feat: take a backup of the sqlite db before executing schema migrations

.gitignore

@@ -9,5 +9,6 @@
 
 *.sqlite3
 *.db
+*.bak
 static/upload/
 ./matemat.conf

matemat/db/wrapper.py

@@ -60,23 +60,31 @@ class DatabaseWrapper(object):
 
     def _setup(self) -> None:
         # Create or update schemas if necessary
-        with self.transaction() as c:
-            version: int = self._user_version
-            if version < 1:
-                # Don't use executescript, as it issues a COMMIT first
+        version: int = self._user_version
+        if version < 1:
+            # Don't use executescript, as it issues a COMMIT first
+            with self.transaction() as c:
                 for command in SCHEMAS[self.SCHEMA_VERSION]:
                     c.execute(command)
-            elif version < self.SCHEMA_VERSION:
-                self._upgrade(from_version=version, to_version=self.SCHEMA_VERSION)
-            elif version > self.SCHEMA_VERSION:
-                raise RuntimeError('Database schema is newer than supported by this version of Matemat.')
-            self._user_version = self.SCHEMA_VERSION
+        elif version < self.SCHEMA_VERSION:
+            self._upgrade(from_version=version, to_version=self.SCHEMA_VERSION)
+        elif version > self.SCHEMA_VERSION:
+            raise RuntimeError('Database schema is newer than supported by this version of Matemat.')
+        self._user_version = self.SCHEMA_VERSION
 
         # Enable foreign key enforcement
         cursor = self._sqlite_db.cursor()
         cursor.execute('PRAGMA foreign_keys=ON')
 
     def _upgrade(self, from_version: int, to_version: int) -> None:
+        if from_version >= to_version:
+            return
+        if self._filename != ':memory:':
+            bakfile = f'{self._filename}_{from_version}_{to_version}.bak'
+            bak = sqlite3.connect(bakfile)
+            with bak:
+                self._sqlite_db.backup(bak, pages=1)
+            bak.close()
         with self.transaction() as c:
             c.execute('PRAGMA foreign_keys=OFF')
             c.execute('PRAGMA legacy_alter_table=ON')

package/debian/matemat/DEBIAN/postinst

@@ -16,6 +16,7 @@ if [[ "$1" == "configure" ]]; then
     chmod 0750 /var/lib/matemat
     ln -sf /var/lib/matemat/upload /usr/lib/matemat/static/upload
 
+    systemctl daemon-reload || true
     deb-systemd-helper enable matemat.service
     deb-systemd-invoke restart matemat.service