Added big endian Exif support. #104

glymur/_uuid_io/Exif.py

@@ -34,8 +34,8 @@ class UUIDExif(object):
         self.read_buffer = read_buffer
 
         # Ignore the first six bytes.
-        # Next 8 should be (73, 73, 42, 8)
-        data = struct.unpack('<BBHI', read_buffer[6:14])
+        # Next 8 should be (73, 73, 42, 8) or (77, 77, 42, 8)
+        data = struct.unpack('<BB', read_buffer[6:8])
         if data[0] == 73 and data[1] == 73:
             # little endian
             self.endian = '<'
@@ -46,7 +46,7 @@ class UUIDExif(object):
             msg = "Bad byte order indication: {0}".format(read_buffer[6:8])
             raise RuntimeError(msg)
 
-        offset = data[3]
+        _, offset = struct.unpack(self.endian + 'HI', read_buffer[8:14])
 
         # This is the 'Exif Image' portion.
         exif = _ExifImageIfd(self.endian, read_buffer[6:], offset)

glymur/test/test_jp2box_uuid.py

@@ -129,5 +129,30 @@ class TestUUIDExif(unittest.TestCase):
 
             self.assertEqual(j.box[-1].box_id, 'uuid')
 
+    def test_big_endian(self):
+        """Verify read of big-endian IFD."""
+        with tempfile.NamedTemporaryFile(suffix='.jp2', mode='wb') as tfile:
+
+            with open(self.jp2file, 'rb') as ifptr:
+                tfile.write(ifptr.read())
+
+            # Write L, T, UUID identifier.
+            tfile.write(struct.pack('>I4s', 52, b'uuid'))
+            tfile.write(b'JpgTiffExif->JP2')
+
+            tfile.write(b'Exif\x00\x00')
+            xbuffer = struct.pack('>BBHI', 77, 77, 42, 8)
+            tfile.write(xbuffer)
+
+            # We will write just a single tag.
+            tfile.write(struct.pack('>H', 1))
+
+            # The "Make" tag is tag no. 271.
+            tfile.write(struct.pack('>HHI4s', 271, 2, 3, b'HTC\x00'))
+            tfile.flush()
+
+            jp2 = glymur.Jp2k(tfile.name)
+            self.assertEqual(jp2.box[-1].data.ifds['Image']['Make'], "HTC")
+
 if __name__ == "__main__":
     unittest.main()