CDP-Client

A simple python interface for the CDP Studio development platform that allows Python scripts to interact with CDP Applications - retrieve CDP Application structures and read-write object values. For more information about CDP Studio see https://cdpstudio.com/

The API makes heavy use of promise library for asynchronous operations. For more information see https://pypi.python.org/pypi/promise

Installation

$ pip install cdp-client

Usage

The example below shows how you subscribe to CDP signal value changes.

from cdp_client import cdp

def on_value_changed(value, timestamp):
    print(value)

def subscribe_to_value_changes(node):
    node.subscribe_to_value_changes(on_value_changed)

client = cdp.Client(host='127.0.0.1')
client.find_node('AppName.ComponentName.SignalName').then(subscribe_to_value_changes)
client.run_event_loop()

API

Before all examples, you need:

from cdp_client import cdp

Global API

Client(host, port, auto_reconnect, notification_listener, encryption_parameters)

• Arguments

  host - String for hosts ip address

  port - Optional port number to connect to. If not specified default port 7689 is used.

  auto_reconnect - Optional argument to enable/disable automatic reconnect when connection is lost. Defaults to True if not specified.

  notification_listener - NotificationListener object whose methods are called on different connection events (e.g. when server requires credentials)

  encryption_parameters - Optional argument to set encryption and its parameters, TLS certificates verification etc. Parameter is compatible with python websocket client 'sslopt' parameter. For more information see https://pypi.org/project/websocket_client

• Returns

  The connected client object.

• Usage example

  client = cdp.Client(host='127.0.0.1')

• Usage example with password authentication

  class MyListener(cdp.NotificationListener):
      def credentials_requested(self, request):
          if request.user_auth_result().code() == cdp.AuthResultCode.CREDENTIALS_REQUIRED:
              # Do something to gather username and password variables (either sync or async way) and then call:
              request.accept({'Username': 'test', 'Password': '12345678'});
  
  client = cdp.Client(host='127.0.0.1', notification_listener=MyListener())

• Usage example with password authentication and encryption in use, without server certificate verification

  import ssl
  
  class MyListener(cdp.NotificationListener):
      def credentials_requested(self, request):
          if request.user_auth_result().code() == cdp.AuthResultCode.CREDENTIALS_REQUIRED:
              # Do something to gather username and password variables (either sync or async way) and then call:
              request.accept({'Username': 'test', 'Password': '12345678'});
  
  client = cdp.Client(host='127.0.0.1', notification_listener=MyListener(),
                      encryption_parameters={'use_encryption': True, 'cert_reqs': ssl.CERT_NONE})

• Usage example with password authentication and encryption in use, with server certificate verification

  import ssl
  
  class MyListener(cdp.NotificationListener):
      def credentials_requested(self, request):
          if request.user_auth_result().code() == cdp.AuthResultCode.CREDENTIALS_REQUIRED:
              # Do something to gather username and password variables (either sync or async way) and then call:
              request.accept({'Username': 'test', 'Password': '12345678'});
  
  client = cdp.Client(host='127.0.0.1', notification_listener=MyListener(),
                      encryption_parameters={'use_encryption': True,
                                             'cert_reqs': ssl.CERT_REQUIRED,
                                             'ca_certs': 'StudioAPI.crt',
                                             'check_hostname': False},

Instance Methods / Client

client.root_node()

Gets the application Node object of the connected application.

• Returns

  Promise containing root Node object when fulfilled.

• Usage

  client.root_node().then(on_success).catch(on_error)

client.find_node(path)

Searches for the node specified by full dot separated path. The requested node must reside in the application client was connected to. Root node is not considered part of the path.

• Arguments

  path - Dot separated string to target node

• Returns

  Promise containing requested Node object when fulfilled. Otherwise NotFoundError when rejected.

• Usage

  client.find_node('AppName.ComponentName.SignalName').then(on_success).catch(on_error)

client.run_event_loop()

Runs the event loop that serves network communication layer for incoming/outgoing data. This is a blocking call that must be run for any communication to happen. The method can be cancelled by calling disconnect.

client.disconnect()

Stops the event loop and closes the connection to connected application. This method also releases the blocking run_event_loop call.

Instance Methods / Node

node.name()

• Returns

  The name of the Node object. Names in a parent node are all unique.

node.path()

• Returns

  A dot separated path of the Node object starting with application name.

node.parent()

• Returns

  The parent Node object.

node.type()

• Returns

  The type of the Node object returned as one of the cdp.NodeType values.

node.class_name()

• Returns

  CDP class name as a string.

node.last_value()

• Returns

  The last known value received by the Node object.

node.set_value(value, timestamp)

Sets a new value for the Node object. Timestamp will be ignored in current implementation.

• Arguments

  value - New value

  timestamp - UTC time in nanoseconds since Epoch

node.is_read_only()

• Returns

  False if nodes value cannot be set, otherwise True.

node.is_leaf()

• Returns

  True if node doesn't have any children, otherwise False.

node.child(name)

• Arguments

  name - Child nodes name to search for

• Returns

  Promise containing requested Node object when fulfilled.

• Usage

  node.child('NodeName').then(on_success).catch(on_error)

node.children()

• Returns

  Promise containing all children of this Node object when fulfilled.

• Usage

  node.children().then(on_success).catch(on_error)

node.for_each_child(callback)

Loops through all children and calls callback function for each of them

• Arguments

  callback - Function(node)

• Returns

  Promise containing all children of this Node object when fulfilled.

• Usage

  def on_callback(child):
      do something
  
  node.for_each_child(on_callback)

node.subscribe_to_structure_changes(callback)

Starts listening structure changes and passes the changes to provided callback funtion

• Arguments

  callback - Function(added_nodes, removed_nodes) where added_nodes and removed_nodes is a list

• Usage

  def on_change(added_nodes, removed_nodes):
      do something
  
  node.subscribe_to_structure_changes(on_change)

node.subscribe_to_value_changes(callback, fs=5, sample_rate=0)

Starts listening value changes and passes the changes to provided callback function

• Arguments

  callback - Function(value, timestamp)

  fs - Maximum frequency that value updates are expected (controls how many changes are sent in a single packet). Defaults to 5 hz.

  sample_rate - Maximum amount of value updates sent per second (controls the amount of data transferred). Zero means all samples must be provided. Defaults to 0.

• Usage

  def on_change(value, timestamp):
      do something
  
  node.subscribe_to_value_changes(on_change)

node.unsubscribe_from_structure_changes(callback)

Stops listening previously subscribed structure changes

• Arguments

  callback - Function(added_nodes, removed_nodes) where added_nodes and removed_nodes is a list

• Usage

  def on_change(added_nodes, removed_nodes):
      do something
  
  node.unsubscribe_from_structure_changes(on_change)

node.unsubscribe_from_value_changes(callback)

Stops listening previously subscribed value changes

• Arguments

  callback - Function(value, timestamp)

• Usage

  def on_change(value, timestamp):
      do something
  
  node.unsubscribe_from_value_changes(on_change)

Notification Listener

To handle different connection events (like prompt user to accept a system use notification message or request user to enter credentials for authentication or idle lockout re-authentication) a notification_listener parameter must be provided to the Client. The notification_listener parameter must be a object of type class cdp.NotificationListener.

class NotificationListener

class NotificationListener:
    def application_acceptance_requested(self, request=AuthRequest()):
        request.accept()

    def credentials_requested(self, request=AuthRequest()):
        raise NotImplementedError("NotificationListener credentials_requested() not implemented!")

NotificationListener.application_acceptance_requested(self, request=AuthRequest())

Called by Client when new application TLS or plain TCP connection is established. Can be used to prompt the user a System Use Notification (a message that can be configured in CDP Studio Security settings).

• Arguments

  request - a object that has method accept() that should be called to accept the connection and a reject() to reject the connection.

• Usage

  class MyListener(cdp.NotificationListener):
      def application_acceptance_requested(self, request):
          if request.system_use_notification():
              # Pop up a System Use Notification message and ask for confirmation to continue,
              # then based on the user answer call either request.accept() or request.reject()
          else:
              request.accept()
  
  client = cdp.Client(host='127.0.0.1', port=7689, notification_listener=MyListener())

NotificationListener.credentials_requested(self, request=AuthRequest())

Called by Client when server is requesting credentials (authentication or idle lockout re-authentication).

• Arguments

  request - a object that has method accept(data=dict()) that should be called (with credentials) for authentication try, and also a method reject() to reject the connection.

• Usage

  class MyListener(cdp.NotificationListener):
      def credentials_requested(self, request):
          if request.user_auth_result().code() == cdp.AuthResultCode.CREDENTIALS_REQUIRED:
              # Do something to gather username and password variables (either sync or async way) and then call:
              request.accept({'Username': 'test', 'Password': '12345678'});
          if request.user_auth_result().code() == cdp.AuthResultCode.REAUTHENTICATION_REQUIRED:
              # Pop user a message that idle lockout was happened and server requires new authentication to continue:
              request.accept({'Username': 'test', 'Password': '12345678'});
  
  client = cdp.Client(host='127.0.0.1', port=7689, notification_listener=MyListener())

Tests

To run the test suite execute the following command in package root folder:

$ python setup.py test

License

MIT License