Tribblix: manual page: curl_global

curl_global_sslset(3) Introduction to Library Functions

NAME

curl_global_sslset - select SSL backend to use

SYNOPSIS

#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.

Names
SSL backend names (case-insensitive): BearSSL, GnuTLS, mbedTLS,
OpenSSL, Rustls, Schannel, Secure-Transport, wolfSSL

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 in
use.

struct
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;

PROTOCOLS

This functionality affects all supported protocols

EXAMPLE

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

Added in curl 7.56.0

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.