2017-02-27
Review
In the previous post, I introduced OPC-UA. In this article, I am going to explore how to extract information about the OPC-UA server itself.
Standard Objects
Part 5, Section 8, of the OPC-UA standard defines the Standard Objects and their Variables. Figure 1 shows that the OPC-UA AddressSpace starts out with a Root element. Below the Root element is the Objects element and under that is the Server element. It is this server element that I want to explore in this post.
Root Folder Object
The python-opcua library makes the Root Folder Object available via the Client.get_root_node method.
>>> from opcua import Client
>>> client = Client('opc.tcp://127.0.0.1:49320')
>>> client.connect()
>>> root = client.get_root_node()
>>> root.get_browse_name()
QualifiedName(0:Root)
In the example above, I import the Client class from the python-opcua library. I then specify an endpoint and connect to the OPC-UA server, as was shown in the previous post. Next, I use the get_root_node method to get a reference to the root node, as described in the standard. Finally, I print out the root node's browse name. This returns a QualifiedName containing '0' and 'Root'. I think that '0' is the Namespace identifier described in the OPC-UA standard. Namespace '0' is the Namespace reserved for Nodes which the standard defines. I will be able to test this theory later on as I dig into this more.
If I continue with this example, I can see that the root node has the children nodes defined by the standard.
>>> root.get_children_descriptions()
[ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:TwoByteNodeId(i=85), BrowseName:QualifiedName(0:Objects), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Objects'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:TwoByteNodeId(i=86), BrowseName:QualifiedName(0:Types), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Types'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:TwoByteNodeId(i=87), BrowseName:QualifiedName(0:Views), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Views'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61))]
The node descriptions returned from get_children_descriptions include the standard nodes of Objects, Types, and Views. I can use this information to navigate to the Objects node and then to the Server node. I took a lucky guess at how to format the argument of get_child after running help(roo.get_child) and reviewing the provided information.
>>> objects = root.get_child("0:Objects")
Now we can run get_children_descriptions() on the Objects node.
>>> objects.get_children_descriptions()
[ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:FourByteNodeId(i=2253), BrowseName:QualifiedName(0:Server), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Server'), NodeClass:NodeClass.Object, TypeDefinition:FourByteNodeId(i=2004)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=_ConnectionSharing), BrowseName:QualifiedName(2:_ConnectionSharing), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'_ConnectionSharing'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=_System), BrowseName:QualifiedName(2:_System), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'_System'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=16ESM-2300-1SCADA), BrowseName:QualifiedName(2:16ESM-2300-1SCADA), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'16ESM-2300-1SCADA'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=BriteSpot), BrowseName:QualifiedName(2:BriteSpot), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'BriteSpot'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=Elixir), BrowseName:QualifiedName(2:Elixir), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Elixir'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=LGC-3530-LPS-ANA-P), BrowseName:QualifiedName(2:LGC-3530-LPS-ANA-P), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'LGC-3530-LPS-ANA-P'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=LGC-3530-LPS-CTRL-P), BrowseName:QualifiedName(2:LGC-3530-LPS-CTRL-P), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'LGC-3530-LPS-CTRL-P'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=Mandan), BrowseName:QualifiedName(2:Mandan), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Mandan'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=Modbus-Serial), BrowseName:QualifiedName(2:Modbus-Serial), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Modbus-Serial'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=35), IsForward:True, NodeId:StringNodeId(ns=2;s=Simulator), BrowseName:QualifiedName(2:Simulator), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Simulator'), NodeClass:NodeClass.Object, TypeDefinition:TwoByteNodeId(i=61))]
This returns a lot of interesting information, most of it I am going to ignore today. it does confirm that the Server node is a child of the Objects node. Therefore, I can not retrieve the Server node.
>>> server = objects.get_child("0:Server")
>>> server.get_children_descriptions()
[ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=46), IsForward:True, NodeId:FourByteNodeId(i=2254), BrowseName:QualifiedName(0:ServerArray), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ServerArray'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=68)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=46), IsForward:True, NodeId:FourByteNodeId(i=2255), BrowseName:QualifiedName(0:NamespaceArray), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'NamespaceArray'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=68)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2256), BrowseName:QualifiedName(0:ServerStatus), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ServerStatus'), NodeClass:NodeClass.Variable, TypeDefinition:FourByteNodeId(i=2138)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=46), IsForward:True, NodeId:FourByteNodeId(i=2267), BrowseName:QualifiedName(0:ServiceLevel), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ServiceLevel'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=68)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=46), IsForward:True, NodeId:FourByteNodeId(i=2994), BrowseName:QualifiedName(0:Auditing), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'Auditing'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=68)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2268), BrowseName:QualifiedName(0:ServerCapabilities), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ServerCapabilities'), NodeClass:NodeClass.Object, TypeDefinition:FourByteNodeId(i=2013)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2274), BrowseName:QualifiedName(0:ServerDiagnostics), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ServerDiagnostics'), NodeClass:NodeClass.Object, TypeDefinition:FourByteNodeId(i=2020)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2295), BrowseName:QualifiedName(0:VendorServerInfo), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'VendorServerInfo'), NodeClass:NodeClass.Object, TypeDefinition:FourByteNodeId(i=2033)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2296), BrowseName:QualifiedName(0:ServerRedundancy), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ServerRedundancy'), NodeClass:NodeClass.Object, TypeDefinition:FourByteNodeId(i=2034))]
Repeating the same process lists the descriptions of the children of Server. I think I want to inspect the VendorServerInfo node. The standard says there are no mandatory components to the VendorServerInfo data type. It is completely up to the server vendor to populate it. Let's see how Kepware did it.
>>> server_status = server.get_child("0:ServerStatus")
>>> server_status.get_children_description()
[ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2257), BrowseName:QualifiedName(0:StartTime), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'StartTime'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2258), BrowseName:QualifiedName(0:CurrentTime), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'CurrentTime'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2259), BrowseName:QualifiedName(0:State), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'State'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2260), BrowseName:QualifiedName(0:BuildInfo), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'BuildInfo'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=0)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2992), BrowseName:QualifiedName(0:SecondsTillShutdown), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'SecondsTillShutdown'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2993), BrowseName:QualifiedName(0:ShutdownReason), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ShutdownReason'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63))]
This node contains a bunch of good information. I am going to focus on the BuildInfo node.
>>> build_info = server_status.get_child("0:BuildInfo")
>>> build_info.get_children_descriptions()
[ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2262), BrowseName:QualifiedName(0:ProductUri), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ProductUri'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2263), BrowseName:QualifiedName(0:ManufacturerName), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ManufacturerName'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2261), BrowseName:QualifiedName(0:ProductName), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'ProductName'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2264), BrowseName:QualifiedName(0:SoftwareVersion), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'SoftwareVersion'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2265), BrowseName:QualifiedName(0:BuildNumber), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'BuildNumber'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63)), ReferenceDescription(ReferenceTypeId:TwoByteNodeId(i=47), IsForward:True, NodeId:FourByteNodeId(i=2266), BrowseName:QualifiedName(0:BuildDate), DisplayName:LocalizedText(Encoding:3, Locale:b'en', Text:b'BuildDate'), NodeClass:NodeClass.Variable, TypeDefinition:TwoByteNodeId(i=63))]
We are getting close to some real information here. Let's go down to the Product Name.
>>> product_name = server_status.get_child("0:ProductName")
>>> product_name.get_value()
'KEPServerEX'
Finally, we have navigated through the nodes to get to some concrete information. In this case, we are able to see that the value of the ProductName node is 'KEPServerEX'.