---
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

~~~c
#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

~~~c
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_SSL_ENABLE_ALPN, 0L);
    result = 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).