img: add _SofMarker.from_stream()

Steve Canny · Steve Canny · commit 72145fe4880b · 2014-02-27T12:08:35.000-08:00
diff --git a/docx/image/jpeg.py b/docx/image/jpeg.py
@@ -290,23 +290,40 @@ def from_stream(cls, stream, marker_code, offset):
         # horz dots per unit  10   short
         # vert dots per unit  12   short
         # ------------------  ---  -----  -------------------
-        length = stream.read_short(offset)
+        segment_length = stream.read_short(offset)
         density_units = stream.read_byte(offset, 9)
         x_density = stream.read_short(offset, 10)
         y_density = stream.read_short(offset, 12)
         return cls(
-            marker_code, offset, length, density_units, x_density, y_density
+            marker_code, offset, segment_length, density_units, x_density,
+            y_density
         )
 
 
 class _SofMarker(_Marker):
     """
     Represents a JFIF start of frame (SOFx) marker segment.
     """
+    def __init__(
+            self, marker_code, offset, segment_length, px_width, px_height):
+        super(_SofMarker, self).__init__(marker_code, offset, segment_length)
+        self._px_width = px_width
+        self._px_height = px_height
+
     @classmethod
     def from_stream(cls, stream, marker_code, offset):
         """
         Return an |_SofMarker| instance for the SOFn marker at *offset* in
         stream.
         """
-        raise NotImplementedError
+        # field                 off  type   notes
+        # ------------------  ---  -----  ----------------------------
+        # segment length       0   short
+        # Data precision       2   byte
+        # Vertical lines       3   short  px_height
+        # Horizontal lines     5   short  px_width
+        # ------------------  ---  -----  ----------------------------
+        segment_length = stream.read_short(offset)
+        px_height = stream.read_short(offset, 3)
+        px_width = stream.read_short(offset, 5)
+        return cls(marker_code, offset, segment_length, px_width, px_height)
diff --git a/tests/image/test_jpeg.py b/tests/image/test_jpeg.py
@@ -207,6 +207,35 @@ def _App0Marker__init_(self, request):
         return initializer_mock(request, _App0Marker)
 
 
+class Describe_SofMarker(object):
+
+    def it_can_construct_from_a_stream_and_offset(self, from_stream_fixture):
+        (stream, marker_code, offset, _SofMarker__init_, length,
+         px_width, px_height) = from_stream_fixture
+        sof_marker = _SofMarker.from_stream(stream, marker_code, offset)
+        _SofMarker__init_.assert_called_once_with(
+            marker_code, offset, length, px_width, px_height
+        )
+        assert isinstance(sof_marker, _SofMarker)
+
+    # fixtures -------------------------------------------------------
+
+    @pytest.fixture
+    def from_stream_fixture(self, request, _SofMarker__init_):
+        bytes_ = b'\x00\x11\x00\x00\x2A\x00\x18'
+        stream_reader = StreamReader(BytesIO(bytes_), BIG_ENDIAN)
+        marker_code, offset, length = JPEG_MARKER_CODE.SOF0, 0, 17
+        px_width, px_height = 24, 42
+        return (
+            stream_reader, marker_code, offset, _SofMarker__init_, length,
+            px_width, px_height
+        )
+
+    @pytest.fixture
+    def _SofMarker__init_(self, request):
+        return initializer_mock(request, _SofMarker)
+
+
 class Describe_MarkerFactory(object):
 
     def it_constructs_the_appropriate_marker_object(self, call_fixture):
