Context

This project proposes a local PDF compression that can be used as a remote API. This project is a fork of another projet: https://github.com/laurentmmeyer/ghostscript-pdf-compress.wasm (itself based on the gs.wasm that @ochachacha compiled).

Run the project

Just add the following code in one of your file to use the PDF compression as a remote API (even if it will run locally)

const libBaseUrl = 'https://unpkg.com/[email protected]';

function loadPDFDataFromWorker(response) {
  return new Promise((resolve, reject) => {
    if (response === null) {
      reject('Compression failure');
    } else {
      const xhr = new XMLHttpRequest();
      xhr.open('GET', response);
      xhr.responseType = 'arraybuffer';
      xhr.onload = () => {
        window.URL.revokeObjectURL(response);
        const blob = new Blob([xhr.response], { type: 'application/pdf' });
        const pdfURL = window.URL.createObjectURL(blob);
        const size = xhr.response.byteLength;
        resolve({ pdfURL, size });
      };
      xhr.send();
    }
  });
}

export async function compress(pdf, params = []) {
  const script = await fetch(`${libBaseUrl}/background-worker.js`);
  const scriptContent = await script.text();
  if (!script.ok) {
    return Promise.reject(`Unable to load script (${scriptContent})`);
  }
  const blob = new Blob([scriptContent], { type: 'application/javascript' });
  const blobURL = URL.createObjectURL(blob);
  const worker = new Worker(blobURL, { type: 'module', name: 'pdfWorker' });
  worker.postMessage({ data: { psDataURL: pdf, params, baseUrl: libBaseUrl }, target: 'wasm' });
  const promise = new Promise((resolve) => {
    const listener = (e) => {
      resolve(e.data);
      worker.removeEventListener('message', listener);
      setTimeout(() => worker.terminate(), 0);
    };
    worker.addEventListener('message', listener);
  });

  const data = await promise;
  return loadPDFDataFromWorker(data);
}

The exported function compress take 2 arguments:

• The first one is the url of an object created by window.URL.createObjectURL()
• The second one is a list of parameters allowing to set up the pdf. The list of suppported arguments can be found at https://ghostscript.readthedocs.io/en/latest/VectorDevices.html#distiller-parameters

The script calls the function

gs -sDEVICE=pdfwrite 

and appends the arguments you give.

The function returns an object containing 2 attributes:

• pdfURL
• size

pdfURL is the url of the new compressed pdf (created by window.URL.createObjectURL()) size is the size of the new pdf (in bytes)