1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_SSL_ENABLE_ALPN
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_SSL_ENABLE_NPN (3)
9  - CURLOPT_SSL_OPTIONS (3)
10Protocol:
11  - TLS
12TLS-backend:
13  - All
14Added-in: 7.36.0
15---
16
17# NAME
18
19CURLOPT_SSL_ENABLE_ALPN - Application Layer Protocol Negotiation
20
21# SYNOPSIS
22
23~~~c
24#include <curl/curl.h>
25
26CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_ENABLE_ALPN, long npn);
27~~~
28
29# DESCRIPTION
30
31Pass a long as parameter, 0 or 1 where 1 is for enable and 0 for disable. This
32option enables/disables ALPN in the SSL handshake (if the SSL backend libcurl
33is built to use supports it), which can be used to negotiate http2.
34
35# DEFAULT
36
371, enabled
38
39# %PROTOCOLS%
40
41# EXAMPLE
42
43~~~c
44int main(void)
45{
46  CURL *curl = curl_easy_init();
47  if(curl) {
48    CURLcode res;
49    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
50    curl_easy_setopt(curl, CURLOPT_SSL_ENABLE_ALPN, 0L);
51    res = curl_easy_perform(curl);
52    curl_easy_cleanup(curl);
53  }
54}
55~~~
56
57# %AVAILABILITY%
58
59# RETURN VALUE
60
61Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
62