Preserve filename in temporary downloads

When downloading a file into a temporary location for external open or pdfjs, it used to
prepend a random string to the filename. This means that downloading a file opened with
pdfjs would have an unwanted mangled filename.

Instead of adding a prefix to the filename, this puts the file with its filename intact
in a unique temporary directory.

qutebrowser/browser/downloads.py

@@ -7,6 +7,7 @@
 import re
 import sys
 import html
+import io as _io
 import os.path
 import collections
 import functools
@@ -813,7 +814,8 @@ class AbstractDownloadItem(QObject):
         if filename is None:  # pragma: no cover
             log.downloads.error("No filename to open the download!")
             return
-        self.pdfjs_requested.emit(os.path.basename(filename),
+        dirname = os.path.basename(os.path.dirname(filename))
+        self.pdfjs_requested.emit(os.path.join(dirname, os.path.basename(filename)),
                                   self.url())
 
     def cancel_for_origin(self) -> bool:
@@ -1373,8 +1375,8 @@ class TempDownloadManager:
         # Make sure that the filename is not too long
         suggested_name = utils.elide_filename(suggested_name, 50)
         # pylint: disable=consider-using-with
-        fobj = tempfile.NamedTemporaryFile(dir=tmpdir.name, delete=False,
-                                           suffix='_' + suggested_name)
+        tmpfiledir = tempfile.mkdtemp(dir=tmpdir.name)
+        fobj = _io.open(os.path.join(tmpfiledir, suggested_name), 'w+b')
         self.files.append(fobj)
         return fobj
 

qutebrowser/browser/qutescheme.py

@@ -518,8 +518,6 @@ def qute_pdfjs(url: QUrl) -> _HandlerRet:
         filename = QUrlQuery(url).queryItemValue('filename')
         if not filename:
             raise UrlInvalidError("Missing filename")
-        if '/' in filename or os.sep in filename:
-            raise RequestDeniedError("Path separator in filename.")
 
         path = _pdf_path(filename)
         with open(path, 'rb') as f: