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curl/docs/DEPRECATE.md
Daniel Stenberg 472f1cbe7e
NPN: remove support for and use of 
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
2022-09-05 07:39:02 +02:00

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Items to be removed from future curl releases

If any of these deprecated features is a cause for concern for you, please email the curl-library mailing list as soon as possible and explain to us why this is a problem for you and how your use case cannot be satisfied properly using a workaround.

NSS

We remove support for building curl with the NSS TLS library in August 2023.

  • There are very few users left who use curl+NSS
  • NSS has very few users outside of curl as well (primarily Firefox)
  • NSS is harder than ever to find documentation for
  • NSS was always "best" used with Red Hat Linux when they provided additional features on top of the regular NSS that is not shipped by the vanilla library

Starting in 7.82.0, building curl to use NSS configure requires the additional flag --with-nss-deprecated in an attempt to highlight these plans.

past removals

  • Pipelining
  • axTLS
  • PolarSSL
  • NPN