bpo-41930: Add support for SQLite serialise/deserialise API (pythonGH…

…-26728)

Co-authored-by: Jelle Zijlstra <[email protected]>
Co-authored-by: Kumar Aditya <[email protected]>

Doc/library/sqlite3.rst

@@ -748,6 +748,44 @@ Connection Objects
       .. versionadded:: 3.11
 
 
+   .. method:: serialize(*, name="main")
+
+      This method serializes a database into a :class:`bytes` object.  For an
+      ordinary on-disk database file, the serialization is just a copy of the
+      disk file.  For an in-memory database or a "temp" database, the
+      serialization is the same sequence of bytes which would be written to
+      disk if that database were backed up to disk.
+
+      *name* is the database to be serialized, and defaults to the main
+      database.
+
+      .. note::
+
+         This method is only available if the underlying SQLite library has the
+         serialize API.
+
+      .. versionadded:: 3.11
+
+
+   .. method:: deserialize(data, /, *, name="main")
+
+      This method causes the database connection to disconnect from database
+      *name*, and reopen *name* as an in-memory database based on the
+      serialization contained in *data*.  Deserialization will raise
+      :exc:`OperationalError` if the database connection is currently involved
+      in a read transaction or a backup operation.  :exc:`DataError` will be
+      raised if ``len(data)`` is larger than ``2**63 - 1``, and
+      :exc:`DatabaseError` will be raised if *data* does not contain a valid
+      SQLite database.
+
+      .. note::
+
+         This method is only available if the underlying SQLite library has the
+         deserialize API.
+
+      .. versionadded:: 3.11
+
+
 .. _sqlite3-cursor-objects:
 
 Cursor Objects

Doc/whatsnew/3.11.rst

@@ -366,6 +366,11 @@ sqlite3
   Instead we leave it to the SQLite library to handle these cases.
   (Contributed by Erlend E. Aasland in :issue:`44092`.)
 
+* Add :meth:`~sqlite3.Connection.serialize` and
+  :meth:`~sqlite3.Connection.deserialize` to :class:`sqlite3.Connection` for
+  serializing and deserializing databases.
+  (Contributed by Erlend E. Aasland in :issue:`41930`.)
+
 
 sys
 ---

Lib/test/test_sqlite3/test_dbapi.py

@@ -29,6 +29,7 @@
 
 from test.support import (
     SHORT_TIMEOUT,
+    bigmemtest,
     check_disallow_instantiation,
     threading_helper,
 )
@@ -603,6 +604,56 @@ def test_uninit_operations(self):
                                        func)
 
 
+@unittest.skipUnless(hasattr(sqlite.Connection, "serialize"),
+                     "Needs SQLite serialize API")
+class SerializeTests(unittest.TestCase):
+    def test_serialize_deserialize(self):
+        with memory_database() as cx:
+            with cx:
+                cx.execute("create table t(t)")
+            data = cx.serialize()
+            self.assertEqual(len(data), 8192)
+
+            # Remove test table, verify that it was removed.
+            with cx:
+                cx.execute("drop table t")
+            regex = "no such table"
+            with self.assertRaisesRegex(sqlite.OperationalError, regex):
+                cx.execute("select t from t")
+
+            # Deserialize and verify that test table is restored.
+            cx.deserialize(data)
+            cx.execute("select t from t")
+
+    def test_deserialize_wrong_args(self):
+        dataset = (
+            (BufferError, memoryview(b"blob")[::2]),
+            (TypeError, []),
+            (TypeError, 1),
+            (TypeError, None),
+        )
+        for exc, arg in dataset:
+            with self.subTest(exc=exc, arg=arg):
+                with memory_database() as cx:
+                    self.assertRaises(exc, cx.deserialize, arg)
+
+    def test_deserialize_corrupt_database(self):
+        with memory_database() as cx:
+            regex = "file is not a database"
+            with self.assertRaisesRegex(sqlite.DatabaseError, regex):
+                cx.deserialize(b"\0\1\3")
+                # SQLite does not generate an error until you try to query the
+                # deserialized database.
+                cx.execute("create table fail(f)")
+
+    @unittest.skipUnless(sys.maxsize > 2**32, 'requires 64bit platform')
+    @bigmemtest(size=2**63, memuse=3, dry_run=False)
+    def test_deserialize_too_much_data_64bit(self):
+        with memory_database() as cx:
+            with self.assertRaisesRegex(OverflowError, "'data' is too large"):
+                cx.deserialize(b"b" * size)
+
+
 class OpenTests(unittest.TestCase):
     _sql = "create table test(id integer)"
 
@@ -1030,6 +1081,10 @@ def test_check_connection_thread(self):
             lambda: self.con.setlimit(sqlite.SQLITE_LIMIT_LENGTH, -1),
             lambda: self.con.getlimit(sqlite.SQLITE_LIMIT_LENGTH),
         ]
+        if hasattr(sqlite.Connection, "serialize"):
+            fns.append(lambda: self.con.serialize())
+            fns.append(lambda: self.con.deserialize(b""))
+
         for fn in fns:
             with self.subTest(fn=fn):
                 self._run_test(fn)

Misc/NEWS.d/next/Library/2021-06-17-00-02-58.bpo-41930.JS6fsd.rst

@@ -0,0 +1,3 @@
+Add :meth:`~sqlite3.Connection.serialize` and
+:meth:`~sqlite3.Connection.deserialize` support to :mod:`sqlite3`. Patch by
+Erlend E. Aasland.