NAME

       CURLOPT_SSL_ENABLE_ALPN - Application Layer Protocol Negotiation

SYNOPSIS

       #include <curl/curl.h>

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

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.

DEFAULT

       1, enabled

PROTOCOLS

       This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

       All TLS backends support this option.

EXAMPLE

       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);
         }
       }

AVAILABILITY

       Added in curl 7.36.0

RETURN VALUE

       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3).

SEE ALSO

       CURLOPT_SSL_ENABLE_NPN(3), CURLOPT_SSL_OPTIONS(3)

libcurl                                            2025-03-05                         CURLOPT_SSL_ENABLE_ALPN(3)