arrowhead-client 0.1.1a1

Arrowhead system and service client library

ARROWHEAD CLIENT PYTHON LIBRARY

This is a library for the creation of client service providers and consumer for the Arrowhead Framework, a service-oriented framework developed for industrial automation.

About

The Arrowhead Client Python Library is a library to make it easy to create your own Arrowhead Framework systems and services in Python. This library provides classes that interface with the Arrowhead Core Systems, and uses Flask to provide services.

Development status

This library has not yet reached a stable development version, and a lot will change. Currently, it is working, but it's still missing many crucial features, such as:

• Error handling
• Logging
• Testing
• Support for the following core services
  • Eventhandler
  • Gateway
  • Gatekeeper
• Support for the following security modes (access policies):
  • Token security
  • Insecure security

As more Arrowhead Core Systems mature and are added to the official docker container, those will be added to this list.

External Depencies

To run an Arrowhead system you need to have the Arrowhead core systems up and running, and the correct certificates need to be provided. A guide on how to create your own certificates can be found on the Arrowhead github.

Requirements

• Python 3.7 or higher
• Requests
• Flask
• Gevent

How To Use

Install the library with pip install arrowhead-client.

Providing Services

To provide services, import the ProviderSystem. Services can be added to the provider with the provided_services decorator. The provided_services decorator will create a service, and register the service with the provider. Then when the provider is started, using the run_forever method, the provider will automatically register the service with the service registry.

Code Example

import datetime
from arrowhead_client.system.provider import ProviderSystem

# Create provider
time_provider = TimeProvider(
		'time_provider',
		'localhost',
		1337,
		'',
		keyfile='certificates/time_provider.key'
		certfile='certificates/time_provider.crt')

# Add service
@time_provider.provided_service('echo', '/time/echo', 'HTTP-SECURE-JSON', 'GET')
def echo():
	return {'now': str(datetime.datetime.now())}

if __name__ == '__main__':
	time_provider.run_forever()

Consuming Services

To consume services, use the ConsumerSystem. To find a consumed service, you first register a service definition using the add_consumed_services method. When the ConsumerSystem is started initialized, it queries the orchestrator and will register the first orchestrated service. That service is then consumed using the consume_service method.

The orchestration query will fail if the orchestrator does not return a service, and crash as a consequence. The plan is to make this robust later.

Code Examples

from arrowhead_client.system.consumer import ConsumerSystem

time_consumer = ConsumerSystem(
		'consumer_test',
		'localhost',
        '1338',
        '',
        'certificates/consumer_test.key',
        'certificates/consumer_test.crt')

# Add orchestration rules
time_consumer.add_orchestration_rule('echo', 'GET')

if __name__ == '__main__':
    # Consume service provided by the 'get_time' rule
    echo = time_consumer.consume_service('echo')
    print(echo['echo'])