---

c: Copyright (C) Daniel Stenberg, daniel@haxx.se, et al. SPDX-License-Identifier: curl Title: CURLOPT_SSL_ENABLE_ALPN Section: 3 Source: libcurl See-also:

• CURLOPT_SSL_ENABLE_NPN (3)
• CURLOPT_SSL_OPTIONS (3) Protocol:
• TLS TLS-backend:
• All Added-in: 7.36.0

---

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%

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%

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).