Bug 1873405 - Test canvas placeholder exemption for pdf.js. r=tjr

Differential Revision: https://phabricator.services.mozilla.com/D197779

toolkit/components/resistfingerprinting/tests/browser/browser.toml

@@ -28,3 +28,6 @@ support-files = [
 ["browser_fpiServiceWorkers_fingerprinting.js"]
 
 ["browser_serviceWorker_fingerprinting_webcompat.js"]
+
+["browser_rfp_canvasplaceholder_pdfjs.js"]
+support-files = ["file_pdf.pdf"]

toolkit/components/resistfingerprinting/tests/browser/browser_rfp_canvasplaceholder_pdfjs.js

@@ -0,0 +1,52 @@
+const PDF_FILE =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "file_pdf.pdf";
+
+add_task(async function canvas_placeholder_pdfjs() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["privacy.resistFingerprinting", true]],
+  });
+
+  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, PDF_FILE);
+
+  const data = await SpecialPowers.spawn(tab.linkedBrowser, [], async () => {
+    function extractCanvasData() {
+      const canvas = document.createElement("canvas");
+      canvas.width = 10;
+      canvas.height = 10;
+
+      const context = canvas.getContext("2d");
+
+      context.fillStyle = "#332211";
+      context.fillRect(0, 0, 10, 10);
+
+      // Add the canvas element to the document
+      document.body.appendChild(canvas);
+
+      return context.getImageData(0, 0, 10, 10).data;
+    }
+
+    return content.eval(`(${extractCanvasData})()`);
+  });
+
+  is(data.length, 10 * 10 * 4, "correct canvas data size");
+
+  let failure = false;
+  for (var i = 0; i < 10 * 10 * 4; i += 4) {
+    if (
+      data[i] != 0x33 ||
+      data[i + 1] != 0x22 ||
+      data[i + 2] != 0x11 ||
+      data[i + 3] != 0xff
+    ) {
+      ok(false, `incorrect data ${data.slice(i, i + 4)} @ ${i}..${i + 3}`);
+      failure = true;
+      break;
+    }
+  }
+  ok(!failure, "canvas is correct");
+
+  BrowserTestUtils.removeTab(tab);
+});

toolkit/components/resistfingerprinting/tests/browser/file_pdf.pdf

@@ -0,0 +1,12 @@
+%PDF-1.0
+1 0 obj<</Type/Catalog/Pages 2 0 R>>endobj 2 0 obj<</Type/Pages/Kids[3 0 R]/Count 1>>endobj 3 0 obj<</Type/Page/MediaBox[0 0 3 3]>>endobj
+xref
+0 4
+0000000000 65535 f
+0000000010 00000 n
+0000000053 00000 n
+0000000102 00000 n
+trailer<</Size 4/Root 1 0 R>>
+startxref
+149
+%EOF