Protect other usage vs grpc protocol changes

Change all uses of protobuf messages other than status and history data so that they will not crash the calling script in the case where the grpc protocol removes the message or field being accessed. Instead, they will return None for the affected field (which most calling scripts interpret as "no data") or raise the same error as when the dish is not reachable.

This is for issue #66.

starlink_grpc.py

@@ -535,7 +535,7 @@ class GrpcError(Exception):
             msg = e.details()
         elif isinstance(e, grpc.RpcError):
             msg = "Unknown communication or service error"
-        elif isinstance(e, (AttributeError, ValueError)):
+        elif isinstance(e, (AttributeError, IndexError, TypeError, ValueError)):
             msg = "Protocol error"
         else:
             msg = str(e)
@@ -829,6 +829,9 @@ def get_location(context: Optional[ChannelContext] = None):
 
     Raises:
         grpc.RpcError: Communication or service error.
+        AttributeError, ValueError: Protocol error. Either the target is not a
+            Starlink user terminal or the grpc protocol has changed in a way
+            this module cannot handle.
     """
     def grpc_call(channel):
         if imports_pending:
@@ -857,7 +860,7 @@ def location_data(context: Optional[ChannelContext] = None) -> LocationDict:
     """
     try:
         location = get_location(context)
-    except grpc.RpcError as e:
+    except (AttributeError, ValueError, grpc.RpcError) as e:
         if isinstance(e, grpc.Call) and e.code() is grpc.StatusCode.PERMISSION_DENIED:
             return {
                 "latitude": None,
@@ -866,11 +869,17 @@ def location_data(context: Optional[ChannelContext] = None) -> LocationDict:
             }
         raise GrpcError(e) from e
 
-    return {
-        "latitude": location.lla.lat,
-        "longitude": location.lla.lon,
-        "altitude": location.lla.alt,
-    }
+    try:
+        return {
+            "latitude": location.lla.lat,
+            "longitude": location.lla.lon,
+            "altitude": getattr(location.lla, "alt", None),
+        }
+    except AttributeError as e:
+        # Allow None for altitude, but since all None values has special
+        # meaning for this function, any other protocol change is flagged as
+        # an error.
+        raise GrpcError(e) from e
 
 
 def history_bulk_field_names():
@@ -1424,6 +1433,9 @@ def get_obstruction_map(context: Optional[ChannelContext] = None):
 
     Raises:
         grpc.RpcError: Communication or service error.
+        AttributeError, ValueError: Protocol error. Either the target is not a
+            Starlink user terminal or the grpc protocol has changed in a way
+            this module cannot handle.
     """
     def grpc_call(channel: grpc.Channel):
         if imports_pending:
@@ -1450,15 +1462,19 @@ def obstruction_map(context: Optional[ChannelContext] = None):
         representation the SNR data instead, see `get_obstruction_map`.
 
     Raises:
-        GrpcError: Failed getting status info from the Starlink user terminal.
+        GrpcError: Failed getting obstruction data from the Starlink user
+            terminal.
     """
     try:
         map_data = get_obstruction_map(context)
-    except grpc.RpcError as e:
+    except (AttributeError, ValueError, grpc.RpcError) as e:
         raise GrpcError(e) from e
 
-    cols = map_data.num_cols
-    return tuple((map_data.snr[i:i + cols]) for i in range(0, cols * map_data.num_rows, cols))
+    try:
+        cols = map_data.num_cols
+        return tuple((map_data.snr[i:i + cols]) for i in range(0, cols * map_data.num_rows, cols))
+    except (AttributeError, IndexError, TypeError) as e:
+        raise GrpcError(e) from e
 
 
 def reboot(context: Optional[ChannelContext] = None) -> None:
@@ -1482,7 +1498,7 @@ def reboot(context: Optional[ChannelContext] = None) -> None:
 
     try:
         call_with_channel(grpc_call, context=context)
-    except grpc.RpcError as e:
+    except (AttributeError, ValueError, grpc.RpcError) as e:
         raise GrpcError(e) from e
 
 
@@ -1509,5 +1525,5 @@ def set_stow_state(unstow: bool = False, context: Optional[ChannelContext] = Non
 
     try:
         call_with_channel(grpc_call, context=context)
-    except grpc.RpcError as e:
+    except (AttributeError, ValueError, grpc.RpcError) as e:
         raise GrpcError(e) from e