model: Notify user if a request fails.

This commit displays an error message in the footer for server requests
involving user interactions. By this the user can be notified for
different failures like:
* Hitting API rate limits.
* Posting in streams where user doesn't have the required permissions.
* Message sending/editing errors.
* Toggling reaction errors.
* etc.

Error responses from some requests are not displayed, since they are not
triggered directly by a user action. Example of these include event
polling requests, event registration, and updating presence.

Fixes #427.

Author: kaustubh-nair

zulipterminal/helper.py

@@ -630,3 +630,10 @@ def notify(title: str, html_text: str) -> str:
             # This likely means the notification command could not be found
             return command_list[0]
     return ""
+
+
+def display_error_if_present(response: Dict[str, Any], controller: Any) -> bool:
+    if response['result'] == 'error':
+        controller.view.set_footer_text(response['msg'], 3)
+        return True
+    return False

zulipterminal/model.py

@@ -14,7 +14,7 @@
 from zulipterminal.config.keys import keys_for_command
 from zulipterminal.helper import (
     Message, asynch, canonicalize_color, classify_unread_counts,
-    index_messages, initial_index, notify, set_count,
+    index_messages, initial_index, notify, display_error_if_present, set_count,
 )
 from zulipterminal.ui_tools.utils import create_msg_box_list
 
@@ -227,6 +227,7 @@ def _notify_server_of_presence(self) -> Dict[str, Any]:
                 }
             )
         self.new_user_input = False
+        display_error_if_present(response, self.controller)
         return response
 
     @asynch
@@ -269,6 +270,7 @@ def react_to_message(self,
             response = self.client.remove_reaction(reaction_to_toggle_spec)
         else:
             response = self.client.add_reaction(reaction_to_toggle_spec)
+        display_error_if_present(response, self.controller)
 
     @asynch
     def toggle_message_star_status(self, message: Message) -> None:
@@ -283,11 +285,12 @@ def toggle_message_star_status(self, message: Message) -> None:
     def mark_message_ids_as_read(self, id_list: List[int]) -> None:
         if not id_list:
             return
-        self.client.update_message_flags({
+        response = self.client.update_message_flags({
             'messages': id_list,
             'flag': 'read',
             'op': 'add',
         })
+        display_error_if_present(response, self.controller)
 
     def send_private_message(self, recipients: str,
                              content: str) -> bool:
@@ -297,6 +300,7 @@ def send_private_message(self, recipients: str,
             'content': content,
         }
         response = self.client.send_message(request)
+        display_error_if_present(response, self.controller)
         return response['result'] == 'success'
 
     def send_stream_message(self, stream: str, topic: str,
@@ -308,6 +312,7 @@ def send_stream_message(self, stream: str, topic: str,
             'content': content,
         }
         response = self.client.send_message(request)
+        display_error_if_present(response, self.controller)
         return response['result'] == 'success'
 
     def update_private_message(self, msg_id: int, content: str) -> bool:
@@ -316,6 +321,7 @@ def update_private_message(self, msg_id: int, content: str) -> bool:
             "content": content,
         }
         response = self.client.update_message(request)
+        display_error_if_present(response, self.controller)
         return response['result'] == 'success'
 
     def update_stream_message(self, topic: str, msg_id: int,
@@ -328,6 +334,7 @@ def update_stream_message(self, topic: str, msg_id: int,
             "subject": topic,
         }
         response = self.client.update_message(request)
+        display_error_if_present(response, self.controller)
         return response['result'] == 'success'
 
     def get_messages(self, *,
@@ -359,6 +366,7 @@ def get_messages(self, *,
                 query_range = num_after + num_before + 1
                 self.found_newest = len(response['messages']) < query_range
             return ""
+        display_error_if_present(response, self.controller)
         return response['msg']
 
     def get_topics_in_stream(self, stream_list: Iterable[int]) -> str:
@@ -373,6 +381,7 @@ def get_topics_in_stream(self, stream_list: Iterable[int]) -> str:
                 self.index['topics'][stream_id] = [topic['name'] for
                                                    topic in response['topics']]
             else:
+                display_error_if_present(response, self.controller)
                 return response['msg']
         return ""
 
@@ -609,6 +618,7 @@ def toggle_stream_muted_status(self, stream_id: int) -> bool:
             # True for muting and False for unmuting.
         }]
         response = self.client.update_subscription_settings(request)
+        display_error_if_present(response, self.controller)
         return response['result'] == 'success'
 
     def _handle_subscription_event(self, event: Event) -> None:
@@ -962,6 +972,7 @@ def _register_desired_events(self, *, fetch_data: bool=False) -> str:
             self.queue_id = response['queue_id']
             self.last_event_id = response['last_event_id']
             return ""
+        display_error_if_present(response, self.controller)
         return response['msg']
 
     @asynch