Historical Read¶
To read the historical values of a variable, the client must use HISTORICALREAD_REQUEST request.
Historical Read Request¶
Field | Description | |
---|---|---|
Header | ||
MessageType | Must be HISTORICALREAD_REQUEST. | |
ClientHandler | See Message Format. | |
Body | ||
Variable | The variable to read | |
StartTime | Beginning of period to read in ISO 8601 format. Example: “2015-09-06T09:03:21Z” | |
Endtime | End of period to read in ISO 8601 format. Example: “2015-09-06T09:03:21Z” |
Historical Read Response¶
Field | Description | ||||
---|---|---|---|---|---|
Header | |||||
MessageType | Must be HISTORICALREAD_RESPONSE. | ||||
ClientHandler | See Message Format. | ||||
Body | |||||
@DataValues | The history data | ||||
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: “2015-09-06T09:03:21.237123” | ||||
ServerTimestamp | The time of the value given by the server in ISO 8601 format. Example: “2015-09-06T09:03:21.237123” |
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':'HISTORICALREAD_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": "Boolean",
# "Body": true
# },
# "SourceTimestamp": "2019-07-26T11:10:20Z",
# "ServerTimestamp": "2019-07-26T11:10:20Z"
# }
#}