Html2canvas: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.

Created on 2 Aug 2018 · 12Comments · Source: niklasvh/html2canvas

var canvasPromise  = html2canvas(document.body, {
                allowTaint: true,
                useCORS: true
            });
canvasPromise.then(function(canvas) {
    document.body.appendChild(canvas);
    console.log(canvas);
    canvas.toDataURL('image/png');
});

Bug reports:

Uncaught (in promise) DOMException: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.

html2canvas version tested with:
Chrome 67.0.3396.99
Windows 10

Source

jamesmarva

Most helpful comment

I have also the same issues.
Did you find a solution or workaround?

samiahakmi on 20 Aug 2018

👍16

All 12 comments

I have also the same issues.
Did you find a solution or workaround?

samiahakmi on 20 Aug 2018

👍16

i'm doing the same thing in Firefox 61.0.2 and i'm getting a SecurityError despite setting allowTaint to true

AkashaP on 24 Aug 2018

No solution as far as I know, but I have a workaround: change every image to base64. That way, you could render it in canvas even though it's originally from different domain.

dorklord23 on 26 Sep 2018

👍4

Have you saw this: CORS_enabled_image

If the source of the foreign content is an HTML element, attempting to retrieve the contents of the canvas isn't allowed.

As soon as you draw into a canvas any data that was loaded from another origin without CORS approval, the canvas becomes tainted.

I use the configuration options like this:

html2canvas(document.body, {
    allowTaint: true,
    foreignObjectRendering: true
});

fairyly on 10 Jan 2019

👍12 ❤1

Hi, we faced the same problem. We followed @dorklord23 suggestion because we already had a proxy url that did the conversion.

If someone found it helpful the solution was:

      html2canvas(document.body, {
        proxy: this._proxyURL,
        allowTaint: true,
        onclone: (cloned) => convertAllImagesToBase64(this._proxyURL, cloned),
      }).then((canvas) => {
        this._postmessageChannel.send(`get.screenshot:${canvas.toDataURL('image/png')}`);
      });

Where the helper function convertAllImagesToBase64 is:

const convertAllImagesToBase64 = (proxyURL, cloned) => {
  const pendingImagesPromises = [];
  const pendingPromisesData = [];

  const images = cloned.getElementsByTagName('img');

  for (let i = 0; i < images.length; i += 1) {
    // First we create an empty promise for each image
    const promise = new Promise((resolve, reject) => {
      pendingPromisesData.push({
        index: i, resolve, reject,
      });
    });
    // We save the promise for later resolve them
    pendingImagesPromises.push(promise);
  }

  for (let i = 0; i < images.length; i += 1) {
    // We fetch the current image
    fetch(`${proxyURL}?url=${images[i].src}`)
      .then((response) => response.json())
      .then((data) => {
        const pending = pendingPromisesData.find((p) => p.index === i);
        images[i].src = data;
        pending.resolve(data);
      })
      .catch((e) => {
        const pending = pendingPromisesData.find((p) => p.index === i);
        pending.reject(e);
      });
  }

  // This will resolve only when all the promises resolve
  return Promise.all(pendingImagesPromises);
};

export { convertAllImagesToBase64 };

By the way this are the tests for that helper function (we are using jest for wrting test and mockFetch packages):

import { convertAllImagesToBase64 } from '../images';

fetch.resetMocks();

// Mock fetch to respond different for each image so we can assert that the image return the correct response
// Also make one of the response be delayed (2 seconds) to simulate the response is not in the same order we do the call (network latency, image size, etc)
fetch.mockImplementation((url) => {
  if (url.includes('imagesrc1')) {
    return Promise.resolve(new Response(JSON.stringify('data:image/png;base64,1')));
  } else if (url.includes('imagesrc2')) {
    return new Promise((resolve) => setTimeout(resolve(new Response(JSON.stringify('data:image/png;base64,2'))), 2000));
  } else if (url.includes('imagesrc3')) {
    return Promise.resolve(new Response(JSON.stringify('data:image/png;base64,3')));
  }
  return Promise.resolve(new Response(JSON.stringify('')));
});

const mocksImages = [
  { id: 1, src: 'imagesrc1' },
  { id: 2, src: 'imagesrc2' },
  { id: 3, src: 'imagesrc3' },
];

const mockClone = {
  getElementsByTagName: jest.fn(() => mocksImages),
};

describe('utils/images', () => {  
  it('convertAllImagesToBase64. Expect to call 3 times to the correct enpoint using the image source', async () => {
    const allPromises = convertAllImagesToBase64('http://localhost/fake_proxy', mockClone);

    // Expect the clone elements gets all the image tags
    expect(mockClone.getElementsByTagName).toBeCalledWith('img');

    allPromises.then(() => {
      // Expect to have done the 3 fetch calls and with the correct params
      expect(fetch).toBeCalledTimes(3);
      expect(fetch).toHaveBeenNthCalledWith(1, 'http://localhost/fake_proxy?url=imagesrc1');
      expect(fetch).toHaveBeenNthCalledWith(2, 'http://localhost/fake_proxy?url=imagesrc2');
      expect(fetch).toHaveBeenNthCalledWith(3, 'http://localhost/fake_proxy?url=imagesrc3');

      // Expect that our images where updated properly
      expect(mocksImages).toContainEqual({
        id: 1, src: 'data:image/png;base64,1',
      });
      expect(mocksImages).toContainEqual({
        id: 2, src: 'data:image/png;base64,2',
      });
      expect(mocksImages).toContainEqual({
        id: 3, src: 'data:image/png;base64,3',
      });
    });
  });
});

Ruby backend enpdoint:

require 'base64'
require 'net/http'

module Api
  module V1
    class ImageProxyController < ApiController
      def index
        url   = URI.parse(params[:url])
        image = Net::HTTP.get_response(url)

        render json: data_url(image).to_json, callback: params[:callback]
      end

      private

        def data_url(image)
          "data:#{image.content_type};base64,#{Base64.encode64(image.body)}"
        end

    end
  end
end

I hope someone find this helpful. I hope it helps someone not to invest as much time as we did to fix this properly.

If you can see any improvment please suggest.
Regards.

sandinosaso on 28 Feb 2019

If you do like below, what will happen?

const TempImage = window.Image

 const Image = function() {
        const img = new TempImage()
        img.crossOrigin = 'anonymous'
        return img
 }

zhaosaisai on 6 May 2019

👍2 👀1 🚀1 🎉1 😄1

Found a solution and it is working

While calling html2canvas,pass useCORS true
html2canvas(selectorElement,{useCORS:true}).then(canvas => {
//do something
});
Correct html2canvas.js file. Theres typo mistake
Change "anonymous" to "Anonymous" in this if block
if (isInlineBase64Image(src) || useCORS) {
img.crossOrigin = 'Anonymous';
}

NishantTeria on 10 Aug 2019

👎3 👍2

var canvasPromise  = html2canvas(document.body, {
                allowTaint: true,
                useCORS: true
            });
canvasPromise.then(function(canvas) {
    document.body.appendChild(canvas);
    console.log(canvas);
    canvas.toDataURL('image/png');
});
Bug reports:

Uncaught (in promise) DOMException: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.

html2canvas version tested with:

Chrome 67.0.3396.99

Windows 10

You will need to use just the property 'useCORS: true', if you use the property 'allowTaint: true' you give permssion to turn your canvas into a tainted canvas

USE THIS:

var canvasPromise  = html2canvas(document.body, {
                useCORS: true
            });
canvasPromise.then(function(canvas) {
    document.body.appendChild(canvas);
    console.log(canvas);
    canvas.toDataURL('image/png');
});

INSTEAD OF THIS:

var canvasPromise  = html2canvas(document.body, {
                allowTaint: true,
                useCORS: true
            });
canvasPromise.then(function(canvas) {
    document.body.appendChild(canvas);
    console.log(canvas);
    canvas.toDataURL('image/png');
});

motarock on 23 Dec 2019

👎6 👍2

Hello, nice work for html2canvas.

Sadly I'm facing the same issue, has anyone solved this?
Already tried @motarock and all before that, plus combinations, etc. The image is white with nothing painted.

downloadQRCode = (fileName) => {
    html2canvas(document.getElementById('generated-qr-code'), {
      useCORS: true,
      // allowTaint: false,
      // logging: true,
    }).then((canvas) => {
      // document.body.appendChild(canvas); // checking
      const data = canvas.toDataURL('image/jpeg');
      const element = document.createElement('a');
      element.setAttribute('href', data);
      element.setAttribute('download', fileName + '.jpeg');
      document.body.appendChild(element);
      element.click();
      // document.body.removeChild(element);
      console.log("%c data", "font-size:2em;", data, fileName);
      console.log("%c canvas", "font-size:2em;", canvas );
      this.setState({
        imageSrc: data // setting the src of a img tag to check the result. Nothing in it either..
      })
    });

Thanks in advance