feat: Add end of pipe clean up hook to Sinks (#750)

* add clean up hook to sinks called at end of pipe drain

* make message more clear for devs and add decorator

* unwrap the comprehension so mypy doesnt get mad

* remove abstract method

* fix flake8 errors

Co-authored-by: Edgar R. M <edgarrm358@gmail.com>

singer_sdk/sinks/core.py

@@ -401,3 +401,12 @@ def activate_version(self, new_version: int) -> None:
             "ACTIVATE_VERSION message received but not implemented by this target. "
             "Ignoring."
         )
+
+    def clean_up(self) -> None:
+        """Perform any clean up actions required at end of a stream.
+
+        Implementations should ensure that clean up does not affect resources
+        that may be in use from other instances of the same sink. Stream name alone
+        should not be relied on, it's recommended to use a uuid as well.
+        """
+        pass

singer_sdk/target_base.py

@@ -273,7 +273,7 @@ def _process_lines(self, file_input: IO[str]) -> Counter[str]:
 
     def _process_endofpipe(self) -> None:
         """Called after all input lines have been read."""
-        self.drain_all()
+        self.drain_all(is_endofpipe=True)
 
     def _process_record_message(self, message_dict: dict) -> None:
         """Process a RECORD message.
@@ -403,15 +403,27 @@ def _process_activate_version_message(self, message_dict: dict) -> None:
     # Sink drain methods
 
     @final
-    def drain_all(self) -> None:
+    def drain_all(self, is_endofpipe: bool = False) -> None:
         """Drains all sinks, starting with those cleared due to changed schema.
 
         This method is internal to the SDK and should not need to be overridden.
+
+        Args:
+            is_endofpipe: This is passed by the
+                          :meth:`~singer_sdk.Sink._process_endofpipe()` which
+                          is called after the target instance has finished
+                          listening to the stdin
         """
         state = copy.deepcopy(self._latest_state)
         self._drain_all(self._sinks_to_clear, 1)
+        if is_endofpipe:
+            for sink in self._sinks_to_clear:
+                sink.clean_up()
         self._sinks_to_clear = []
         self._drain_all(list(self._sinks_active.values()), self.max_parallelism)
+        if is_endofpipe:
+            for sink in self._sinks_active.values():
+                sink.clean_up()
         self._write_state_message(state)
         self._reset_max_record_age()