CURLOPT_SSL_ENABLE_NPN(3) Library Functions Manual CURLOPT_SSL_ENABLE_NPN(3) NAME CURLOPT_SSL_ENABLE_NPN - use NPN SYNOPSIS #include CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_ENABLE_NPN, long npn); DESCRIPTION Deprecated since 7.86.0. Setting this option has no function. 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. 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_NPN, 1L); res = curl_easy_perform(curl); curl_easy_cleanup(curl); } } DEPRECATED Deprecated since 7.86.0. 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_ALPN(3), CURLOPT_SSL_OPTIONS(3) libcurl 2025-02-13 CURLOPT_SSL_ENABLE_NPN(3)