.. _write:

Write Value
===========

To write the value of a variable, the client should use *WRITE_REQUEST* request.

.. _write_request:

Write Request
-------------

+------------------------------------+----------------------------------------------------+
| Field                              | Description                                        | 
+============+=======================+====================================================+
| **Header** |                       |                                                    |
+------------+-----------------------+----------------------------------------------------+
|            | MessageType           | Must be *WRITE_REQUEST*.                           |
+------------+-----------------------+----------------------------------------------------+
|            | ClientHandler         | See :ref:`message_format`.                         |
+------------+-----------------------+----------------------------------------------------+
| **Body**   |                       |                                                    |
+------------+-----------------------+----------------------------------------------------+
|            | Variable              | The name of the variable to write                  |
+------------+-----------------------+----------------------------------------------------+
|            | Value                 |                                                    |
+------------+---+-------------------+----------------------------------------------------+
|            |   | Value             |                                                    |
+------------+---+---+---------------+----------------------------------------------------+
|            |   |   | Body          | The value of the variable.                         |
+------------+---+---+---------------+----------------------------------------------------+
|            |   |   | Type          | The type ID of the variable.                       |
+------------+---+---+---------------+----------------------------------------------------+
|            |   | [Status]          | The OPC UA status of the variable.                 |
+------------+---+-------------------+----------------------------------------------------+
|            |   | [SourceTimestamp] | The time of the value given by the source in ISO   |
|            |   |                   | 8601 format. Example: "2015-09-06T09:03:21Z"       |
+------------+---+-------------------+----------------------------------------------------+
|            |   | [ServerTimestamp] | The time of the value given by the server in ISO   |
|            |   |                   | 8601 format. Example: "2015-09-06T09:03:21Z"       |
+------------+---+-------------------+----------------------------------------------------+


.. _write_response:

Write Response
--------------

+--------------------------------+----------------------------------------------------+
| Field                          | Description                                        | 
+============+===================+====================================================+
| **Header** |                   |                                                    |
+------------+-------------------+----------------------------------------------------+
|            | MessageType       | Must be *WRITE_RESPONSE*.                          |
+------------+-------------------+----------------------------------------------------+
|            | ClientHandler     | See :ref:`message_format`.                         |
+------------+-------------------+----------------------------------------------------+
| **Body**   |                   |                                                    |
+------------+-------------------+----------------------------------------------------+
|            | [Status]          | The OPC UA status of the variable                  |
|            |                   | if it is not *Success*.                            |
+------------+-------------------+----------------------------------------------------+

Status Codes
------------

+-----------------------+-----------------------------------------------------------+
| Status Code           | Description                                               |
+=======================+===========================================================+
| BadInternalError      | The server failed to process the request due to internal  |
|                       | error.                                                    |
+-----------------------+-----------------------------------------------------------+
| BadAttributeInvalid   | The server failed decode the body of the message.         | 
+-----------------------+-----------------------------------------------------------+
| BadNodeIdUnknown      | The variable name isn't found in the server configuration.| 
+-----------------------+-----------------------------------------------------------+
| BadSessionClosed      | The connection with OPC UA server is lost.                | 
+-----------------------+-----------------------------------------------------------+

Example in Python
-----------------

.. code-block:: python

  import websocket
  import json

  msg = {
     'Header': {
      'ClientHandle': '1', 
      'MessageType': 'WRITE_REQUEST'
     }, 
     'Body': {
       'Variable': 'Int32Test',
       'Value': {
         'Value': {
           'Body': '555', 
           'Type': '8'
         }
       }
     }
  }

  ws = websocket.create_connection('ws://127.0.0.1:8081')

  resp = ws.recv()  
  json.loads(resp)  #=> {
                    # "Header": {
                    #    "MessageType": "WRITE_RESPONSE",
                    #    "ClientHandle": "1"
                    # },
                    # "Body": {}
                    #}