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Next Protocol Negotiation is a TLS extension that was created and used for agreeing to use the SPDY protocol (the precursor to HTTP/2) for HTTPS. In the early days of HTTP/2, before the spec was finalized and shipped, the protocol could be enabled using this extension with some servers. curl supports the NPN extension with some TLS backends since then, with a command line option `--npn` and in libcurl with `CURLOPT_SSL_ENABLE_NPN`. HTTP/2 proper is made to use the ALPN (Application-Layer Protocol Negotiation) extension and the NPN extension has no purposes anymore. The HTTP/2 spec was published in May 2015. Today, use of NPN in the wild should be extremely rare and most likely totally extinct. Chrome removed NPN support in Chrome 51, shipped in June 2016. Removed in Firefox 53, April 2017. Closes #9307
19 lines
575 B
Makefile
19 lines
575 B
Makefile
c: Copyright (C) 1998 - 2022, Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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Long: no-npn
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Tags: Versions HTTP/2
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Protocols: HTTPS
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Added: 7.36.0
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Mutexed:
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See-also: no-alpn http2
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Requires: TLS
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Help: Disable the NPN TLS extension
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Category: tls http
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Example: --no-npn $URL
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---
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In curl 7.86.0 and later, curl never uses NPN.
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Disable the NPN TLS extension. NPN is enabled by default if libcurl was built
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with an SSL library that supports NPN. NPN is used by a libcurl that supports
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HTTP/2 to negotiate HTTP/2 support with the server during https sessions.
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