Fix connection leak on query retry reconnect (#79)

* Close released conn on a reconnect attempt

* fix err message

* tests: do actual DB connection on each driver connect

datasource.go

@@ -227,11 +227,10 @@ func (ds *SQLDatasource) handleQuery(ctx context.Context, req backend.DataQuery,
 	if errors.Is(err, ErrorQuery) && !errors.Is(err, context.DeadlineExceeded) {
 		for i := 0; i < ds.driverSettings.Retries; i++ {
 			backend.Logger.Warn(fmt.Sprintf("query failed. retrying %d times", i))
-			db, err := ds.c.Connect(dbConn.settings, q.ConnectionArgs)
+			db, err := ds.dbReconnect(dbConn, q, cacheKey)
 			if err != nil {
 				return nil, err
 			}
-			ds.storeDBConnection(cacheKey, dbConnection{db, dbConn.settings})
 
 			if ds.driverSettings.Pause > 0 {
 				time.Sleep(time.Duration(ds.driverSettings.Pause * int(time.Second)))
@@ -247,11 +246,10 @@ func (ds *SQLDatasource) handleQuery(ctx context.Context, req backend.DataQuery,
 	if errors.Is(err, context.DeadlineExceeded) {
 		for i := 0; i < ds.driverSettings.Retries; i++ {
 			backend.Logger.Warn(fmt.Sprintf("connection timed out. retrying %d times", i))
-			db, err := ds.c.Connect(dbConn.settings, q.ConnectionArgs)
+			db, err := ds.dbReconnect(dbConn, q, cacheKey)
 			if err != nil {
 				continue
 			}
-			ds.storeDBConnection(cacheKey, dbConnection{db, dbConn.settings})
 
 			res, err = QueryDB(ctx, db, ds.c.Converters(), fillMode, q)
 			if err == nil {
@@ -263,6 +261,19 @@ func (ds *SQLDatasource) handleQuery(ctx context.Context, req backend.DataQuery,
 	return nil, err
 }
 
+func (ds *SQLDatasource) dbReconnect(dbConn dbConnection, q *Query, cacheKey string) (*sql.DB, error) {
+	if err := dbConn.db.Close(); err != nil {
+		backend.Logger.Warn(fmt.Sprintf("closing existing connection failed: %s", err.Error()))
+	}
+
+	db, err := ds.c.Connect(dbConn.settings, q.ConnectionArgs)
+	if err != nil {
+		return nil, err
+	}
+	ds.storeDBConnection(cacheKey, dbConnection{db, dbConn.settings})
+	return db, nil
+}
+
 // CheckHealth pings the connected SQL database
 func (ds *SQLDatasource) CheckHealth(ctx context.Context, req *backend.CheckHealthRequest) (*backend.CheckHealthResult, error) {
 	key := defaultKey(getDatasourceUID(*req.PluginContext.DataSourceInstanceSettings))

datasource_test.go

@@ -18,13 +18,13 @@ import (
 )
 
 type fakeDriver struct {
-	db *sql.DB
+	openDBfn func() (*sql.DB, error)
 
 	Driver
 }
 
 func (d fakeDriver) Connect(backend.DataSourceInstanceSettings, json.RawMessage) (db *sql.DB, err error) {
-	return d.db, nil
+	return d.openDBfn()
 }
 
 func (d fakeDriver) Macros() Macros {
@@ -41,7 +41,7 @@ func Test_getDBConnectionFromQuery(t *testing.T) {
 	db := &sql.DB{}
 	db2 := &sql.DB{}
 	db3 := &sql.DB{}
-	d := &fakeDriver{db: db3}
+	d := &fakeDriver{openDBfn: func() (*sql.DB, error) { return db3, nil }}
 	tests := []struct {
 		desc        string
 		dsUID       string
@@ -144,7 +144,7 @@ func Test_timeout_retries(t *testing.T) {
 		t.Errorf("failed to connect to mock driver: %v", err)
 	}
 	timeoutDriver := fakeDriver{
-		db: db,
+		openDBfn: func() (*sql.DB, error) { return db, nil },
 	}
 	retries := 5
 	max := time.Duration(testTimeout) * time.Second
@@ -178,12 +178,15 @@ func Test_error_retries(t *testing.T) {
 	}
 	mockDriver := "sqlmock-error"
 	mock.RegisterDriver(mockDriver, handler)
-	db, err := sql.Open(mockDriver, "")
-	if err != nil {
-		t.Errorf("failed to connect to mock driver: %v", err)
-	}
+
 	timeoutDriver := fakeDriver{
-		db: db,
+		openDBfn: func() (*sql.DB, error) {
+			db, err := sql.Open(mockDriver, "")
+			if err != nil {
+				t.Errorf("failed to connect to mock driver: %v", err)
+			}
+			return db, nil
+		},
 	}
 	retries := 5
 	max := time.Duration(10) * time.Second
@@ -192,6 +195,7 @@ func Test_error_retries(t *testing.T) {
 
 	key := defaultKey(dsUID)
 	// Add the mandatory default db
+	db, _ := timeoutDriver.Connect(settings, nil)
 	ds.storeDBConnection(key, dbConnection{db, settings})
 	ctx := context.Background()