From 790efc16aa2787b7afc9be2b09116055eb75fc1f Mon Sep 17 00:00:00 2001
From: Alex Jbanca <alexjb@status.im>
Date: Tue, 30 May 2023 20:29:29 +0300
Subject: [PATCH] fix(databaseLocks): Fixing database lock errors on
 transactions

The default transaction lock is `deferred`. This means that the transaction will automatically become read or write transaction based on the first DB operation. In case the first operation is `SELECT` the transaction becomes read transaction, otherwise write transaction. When a read transaction tries to write the DB sqlite will promote the transaction to a write transaction if there is no other transaction that holds a lock. When the promotion fails `database is locked` error is returned. The error is returned immediately and does not use the busy handler.
In our case almost all read transaction would fail with `database is locked` error.

This fix is changing the default transaction lock to `IMMEDIATE`. It translates to `BEGIN IMMEDIATE` instead of `BEGIN`. In this mode, the transaction will be created as a write transaction no matter what DB operation will run as part of the transaction. The write transaction will try to obtain the DB lock immediately when `BEGIN IMMEDIATE` is called and the busy handler is used when the DB is locked by other transaction.

Fixing: https://github.com/status-im/status-desktop/issues/10838
---
 sqlite/sqlite.go | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/sqlite/sqlite.go b/sqlite/sqlite.go
index 35980b6d4..4f130cfb4 100644
--- a/sqlite/sqlite.go
+++ b/sqlite/sqlite.go
@@ -5,8 +5,10 @@ import (
 	"database/sql/driver"
 	"errors"
 	"fmt"
+	"net/url"
 	"os"
 	"runtime"
+	"strings"
 
 	sqlcipher "github.com/mutecomm/go-sqlcipher" // We require go sqlcipher that overrides default implementation
 
@@ -77,6 +79,31 @@ func EncryptDB(unencryptedPath string, encryptedPath string, key string, kdfIter
 	return err
 }
 
+func buildSqlcipherDSN(path string) (string, error) {
+	if path == InMemoryPath {
+		return InMemoryPath, nil
+	}
+
+	// Adding sqlcipher query parameter to the DSN
+	queryOperator := "?"
+
+	if queryStart := strings.IndexRune(path, '?'); queryStart != -1 {
+		params, err := url.ParseQuery(path[queryStart+1:])
+		if err != nil {
+			return "", err
+		}
+
+		if len(params) > 0 {
+			queryOperator = "&"
+		}
+	}
+
+	// We need to set txlock=immediate to avoid "database is locked" errors during concurrent write operations
+	// This could happen when a read transaction is promoted to write transaction
+	// https://www.sqlite.org/lang_transaction.html
+	return path + queryOperator + "_txlock=immediate", nil
+}
+
 func openDB(path string, key string, kdfIterationsNumber int) (*sql.DB, error) {
 	driverName := fmt.Sprintf("sqlcipher_with_extensions-%d", len(sql.Drivers()))
 	sql.Register(driverName, &sqlcipher.SQLiteDriver{
@@ -111,7 +138,13 @@ func openDB(path string, key string, kdfIterationsNumber int) (*sql.DB, error) {
 		},
 	})
 
-	db, err := sql.Open(driverName, path)
+	dsn, err := buildSqlcipherDSN(path)
+
+	if err != nil {
+		return nil, err
+	}
+
+	db, err := sql.Open(driverName, dsn)
 	if err != nil {
 		return nil, err
 	}