py3: port oeb rasterize string types

The problem is I'm not sure what manifest's item.data is supposed to be.
The docs for calibre.ebooks.oeb.base.Manifest.Item.data say "it should
be a str type", but that doesn't seem to make sense for a binary file
(at least for python3). More likely it should be a string_or_bytes, and
consumers should check whether the item data is an instance of bytes
(which it should be for image files that aren't representable as decoded
bytes).

src/calibre/ebooks/oeb/base.py

@@ -1024,8 +1024,8 @@ class Manifest(object):
             - XML content is parsed and returned as an lxml.etree element.
             - CSS and CSS-variant content is parsed and returned as a css_parser
               CSS DOM stylesheet.
-            - All other content is returned as a :class:`str` object with no
+            - All other content is returned as a :class:`str` or :class:`bytes`
-              special parsing.
+              object with no special parsing.
             """
             data = self._data
             if data is None:

src/calibre/ebooks/oeb/transforms/rasterize.py

@@ -1,7 +1,7 @@
 '''
 SVG rasterization transform.
 '''
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2008, Marshall T. Vandegrift <llasram@gmail.com>'
@@ -77,7 +77,7 @@ class SVGRasterizer(object):
                     logger.info('Found SVG image height in %, trying to convert...')
                     try:
                         h = float(image.get('height').replace('%', ''))/100.
-                        image.set('height', str(h*sizes[1]))
+                        image.set('height', unicode_type(h*sizes[1]))
                     except:
                         logger.exception('Failed to convert percentage height:',
                                 image.get('height'))
@@ -101,7 +101,7 @@ class SVGRasterizer(object):
         buffer = QBuffer(array)
         buffer.open(QIODevice.WriteOnly)
         image.save(buffer, format)
-        return str(array)
+        return array.data()
 
     def dataize_manifest(self):
         for item in self.oeb.manifest.values():
@@ -121,10 +121,10 @@ class SVGRasterizer(object):
             if abshref not in hrefs:
                 continue
             linkee = hrefs[abshref]
-            data = str(linkee)
+            data = unicode_type(linkee)
             ext = what(None, data) or 'jpg'
             with PersistentTemporaryFile(suffix='.'+ext) as pt:
-                pt.write(data)
+                pt.write(data.encode('utf-8'))
                 self.temp_files.append(pt.name)
             elem.attrib[XLINK('href')] = pt.name
         return svg
@@ -182,7 +182,7 @@ class SVGRasterizer(object):
         height = style['height']
         width = (width / 72) * self.profile.dpi
         height = (height / 72) * self.profile.dpi
-        data = QByteArray(str(svgitem))
+        data = QByteArray(unicode_type(svgitem).encode('utf-8'))
         svg = QSvgRenderer(data)
         size = svg.defaultSize()
         size.scale(width, height, Qt.KeepAspectRatio)
@@ -202,7 +202,7 @@ class SVGRasterizer(object):
             buffer = QBuffer(array)
             buffer.open(QIODevice.WriteOnly)
             image.save(buffer, 'PNG')
-            data = str(array)
+            data = array.data()
             manifest = self.oeb.manifest
             href = os.path.splitext(svgitem.href)[0] + '.png'
             id, href = manifest.generate(svgitem.id, href)