Add bytearray support back to imdecode (#12855, #12868)

1. Avoid raise exception when input is bytearray.
2. Avoid OpenCV crash for empty input.
3. Added unittests.

python/mxnet/image/image.py

@@ -93,7 +93,7 @@ def imdecode(buf, *args, **kwargs):
 
     Parameters
     ----------
-    buf : str/bytes or numpy.ndarray
+    buf : str/bytes/bytearray or numpy.ndarray
         Binary image data as string or numpy ndarray.
     flag : int, optional, default=1
         1 for three channel color output. 0 for grayscale output.
@@ -135,10 +135,15 @@ def imdecode(buf, *args, **kwargs):
     <NDArray 224x224x3 @cpu(0)>
     """
     if not isinstance(buf, nd.NDArray):
-        if sys.version_info[0] == 3 and not isinstance(buf, (bytes, np.ndarray)):
-            raise ValueError('buf must be of type bytes or numpy.ndarray,'
+        if sys.version_info[0] == 3 and not isinstance(buf, (bytes, bytearray, np.ndarray)):
+            raise ValueError('buf must be of type bytes, bytearray or numpy.ndarray,'
                              'if you would like to input type str, please convert to bytes')
         buf = nd.array(np.frombuffer(buf, dtype=np.uint8), dtype=np.uint8)
+
+    if len(buf) == 0:
+        # empty buf causes OpenCV crash.
+        raise ValueError("input buf cannot be empty.")
+
     return _internal._cvimdecode(buf, *args, **kwargs)
 
 

tests/python/unittest/test_image.py

@@ -92,6 +92,22 @@ def test_imdecode(self):
             cv_image = cv2.imread(img)
             assert_almost_equal(image.asnumpy(), cv_image)
 
+    def test_imdecode_bytearray(self):
+        try:
+            import cv2
+        except ImportError:
+            return
+        for img in TestImage.IMAGES:
+            with open(img, 'rb') as fp:
+                str_image = bytearray(fp.read())
+                image = mx.image.imdecode(str_image, to_rgb=0)
+            cv_image = cv2.imread(img)
+            assert_almost_equal(image.asnumpy(), cv_image)
+
+    @raises(ValueError)
+    def test_imdecode_empty_buffer(self):
+        mx.image.imdecode(b'', to_rgb=0)
+
     def test_scale_down(self):
         assert mx.image.scale_down((640, 480), (720, 120)) == (640, 106)
         assert mx.image.scale_down((360, 1000), (480, 500)) == (360, 375)