img: add _TiffParser._make_stream_reader()

Steve Canny · Steve Canny · commit 86ea283420a7 · 2014-02-27T12:08:35.000-08:00
diff --git a/docx/image/tiff.py b/docx/image/tiff.py
@@ -2,6 +2,7 @@
 
 from __future__ import absolute_import, division, print_function
 
+from .helpers import BIG_ENDIAN, LITTLE_ENDIAN, StreamReader
 from .image import Image
 
 
@@ -80,14 +81,25 @@ def vert_dpi(self):
         """
         raise NotImplementedError
 
+    @classmethod
+    def _detect_endian(cls, stream):
+        """
+        Return either BIG_ENDIAN or LITTLE_ENDIAN depending on the endian
+        indicator found in the TIFF *stream* header, either 'MM' or 'II'.
+        """
+        stream.seek(0)
+        endian_str = stream.read(2)
+        return BIG_ENDIAN if endian_str == b'MM' else LITTLE_ENDIAN
+
     @classmethod
     def _make_stream_reader(cls, stream):
         """
         Return a |StreamReader| instance with wrapping *stream* and having
         "endian-ness" determined by the 'MM' or 'II' indicator in the TIFF
         stream header.
         """
-        raise NotImplementedError
+        endian = cls._detect_endian(stream)
+        return StreamReader(stream, endian)
 
 
 class _IfdEntries(object):
diff --git a/tests/image/test_tiff.py b/tests/image/test_tiff.py
@@ -9,7 +9,7 @@
 import pytest
 
 from docx.compat import BytesIO
-from docx.image.helpers import StreamReader
+from docx.image.helpers import BIG_ENDIAN, LITTLE_ENDIAN, StreamReader
 from docx.image.tiff import _IfdEntries, Tiff, _TiffParser
 
 from ..unitutil import (
@@ -87,6 +87,12 @@ def it_can_parse_the_properties_from_a_tiff_stream(
         _TiffParser__init_.assert_called_once_with(ifd_entries_)
         assert isinstance(tiff_parser, _TiffParser)
 
+    def it_makes_a_stream_reader_to_help_parse(self, mk_stream_rdr_fixture):
+        stream, StreamReader_, endian, stream_rdr_ = mk_stream_rdr_fixture
+        stream_rdr = _TiffParser._make_stream_reader(stream)
+        StreamReader_.assert_called_once_with(stream, endian)
+        assert stream_rdr is stream_rdr_
+
     # fixtures -------------------------------------------------------
 
     @pytest.fixture
@@ -119,10 +125,25 @@ def _make_stream_reader_(self, request, stream_rdr_):
             return_value=stream_rdr_
         )
 
+    @pytest.fixture(params=[
+        (b'MM\x00*', BIG_ENDIAN),
+        (b'II*\x00', LITTLE_ENDIAN),
+    ])
+    def mk_stream_rdr_fixture(self, request, StreamReader_, stream_rdr_):
+        bytes_, endian = request.param
+        stream = BytesIO(bytes_)
+        return stream, StreamReader_, endian, stream_rdr_
+
     @pytest.fixture
     def stream_(self, request):
         return instance_mock(request, BytesIO)
 
+    @pytest.fixture
+    def StreamReader_(self, request, stream_rdr_):
+        return class_mock(
+            request, 'docx.image.tiff.StreamReader', return_value=stream_rdr_
+        )
+
     @pytest.fixture
     def stream_rdr_(self, request, ifd0_offset_):
         stream_rdr_ = instance_mock(request, StreamReader)
