add support for ArrayBuffer and check non-Uint8Array types (#14)

* code change

* compiled version

* put set in branch

suite.js

@@ -16,14 +16,41 @@ function tests(isNative, TextEncoder, TextDecoder) {
       const out = dec.decode(buffer);
 
       assert.equal(out, s);
-
     });
 
     suite('decoder', () => {
 
       test('basic', () => {
         const buffer = new Uint8Array([104, 101, 108, 108, 111]);
-        assert.equal(dec.decode(buffer), 'hello');
+        assert.equal(dec.decode(buffer), 'hello', 'directly Uint8Array');
+        assert.equal(dec.decode(buffer.buffer), 'hello', 'pass underlying ArrayBuffer');
+      });
+
+      test('non-8 backing', () => {
+        // If passed a Uint32Array, TextDecoder will still decode the real
+        // underlying bytes. Source data must be aligned.
+        const padded = new Uint8Array([104, 101, 108, 108, 111, 33, 46, 46]);
+        const u32 = new Uint32Array(padded.buffer);
+        assert.equal(padded.length >> 2, u32.length, 'u32 must be 1/4 of real data');
+        assert.equal(dec.decode(u32), 'hello!..', 'pass Uint32Array');
+        assert.equal(dec.decode(u32.buffer), 'hello!..', 'pass Uint32Array\'s buffer');
+
+        // Ensure that we don't parse larger typed arrays as uint8's. We expect
+        // nulls here to pad out the remaining three bytes in every word.
+        const u32raw = new Uint32Array([104, 105, 33, 46]);
+        assert.equal(dec.decode(u32raw), 'h\0\0\0i\0\0\0!\0\0\0.\0\0\0', 'u32 with nulls');
+      });
+
+      test('arraylike', () => {
+        const arr = [104, 101, 108, 108, 111];
+
+        if (isNative) {
+          // Native can't take Array.
+          assert.throws(() => dec.decode(arr));
+        } else {
+          // Polyfill can accept Array or array-like.
+          assert.equal(dec.decode(arr), 'hello', 'decode arraylike');
+        }
       });
 
       test('constructor', () => {

text.js

@@ -254,14 +254,21 @@ FastTextDecoder.prototype['decode'] = function(buffer, options={stream: false})
     throw new Error(`Failed to decode: the 'stream' option is unsupported.`);
   }
 
-  // Accept Uint8Array instances as-is.
-  let bytes = buffer;
-
-  // Look for ArrayBufferView, which isn't a real type, but basically represents
-  // all the valid TypedArray types plus DataView. They all have ".buffer" as
-  // an instance of ArrayBuffer.
-  if (!(bytes instanceof Uint8Array) && bytes.buffer instanceof ArrayBuffer) {
+  let bytes;
+
+  if (buffer instanceof Uint8Array) {
+    // Accept Uint8Array instances as-is.
+    bytes = buffer;
+  } else if (buffer.buffer instanceof ArrayBuffer) {
+    // Look for ArrayBufferView, which isn't a real type, but basically
+    // represents all the valid TypedArray types plus DataView. They all have
+    // ".buffer" as an instance of ArrayBuffer.
     bytes = new Uint8Array(buffer.buffer);
+  } else {
+    // The only other valid argument here is that "buffer" is an ArrayBuffer.
+    // We also try to convert anything else passed to a Uint8Array, as this
+    // catches anything that's array-like. Native code would throw here.
+    bytes = new Uint8Array(buffer);
   }
 
   return decodeImpl(/** @type {!Uint8Array} */ (bytes));