HTTP/2: many messages exchanged in one connection

Useful to know

A web page rarely consists of just one file. In addition to the main document, the browser can request styles, images, fonts, and program modules. HTTP/2 is designed to use network resources more efficiently in such an exchange. Among its main features are simultaneous exchanges in a relationship and compression of header fields. These are changes in the way messages are transmitted, not a new system for writing the pages themselves. [1]

The important concept is flow. Through streams, individual requests and responses can be distinguished, even though they share the connection. Instead of thinking of a long text conversation, it is more useful to imagine several marked exchanges. HTTP/2 uses binary framing, by which data is organized for transfer. The standard describes how this representation preserves the meaning of HTTP, including the methods, statuses, and message fields. [2]

Take a fictional page of a museum with eight photos. For the visitor, the successful result is easy to describe: the title is visible, the photos are arranged and the information button works. For the developer, the question is more detailed: when does each download start, what ends last, and what waits for the user. This example helps to distinguish the content of the page and the organization of the network exchange. The newer version of the protocol does not choose in place of the editor how many photos are needed or which is most important.

The compression of headers in HTTP/2 is called HPACK. It refers to HTTP fields and should not be mixed with image compression or the text body. [1] There are flow and exchange management mechanisms in the protocol. [2] For practical comparison, it is useful to record the conditions of observation: same page, same resources, and a clearly described network. Without such a framework, two outcomes can seem comparable when they actually measure different things.

A common confusion is the expectation that switching to HTTP/2 changes the meaning of status 404 or the way the application understands POST. The underlying semantics remain the same. [1] Therefore, in the event of a malfunction, one can first check whether the server returns the correct answer, and separately establish which version of the protocol was used. Thus, a missing file does not automatically become an assumed multiplexing problem.

When evaluating a renovation, it is good to have a specific goal. For example, the team can select one representative page and track the time until its main content appears. Then the check is repeated under the same conditions and the observations are recorded. This approach gives a more meaningful conversation than a promise of universal acceleration. HTTP/2 provides a mechanism for more efficient exchange, and the result for the person is evaluated on the real page and its behavior.