Stop blindly extracting uint8array.buffer after calling compress()

src/test/store/receive-profile.test.ts

@@ -88,6 +88,22 @@ function simulateSymbolStoreHasNoCache() {
   }));
 }
 
+// Returns an ArrayBuffer which contains only the bytes that
+// are covered by the Uint8Array, making a copy if needed.
+function extractArrayBuffer(bufferView: Uint8Array<ArrayBuffer>): ArrayBuffer {
+  if (
+    bufferView.byteOffset === 0 &&
+    bufferView.byteLength === bufferView.buffer.byteLength
+  ) {
+    return bufferView.buffer;
+  }
+
+  // There was extra data at the start or at the end. Make a copy.
+  const copy = new Uint8Array(bufferView.byteLength);
+  copy.set(bufferView);
+  return copy.buffer;
+}
+
 describe('actions/receive-profile', function () {
   beforeEach(() => {
     // The SymbolStore requires the use of IndexedDB, ensure that it exists so that
@@ -676,10 +692,11 @@ describe('actions/receive-profile', function () {
           case 'json':
             return profileJSON;
           case 'arraybuffer':
-            return toUint8Array(profileJSON).buffer as ArrayBuffer;
+            return extractArrayBuffer(toUint8Array(profileJSON));
           case 'gzip':
-            return (await compress(toUint8Array(profileJSON)))
-              .buffer as ArrayBuffer;
+            return extractArrayBuffer(
+              await compress(toUint8Array(profileJSON))
+            );
           default:
             throw new Error('unknown profiler format');
         }
@@ -1314,7 +1331,7 @@ describe('actions/receive-profile', function () {
         const profileOrZip = await _fetchProfile(args);
         expect(profileOrZip).toEqual({
           responseType: 'PROFILE',
-          profile: profile.buffer,
+          profile: extractArrayBuffer(profile),
         });
       } catch (error) {
         userFacingError = error;
@@ -1446,7 +1463,7 @@ describe('actions/receive-profile', function () {
 
       const { getState, view } = await setupTestWithFile({
         type: '',
-        payload: (await compress(serializeProfile(profile))).buffer,
+        payload: extractArrayBuffer(await compress(serializeProfile(profile))),
       });
       expect(view.phase).toBe('DATA_LOADED');
       expect(ProfileViewSelectors.getProfile(getState()).meta.product).toEqual(
@@ -1478,7 +1495,7 @@ describe('actions/receive-profile', function () {
 
       const { getState, view } = await setupTestWithFile({
         type: 'application/gzip',
-        payload: (await compress(serializeProfile(profile))).buffer,
+        payload: extractArrayBuffer(await compress(serializeProfile(profile))),
       });
       expect(view.phase).toBe('DATA_LOADED');
       expect(ProfileViewSelectors.getProfile(getState()).meta.product).toEqual(
@@ -1492,7 +1509,7 @@ describe('actions/receive-profile', function () {
 
       const { getState, view } = await setupTestWithFile({
         type: 'application/json',
-        payload: (await compress(serializeProfile(profile))).buffer,
+        payload: extractArrayBuffer(await compress(serializeProfile(profile))),
       });
       expect(view.phase).toBe('DATA_LOADED');
       expect(ProfileViewSelectors.getProfile(getState()).meta.product).toEqual(
@@ -1506,7 +1523,7 @@ describe('actions/receive-profile', function () {
         .mockImplementation(() => {});
       const { view } = await setupTestWithFile({
         type: 'application/gzip',
-        payload: (await compress('{}')).buffer,
+        payload: extractArrayBuffer(await compress('{}')),
       });
       expect(view.phase).toBe('FATAL_ERROR');
 
@@ -1525,14 +1542,9 @@ describe('actions/receive-profile', function () {
       zip.file(fileName, serializedProfile);
       const array = await zip.generateAsync({ type: 'uint8array' });
 
-      // Create a new ArrayBuffer instance and copy the data into it, in order
-      // to work around https://github.com/facebook/jest/issues/6248
-      const bufferCopy = new ArrayBuffer(array.buffer.byteLength);
-      new Uint8Array(bufferCopy).set(new Uint8Array(array.buffer));
-
       return setupTestWithFile({
         type: 'application/zip',
-        payload: bufferCopy,
+        payload: extractArrayBuffer(array as Uint8Array<ArrayBuffer>),
       });
     }
 

src/utils/gz.ts

@@ -43,7 +43,7 @@ export async function compress(
         if (errorOrNull) {
           reject(errorOrNull);
         } else {
-          resolve(new Uint8Array(result.buffer as ArrayBuffer));
+          resolve(result);
         }
       });
     });
@@ -67,7 +67,7 @@ export async function decompress(
         if (errorOrNull) {
           reject(errorOrNull);
         } else {
-          resolve(new Uint8Array(result.buffer as ArrayBuffer));
+          resolve(result);
         }
       });
     });