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|International standard||Hypertext Transfer Protocol Version 3 (HTTP/3) (draft)|
|Introduced||Internet-Draft as of October 2020[update]|
HTTP semantics are consistent across versions: the same request methods, status codes, and message fields are typically applicable to all versions. The differences are in the mapping of these semantics to underlying transports. Both HTTP/1.1 and HTTP/2 use TCP as their transport. HTTP/3 uses QUIC, a transport layer network protocol developed initially by Google where user space congestion control is used over the User Datagram Protocol (UDP). The switch to QUIC aims to fix a major problem of HTTP/2 called "head-of-line blocking": because the parallel nature of HTTP/2's multiplexing is not visible to TCP's loss recovery mechanisms, a lost or reordered packet causes all active transactions to experience a stall regardless of whether that transaction was impacted by the lost packet. Because QUIC provides native multiplexing, lost packets only impact the streams where data has been lost.
As of October 2020[update], the HTTP/3 protocol is an Internet-Draft and has multiple implementations. According to W3Techs 8% of the top 10 million websites support HTTP/3. Stable versions of Firefox and Chrome support HTTP/3 in its current form, but have it disabled by default. Safari 14, on macOS Big Sur, was the first browser with HTTP/3 enabled by default.
HTTP/3 is an Internet draft adopted by the QUIC working group. The original proposal was named "HTTP/2 Semantics Using The QUIC Transport Protocol", and later named "Hypertext Transfer Protocol (HTTP) over QUIC".
On 28 October 2018 in a mailing list discussion, Mark Nottingham, Chair of the IETF HTTP and QUIC Working Groups, proposed to rename HTTP-over-QUIC to HTTP/3, to "clearly identify it as another binding of HTTP semantics to the wire protocol ... so people understand its separation from QUIC". Nottingham's proposal was accepted by fellow IETF members a few days later in November 2018. The HTTP working group is chartered to assist the QUIC working group during the design of HTTP/3, then assume responsibility for maintenance after publication.
Support for HTTP/3 was added to Chrome (Canary build) in September 2019 and then eventually reached stable builds, but is disabled by a flag. As of 2020 HTTP/3 has non-default support in stable versions of Chrome and Firefox and can be enabled with a configuration change. Experimental support for HTTP/3 was added to Safari Technology Preview on April 8, 2020 and will be officially released with Safari 14 that ships with upcoming iOS 14 and macOS 11.
(disabled by default)
(enabled by default)
|Chrome||Stable build (79)||December 2019||TBA|
|Firefox||Stable build (72.0.1)||January 2020||TBA|
|Safari||Safari Technology Preview 104||April 2020||Safari 14||September 2020|
|Edge||Edge (Canary build)||2020||TBA|
Open source libraries that implement client or server logic for QUIC and HTTP/3 are available.
- Litespeed's Web Server supports HTTP/3 natively.
- Nginx support for HTTP/3 is slated for the 1.19 release. A technology preview of nginx with HTTP/3 support has been released in June 2020.
- Cloudflare distributes an nginx patch integrating the quiche HTTP/3 library into it.
- The Caddy webserver has experimental support for HTTP/3 as of 2.0 beta 17.
There are a number of libraries that implement an older draft of the protocol or Google's versions of QUIC (e.g. Q046 used in Chrome 76), such as nghttp3.
- Bishop, Mike (25 September 2020). Hypertext Transfer Protocol Version 3 (HTTP/3). IETF. I-D draft-ietf-quic-http.
- "Usage of HTTP/3 for websites". World Wide Web Technology Surveys. W3Techs. Retrieved 12 October 2020.
- Shade, Robbie (23 November 2016). HTTP/2 Semantics Using The QUIC Transport Protocol. IETF. I-D draft-shade-quic-http2-mapping.
- Cimpanu, Catalin (12 November 2018). "HTTP-over-QUIC to be renamed HTTP/3 | ZDNet". ZDNet. Retrieved 12 November 2018.
- Nottingham, Mark (28 October 2018). "Identifying our deliverables". IETF Mail Archive.
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- "Apple Developer Documentation". developer.apple.com. Retrieved 23 June 2020.
- Inc, Cloudflare. "Microsoft Edge - HTTP/3 Docs". developers.cloudflare.com. Retrieved 2 May 2020.
- Internet-Drafts that make up the base QUIC specification: quicwg/base-drafts, IETF QUIC WG, 12 November 2019, retrieved 13 November 2019
- "First HTTP/3 with curl". Daniel Stenberg. 5 August 2019. Retrieved 2 October 2019.
- "cURL HTTP3 wiki". Daniel Stenberg. 26 September 2019. Retrieved 2 October 2019.
- "MsQuic is Open Source". 28 April 2020. Retrieved 28 April 2020.
- "LiteSpeed Web Server Release Log". LiteSpeed Web Server Release Log. 17 April 2020. Retrieved 26 June 2020.
- "Milestone nginx-1.19". trac.nginx.org. Retrieved 30 September 2020.
- "Introducing a Technology Preview of NGINX Support for QUIC and HTTP/3". NGINX. 10 June 2020. Retrieved 11 June 2020.
- "Experiment with HTTP/3 using NGINX and quiche". The Cloudflare Blog. 17 October 2019. Retrieved 9 November 2019.
- "Release 2.0 beta 17 · caddyserver/caddy". Github. 13 March 2020. Retrieved 11 August 2020.
- "ngtcp2/nghttp3". 6 August 2020. Retrieved 7 August 2020 – via GitHub.