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| c | SPDX-License-Identifier | Long | Tags | Protocols | Added | Mutexed | Requires | Help | Category | Multi | See-also | Example | |||
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| Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. | curl | http3 | Versions | HTTP | 7.66.0 | http1.1 http1.0 http2 http2-prior-knowledge http3-only | HTTP/3 | Use HTTP v3 | http | mutex |
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--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.