flat-bot / netless-app-pdfjs

PDF.js

@netless/app-pdfjs

A Netless App that renders PDF files with PDF.js.

Install

npm add @netless/app-pdfjs

Usage

Important

This app only implements viewing PDF files.
It does not support dispatchDocsEvent() nor export PDF.

1. Get a static URL pointing to the PDF file.

   This package only synces the URL for each client to download the PDF. You have to obtain a static URL to the file first to continue. For example, you can use an OSS to achieve this.

2. Register this app before joinning room.

   import { register } from "@netless/fastboard"
   import { install } from "@netless/app-pdfjs"
   
   install(register) // the app is named 'PDFjs'

3. Add this app after joinning room.

   fastboard.manager.addApp({
     kind: 'PDFjs',
     options: {
       title: 'a.pdf',
       scenePath: '/pdf/paper' // ! This is required.
     },
     attributes: {
       src: 'https://cdn.jsdelivr.net/gh/mfogel/polygon-clipping/paper.pdf'
     }
   })

Troubleshooting

Failed to fetch pdf.min.mjs

This package downloads the latest PDF.js release from jsDelivr:
https://cdn.jsdelivr.net/npm/pdfjs-dist@latest/build/

To alter this URL or choose a different version, set the app option:

install(register, {
  appOptions: {
    pdfjsLib: 'https://cdn.jsdelivr.net/npm/pdfjs-dist@latest/build/pdf.min.mjs',
    workerSrc: 'https://cdn.jsdelivr.net/npm/pdfjs-dist@latest/build/pdf.worker.min.mjs'
  }
})

If the URL is blocked by your CSP, you have to add them to your script-src policy:

Content-Security-Policy: script-src https://cdn.jsdelivr.net/

TypeError: Promise.withResolvers is not a function

PDF.js uses Promise.withResolvers(), which is a brand new feature in JavaScript. In case your target environment does not support this, you need to add the following code to the first line of pdf.min.mjs and pdf.worker.min.mjs to resolve this issue.

if (typeof Promise.withResolvers === 'undefined') {
  Promise.withResolvers = function () {
    let resolve, reject
    const promise = new Promise((res, rej) => {
      resolve = res
      reject = rej
    })
    return { promise, resolve, reject }
  }
}

For convenience, you can run node ./scripts/patch.mjs in this repo to generate patched pdf.min.mjs and pdf.worker.min.mjs. The 2 files will be placed at the dist folder.

Uncaught SyntaxError / Uncaught ReferenceError

This package only targets modern browsers that support native ES modules.

A certain PDF file opens exceptionally slowly, even several times slower than smaller PDFs.

Most PDF files are designed for easy transmission, allowing us to render a single page by requesting a portion of the file through Range requests. However, a few PDF files require a complete download before they can be rendered. You can check the browser's requests to confirm if the slow rendering of the first page is due to the complete download of a PDF file. If so, you need to use qpdf to convert the PDF into a structure that is easier to transmit.

PDF Rendering Issue

As the package name implies, it uses PDF.js to render the file. It is possible that PDF.js has a bug when rendering some files. Please raise an issue there to ask for help.

License

MIT @ netless