Tribblix: manual page: CURLINFO_TLS_SSL

CURLINFO_TLS_SSL_PTR(3) Introduction to Library Functions

NAME

CURLINFO_TLS_SESSION, CURLINFO_TLS_SSL_PTR - get TLS session info

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_TLS_SSL_PTR,
struct curl_tlssessioninfo **session);

/* if you need compatibility with libcurl < 7.48.0 use
CURLINFO_TLS_SESSION instead: */

CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_TLS_SESSION,
struct curl_tlssessioninfo **session);

DESCRIPTION

Pass a pointer to a struct curl_tlssessioninfo *. The pointer is
initialized to refer to a struct curl_tlssessioninfo * that contains
an enum indicating the SSL library used for the handshake and a
pointer to the respective internal TLS session structure of this
underlying SSL library.

This option may be useful for example to extract certificate
information in a format convenient for further processing, such as
manual validation. Refer to the LIMITATIONS section.

struct curl_tlssessioninfo {
curl_sslbackend backend;
void *internals;
};

The backend struct member is one of the defines in the
CURLSSLBACKEND_* series: CURLSSLBACKEND_NONE (when built without TLS
support), CURLSSLBACKEND_WOLFSSL, CURLSSLBACKEND_SECURETRANSPORT,
CURLSSLBACKEND_GNUTLS, CURLSSLBACKEND_MBEDTLS, CURLSSLBACKEND_NSS,
CURLSSLBACKEND_OPENSSL or CURLSSLBACKEND_SCHANNEL. (Note that the
OpenSSL forks are all reported as just OpenSSL here.)

The internals struct member points to a TLS library specific pointer
for the active ("in use") SSL connection, with the following
underlying types:

GnuTLS gnutls_session_t

OpenSSL
CURLINFO_TLS_SESSION(3): SSL_CTX *

CURLINFO_TLS_SSL_PTR(3): SSL * Since 7.48.0 the internals
member can point to these other SSL backends as well:

mbedTLS
mbedTLS_ssl_context *

Secure Channel
CtxtHandle *

Secure Transport
SSLContext *

wolfSSL
SSL *

If the internals pointer is NULL then either the SSL backend is not
supported, an SSL session has not yet been established or the
connection is no longer associated with the easy handle (e.g.
curl_easy_perform(3) has returned).

LIMITATIONS

This option has some limitations that could make it unsafe when it
comes to the manual verification of certificates.

This option only retrieves the first in-use SSL session pointer for
your easy handle, however your easy handle may have more than one
in-use SSL session if using FTP over SSL. That is because the FTP
protocol has a control channel and a data channel and one or both may
be over SSL. Currently there is no way to retrieve a second in-use
SSL session associated with an easy handle.

This option has not been thoroughly tested with clear text protocols
that can be upgraded/downgraded to/from SSL: FTP, SMTP, POP3, IMAP
when used with CURLOPT_USE_SSL(3). Though you can to retrieve the SSL
pointer, it is possible that before you can do that, data (including
auth) may have already been sent over a connection after it was
upgraded.

Renegotiation. If unsafe renegotiation or renegotiation in a way that
the certificate is allowed to change is allowed by your SSL library
this may occur and the certificate may change, and data may continue
to be sent or received after renegotiation but before you are able to
get the (possibly) changed SSL pointer, with the (possibly) changed
certificate information.

Instead of using this option to poll for certificate changes use
CURLOPT_SSL_CTX_FUNCTION(3) to set a verification callback, if
supported. That is safer and does not suffer from any of the
problems above.

How are you using this option? Are you affected by any of these
limitations? Please let us know by making a comment at
https://github.com/curl/curl/issues/685

PROTOCOLS

This functionality affects all TLS based protocols: HTTPS, FTPS,
IMAPS, POP3S, SMTPS etc.

This option works only with the following TLS backends: BearSSL,
GnuTLS, OpenSSL, Schannel, Secure Transport, mbedTLS and wolfSSL

EXAMPLE

#include <curl/curl.h>
#include <openssl/ssl.h>

CURL *curl;
static size_t wf(void *ptr, size_t size, size_t nmemb, void *stream)
{
const struct curl_tlssessioninfo *info = NULL;
CURLcode res = curl_easy_getinfo(curl, CURLINFO_TLS_SSL_PTR, &info);
if(info && !res) {
if(CURLSSLBACKEND_OPENSSL == info->backend) {
printf("OpenSSL ver. %s\n", SSL_get_version((SSL*)info->internals));
}
}
return size * nmemb;
}

int main(int argc, char **argv)
{
CURLcode res;
curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, wf);
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
return res;
}

HISTORY

This option supersedes CURLINFO_TLS_SESSION(3) which was added in
7.34.0. This option is exactly the same as that option except in the
case of OpenSSL.

AVAILABILITY

Added in curl 7.48.0

RETURN VALUE

curl_easy_getinfo(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).