fix(pluginapi/store): init master db if no replica (mattermost#29674)

* fix(pluginapi/store): init master db if no replica

GetReplicaDB return nil because masterDB is not initialized.

* chore: add test

server/public/pluginapi/store.go

@@ -55,6 +55,10 @@ func (s *StoreService) GetReplicaDB() (*sql.DB, error) {
 		return s.replicaDB, nil
 	}
 
+	if err := s.initializeMaster(); err != nil {
+		return nil, err
+	}
+
 	return s.masterDB, nil
 }
 

server/public/pluginapi/store_test.go

@@ -66,6 +66,39 @@ func TestStore(t *testing.T) {
 		require.NoError(t, store.Close())
 	})
 
+	t.Run("master db fallback without get master first", func(t *testing.T) {
+		config := &model.Config{
+			SqlSettings: model.SqlSettings{
+				DriverName:                  model.NewPointer("ramsql"),
+				DataSource:                  model.NewPointer("TestStore-master-db"),
+				ConnMaxLifetimeMilliseconds: model.NewPointer(2),
+			},
+		}
+
+		driver := &plugintest.Driver{}
+		defer driver.AssertExpectations(t)
+		driver.On("Conn", true).Return("test", nil)
+		driver.On("ConnPing", "test").Return(nil)
+		driver.On("ConnClose", "test").Return(nil)
+
+		api := &plugintest.API{}
+		defer api.AssertExpectations(t)
+		store := pluginapi.NewClient(api, driver).Store
+
+		api.On("GetUnsanitizedConfig").Return(config)
+		// No replica is set up, should fallback to master
+		replicaDB, err := store.GetReplicaDB()
+		require.NoError(t, err)
+		require.NotNil(t, replicaDB)
+
+		masterDB, err := store.GetMasterDB()
+		require.NoError(t, err)
+		require.NotNil(t, masterDB)
+		require.Same(t, replicaDB, masterDB)
+
+		require.NoError(t, store.Close())
+	})
+
 	t.Run("replica db singleton", func(t *testing.T) {
 		config := &model.Config{
 			SqlSettings: model.SqlSettings{