add pre_deletion_hook

closes https://github.com/pimutils/vdirsyncer/issues/1107

docs/config.rst

@@ -378,6 +378,7 @@ Local
       fileext = "..."
       #encoding = "utf-8"
       #post_hook = null
+      #pre_deletion_hook = null
       #fileignoreext = ".tmp"
 
     Can be used with `khal <http://lostpackets.de/khal/>`_. See :doc:`vdir` for
@@ -399,6 +400,8 @@ Local
     :param post_hook: A command to call for each item creation and
         modification. The command will be called with the path of the
         new/updated file.
+    :param pre_deletion_hook: A command to call for each item deletion.
+        The command will be called with the path of the deleted file.
     :param fileeignoreext: The file extention to ignore. It is only useful
         if fileext is set to the empty string. The default is ``.tmp``.
 

vdirsyncer/storage/filesystem.py

@@ -29,6 +29,7 @@ class FilesystemStorage(Storage):
         fileext,
         encoding="utf-8",
         post_hook=None,
+        pre_deletion_hook=None,
         fileignoreext=".tmp",
         **kwargs,
     ):
@@ -40,6 +41,7 @@ class FilesystemStorage(Storage):
         self.fileext = fileext
         self.fileignoreext = fileignoreext
         self.post_hook = post_hook
+        self.pre_deletion_hook = pre_deletion_hook
 
     @classmethod
     async def discover(cls, path, **kwargs):
@@ -166,6 +168,9 @@ class FilesystemStorage(Storage):
         actual_etag = get_etag_from_file(fpath)
         if etag != actual_etag:
             raise exceptions.WrongEtagError(etag, actual_etag)
+        if self.pre_deletion_hook:
+            self._run_pre_deletion_hook(fpath)
+
         os.remove(fpath)
 
     def _run_post_hook(self, fpath):
@@ -175,6 +180,13 @@ class FilesystemStorage(Storage):
         except OSError as e:
             logger.warning(f"Error executing external hook: {str(e)}")
 
+    def _run_pre_deletion_hook(self, fpath):
+        logger.info(f"Calling pre_deletion_hook={self.pre_deletion_hook} with argument={fpath}")
+        try:
+            subprocess.call([self.pre_deletion_hook, fpath])
+        except OSError as e:
+            logger.warning(f"Error executing external hook: {str(e)}")
+
     async def get_meta(self, key):
         fpath = os.path.join(self.path, key)
         try: