1 c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 2 SPDX-License-Identifier: curl 3 Long: http3 4 Tags: Versions 5 Protocols: HTTP 6 Added: 7.66.0 7 Mutexed: http1.1 http1.0 http2 http2-prior-knowledge http3-only 8 Requires: HTTP/3 9 Help: Use HTTP v3 10 See-also: http1.1 http2 11 Category: http 12 Example: --http3 $URL 13 Multi: mutex 14 Experimental: yes 15 --- 16 Tells curl to try HTTP/3 to the host in the URL, but fallback to earlier 17 HTTP versions if the HTTP/3 connection establishment fails. HTTP/3 is only 18 available for HTTPS and not for HTTP URLs. 19 20 This option allows a user to avoid using the Alt-Svc method of upgrading to 21 HTTP/3 when you know that the target speaks HTTP/3 on the given host and port. 22 23 When asked to use HTTP/3, curl issues a separate attempt to use older HTTP 24 versions with a slight delay, so if the HTTP/3 transfer fails or is slow, curl 25 still tries to proceed with an older HTTP version. 26 27 Use --http3-only for similar functionality *without* a fallback. 28