Read Value

To read the value of a variable, the client must use READ_REQUEST request.

Read Request

Field		Description
Header
	MessageType	Must be READ_REQUEST.
	ClientHandler	See Message Format.
Body
	Variable	The variable to read.

Read Response

Field			Description
Header
	MessageType		Must be READ_RESPONSE.
	ClientHandler		See Message Format.
Body
	Value
		Body	The value of the variable.
		Type	The type of the variable.
	[Status]		The OPC UA status of the variable if it is not Success.
	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”

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': {
      'MessageType':'READ_REQUEST',
      'ClientHandle':'1'
    },
    'Body': { 'Variable' : 'Boolean'}
 }

ws = websocket.create_connection('ws://127.0.0.1:8081')
ws.send(json.dumps(msg))
resp = ws.recv()
json.loads(resp)  #=> {
                  # "Header": {
                  #    "MessageType": "READ_RESPONSE",
                  #    "ClientHandle": "1"
                  # },
                  # "Body": {
                  #    "Value": {
                  #        "Type": 1,
                  #        "Body": true
                  #    },
                  #    "SourceTimestamp": "2019-07-26T11:10:20Z",
                  #    "ServerTimestamp": "2019-07-26T11:10:20Z"
                  # }
                  #}