img: add Png._parse_IHDR()

Steve Canny · Steve Canny · commit 3042292e5cb5 · 2014-02-27T12:08:34.000-08:00
diff --git a/docx/image/png.py b/docx/image/png.py
@@ -2,6 +2,7 @@
 
 from __future__ import absolute_import, division, print_function
 
+from .constants import TAG
 from .exceptions import InvalidImageStreamError
 from .helpers import StreamReader
 from .image import Image
@@ -98,7 +99,10 @@ def _parse_IHDR(cls, stream, offset):
         Return a dict containing values for TAG.PX_WIDTH and TAG.PX_HEIGHT
         extracted from the IHDR chunk in *stream* at *offset*.
         """
-        raise NotImplementedError
+        return {
+            TAG.PX_WIDTH:  stream.read_long(offset),
+            TAG.PX_HEIGHT: stream.read_long(offset, 4)
+        }
 
     @classmethod
     def _parse_pHYs(cls, stream, offset):
diff --git a/tests/image/test_png.py b/tests/image/test_png.py
@@ -61,6 +61,11 @@ def it_raises_on_png_having_no_IHDR_chunk(self, no_IHDR_fixture):
         with pytest.raises(InvalidImageStreamError):
             Png._parse_chunks(stream_, chunk_offsets)
 
+    def it_can_parse_an_IHDR_chunk(self, parse_IHDR_fixture):
+        stream, offset, expected_attrs = parse_IHDR_fixture
+        attrs = Png._parse_IHDR(stream, offset)
+        assert attrs == expected_attrs
+
     # fixtures -------------------------------------------------------
 
     @pytest.fixture
@@ -128,6 +133,15 @@ def parse_chunks_fixture(
             _parse_pHYs_, phys_offset, expected_attrs
         )
 
+    @pytest.fixture
+    def parse_IHDR_fixture(self):
+        bytes_ = b'\x00\x00\x00\x2A\x00\x00\x00\x18'
+        stream = BytesIO(bytes_)
+        stream_rdr = StreamReader(stream, BIG_ENDIAN)
+        offset = 0
+        expected_attrs = {TAG.PX_WIDTH: 42, TAG.PX_HEIGHT: 24}
+        return stream_rdr, offset, expected_attrs
+
     @pytest.fixture
     def parse_png_fixture(
             self, stream_rdr_, _parse_chunk_offsets_, _parse_chunks_,
