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OPC UA Web Platform

OPC UA Web Platform is a web application based on ASP.NET Core 2. It provides a REST interface between OPC UA Servers and generic clients which have no knowledge about OPC UA specification. Furthermore, the communication is is stateless and no session must be maintained between clients and platform. Such clients could be represented by web browser or constrained IoT-device.

A generic client of the platform owns a reduced view of the Address Space handled by an OPC UA Server. Web Platform provides access to OPC UA Servers exposing them as Data Set resources. Clients can access this Data Set in order to explore the Address Space as if this were a simple graph composed by nodes and edges.

Furthermore, web platform manage the monitoring of variables by means of publish/subscribe communication based on MQTT and/or SignalR.

webplatformarc

Features

OPC UA Web Platform exposes the following resources through a RESTful interface:

Resource Description
/authenticate It defines a routine that return a JWT Token used by the platform in order to authenticate client's requests
/data-sets A collection of all OPC UA Servers exposed by the platform.
/data-sets/{dataset-id}/nodes Returns the entry point of the Address Space relevant to the Data Set with {node-id}. It redirect the request to /data-sets/{dataset-id}/nodes/0-85 which is relevant to the node representing the standard OPC UA Node Object.
/data-sets/{dataset-id}/nodes/{node-id} Returns the state of the node with {node-id}.
/data-sets/{dataset-id}/monitor It defines a routine that takes a node-id, a broker url and a topic as inputs, and start publishing notification to the broker. Broker url must have a prefix relevant to the supported technology, e.g. "mqtt:localhost" or "signalr:http:localhost:8080"
/data-sets/{dataset-id}/stop-monitor It defines a routine that takes topic and broker url as inputs and stop publishing notification relevant the provided couple <topc, broker url>.

You can more information in the API Documentation

Features currently being implemented by means of the REST interface are:

  • Authentication with JWT Token
  • Read state of nodes Variable, Object, Method
    • Read Variable's value of all Built-In Data Type for scalar, arrays and multidimensional arrays values.
    • Read Variable's value of all Standard Data Type for scalar and array values.
    • Read Variable's value of vendor-specific Structured Data Type for scalar and array values.
  • Write new values for nodes Variable.
    • Write Variable's value of all Built-In Data Type for scalar, arrays and multidimensional arrays values.
    • Write Variable's value of all Standard Data Type for scalar and array values.
    • Write Variable's value of vendor-specific Structured Data Type for scalar and array values.
  • Monitor Variable's value through Pubish/Subscribe communication based on MQTT and SignalR. Variables may support 3 kind of deadband notification (None, Absolute, Percent) as described in OPC UA specification. All variables exposed by the platform support at leas None

Rid of DataTypes

The powerful concept of the OPC UA Web Platform is the lack of knowledge about OPC UA protocol specification of the client. So that, a client have no understanding about DataTypes of the OPC UA standard and relies only on the meaning of the JSON base types.

In order to enable the client to interact with an OPC UA Server anyway, the OPC UA platform provides a JSON schema for all the data values exposed by an OPC UA Server. That is, a client is able to validate (and understand description) of values and write new well-formed values to the platform.

All schema concerning values of Variable Nodes will be contained in a field "value-schema" of the response body, as will be shown in the following examples.

Getting started

OPC UA Web Platfrom requires .NET Core 2, available for Windows, Linux and MacOS here.

Start cloning the project in your local machine and configure it in order to expose your OPC UA Servers through the OPC UA Web Platform interface:

  1. Clone the project in a local folder:

    git clone https://github.com/OPCUAUniCT/OPCUAWebPlatformUniCT

  2. Edit the application configuration file appsettings.json setting all the information relevant to the OPC UA servers you want to be exposed by the platform

    "OPCUAServersOptions": {
        "Servers": [
          {
            "Name": "UaCppLocalServer",
            "Url": "opc.tcp://localhost:48010"
          },
          {
            "Name": "Raspberry Server",
            "Url": "opc.tcp://192.168.1.101:48010"
          }
        ]
      }
    

    You can edit the configuration file in order to change JWT authentication parameter too.

  3. Edit the file OPCUAWebClatform.Config.xml in order to set all the configuration relevant to the OPC UA Middleware embedded in the platform (which is itself an OPC UA Client, so it requires its own configuration).

  4. Go in the project directory and run the project

    dotnet run

    N.B. You have to take care about running the Web Platform in Development or Production configuration. You can choose the configuration setting the environment variable ASPNETCORE_ENVIRONMENT, as explained here.

Run on Docker container

It si possible running OPC UA Web Platform on Docker container with the following command

docker run --rm -it -p 5000:80 marsala/opcua-web-platform:1.0.0

Troubleshooting

You may occur in error like "DataSet Not Available" even if all the ip addresses or your OPC UA Server are perfectly configured. Be aware you have configured the platform Instance Certificate in the OPC UA Servers Trusted certificate store.

Examples

In the following will be highlighted some common use cases for the OPC UA Web Platform. Remember that all request to the Api with the initial enpoint /api/ require an authentication token. A valid token can be obtained with a simple request to the following API endpoint:

POST http://{{base_url}}/auth/authenticate

The response will contain a valid token that must be included in an header "Authorization" like shown in the following examples.

This is an example request of authentication using the default Authentication service mock:

curl -X POST \
  http://localhost:5000/auth/authenticate \
  -F username=admin \
  -F password=password

Read the standard OPC UA Server Object Node

Suppose that the DataSet with dataset-id = 3 correspond to the OPC UA Server exposed by the platform you are interested. So, if you want to start browsing the data set you have to make a request like the following:

GET http://{{base_url}}/api/data-sets/3/nodes

You can make a request with:

curl -X GET http://{{YOUR-URL}}:5000/api/data-sets/2/nodes 
  -H 'Authorization: Bearer {YOUR-AUTHENTICATION-TOKEN}'

It will return the response:

{
    "node-id": "0-85",
    "name": "Objects",
    "type": "folder",
    "edges": [
        {
            "node-id": "0-2253",
            "name": "Server",
            "Type": "object",
            "relationship": "Organizes"
        },
        {
            "node-id": "3-BuildingAutomation",
            "name": "BuildingAutomation",
            "Type": "folder",
            "relationship": "Organizes"
        },
        {
            "node-id": "2-Demo",
            "name": "Demo",
            "Type": "folder",
            "relationship": "Organizes"
        },
        {
            "node-id": "5-Demo",
            "name": "DemoUANodeSetXML",
            "Type": "folder",
            "relationship": "Organizes"
        }
    ]
}

Read the a Node

Read the state of a Variable Node:

GET http://{{base_url}}/api/data-sets/3/nodes/2-Demo.Static.Scalar.WorkOrder

You can make a request with:

curl -X GET \
  http://{YOUR-URL}/api/data-sets/3/nodes/2-Demo.Static.Scalar.WorkOrder \
  -H 'Authorization: Bearer {YOUR-AUTHENTICATION-TOKEN}' \

It will return the response:

{
    "node-id": "2-Demo.Static.Scalar.WorkOrder",
    "name": "WorkOrder",
    "type": "variable",
    "value": {
        "ID": "9240890a-6ea8-41fc-8e84-f47edd3e3595",
        "AssetID": "123-X-Y-Z",
        "StartTime": "2018-04-20T14:24:39.085941Z",
        "NoOfStatusComments": 3,
        "StatusComments": [
            {
                "Actor": "Wendy Terry",
                "Timestamp": "2018-04-20T14:24:39.085941Z",
                "Comment": {
                    "Locale": "en-US",
                    "Text": "Mission accomplished!"
                }
            },
            {
                "Actor": "Gavin Mackenzie",
                "Timestamp": "2018-04-20T14:24:39.085941Z",
                "Comment": {
                    "Locale": "en-US",
                    "Text": "I think clients would love this."
                }
            },
            {
                "Actor": "Phil Taylor",
                "Timestamp": "2018-04-20T14:24:39.085941Z",
                "Comment": {
                    "Locale": "en-US",
                    "Text": "And justice for all."
                }
            }
        ]
    },
    "value-schema": {
        "type": "object",
        "properties": {
            "ID": {
                "type": "string"
            },
            "AssetID": {
                "type": "string"
            },
            "StartTime": {
                "type": "string"
            },
            "NoOfStatusComments": {
                "type": "number"
            },
            "StatusComments": {
                "type": "array",
                "items": {
                    "type": "object",
                    "properties": {
                        "Actor": {
                            "type": "string"
                        },
                        "Timestamp": {
                            "type": "string"
                        },
                        "Comment": {
                            "type": "object",
                            "properties": {
                                "Locale": {
                                    "type": "string"
                                },
                                "Text": {
                                    "type": "string"
                                }
                            }
                        }
                    }
                },
                "minItems": 3,
                "maxItems": 3
            }
        }
    },
    "status": "Good",
    "deadBand": "None",
    "minimumSamplingInterval": 0,
    "edges": []
}

Write a new value for a Variable Node

Update the value of a Variable Node:

POST http://{{base_url}}/api/data-sets/3/nodes/2-Demo.Static.Scalar.WorkOrder { "value": <YOUR-NEW-VALUE> }

You can make a request with:

curl -X POST \
  http://{YOUR-URL}/api/data-sets/3/nodes/2-Demo.Static.Scalar.WorkOrder \
  -H 'Authorization: Bearer {YOUR-AUTHENTICATION-TOKEN} \
  -d '{
  "value": {
        "ID": "9240890a-6ea8-41fc-8e84-f47edd3e3595",
        "AssetID": "123-X-Y-Z",
        "StartTime": "2018-04-20T14:24:39.085941Z",
        "NoOfStatusComments": 2,
        "StatusComments": [
            {
                "Actor": "Dylan Thomas",
                "Timestamp": "2018-04-20T14:24:39.085941Z",
                "Comment": {
                    "Locale": "en-US",
                    "Text": "Do not go gentle into that good night"
                }
            },
            {
                "Actor": "William Shakespeare",
                "Timestamp": "2018-04-20T14:24:39.085941Z",
                "Comment": {
                    "Locale": "en-US",
                    "Text": "There is nothing either good or bad, but thinking makes it so."
                }
            }
        ]
    }
}'

It worth noting how a client not compliant with the OPC UA specification is able to write new well-formed values with the aid of JSON Schemas.

Papers

The foundation ideas of OPC UA Web Platform are discussed in the following papers. The platform described in these papers may differs for some aspects but the concepts are quite similar:


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