buffer: fix Blob constructor on various TypedArrays

Fixes: #40705
    
PR-URL: #40706
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/blob.js

@@ -114,10 +114,10 @@ function getSource(source, endings) {
 
   // We copy into a new Uint8Array because the underlying
   // BackingStores are going to be detached and owned by
-  // the Blob. We also don't want to have to worry about
-  // byte offsets.
-  source = new Uint8Array(source);
-  return [source.byteLength, source];
+  // the Blob.
+  const { buffer, byteOffset, byteLength } = source;
+  const slice = buffer.slice(byteOffset, byteOffset + byteLength);
+  return [byteLength, new Uint8Array(slice)];
 }
 
 class Blob {

test/parallel/test-blob.js

@@ -229,3 +229,18 @@ assert.throws(() => new Blob({}), {
     });
   });
 }
+
+(async () => {
+  const blob = new Blob([
+    new Uint8Array([0x50, 0x41, 0x53, 0x53]),
+    new Int8Array([0x50, 0x41, 0x53, 0x53]),
+    new Uint16Array([0x4150, 0x5353]),
+    new Int16Array([0x4150, 0x5353]),
+    new Uint32Array([0x53534150]),
+    new Int32Array([0x53534150]),
+    new Float32Array([0xD341500000]),
+  ]);
+
+  assert.strictEqual(blob.size, 28);
+  assert.strictEqual(blob.type, '');
+})().then(common.mustCall());