:exonum/exonum-python-client.git
pip3 install -e exonum-python-client --no-binary=protobuf

Exonum Client Initialization

from exonum_client import ExonumClient, ModuleManager, MessageGenerator
from exonum_client.crypto import KeyPair

client = ExonumClient(hostname="localhost", public_api_port=8080, private_api_port=8081, ssl=False)

Compiling Proto Files

To compile proto files into the Python analogues we need a protobuf loader:

with client.protobuf_loader() as loader:
    #  Your code goes here.

Since loader acquires resources on initialization, creating via context manager is recommended. Otherwise you should initialize and deinitialize client manually:

loader = client.protobuf_loader()
loader.initialize()
# ... Some usage
loader.deinitialize()

Then we need to run the following code:

loader.load_main_proto_files()  # Load and compile main proto files, such as `runtime.proto`, `consensus.proto`, etc.
loader.load_service_proto_files(runtime_id=0, service_name='exonum-supervisor:0.12.0')  # Same for specific service.

• runtime_id=0 here means, that service works in Rust runtime.

Creating Transaction Messages

The following example shows how to create a transaction message:

alice_keys = KeyPair.generate()

cryptocurrency_service_name = 'exonum-cryptocurrency-advanced:0.12.0'
loader.load_service_proto_files(runtime_id=0, service_name=cryptocurrency_service_name)

cryptocurrency_module = ModuleManager.import_service_module(cryptocurrency_service_name, 'service')

cryptocurrency_message_generator = MessageGenerator(instance_id=1024, artifact_name=cryptocurrency_service_name)

create_wallet_alice = cryptocurrency_module.CreateWallet()
create_wallet_alice.name = 'Alice'

create_wallet_alice_tx = cryptocurrency_message_generator.create_message(create_wallet_alice)
create_wallet_alice_tx.sign(alice_keys)

• 1024 - service instance ID.
• alice_keys - public and private keys of the ed25519 public-key signature system.

After invoking the sign method, we get a signed transaction. This transaction is ready for sending to the Exonum node.

Sending Transaction to the Exonum Node

After successfully sending the message, we'll get a response which will contain a hash of the transaction:

response = client.public_api.send_transaction(create_wallet_alice_tx)

{
    "tx_hash": "3541201bb7f367b802d089d8765cc7de3b7dfc253b12330b8974268572c54c01"
}

Subscribing to events

If you want to subscribe to events (subscription_type: "transactions" or "blocks"), use the following code:

with client.create_subscriber(subscription_type="blocks") as subscriber:
    subscriber.wait_for_new_event()
    subscriber.wait_for_new_event()

Context manager will automatically create a connection and will disconnect after use. Or you can manually do the same:

subscriber = client.create_subscriber(subscription_type="blocks")
subscriber.connect()
# ... Your code
subscriber.stop()

Keep in mind that if you forget to stop the subscriber, you may discover HTTP errors when you try to use Exonum API.

Getting Data on the Available Services

client.public_api.available_services().json()

The code will show a list of the artifacts available for the start and a list of working services:

{
  'artifacts': [
    {
      'runtime_id': 0,
      'name': 'exonum-cryptocurrency-advanced:0.12.0'
    },
    {
      'runtime_id': 0,
      'name': 'exonum-supervisor:0.12.0'
    }
  ],
  'services': [
    {
      'id': 1024,
      'name': 'XNM',
      'artifact': {
        'runtime_id': 0,
        'name': 'exonum-cryptocurrency-advanced:0.12.0'
      }
    },
    {
      'id': 0,
      'name': 'supervisor',
      'artifact': {
        'runtime_id': 0,
        'name': 'exonum-supervisor:0.12.0'
      }
    }
  ]
}

More Examples

To see more examples and find out how to work with proofs go here.

Also you can find the sample scripts at the examples section.

Testing

To run tests, use the following command:

python3 -m unittest

Contributing

You can see notes for developers in the Contribution Guide page.

Known Problems

If within use you discover the following error:

TypeError: Couldn't build proto file into descriptor pool!

It is due to the issue with Protobuf binary wheels. The only work around is to install the pure Python implementation.

pip uninstall protobuf
pip install --no-binary=protobuf protobuf

License

Apache 2.0 - see LICENSE for more information.