Add API for temporary downloads

Closes https://github.com/qutebrowser/qutebrowser-extensions/issues/9

qutebrowser/api/downloads.py

@@ -0,0 +1,56 @@
+# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et:
+
+# Copyright 2018 Florian Bruhin (The Compiler) <mail@qutebrowser.org>
+#
+# This file is part of qutebrowser.
+#
+# qutebrowser is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# qutebrowser is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with qutebrowser.  If not, see <http://www.gnu.org/licenses/>.
+
+
+import io
+
+from PyQt5.QtCore import QObject, pyqtSignal, pyqtSlot, QUrl
+
+from qutebrowser.browser import downloads, qtnetworkdownloads
+from qutebrowser.utils import objreg
+
+
+class TempDownload(QObject):
+
+    """A download of some data into a file object."""
+
+    finished = pyqtSignal()
+
+    def __init__(self, item: qtnetworkdownloads.DownloadItem) -> None:
+        self._item = item
+        self._item.finished.connect(self._on_download_finished)
+        self.successful = False
+        self.fileobj = item.fileobj
+
+    @pyqtSlot()
+    def _on_download_finished(self) -> None:
+        self.successful = self._item.successful
+        self.finished.emit()
+
+
+def download_temp(url: QUrl) -> TempDownload:
+    """Download the given URL into a file object.
+
+    The download is not saved to disk.
+    """
+    fobj = io.BytesIO()
+    fobj.name = 'temporary: ' + url.host()
+    target = downloads.FileObjDownloadTarget(fobj)
+    download_manager = objreg.get('qtnetwork-download-manager')
+    return download_manager.get(url, target=target, auto_remove=True)

qutebrowser/browser/adblock.py

@@ -25,7 +25,7 @@ import functools
 import posixpath
 import zipfile
 
-from qutebrowser.browser import downloads
+from qutebrowser.api import downloads
 from qutebrowser.config import config
 from qutebrowser.utils import objreg, standarddir, log, message
 from qutebrowser.api import cmdutils
@@ -173,7 +173,6 @@ class HostBlocker:
                               self._config_blocked_hosts)
         self._blocked_hosts = set()
         self._done_count = 0
-        download_manager = objreg.get('qtnetwork-download-manager')
         for url in config.val.content.host_blocking.lists:
             if url.scheme() == 'file':
                 filename = url.toLocalFile()
@@ -184,11 +183,7 @@ class HostBlocker:
                 else:
                     self._import_local(filename)
             else:
-                fobj = io.BytesIO()
+                download = downloads.download_temp(url)
-                fobj.name = 'adblock: ' + url.host()
-                target = downloads.FileObjDownloadTarget(fobj)
-                download = download_manager.get(url, target=target,
-                                                auto_remove=True)
                 self._in_progress.append(download)
                 download.finished.connect(
                     functools.partial(self._on_download_finished, download))