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---
c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
SPDX-License-Identifier: curl
Title: curl_global_sslset
Section: 3
Source: libcurl
See-also:
- curl_global_init (3)
- libcurl (3)
---
# NAME
curl_global_sslset - Select SSL backend to use with libcurl
# SYNOPSIS
~~~c
#include <curl/curl.h>
CURLsslset curl_global_sslset(curl_sslbackend id,
const char *name,
const curl_ssl_backend ***avail);
~~~
# DESCRIPTION
This function configures at runtime which SSL backend to use with
libcurl. This function can only be used to select an SSL backend once, and it
must be called **before** curl_global_init(3).
The backend can be identified by the *id*
(e.g. **CURLSSLBACKEND_OPENSSL**). The backend can also be specified via the
*name* parameter for a case insensitive match (passing
**CURLSSLBACKEND_NONE** as *id*). If both *id* and *name* are
specified, the *name* is ignored.
If neither *id* nor *name* are specified, the function fails with
**CURLSSLSET_UNKNOWN_BACKEND** and set the *avail* pointer to the
NULL-terminated list of available backends. The available backends are those
that this particular build of libcurl supports.
Since libcurl 7.60.0, the *avail* pointer is always set to the list of
alternatives if non-NULL.
Upon success, the function returns **CURLSSLSET_OK**.
If the specified SSL backend is not available, the function returns
**CURLSSLSET_UNKNOWN_BACKEND** and sets the *avail* pointer to a
NULL-terminated list of available SSL backends. In this case, you may call the
function again to try to select a different backend.
The SSL backend can be set only once. If it has already been set, a subsequent
attempt to change it results in a **CURLSSLSET_TOO_LATE** getting returned.
This function is thread-safe since libcurl 7.84.0 if
curl_version_info(3) has the CURL_VERSION_THREADSAFE feature bit set
(most platforms).
If this is not thread-safe, you must not call this function when any other
thread in the program (i.e. a thread sharing the same memory) is running.
This does not just mean no other thread that is using libcurl.
# OpenSSL
The name "OpenSSL" is used for all versions of OpenSSL and its associated
forks/flavors in this function. OpenSSL, BoringSSL, libressl, quictls and
AmiSSL are all supported by libcurl, but in the eyes of
curl_global_sslset(3) they are all just "OpenSSL". They all mostly
provide the same API.
curl_version_info(3) can return more specific info about the exact
OpenSSL flavor and version number is use.
# struct
~~~c
typedef struct {
curl_sslbackend id;
const char *name;
} curl_ssl_backend;
typedef enum {
CURLSSLBACKEND_NONE = 0,
CURLSSLBACKEND_OPENSSL = 1, /* or one of its forks */
CURLSSLBACKEND_GNUTLS = 2,
CURLSSLBACKEND_NSS = 3,
CURLSSLBACKEND_GSKIT = 5, /* deprecated */
CURLSSLBACKEND_POLARSSL = 6, /* deprecated */
CURLSSLBACKEND_WOLFSSL = 7,
CURLSSLBACKEND_SCHANNEL = 8,
CURLSSLBACKEND_SECURETRANSPORT = 9,
CURLSSLBACKEND_AXTLS = 10, /* deprecated */
CURLSSLBACKEND_MBEDTLS = 11,
CURLSSLBACKEND_MESALINK = 12, /* deprecated */
CURLSSLBACKEND_BEARSSL = 13,
CURLSSLBACKEND_RUSTLS = 14
} curl_sslbackend;
~~~
# EXAMPLE
~~~c
int main(void)
{
int i;
/* choose a specific backend */
curl_global_sslset(CURLSSLBACKEND_WOLFSSL, NULL, NULL);
/* list the available ones */
const curl_ssl_backend **list;
curl_global_sslset(CURLSSLBACKEND_NONE, NULL, &list);
for(i = 0; list[i]; i++)
printf("SSL backend #%d: '%s' (ID: %d)\n",
i, list[i]->name, list[i]->id);
}
~~~
# AVAILABILITY
This function was added in libcurl 7.56.0. Before this version, there was no
support for choosing SSL backends at runtime.
# RETURN VALUE
If this function returns *CURLSSLSET_OK*, the backend was successfully
selected.
If the chosen backend is unknown (or support for the chosen backend has not
been compiled into libcurl), the function returns
*CURLSSLSET_UNKNOWN_BACKEND*.
If the backend had been configured previously, or if curl_global_init(3)
has already been called, the function returns *CURLSSLSET_TOO_LATE*.
If this libcurl was built completely without SSL support, with no backends at
all, this function returns *CURLSSLSET_NO_BACKENDS*.
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