Google has warned that support for Server Push technology will be disabled in the release of Chrome 106, scheduled for September 27th. The changes will also affect other browsers based on the Chromium codebase. Server Push technology is defined in the HTTP/2 and HTTP/3 standards, and allows the server to send resources to the client without waiting for them to be explicitly requested. It is assumed that in this way the server can speed up the loading of the page, since the CSS files, scripts and images necessary for rendering the page will already be transferred to its side by the time the client requests it.
The reason cited for discontinuing support is the unnecessary complexity of implementing the technology when simpler and equally effective alternatives are available, such as the tag , on the basis of which the browser can request a resource without waiting for it to be used on the page. On the one hand, preload, compared to Server Push, leads to unnecessary packet exchange (RTT), but on the other hand, it avoids sending resources that are already in the browser cache. In general, the differences in latency when using Server Push and preload are noted as insignificant.
To initiate pre-loading on the server side, it is proposed to use HTTP response code 103, which allows you to inform the client about the contents of some HTTP headers immediately after the request, without waiting for the server to complete all operations related to the request and start serving the content. Similarly, you can provide hints about elements related to the page being served that may be preloaded (for example, you can provide links to the CSS and JavaScript used on the page). Having received information about such resources, the browser can begin downloading them without waiting for the main page to finish rendering, which reduces the overall request processing time.
In addition to optimizing resource loading, the Server Push mechanism could also be used to stream data from the server to the client, but for these purposes the W3C consortium is developing the WebTransport protocol. The communication channel in WebTransport is organized on top of HTTP/3 using the QUIC protocol as a transport. WebTransport offers such advanced features as organizing transmission into multiple streams, unidirectional streams, delivery without taking into account the order in which packets are sent (out-of-order), reliable and unreliable delivery modes.
According to Google statistics, Server Push technology is not widely used. Although Server Push is included in the HTTP/3 specification, in practice many server and client software products, including the Chrome browser, do not implement it natively. In 2021, about 1.25% of sites running HTTP/2 used Server Push. This year this figure has dropped to 0.7%.
Source: opennet.ru