Preserve blob content type when stripping EXIF data

ts/test-electron/util/scaleImageToLevel_test.ts

@@ -0,0 +1,68 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import { IMAGE_JPEG, IMAGE_PNG } from '../../types/MIME';
+import * as log from '../../logging/log';
+
+import { scaleImageToLevel } from '../../util/scaleImageToLevel';
+
+describe('scaleImageToLevel', () => {
+  // NOTE: These tests are incomplete.
+
+  let objectUrlsToRevoke: Array<string>;
+  function createObjectUrl(blob: Blob): string {
+    const result = URL.createObjectURL(blob);
+    objectUrlsToRevoke.push(result);
+    return result;
+  }
+
+  beforeEach(() => {
+    objectUrlsToRevoke = [];
+  });
+
+  afterEach(() => {
+    objectUrlsToRevoke.forEach(objectUrl => {
+      URL.revokeObjectURL(objectUrl);
+    });
+  });
+
+  it("doesn't scale images that are already small enough", async () => {
+    const testCases = [
+      {
+        path: '../fixtures/kitten-1-64-64.jpg',
+        contentType: IMAGE_JPEG,
+        expectedWidth: 64,
+        expectedHeight: 64,
+      },
+      {
+        path: '../fixtures/20x200-yellow.png',
+        contentType: IMAGE_PNG,
+        expectedWidth: 20,
+        expectedHeight: 200,
+      },
+    ];
+
+    await Promise.all(
+      testCases.map(
+        async ({ path, contentType, expectedWidth, expectedHeight }) => {
+          const blob = await (await fetch(path)).blob();
+          const scaled = await scaleImageToLevel(blob, contentType, true);
+
+          const {
+            width,
+            height,
+          } = await window.Signal.Types.VisualAttachment.getImageDimensions({
+            objectUrl: createObjectUrl(scaled.blob),
+            logger: log,
+          });
+
+          assert.strictEqual(width, expectedWidth);
+          assert.strictEqual(height, expectedHeight);
+          assert.strictEqual(scaled.contentType, contentType);
+          assert.strictEqual(scaled.blob.type, contentType);
+        }
+      )
+    );
+  });
+});

ts/util/scaleImageToLevel.ts

@@ -102,10 +102,13 @@ async function getCanvasBlobAsJPEG(
   return canvasToBlob(canvas, IMAGE_JPEG, quality);
 }
 
-async function stripImageFileEXIFData(file: File | Blob): Promise<Blob> {
+async function stripImageFileEXIFData(
+  file: File | Blob,
+  type: MIMEType
+): Promise<Blob> {
   const arrayBuffer = await file.arrayBuffer();
   const xArrayBuffer = await sharp(new Uint8Array(arrayBuffer)).toBuffer();
-  return new Blob([xArrayBuffer]);
+  return new Blob([xArrayBuffer], { type });
 }
 
 export async function scaleImageToLevel(
@@ -139,7 +142,7 @@ export async function scaleImageToLevel(
     MEDIA_QUALITY_LEVEL_DATA.get(level) || DEFAULT_LEVEL_DATA;
 
   if (fileOrBlobOrURL.size <= thresholdSize) {
-    const blob = await stripImageFileEXIFData(fileOrBlobOrURL);
+    const blob = await stripImageFileEXIFData(fileOrBlobOrURL, contentType);
     return {
       blob,
       contentType,