Qt WebSockets Overview
Qt WebSockets enables you to build WebSocket-aware applications. It provides an implementation for the WebSocket protocol, which is offered by IETF (Internet Engineering Task Force) as a better alternative for bidirectional communication using the existing web infrastructure.
Historically, web applications that needed bidirectional communication or push notifications had to use one of the HTTP-based solutions available. These solutions employed different techniques such as polling, long-polling, and streaming, to overcome the limitations of HTTP protocol, which is not designed for such use cases. As a result, high network latency, unnecessary data exchange, and stale or old data. The WebSocket offering by IETF helps to overcome these problems to a large extent.
How does it Work?
A WebSocket connection begins with a initial HTTP-compatible handshake, which ensures backwards compatibility so that the WebSocket connections can share the default HTTP (80) and HTTPS (443) ports. On successful handshake, the connection is open for data exchange, until one of the two entities end the connection.
The WebSocket protocol uses
wss: URL schemes to represent unsecure and secure WebSocket requests, respectively. During the initial handshake, if a proxy server is detected, the protocol tries to set up a tunnel by issuing an
HTTP CONNECT statement to the proxy. The tunnel approach to handle proxies is used irrespective of the request type, although it is proved to work better with TLS (Transport Layer Security) in secure connections.
Typical Use Cases
WebSocket suits best for scenarios where,
- data presented must be up-to-date,
- low network latency and minimal data exchange is crucial.
A few example applications where we struggle to achieve these using the traditional approach are, instant messaging, online gaming, online stock trading, and so on.
Role of Qt WebSockets
The Qt WebSockets module provides APIs to develop WebSocket-based server and client applications. An example of where these APIs can be used is a server application that provides stock data, and a client application that registers for push notification when there is a change in price of a few stocks.
The module provides both C++ and QML versions of the API, so you can choose the alternative that suits your need.
Qt WebSockets with Qt Cloud Services
The client application usually depends on an external service for data. Most of these service providers do not support WebSocket yet, so you end up developing a WebSocket-aware server application to bridge the gap. You can choose to run the server on an enterprise WebSocket gateway service such as Qt Cloud Services, avoiding the hassle of maintaining the necessary infrastructure required to host such a service.
The Qt Cloud Services provides a Managed Application Runtime (MAR) backend, which enables deploying and running an instance of server application on the cloud. The server instance running on MAR gets a WebSocket URL, which can be used by the client applications to connect and receive data.