VISA Print Client

This is an angular library providing a service to manage websocket connections to a VISA Print Server and enabling printing of PDF documents from a VISA instance on the user's host computer. This angular module is intended to be integrated into the VISA front end

The transfer is initially triggered by a request from the VISA CUPS Driver to the VISA Print Server when a user prints a document in an instance.

PDFs are then sent from the server via the websocket to the client. A notification is received, the user is informed of a print request, and the PDF is rendered in a hidden iframe: after rendering the print dialog is opened from the iframe content.

The user then selects a local printer to print the document or saves the PDF as a local file.

An authentication proxy is used to ensure that only the owner of an instance can connect to the VISA Print Server and receive print requests.

Installation

To use visa-print-client in your project, install it via npm:

npm i @illgrenoble/visa-print-client --save

You also need to install the socket.io-client peer dependency:

npm i socket.io-client --save

Usage

Integration into a module:

app.module.ts

import { VisaPrintModule } from '@illgrenoble/visa-print-client';
// etc.

@NgModule({
    imports: [
        // etc.
        VisaPrintModule,
    ],
    declarations: [
        AppComponent,
        // etc.
    ],
    bootstrap: [
        AppComponent
    ]
})
export class AppModule {
}

This provides the VisaPrintService that can be integrated into a component:

app.component.ts

export class AppComponent implement OnInit {
    constructor(private printService: VisaPrintService) {}
    
    public ngOnInit(): void {
        this.printService.connect({path: `ws/print`, token: 'MY_SECRET_TOKEN'}).subscribe(event => {
            if (event.type === 'CONNECTED') {
                const connectionId = event.connectionId;

                // enable printing
                this.printService.enablePrinting(connectionId);
                
            } else if (event.type === 'PRINT_JOB_AVAILABLE') {
                const printJob = event.data as PrintJobAvailableEvent;
                this.printService.openPrintable(event.connectionId, printJob.jobId);
            }
        });
    }

}

Configuration

The connection to the VISA Print Client is configured with a path and a token:

• path: string

  Requests to the VISA Print Client are made to the same host as the angular app: a proxy is required to forward the requests to the server. In development mode this can be using the webpack proxy config, for example with the path of ws/print we can specify a proxy conf to forward the requests to the socket.io path of the server, such as:

  {
       "/ws/print/": {
           "target": "http://localhost:8091",
           "secure": false,
           "pathRewrite": {
               "^/ws/print/": "/socket.io/"
           },
           "changeOrigin": true,
           "logLevel": "debug",
           "ws": true
       }
  }
    

• token: string (optional)

  If the server is configured with an accessToken, it can be specified here.

  Note that the proxy provides authentication and ensures that only the owner of an instance receives print requests.

Demo

A demo is available to quickly test the connection between a client and a server, the transfer of a PDF file via websocket and the opening of the print dialog in the client.

To start the server locally run the following commands in a terminal:

npm i -g @illgrenoble/visa-print-server
visa-print-server

This will start up the VISA Print Server on localhost:8091 without authentication enabled.

In another terminal, use the following commands to build and run the client:

git clone https://github.com/ILLGrenoble/visa-print-client.git
cd visa-print-client
npm install
npm run build:lib
npm start

The client will automatically connect to the websocket server on localhost and enable the printing queue. Open a browser window at http://localhost:4200 (you should only see a grey window). In a debug console you should see that the websocket is connected and printing enabled.

To test the transfer of a PDF file, from another terminal perform the following command:

curl -X POST http://localhost:8091/api/printer --data-urlencode "path=<path_to_a_pdf>" --data-urlencode "jobId=1"

Change path_to_a_pdf to the absolute path of a PDF file on your computer. The print dialog should open on the client app with the PDF available for printing.