Write Value

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

Write Request

Field				Description
Header
	MessageType			Must be WRITE_REQUEST.
	ClientHandler			See 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

Field		Description
Header
	MessageType	Must be WRITE_RESPONSE.
	ClientHandler	See 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

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": {}
                  #}