Work around sqlite's incorrect handling of umask when creating databases.

Refactored some common code into initDb.

This only deals with the problem when creating new databases. If a repo
got bad permissions into it, it's up to the user to deal with it.

This commit was sponsored by Ole-Morten Duesund on Patreon.

Database/Init.hs

@@ -0,0 +1,55 @@
+{- Persistent sqlite database initialization
+ -
+ - Copyright 2015-2017 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Database.Init where
+
+import Annex.Common
+import Annex.Perms
+import Utility.FileMode
+
+import Database.Persist.Sqlite
+import qualified Database.Sqlite as Sqlite
+import Control.Monad.IO.Class (liftIO)
+import qualified Data.Text as T
+
+{- Ensures that the database is freshly initialized. Deletes any
+ - existing database. Pass the migration action for the database.
+ -
+ - The database is initialized using WAL mode, to prevent readers
+ - from blocking writers, and prevent a writer from blocking readers.
+ -
+ - The permissions of the database are set based on the
+ - core.sharedRepository setting. Setting these permissions on the main db
+ - file causes Sqlite to always use the same permissions for additional
+ - files it writes later on
+ -}
+initDb :: FilePath -> SqlPersistM () -> Annex ()
+initDb db migration = do
+	let dbdir = takeDirectory db
+	let tmpdbdir = dbdir ++ ".tmp"
+	let tmpdb = tmpdbdir </> "db"
+	liftIO $ do
+		createDirectoryIfMissing True tmpdbdir
+		let tdb = T.pack tmpdb
+		enableWAL tdb
+		runSqlite tdb migration
+	setAnnexDirPerm tmpdbdir
+	-- Work around sqlite bug that prevents it from honoring
+	-- less restrictive umasks.
+	liftIO $ setFileMode tmpdb =<< defaultFileMode
+	setAnnexFilePerm tmpdb
+	liftIO $ do
+		void $ tryIO $ removeDirectoryRecursive dbdir
+		rename tmpdbdir dbdir
+
+enableWAL :: T.Text -> IO ()
+enableWAL db = do
+	conn <- Sqlite.open db
+	stmt <- Sqlite.prepare conn (T.pack "PRAGMA journal_mode=WAL;")
+	void $ Sqlite.step stmt
+	void $ Sqlite.finalize stmt
+	Sqlite.close conn