[Issue apache#11912] throw mxnet exceptions when decoding invalid ima…

…ges. (apache#12999)

* Raise an excption when passing an empty buffer to imdecode.

* src/io/image_io.cc: Check the length of the input buffer.
* tests/python/unittest/test_image.py: Update the (already existing) test to expect a mx.base.MXNetError.

* Raise an exception when passing an invalid data buffer to imdecode.

* src/io/image_io.cc: Raise an exception when the image could not be decoded instead of just logging.
* tests/python/unittest/test_image.py: Add a new test test_imdecode_invalid_image.

* Raise an exception when passing an invalid data buffer to imdecode.

* src/io/image_io.cc: Raise an exception when the image could not be decoded instead of just logging.
* tests/python/unittest/test_image.py: Add a new test test_imdecode_invalid_image.

* Rollback a "empty buffer" check in the image python bindings that's now more generally handled
in the core code.

* python/mxnet/image/image.py: remove buffer length check.

python/mxnet/image/image.py

@@ -140,10 +140,6 @@ def imdecode(buf, *args, **kwargs):
                              '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)
 
 

src/io/image_io.cc

@@ -143,11 +143,8 @@ void ImdecodeImpl(int flag, bool to_rgb, void* data, size_t size,
   cv::Mat dst;
   if (out->is_none()) {
     cv::Mat res = cv::imdecode(buf, flag);
-    if (res.empty()) {
-      LOG(INFO) << "Decoding failed. Invalid image file.";
-      *out = NDArray();
-      return;
-    }
+    CHECK(!res.empty()) << "Decoding failed. Invalid image file.";
+
     *out = NDArray(mshadow::Shape3(res.rows, res.cols, flag == 0 ? 1 : 3),
                    Context::CPU(), false, mshadow::kUint8);
     dst = cv::Mat(out->shape()[0], out->shape()[1], flag == 0 ? CV_8U : CV_8UC3,
@@ -189,6 +186,8 @@ void Imdecode(const nnvm::NodeAttrs& attrs,
 
   uint8_t* str_img = inputs[0].data().dptr<uint8_t>();
   size_t len = inputs[0].shape().Size();
+  CHECK(len > 0) << "Input cannot be an empty buffer";
+
   TShape oshape(3);
   oshape[2] = param.flag == 0 ? 1 : 3;
   if (get_jpeg_size(str_img, len, &oshape[1], &oshape[0])) {

tests/python/unittest/test_image.py

@@ -104,10 +104,15 @@ def test_imdecode_bytearray(self):
             cv_image = cv2.imread(img)
             assert_almost_equal(image.asnumpy(), cv_image)
 
-    @raises(ValueError)
+    @raises(mx.base.MXNetError)
     def test_imdecode_empty_buffer(self):
         mx.image.imdecode(b'', to_rgb=0)
 
+    @raises(mx.base.MXNetError)
+    def test_imdecode_invalid_image(self):
+        image = mx.image.imdecode(b'clearly not image content')
+        assert_equal(image, None)
+
     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)