curl_global_sslset(3) Library Functions Manual curl_global_sslset(3) 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 speci- fied, 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 par- ticular build of libcurl supports. Since libcurl 7.60.0, the avail pointer is always set to the list of alter- natives 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 subse- quent attempt to change it results in a CURLSSLSET_TOO_LATE getting re- turned. 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 only mean no other thread that is using libcurl. Names SSL backend names (case-insensitive): GnuTLS, mbedTLS, OpenSSL, Rustls, Schannel, wolfSSL The name "OpenSSL" is used for all versions of OpenSSL and its associated forks/flavors in this function. AmiSSL, AWS-LC, BoringSSL, LibreSSL, OpenSSL and quictls are all supported by libcurl, but in the eyes of curl_global_sslset(3) they are all called "OpenSSL". They all mostly pro- vide 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, /* deprecated */ CURLSSLBACKEND_AXTLS = 10, /* deprecated */ CURLSSLBACKEND_MBEDTLS = 11, CURLSSLBACKEND_MESALINK = 12, /* deprecated */ CURLSSLBACKEND_BEARSSL = 13, /* deprecated */ 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 se- lected. If the chosen backend is unknown (or support for the chosen backend has not been compiled into libcurl), the function returns CURLSSLSET_UNKNOWN_BACK- END. 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. SEE ALSO curl_global_init(3), libcurl(3) libcurl 2026-08-27 curl_global_sslset(3)
NAME | SYNOPSIS | DESCRIPTION | Names | struct | PROTOCOLS | EXAMPLE | AVAILABILITY | RETURN VALUE | SEE ALSO
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