@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.

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.
Convert this PDF file using the Agora File Conversion service. Remember to set outputFormat: "qpdf".

You will get a taskId and prefix URL in the response of Query Task Status API.

import { register } from "@netless/fastboard"
import { install } from "@netless/app-pdfjs"

install(register, options) // the app is named 'PDFjs'

Add this app after joinning room.

fastboard.manager.addApp({
  kind: 'PDFjs',
  options: {
    title: 'a.pdf', // ! Required for window title.
    scenePath: '/pdf/paper' // ! Required for displaying whiteboard on it.
  },
  attributes: {
    prefix, // ! Required.
    taskId, // ! Required.
  }
})

Make sure scenePath starts with / and not ends with /.
The prefix will be like "https://white-cover.oss-cn-hangzhou.aliyuncs.com/flat/".
The taskId will be like "b444a180c2f44a409a4d081e8f1a6d5f".

You can get the prefix and taskId from the conversion response JSON.

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/

Note: If you want to load PDFs on demand (without having to download the entire PDF before rendering), you need to expose the 'Accept-Ranges' headers on your stored OSS. If our library cannot obtain this header, it will not make segmented requests.

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.

What should I do if the OSS I entered in the `Agora Console` is private?

You can add a new property urlInterrupter to the second parameter options when calling register. This property is a function that returns a publicly accessible address by passing in the URL.

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.

Changelog

License

MIT @ netless