The QUIC protocol in action: how Uber implemented it to optimize performance

Events bean is a simple facade for ApplicationEventPublisher of the Spring Framework. The load(), loadList(), loadValues() and getCount() methods check user’s READ permission for entities being loaded. Additionally, loading entities from the database is subject for access group constraints. Please note that the changes to property values stored in files are not persistent, and are valid only until restart of the application block. Such field is required when an entity class implements the Versioned interface (StandardEntity base class already contains such field). If decimalSeparator and/or groupingSeparator are not specified, the framework uses corresponding values from the format strings for the current user’s locale.

5.2. Visual Components Library

OnAfterDelete() method is called after a record is deleted from the database (in the case of soft deletion – after updating a record), but before transaction commit. This method does not allow modifications of the current persistence context, however, database modifications can be done using QueryRunner. OnAfterUpdate() method is called after a record was updated in the database, but before transaction commit. The cuba.additionalStores and cuba.persistenceConfig_db1 properties should also be specified in the property files of all used application blocks (web-app.properties, portal-app.properties, etc.). A usual way of working with data in CUBA applications is manipulating entities – either declaratively through data-aware visual components, or programmatically via DataManager or EntityManager. The entities are mapped to data in a data store, which is usually a relational database.

State of the Art: TCP

A screen controller is a Java or Groovy class that contains the screen initialization and event handling logic. Normally, the controller is linked to an XML descriptor which defines the screen layout and data containers, but it can also create all visual and non-visual components programmatically. When executing user requests, the Middleware program code always has access to the information on the current user via the UserSessionSource interface. This is possible because the corresponding SecurityContext object is automatically set for the current thread when a request is received from the client tier.

• The interface helps to obtain references to configuration interfaces.
• Note that access group constraints (row-level security) are always applied regardless of the above conditions.
• A listener is a class implementing one or several interfaces from the com.haulmont.cuba.core.listener package.
• The reference to it may be obtained from the current EntityManager instance by calling createQuery() method.
• The framework enables building multi-tiered applications with the distinct client, middle and database tiers.
• We used the network library Cronet of Chromium Projects, which contains the original, Google version of the protocol – gQUIC.
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2.8. Application Lifecycle Events

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2.14. Entity Attribute Access Control

This object can be used to check additional permissions, read User properties and session attributes. The SYS_QUERY_RESULT table is periodically cleaned of old query results left by terminated user sessions. This is done sell mobile proxies by the deleteForInactiveSessions() method of the QueryResultsManagerAPI bean which is invoked by a Spring scheduler defined in cuba-spring.xml. By default, it is done once in 10 minutes, but you can set a desired interval in milliseconds using the cuba.deleteOldQueryResultsInterval application property of the core module. The table below describes the recommended mapping of data types between entity attributes in Java and table columns in different DBMS. CUBA Studio automatically chooses these types when generates scripts to create and update the database.

4.2. Data Stores

To do this, create a Query or TypedQuery object by calling one of the EntityManager.createNativeQuery() methods. The interface containing methods for conversion between data model attribute values and parameters/results of JDBC queries. An object of this interface can be obtained through the Persistence.getDbTypeConverter() method. Obviously, the application should have been built and deployed on the server – e.g. a production or developer’s Tomcat instance. This mechanism is generally used by application developers for updating their own database instance.

Events.publish() notifies all matching listeners registered with this application of an application event. You can use PayloadApplicationEvent to publish any object as an event. See Decouple Business Logic with Application Events guide to learn different examples of application events.

1.1. Application Tiers and Blocks

• It is an input field, inside which there is a button with a drop-down calendar.
• Its handle() method should process the exception and return true, or immediately return false if this handler is not able to handle the passed exception.
• The @Valid annotation can be used if you need the cascaded validation of method parameters.
• The working group is currently IETF standardizes QUIC as HTTP / 3.
• The recommended way of passing parameters to an opened screen is to use public setters of the screen controller, as demonstrated in the example above.
• If at the moment of creation there was another transaction, it will be suspended and resumed after the completion of the newly created one.
• When you work with data on the client tier, you have only one option – DataManager.
• Any CUBA application can be easily turned into a component and provide some functionality to another application.
• This chain can contain classes which are inaccessible for the client tier (for example, JDBC driver exceptions).

EntityChangedEvent is a Spring’s ApplicationEvent which is sent by the framework on the middle tier when an entity instance is saved to the database. The event can be handled both inside the transaction (using @EventListener) and after its completion (using @TransactionalEventListener). OnAfterInsert() is called after a record is inserted into database, but before transaction commit. ORM enables execution of SQL queries returning either the lists of individual fields or entity instances.

Proxy Settings and FoxyProxy

Use cacheable queries only if entity cache is enabled for the returned entity. Otherwise on every query entity instances will be fetched from the database by their identifiers one by one. It stores recently read or written entity instance in memory, which minimizes database access and improves the application performance. AfterComplete() method is called after transaction is completed.

State of the Art: TCP

• If an exception is thrown on Middleware as a result of handling a client request, the execution terminates and the exception object is returned to the client.
• Alas, they were severely lacking in many security settings, and they also required an additional TCP connection for metadata and control information.
• Unlike the operations described above, the getConfigValue() operation returns exactly the same value as the corresponding method of the configuration interface invoked in the application code.
• And for the Order editor screen, you need to fetch the collection of Items, in addition to that each Item should contain a related Product instance to display its name.

EntityManager automatically flushes to the database all changes made in its persistence context on the transaction commit or when the EntityManager.flush() method is called. In any CUBA application, there is always the main data store which contains system and security entities and where the users log in. When we mention a database in this manual, we always mean the main data store if not explicitly stated otherwise. The main data store must be a relational database connected through a JDBC data source. An additional data store can be any implementation of the DataStore interface.

QUIC optimization

The server system locale characters are used in this case for formatting the attribute values with locale-independent methods. The usage of JPA cascade annotation attribute is not recommended. Explicitly defines the name of a database sequence that should be used for generating identifiers if the entity is a subclass of BaseLongIdEntity or BaseIntegerIdEntity. If the entity is not annotated, the framework creates a sequence with an automatically generated name. Inherit from BaseGenericIdEntity directly if you need to map the entity to a table with a composite key.

1.1. Application Tiers and Blocks

In order to configure connection pool settings, specify the HikariCP properties prefixed with cuba.dataSource., for example cuba.dataSource.maximumPoolSize or cuba.dataSource.connectionTimeout. See the full list of supported parameters and their default values in the HikariCP documentation. If the source exception is annotated by @SupportedByClient, the caller will receive it directly.

Proxysite

• On Microsoft SQL Server, providing a connection property is not enough, you have to link the schema with the database user.
• If the screen has unsaved changes in DataContext, a dialog with a corresponding message will be displayed before the screen is closed.
• If an event is UiEvent and fired using the Events bean from UI thread then opened windows and/or frames with such methods will receive the event.
• The id attribute of the entity (i.e. getId()/setId() methods) will be of type IdProxy which is designed to substitute the real identifier until it is generated by the database on insert.
• Such method does not require invoking Persistence.createTransaction(), you can immediately get EntityManager and work with it.
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• To do this, obtain a datatype instance from DatatypeRegistry using its get(Class) or getNN(Class) methods, passing the Java type that you want to convert.

Note that access group constraints (row-level security) are always applied regardless of the above conditions. You have to open a transaction before working with EntityManager. It is recommended to give descriptive names to the shared views. Defines a reference attribute with one-to-one relationship type.

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Security Considerations When Using Proxy Websites

• At runtime, a proxy is created for the service interface on the client tier.
• This section describes the lifecycle events that can be handled in fragment controllers.
• If the source exception is annotated by @SupportedByClient, the caller will receive it directly.
• This section describes all annotations of entity classes and attributes supported by the platform.
• In addition, the Web Client platform block includes the JMX console, which provides the basic tools to view the status and call the methods of the JMX beans.
• In the example above, the constraints declared on the Task object will be validated as well.

You can implement DataStore in your project to provide integration, for example, with a non-relational database or an external system having REST interface. CUBA Studio automatically registers services in all client blocks of the project. The service implementation bean is located in the core module and is available on the middle tier only. The following figure shows the main components of the CUBA application middle tier. Groovy scripts are executed only by the server mechanism to launch database scripts.

2.9. Application Properties

Indicates that metadata should include the annotated attribute. This annotation can be set for a field or for a getter method, if there is no corresponding field. Indicates that a field which is marked by this annotation contains currency value. If used, the CurrencyField is generated by Studio for this attribute in a Form of the entity editor screen. See Initial Entity Values guide for an example of defining initial values directly in the entity class using the @PostConstruct annotation. This chapter covers platform components, which are common for all tiers of the application.

You can adjust the dialog type using the cuba.gui.useSaveConfirmation application property. Mixins enable creating features that can be reused in multiple UI screens without the need to inherit your screens from common base classes. Mixins are implemented using Java interfaces with default methods. As you can see, when values are returned through a custom CloseAction, the caller doesn’t have to know the opened screen class because it doesn’t invoke methods of the concrete screen controller. Screen descriptor is an XML file containing declarative definition of visual components, data components and some screen parameters. AfterDetachEvent is sent after the screen is removed from the application UI when it is closed by the user or when the user logs out.

• Managed beans are Spring beans that contain the business logic of the application.
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• A screen fragment can have its own data containers and loaders, defined in the data XML element.
• The view mode is determined from the date range of the calendar, defined by the start date and the end date.
• This is done by the deleteForInactiveSessions() method of the QueryResultsManagerAPI bean which is invoked by a Spring scheduler defined in cuba-spring.xml.
• They intercept cheap airline tickets or tickets to concerts first, create artificial shortages of goods, and imitate real people on social media to spread misinformation.
• For example, you can dynamically generate HTML content at runtime from the user input.
• Also, UnsupportedCredentialsException is thrown if passed credentials object cannot be processed by available AuthenticationProvider beans.

If an event is UiEvent and fired using the Events bean from UI thread then opened windows and/or frames with such methods will receive the event. Only UI screens of the current web browser tab opened by the user receive the event. Events bean encapsulates the application-scope event publication functionality. Application events can be used to exchange information between loosely coupled components.

Finally, we evaluated several UDP-based protocols that troubleshoot video streaming – we wanted to see if these protocols would help in our case. Alas, they were severely lacking in many security settings, and they also required an additional TCP connection for metadata and control information. Finally, cellular network performance varies by carrier, region, and time. In Figure 2, we have collected the median delays of HTTPS traffic across cells over a range of 2 kilometers. The data is collected for the two largest mobile operators in Delhi, India. Also, the performance of one operator differs from the performance of the second one.