HTTP/2

HTTP/2 (originally named HTTP/2.0) is a major revision of the HTTP network protocol used by the World Wide Web. It was derived from the earlier experimental SPDY protocol, originally developed by Google. HTTP/2 was developed by the Hypertext Transfer Protocol working group httpbis (where bis means 'second') of the Internet Engineering Task Force. HTTP/2 is the first new version of HTTP since HTTP 1.1, which was standardized in RFC 2068 in 1997. The Working Group presented HTTP/2 to IESG for consideration as a Proposed Standard in December 2014, and IESG approved it to publish as Proposed Standard on February 17, 2015. The HTTP/2 specification was published as RFC 7540 in May 2015. The standardization effort was supported by Chrome, Opera, Firefox, Internet Explorer 11, Safari, Amazon Silk, and Edge browsers. Most major browsers had added HTTP/2 support by the end of 2015. According to W3Techs, as of August 2019, 39.3% of the top 10 million websites supported HTTP/2. Its proposed successor is HTTP/3, a forthcoming new major revision of the HTTP protocol that builds on the concepts established by HTTP/2. The working group charter mentions several goals and issues of concern: The proposed changes do not require any changes to how existing web applications work, but new applications can take advantage of new features for increased speed. HTTP/2 leaves most of HTTP 1.1's high-level syntax, such as methods, status codes, header fields, and URIs, the same. What is new is how the data is framed and transported between the client and the server. Websites that are efficient minimize the number of requests required to render an entire page by minifying (reducing the amount of code and packing smaller pieces of code into bundles, without reducing its ability to function) resources such as images and scripts. However, minification is not necessarily convenient nor efficient and may still require separate HTTP connections to get the page and the minified resources. HTTP/2 allows the server to 'push' content, that is, to respond with data for more queries than the client requested. This allows the server to supply data it knows a web browser will need to render a web page, without waiting for the browser to examine the first response, and without the overhead of an additional request cycle. Additional performance improvements in the first draft of HTTP/2 (which was a copy of SPDY) come from multiplexing of requests and responses to avoid some of the head-of-line blocking problem in HTTP 1 (even when HTTP pipelining is used), header compression, and prioritization of requests. However, as HTTP/2 runs on top of a single TCP connection there is still potential for head-of-line blocking to occur if TCP packets are lost or delayed in transmission.HTTP/2 no longer supports HTTP 1.1's chunked transfer encoding mechanism, as it provides its own, more efficient, mechanisms for data streaming.