img: add _ChunkParser.from_stream()

Steve Canny · Steve Canny · commit 98b4ab2b0d7c · 2014-03-01T01:35:30.000-08:00
diff --git a/docx/image/png.py b/docx/image/png.py
@@ -4,6 +4,7 @@
 
 from .constants import MIME_TYPE, TAG
 from .exceptions import InvalidImageStreamError
+from .helpers import BIG_ENDIAN, StreamReader
 from .image import BaseImageHeader
 
 
@@ -224,13 +225,18 @@ class _ChunkParser(object):
     """
     Extracts chunks from a PNG image stream
     """
+    def __init__(self, stream_rdr):
+        super(_ChunkParser, self).__init__()
+        self._stream_rdr = stream_rdr
+
     @classmethod
     def from_stream(cls, stream):
         """
         Return a |_ChunkParser| instance that can extract the chunks from the
         PNG image in *stream*.
         """
-        raise NotImplementedError
+        stream_rdr = StreamReader(stream, BIG_ENDIAN)
+        return cls(stream_rdr)
 
     def iter_chunks(self):
         """
diff --git a/tests/image/test_png.py b/tests/image/test_png.py
@@ -325,3 +325,40 @@ def _Chunks__init_(self, request):
     @pytest.fixture
     def stream_(self, request):
         return instance_mock(request, BytesIO)
+
+
+class Describe_ChunkParser(object):
+
+    def it_can_construct_from_a_stream(self, from_stream_fixture):
+        stream_, StreamReader_, stream_rdr_, _ChunkParser__init_ = (
+            from_stream_fixture
+        )
+        chunk_parser = _ChunkParser.from_stream(stream_)
+        StreamReader_.assert_called_once_with(stream_, BIG_ENDIAN)
+        _ChunkParser__init_.assert_called_once_with(stream_rdr_)
+        assert isinstance(chunk_parser, _ChunkParser)
+
+    # fixtures -------------------------------------------------------
+
+    @pytest.fixture
+    def from_stream_fixture(
+            self, stream_, StreamReader_, stream_rdr_, _ChunkParser__init_):
+        return stream_, StreamReader_, stream_rdr_, _ChunkParser__init_
+
+    @pytest.fixture
+    def _ChunkParser__init_(self, request):
+        return initializer_mock(request, _ChunkParser)
+
+    @pytest.fixture
+    def StreamReader_(self, request, stream_rdr_):
+        return class_mock(
+            request, 'docx.image.png.StreamReader', return_value=stream_rdr_
+        )
+
+    @pytest.fixture
+    def stream_(self, request):
+        return instance_mock(request, BytesIO)
+
+    @pytest.fixture
+    def stream_rdr_(self, request):
+        return instance_mock(request, StreamReader)
