trustedcoin: better UX in Qt when cannot connect to TC server

closes #5184

electrum/plugins/trustedcoin/qt.py

@@ -121,10 +121,20 @@ class Plugin(TrustedCoinPlugin):
     def prompt_user_for_otp(self, wallet, tx, on_success, on_failure):
         wallet.handler_2fa.prompt_user_for_otp(wallet, tx, on_success, on_failure)
 
-    def waiting_dialog(self, window, on_finished=None):
-        task = partial(self.request_billing_info, window.wallet)
-        return WaitingDialog(window, 'Getting billing information...', task,
-                             on_finished)
+    def waiting_dialog_for_billing_info(self, window, *, on_finished=None):
+        def task():
+            return self.request_billing_info(window.wallet, suppress_connection_error=False)
+        def on_error(exc_info):
+            e = exc_info[1]
+            window.show_error("{header}\n{exc}\n\n{tor}"
+                              .format(header=_('Error getting TrustedCoin account info.'),
+                                      exc=str(e),
+                                      tor=_('If you keep experiencing network problems, try using a Tor proxy.')))
+        return WaitingDialog(parent=window,
+                             message=_('Requesting account info from TrustedCoin server...'),
+                             task=task,
+                             on_success=on_finished,
+                             on_error=on_error)
 
     @hook
     def abort_send(self, window):
@@ -134,14 +144,13 @@ class Plugin(TrustedCoinPlugin):
         if wallet.can_sign_without_server():
             return
         if wallet.billing_info is None:
-            self.start_request_thread(wallet)
-            window.show_error(_('Requesting account info from TrustedCoin server...') + '\n' +
-                                _('Please try again.'))
+            self.waiting_dialog_for_billing_info(window)
             return True
         return False
 
     def settings_dialog(self, window):
-        self.waiting_dialog(window, partial(self.show_settings_dialog, window))
+        self.waiting_dialog_for_billing_info(window,
+                                             on_finished=partial(self.show_settings_dialog, window))
 
     def show_settings_dialog(self, window, success):
         if not success:

electrum/plugins/trustedcoin/trustedcoin.py

@@ -465,15 +465,17 @@ class TrustedCoinPlugin(BasePlugin):
         return f
 
     @finish_requesting
-    def request_billing_info(self, wallet: 'Wallet_2fa'):
+    def request_billing_info(self, wallet: 'Wallet_2fa', *, suppress_connection_error=True):
         if wallet.can_sign_without_server():
             return
         self.print_error("request billing info")
         try:
             billing_info = server.get(wallet.get_user_id()[1])
         except ErrorConnectingServer as e:
-            self.print_error(str(e))
-            return
+            if suppress_connection_error:
+                self.print_error(str(e))
+                return
+            raise
         billing_index = billing_info['billing_index']
         # add segwit billing address; this will be used for actual billing
         billing_address = make_billing_address(wallet, billing_index, addr_type='segwit')