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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 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 is currently in alpha, the basic pieces are in place but the specific interfaces are not yet finalized. Many things will change between this version and the first release.

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
• Requests
• Flask

How To Use

Currently, you need to create separate systems for providers and consumers, a system cannot easily do both. It is possible to do both, but it is not clean.

Providing Services

To provider services, use the ProviderSystem from the arrowhead_system module. Services can be added to the provider by decorating a function with the add_service, inspired by Flask's add_route method. The add_service method will register the service in the provider, and when the provider is started it will automatically register the service with the service registry.

Code Example

import datetime
from arrowhead_client.arrowhead_system import ProviderSystem
from arrowhead_client.provider import provided_service
from flask import request
#from source.service_provider import ServiceProvider

class TimeProvider(ProviderSystem):
    def __init__(self, *args, **kwargs):
       ProviderSystem.__init__(self, *args, **kwargs)
       self.format = '%H:%M:%S'

if __name__ == '__main__':
    # Create provider
    time_provider = TimeProvider.from_properties('examples/time_provider.properties')

    # Register services
    @time_provider.add_service('time', '/time', 'HTTP-SECURE-JSON')
    def get_time():
        return datetime.datetime.now().strftime(time_provider.format)

    @time_provider.add_service('format', '/time/format', 'HTTP-SECURE-JSON', ['POST'])
    def change_format():
        data = request.data

        time_provider.format = data.decode()

        return data

    # Run provider until shutdown
    time_provider.run_forever()

Consuming Services

To consume services, use the ConsumerSystem to create a consumer. The add_orchestration_rule method is used to query the orchestrator and to set up the consumer to easily consume the service provided by the orchestrator.

Code Examples

from arrowhead_client.arrowhead_system import ConsumerSystem

time_consumer = ConsumerSystem('consumer_test',
                                  'localhost',
                                  '1338',
                                  '',
                                  '127.0.0.1',
                                  '8443',
                                  'certificates/consumer_test.key',
                                  'certificates/consumer_test.crt')

# Add orchestration rules
time_consumer.add_orchestration_rule('get_time', 'GET', 'time')
time_consumer.add_orchestration_rule('change_format', 'POST', 'format')

if __name__ == '__main__':
    # Consume service provided by the 'get_time' rule
    time = time_consumer.consume('get_time')
    print(time.text)
    input()
    # Consume service provided by the 'change_format' rule
    time_consumer.consume('change_format', payload='%S:%M:%H')
    # Consume service provided by the 'get_time' rule
    time = time_consumer.consume('get_time')
    print(time.text)