| --- | |
| c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. | |
| SPDX-License-Identifier: curl | |
| Long: http3 | |
| Tags: Versions | |
| Protocols: HTTP | |
| Added: 7.66.0 | |
| Mutexed: http1.1 http1.0 http2 http2-prior-knowledge http3-only | |
| Requires: HTTP/3 | |
| Help: Use HTTP v3 | |
| Category: http | |
| Multi: mutex | |
| See-also: | |
| - http1.1 | |
| - http2 | |
| Example: | |
| - --http3 $URL | |
| --- | |
| # `--http3` | |
| Attempt HTTP/3 to the host in the URL, but fallback to earlier HTTP versions | |
| if the HTTP/3 connection establishment fails or is slow. HTTP/3 is only | |
| available for HTTPS and not for HTTP URLs. | |
| This option allows a user to avoid using the Alt-Svc method of upgrading to | |
| HTTP/3 when you know or suspect that the target speaks HTTP/3 on the given | |
| host and port. | |
| When asked to use HTTP/3, curl issues a separate attempt to use older HTTP | |
| versions with a slight delay, so if the HTTP/3 transfer fails or is slow, curl | |
| still tries to proceed with an older HTTP version. The fallback performs the | |
| regular negotiation between HTTP/1 and HTTP/2. | |
| Use --http3-only for similar functionality *without* a fallback. |