Nothing Prevents Misery

    opcua
    TypeScript icon, indicating that this package has built-in type declarations

    1.0.0 • Public • Published

    opcua

    TypeScript / JavaScript OPC UA client for the browser.

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    ... work in progress ...

    Features

    Usage

    npm i opcua
    import Client from 'opcua'
     
    const client = new Client()
     
    // wait for an active session
    client.addEventListener('session:activate', async event => {
     
      // browse the root folder
      const req = new BrowseRequest({
        NodesToBrowse: [
          new BrowseDescription({
            NodeId: NewTwoByteNodeId(IdRootFolder)
          })
        ]
      })
     
      // all requests use async / await
      const res = await client.browse(req)
      console.log(res)
    })

    Development

    The source code is written in TypeScript. We use the TypeScript compiler to create the JavaScript files for the browser.

    Some source code files are autogenerated.

    • src/ua/generated.ts by cmd/service/main.go
    • src/id/id.ts by cmd/id/main.go

    Do not edit them by hand. You need Go on your machine to execute those generators. The schema definition files are located at ./schema.

    We rely on reflection and decorators to get types (e.g. uint32, CreateSessionRequest or arrays of certain types string[]) during runtime. In JavaScript a number is always double-precision 64-bit. OPC UA has much more number types like int8, uint8, int16, uint16 and so on. In order to get the binary encoding / decoding right we must know exactly how many bits represent a number.

    The client architecture consists of multiple layers. They closely follow the official OPC UA specification. Read the following diagram from bottom to top. On the right side you find the responsibilities for each layer.

    layers

    The OPC UA handshake is quite complex and several steps are necessary to get an active session. Those steps are

    1. Hello / Acknowledge
    2. Open Secure Channel
    3. Create Session
    4. Activate Session

    The following diagram shows this sequence and highlights response parameters that the client has to store internally (e.g. channel id, token id, authentication token, sequence number, request id).

    handshake

    You need an OPC UA server implementation that supports WebSockets to test the client. Two options exist:

    1. Use open62541 with WebSockets enabled
    2. Use websockify for servers that do not support WebSockets (that only support TCP connections)

    Keywords

    none

    Install

    npm i opcua

    DownloadsWeekly Downloads

    6

    Version

    1.0.0

    License

    MIT

    Unpacked Size

    8.31 MB

    Total Files

    301

    Last publish

    Collaborators

    • zemirco