img: add Png._parse_pHYs()

Steve Canny · Steve Canny · commit a20f25befa96 · 2014-02-27T12:08:34.000-08:00
diff --git a/docx/image/helpers.py b/docx/image/helpers.py
@@ -25,6 +25,15 @@ def __init__(self, stream, byte_order, base_offset=0):
         )
         self._base_offset = base_offset
 
+    def read_byte(self, base=None, offset=0):
+        """
+        Return the int value of the byte at the file position defined by
+        self._base_offset + *base* + *offset*. If *base* is None, the byte is
+        read from the current position in the stream.
+        """
+        fmt = 'B'
+        return self._read_int(fmt, base, offset)
+
     def read_long(self, base=None, offset=0):
         """
         Return the int value of the four bytes at the file position defined by
diff --git a/docx/image/png.py b/docx/image/png.py
@@ -111,4 +111,8 @@ def _parse_pHYs(cls, stream, offset):
         TAG.VERT_PX_PER_UNIT, and TAG.UNITS_SPECIFIER parsed from the pHYs
         chunk at *offset* in *stream*.
         """
-        raise NotImplementedError
+        return {
+            TAG.HORZ_PX_PER_UNIT: stream.read_long(offset),
+            TAG.VERT_PX_PER_UNIT: stream.read_long(offset, 4),
+            TAG.UNITS_SPECIFIER:  stream.read_byte(offset, 8)
+        }
diff --git a/tests/image/test_png.py b/tests/image/test_png.py
@@ -66,6 +66,11 @@ def it_can_parse_an_IHDR_chunk(self, parse_IHDR_fixture):
         attrs = Png._parse_IHDR(stream, offset)
         assert attrs == expected_attrs
 
+    def it_can_parse_an_pHYs_chunk(self, parse_pHYs_fixture):
+        stream, offset, expected_attrs = parse_pHYs_fixture
+        attrs = Png._parse_pHYs(stream, offset)
+        assert attrs == expected_attrs
+
     # fixtures -------------------------------------------------------
 
     @pytest.fixture
@@ -142,6 +147,18 @@ def parse_IHDR_fixture(self):
         expected_attrs = {TAG.PX_WIDTH: 42, TAG.PX_HEIGHT: 24}
         return stream_rdr, offset, expected_attrs
 
+    @pytest.fixture
+    def parse_pHYs_fixture(self):
+        bytes_ = b'\x00\x00\x17\x12\x00\x00\x1E\xC2\x01'
+        stream = BytesIO(bytes_)
+        stream_rdr = StreamReader(stream, BIG_ENDIAN)
+        offset = 0
+        expected_attrs = {
+            TAG.HORZ_PX_PER_UNIT: 5906, TAG.VERT_PX_PER_UNIT: 7874,
+            TAG.UNITS_SPECIFIER: 1
+        }
+        return stream_rdr, offset, expected_attrs
+
     @pytest.fixture
     def parse_png_fixture(
             self, stream_rdr_, _parse_chunk_offsets_, _parse_chunks_,
