Add a mechanism to abort conversions and show the user a simple message instead of an error dialog

src/calibre/ebooks/conversion/__init__.py

@@ -1,4 +1,25 @@
-from __future__ import with_statement
-__license__ = 'GPL 3'
-__copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
+# vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import (unicode_literals, division, absolute_import,
+                        print_function)
+
+__license__   = 'GPL v3'
+__copyright__ = '2011, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
+
+
+class ConversionUserFeedBack(Exception):
+
+    def __init__(self, title, msg, level='info', det_msg=''):
+        ''' Show a simple message to the user
+
+        :param title: The title (very short description)
+        :param msg: The message to show the user
+        :param level: Must be one of 'info', 'warn' or 'error'
+        :param det_msg: Optional detailed message to show the user
+        '''
+        import json
+        Exception.__init__(self, json.dumps({'msg':msg, 'level':level,
+            'det_msg':det_msg, 'title':title}))
+        self.title, self.msg, self.det_msg = title, msg, det_msg
+        self.level = level
+

src/calibre/ebooks/conversion/cli.py

@@ -15,6 +15,7 @@ from calibre.utils.logging import Log
 from calibre.constants import preferred_encoding
 from calibre.customize.conversion import OptionRecommendation
 from calibre import patheq
+from calibre.ebooks.conversion import ConversionUserFeedBack
 
 USAGE = '%prog ' + _('''\
 input_file output_file [options]
@@ -320,7 +321,16 @@ def main(args=sys.argv):
                                         if n.dest]
     plumber.merge_ui_recommendations(recommendations)
 
-    plumber.run()
+    try:
+        plumber.run()
+    except ConversionUserFeedBack as e:
+        ll = {'info': log.info, 'warn': log.warn,
+                'error':log.error}.get(e.level, log.info)
+        ll(e.title)
+        if e.det_msg:
+            log.debug(e.detmsg)
+        ll(e.msg)
+        raise SystemExit(1)
 
     log(_('Output saved to'), ' ', plumber.output)
 

src/calibre/gui2/ui.py

@@ -24,9 +24,9 @@ from calibre.utils.config import prefs, dynamic
 from calibre.utils.ipc.server import Server
 from calibre.library.database2 import LibraryDatabase2
 from calibre.customize.ui import interface_actions, available_store_plugins
-from calibre.gui2 import error_dialog, GetMetadata, open_url, \
-        gprefs, max_available_height, config, info_dialog, Dispatcher, \
-        question_dialog
+from calibre.gui2 import (error_dialog, GetMetadata, open_url,
+        gprefs, max_available_height, config, info_dialog, Dispatcher,
+        question_dialog, warning_dialog)
 from calibre.gui2.cover_flow import CoverFlowMixin
 from calibre.gui2.widgets import ProgressIndicator
 from calibre.gui2.update import UpdateMixin
@@ -653,6 +653,23 @@ class Main(MainWindow, MainWindowMixin, DeviceMixin, EmailMixin, # {{{
                     d.show()
                     self._modeless_dialogs.append(d)
                 return
+
+            if 'calibre.ebooks.conversion.ConversionUserFeedBack:' in job.details:
+                if not minz:
+                    import json
+                    payload = job.details.rpartition(
+                        'calibre.ebooks.conversion.ConversionUserFeedBack:')[-1]
+                    payload = json.loads('{' + payload.partition('{')[-1])
+                    d = {'info':info_dialog, 'warn':warning_dialog,
+                            'error':error_dialog}.get(payload['level'],
+                                    error_dialog)
+                    d = d(self, payload['title'],
+                            '<p>%s</p>'%payload['msg'],
+                            det_msg=payload['det_msg'])
+                    d.setModal(False)
+                    d.show()
+                    self._modeless_dialogs.append(d)
+                return
         except:
             pass
         if job.killed:

src/calibre/web/feeds/news.py

@@ -656,9 +656,22 @@ class BasicNewsRecipe(Recipe):
 
         For an example, see the recipe for downloading `The Atlantic`.
         In addition, you can add 'author' for the author of the article.
+
+        If you want to abort processing for some reason and have
+        calibre show the user a simple message instead of an error, call
+        :meth:`abort_recipe_processing`.
         '''
         raise NotImplementedError
 
+    def abort_recipe_processing(self, msg):
+        '''
+        Causes the recipe download system to abort the download of this recipe,
+        displaying a simple feedback message to the user.
+        '''
+        from calibre.ebooks.conversion import ConversionUserFeedBack
+        raise ConversionUserFeedBack(_('Failed to download %s')%self.title,
+                msg)
+
     def get_obfuscated_article(self, url):
         '''
         If you set `articles_are_obfuscated` this method is called with