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.\" generated by cd2nroff 0.1 from CURLOPT_SSL_ENABLE_ALPN.md
.TH CURLOPT_SSL_ENABLE_ALPN 3 "2025-06-27" libcurl
.SH NAME
CURLOPT_SSL_ENABLE_ALPN \- Application Layer Protocol Negotiation
.SH SYNOPSIS
.nf
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_ENABLE_ALPN, long npn);
.fi
.SH DESCRIPTION
Pass a long as parameter, 0 or 1 where 1 is for enable and 0 for disable. This
option enables/disables ALPN in the SSL handshake (if the SSL backend libcurl
is built to use supports it), which can be used to negotiate http2.
.SH DEFAULT
1, enabled
.SH PROTOCOLS
This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.
All TLS backends support this option.
.SH EXAMPLE
.nf
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode res;
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
curl_easy_setopt(curl, CURLOPT_SSL_ENABLE_ALPN, 0L);
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
.fi
.SH AVAILABILITY
Added in curl 7.36.0
.SH RETURN VALUE
\fIcurl_easy_setopt(3)\fP returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non\-zero means an error occurred, see
\fIlibcurl\-errors(3)\fP.
.SH SEE ALSO
.BR CURLOPT_SSL_ENABLE_NPN (3),
.BR CURLOPT_SSL_OPTIONS (3)