DOKK / manpages / debian 10 / libcurl4-doc / CURLOPT_SSL_ENABLE_NPN.3.en
CURLOPT_SSL_ENABLE_NPN(3) curl_easy_setopt options CURLOPT_SSL_ENABLE_NPN(3)

CURLOPT_SSL_ENABLE_NPN - enable NPN

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_ENABLE_NPN, long npn);

Pass a long as parameter, 0 or 1 where 1 is for enable and 0 for disable. This option enables/disables NPN in the SSL handshake (if the SSL backend libcurl is built to use supports it), which can be used to negotiate http2.

1, enabled

HTTP

CURL *curl = curl_easy_init();
if(curl) {

curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
curl_easy_setopt(curl, CURLOPT_SSL_ENABLE_NPN, 1L);
ret = curl_easy_perform(curl);
curl_easy_cleanup(curl); }

Added in 7.36.0

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

CURLOPT_SSL_ENABLE_ALPN(3), CURLOPT_SSL_OPTIONS(3),

May 31, 2017 libcurl 7.64.0