Reject CachingMiddleware reads and writes after close

tests/test_middlewares.py

@@ -1,5 +1,7 @@
 import os
 
+import pytest
+
 from tinydb import TinyDB
 from tinydb.middlewares import CachingMiddleware
 from tinydb.storages import MemoryStorage, JSONStorage
@@ -98,6 +100,19 @@ def test_caching_json_write(tmpdir):
     # Assert JSON file has been closed
     assert db._storage._handle.closed
 
+
+def test_caching_rejects_use_after_close(tmpdir):
+    path = str(tmpdir.join('closed.db'))
+    db = TinyDB(path, storage=CachingMiddleware(JSONStorage))
+    db.insert({'key': 'value'})
+    db.close()
+
+    with pytest.raises(ValueError, match='closed'):
+        db.insert({'key': 'again'})
+
+    with pytest.raises(ValueError, match='closed'):
+        db.all()
+
     del db
 
     # Reopen database

tinydb/middlewares.py

@@ -92,8 +92,12 @@ def __init__(self, storage_cls):
         # Prepare the cache
         self.cache = None
         self._cache_modified_count = 0
+        self._closed = False
 
     def read(self):
+        if self._closed:
+            raise ValueError('I/O operation on closed storage')
+
         if self.cache is None:
             # Empty cache: read from the storage
             self.cache = self.storage.read()
@@ -102,6 +106,9 @@ def read(self):
         return self.cache
 
     def write(self, data):
+        if self._closed:
+            raise ValueError('I/O operation on closed storage')
+
         # Store data in cache
         self.cache = data
         self._cache_modified_count += 1
@@ -114,14 +121,22 @@ def flush(self):
         """
         Flush all unwritten data to disk.
         """
+        if self._closed:
+            raise ValueError('I/O operation on closed storage')
+
         if self._cache_modified_count > 0:
             # Force-flush the cache by writing the data to the storage
             self.storage.write(self.cache)
             self._cache_modified_count = 0
 
     def close(self):
+        if self._closed:
+            return
+
         # Flush potentially unwritten data
         self.flush()
 
         # Let the storage clean up too
         self.storage.close()
+        self._closed = True
+        self.cache = None