Return protocol prefixed source

src/ophyd_async/epics/_backend/_aioca.py

@@ -41,7 +41,7 @@
 _floating_dbr = {dbr.DBR_FLOAT, dbr.DBR_DOUBLE}
 
 
-def _data_key_from_augmented_value(value: AugmentedValue) -> DataKey:
+def _data_key_from_augmented_value(source: str, value: AugmentedValue) -> DataKey:
     """Use the return value of get with FORMAT_CTRL to construct a DataKey
     describing the signal. See docstring of AugmentedValue for expected
     value fields by DBR type.
@@ -54,9 +54,8 @@ def _data_key_from_augmented_value(value: AugmentedValue) -> DataKey:
     """
 
     # Always present keys
-    source = value.name
     if not value.ok:
-        raise Exception(f"{value.name} error: {value.errorcode}: {str(value)}")
+        raise Exception(f"{source} error: {value.errorcode}: {str(value)}")
 
     scalar = value.element_count == 1
 
@@ -108,8 +107,8 @@ def reading(self, value: AugmentedValue):
             alarm_severity=-1 if value.severity > 2 else value.severity,
         )
 
-    def descriptor(self, value: AugmentedValue) -> DataKey:
-        return _data_key_from_augmented_value(value)
+    def descriptor(self, source: str, value: AugmentedValue) -> DataKey:
+        return _data_key_from_augmented_value(source, value)
 
 
 class CaLongStrConverter(CaConverter):
@@ -271,7 +270,7 @@ async def _caget(self, format: Format) -> AugmentedValue:
 
     async def get_descriptor(self) -> DataKey:
         value = await self._caget(FORMAT_CTRL)
-        return self.converter.descriptor(value)
+        return self.converter.descriptor(self.source, value)
 
     async def get_reading(self) -> Reading:
         value = await self._caget(FORMAT_TIME)