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Fix image uploads being random data when canvas read access is blocked (#15180) 

Fixes #15178

PR #11499 introduced a way to deal with all-white canvas, but newer
Firefox versions set random data instead.

This PR detects whether canvas operations are reliable by comparing
the results on a hardcoded 2×2 pixels image, and memoizing the result.

This should be both more reliable and faster than the previous check.
gh/stable
ThibG 2020-11-18 18:01:58 +01:00 committed by GitHub
parent 18ca4e0e9a
commit d8d43a427a
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1 changed files with 41 additions and 9 deletions
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50
app/javascript/mastodon/utils/resize_image.js
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@ -41,6 +41,45 @@ const dropOrientationIfNeeded = (orientation) => new Promise(resolve => {
}
});
// Some browsers don't allow reading from a canvas and instead return all-white
// or randomized data. Use a pre-defined image to check if reading the canvas
// works.
const checkCanvasReliability = () => new Promise((resolve, reject) => {
switch(_browser_quirks['canvas-read-unreliable']) {
case true:
reject('Canvas reading unreliable');
break;
case false:
resolve();
break;
default:
// 2×2 GIF with white, red, green and blue pixels
const testImageURL =
'data:image/gif;base64,R0lGODdhAgACAKEDAAAA//8AAAD/AP///ywAAAAAAgACAAACA1wEBQA7';
const refData =
[255, 255, 255, 255, 255, 0, 0, 255, 0, 255, 0, 255, 0, 0, 255, 255];
const img = new Image();
img.onload = () => {
const canvas = document.createElement('canvas');
const context = canvas.getContext('2d');
context.drawImage(img, 0, 0, 2, 2);
const imageData = context.getImageData(0, 0, 2, 2);
if (imageData.data.every((x, i) => refData[i] === x)) {
_browser_quirks['canvas-read-unreliable'] = false;
resolve();
} else {
_browser_quirks['canvas-read-unreliable'] = true;
reject('Canvas reading unreliable');
}
};
img.onerror = () => {
_browser_quirks['canvas-read-unreliable'] = true;
reject('Failed to load test image');
};
img.src = testImageURL;
}
});
const getImageUrl = inputFile => new Promise((resolve, reject) => {
if (window.URL && URL.createObjectURL) {
try {
@ -110,14 +149,6 @@ const processImage = (img, { width, height, orientation, type = 'image/png' }) =
context.drawImage(img, 0, 0, width, height);
// The Tor Browser and maybe other browsers may prevent reading from canvas
// and return an all-white image instead. Assume reading failed if the resized
// image is perfectly white.
const imageData = context.getImageData(0, 0, width, height);
if (imageData.data.every(value => value === 255)) {
throw 'Failed to read from canvas';
}
canvas.toBlob(resolve, type);
});
@ -127,7 +158,8 @@ const resizeImage = (img, type = 'image/png') => new Promise((resolve, reject) =
const newWidth = Math.round(Math.sqrt(MAX_IMAGE_PIXELS * (width / height)));
const newHeight = Math.round(Math.sqrt(MAX_IMAGE_PIXELS * (height / width)));
getOrientation(img, type)
checkCanvasReliability()
.then(getOrientation(img, type))
.then(orientation => processImage(img, {
width: newWidth,
height: newHeight,