[gnome-keysign: 1/5] Create a dialog at startup informing about the missing Avahi service

[Tobias Mueller <tobiasmue src gnome org>]

commit 951e59ca2029a655ddb9a615e8f098aafe652fb8
Author: RyuzakiKK <aasonykk gmail com>
Date:   Thu Jul 12 13:54:10 2018 +0200

    Create a dialog at startup informing about the missing Avahi service
    
    This gracefully handles the error reported in the issue #56

 keysign/app.py                  | 54 ++++++++++++++++++++++++++---------------
 keysign/dialog_avahi.ui         | 45 ++++++++++++++++++++++++++++++++++
 keysign/errors.py               |  6 +++++
 keysign/network/AvahiBrowser.py | 12 +++++++--
 4 files changed, 96 insertions(+), 21 deletions(-)
---
diff --git a/keysign/app.py b/keysign/app.py
index 22341b1..51d51d3 100755
--- a/keysign/app.py
+++ b/keysign/app.py
@@ -48,6 +48,7 @@ if  __name__ == "__main__" and __package__ is None:
 
 from .avahioffer import AvahiHTTPOffer
 from .avahidiscovery import AvahiKeysignDiscoveryWithMac
+from .errors import NoAvahiDbus
 from .keyconfirm import PreSignWidget
 from .keyfprscan import KeyFprScanWidget
 from .keylistwidget import KeyListWidget
@@ -149,31 +150,46 @@ class KeysignApp(Gtk.Application):
 
 
         # Load Receive part
-        self.receive = PswMappingReceiveApp(self.on_presign_mapped)
-        rs = self.receive.stack
+        try:
+            self.receive = PswMappingReceiveApp(self.on_presign_mapped)
+        except NoAvahiDbus as de:
+            log.info("Probably Avahi needs to be manually started: %s", de)
+            ui_file_path = os.path.join(
+                os.path.dirname(os.path.abspath(__file__)),
+                "dialog_avahi.ui")
+            appwindow = 'dialog_avahi'
+            builder = Gtk.Builder()
+            builder.add_objects_from_file(ui_file_path, [appwindow])
+            window.set_wmclass("GNOME Keysign", "GNOME Keysign")
+            window.set_title("GNOME Keysign")
+            ok_button = builder.get_object("avahi_ok")
+            ok_button.connect('clicked', self.on_delete_window)
+            window = builder.get_object(appwindow)
+        else:
+            rs = self.receive.stack
 
-        rs.connect('notify::visible-child',
-            self.on_receive_stack_switch)
+            rs.connect('notify::visible-child',
+                self.on_receive_stack_switch)
 
 
-        scanner = self.receive.scanner
-        scanner.connect("map", self.on_scanner_mapped)
-        self.receive_stack = rs
+            scanner = self.receive.scanner
+            scanner.connect("map", self.on_scanner_mapped)
+            self.receive_stack = rs
 
 
-        # Hm. Leaving comments for translators does not seem to work
-        self.send_receive_stack.add_titled(self.send_stack,
-            "send_stack", _("Send"))
-        self.send_receive_stack.add_titled(rs,
-            "receive_stack", _("Receive"))
+            # Hm. Leaving comments for translators does not seem to work
+            self.send_receive_stack.add_titled(self.send_stack,
+                "send_stack", _("Send"))
+            self.send_receive_stack.add_titled(rs,
+                "receive_stack", _("Receive"))
 
-        # These properties must be set after the stacks has been added to the window
-        # because they require a window element that "receive.ui" file doesn't provide.
-        accel_group = Gtk.AccelGroup()
-        window.add_accel_group(accel_group)
-        self.receive.accept_button.add_accelerator("clicked", accel_group, ord('o'), 
Gdk.ModifierType.MOD1_MASK,
-                                                   Gtk.AccelFlags.VISIBLE)
-        self.receive.accept_button.set_can_default(True)
+            # These properties must be set after the stacks has been added to the window
+            # because they require a window element that "receive.ui" file doesn't provide.
+            accel_group = Gtk.AccelGroup()
+            window.add_accel_group(accel_group)
+            self.receive.accept_button.add_accelerator("clicked", accel_group, ord('o'), 
Gdk.ModifierType.MOD1_MASK,
+                                                       Gtk.AccelFlags.VISIBLE)
+            self.receive.accept_button.set_can_default(True)
 
         window.show_all()
         self.add_window(window)
diff --git a/keysign/dialog_avahi.ui b/keysign/dialog_avahi.ui
new file mode 100644
index 0000000..0a615ca
--- /dev/null
+++ b/keysign/dialog_avahi.ui
@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Generated with glade 3.22.1 -->
+<interface>
+  <requires lib="gtk+" version="3.20"/>
+  <object class="GtkMessageDialog" id="dialog_avahi">
+    <property name="can_focus">False</property>
+    <property name="type_hint">dialog</property>
+    <property name="text" translatable="yes">Unable to Start Avahi</property>
+    <property name="secondary_text" translatable="yes">Keysign is unable to automatically start Avahi. You 
can try to execute `systemctl start avahi-daemon` for solving this problem.</property>
+    <child internal-child="vbox">
+      <object class="GtkBox">
+        <property name="can_focus">False</property>
+        <property name="orientation">vertical</property>
+        <property name="spacing">2</property>
+        <child internal-child="action_area">
+          <object class="GtkButtonBox">
+            <property name="can_focus">False</property>
+            <property name="hexpand">True</property>
+            <property name="homogeneous">True</property>
+            <property name="layout_style">expand</property>
+            <child>
+              <object class="GtkButton" id="avahi_ok">
+                <property name="label" translatable="yes">OK</property>
+                <property name="name">avahi_ok</property>
+                <property name="visible">True</property>
+                <property name="can_focus">True</property>
+                <property name="receives_default">True</property>
+              </object>
+              <packing>
+                <property name="expand">True</property>
+                <property name="fill">True</property>
+                <property name="position">0</property>
+              </packing>
+            </child>
+          </object>
+          <packing>
+            <property name="expand">True</property>
+            <property name="fill">True</property>
+            <property name="position">0</property>
+          </packing>
+        </child>
+      </object>
+    </child>
+  </object>
+</interface>
diff --git a/keysign/errors.py b/keysign/errors.py
index 1016972..d712130 100644
--- a/keysign/errors.py
+++ b/keysign/errors.py
@@ -14,3 +14,9 @@ class UnpoweredAdapter(BluetoothException):
     """The Bluetooth adapter is turned off"""
 
 
+class AvahiException(Exception):
+    """Parent class for all Avahi-related errors"""
+
+
+class NoAvahiDbus(AvahiException):
+    """The required avahi dbus is not available"""
diff --git a/keysign/network/AvahiBrowser.py b/keysign/network/AvahiBrowser.py
index c021af9..5ef2402 100644
--- a/keysign/network/AvahiBrowser.py
+++ b/keysign/network/AvahiBrowser.py
@@ -27,10 +27,14 @@ from gi.repository import GObject
 
 import logging
 
+from ..errors import NoAvahiDbus
+
 __all__ = ["AvahiBrowser"]
 
 DBusGMainLoop( set_as_default=True )
 
+log = logging.getLogger(__name__)
+
 # This should probably be upstreamed.
 # Unfortunately, upstream seems rather inactive.
 if getattr(avahi, 'txt_array_to_dict', None) is None:
@@ -83,8 +87,12 @@ class AvahiBrowser(GObject.GObject):
         self.loop = loop or DBusGMainLoop()
         self.bus = dbus.SystemBus(mainloop=self.loop)
 
-        self.server = dbus.Interface( self.bus.get_object(avahi.DBUS_NAME, '/'),
-                'org.freedesktop.Avahi.Server')
+        try:
+            self.server = dbus.Interface(self.bus.get_object(avahi.DBUS_NAME, '/'),
+                                         'org.freedesktop.Avahi.Server')
+        except dbus.exceptions.DBusException as de:
+            log.exception("Avahi cannot be started: %s", de)
+            raise NoAvahiDbus(de)
 
         self.sbrowser = dbus.Interface(self.bus.get_object(avahi.DBUS_NAME,
             self.server.ServiceBrowserNew(avahi.IF_UNSPEC,