CURLINFO_TLS_SSL_PTR(3) curl_easy_getinfo options CURLINFO_TLS_SSL_PTR(3)
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 will
be initialized to refer to a 'struct curl_tlssessioninfo *' that will
contain 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_GSKIT, CURLSSLBACKEND_MBEDTLS,
CURLSSLBACKEND_NSS, CURLSSLBACKEND_OPENSSL, CURLSSLBACKEND_SCHANNEL or
CURLSSLBACKEND_MESALINK. (Note that the OpenSSL forks are all reported
as just OpenSSL here.)
The internals struct member will point to a TLS library specific
pointer for the active ("in use") SSL connection, with the following
underlying types:
GnuTLS gnutls_session_t
gskit gsk_handle
NSS PRFileDesc *
OpenSSL
CURLINFO_TLS_SESSION: SSL_CTX *
CURLINFO_TLS_SSL_PTR: 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 *
MesaLink
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 (eg
curl_easy_perform 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 plaintext protocols
that can be upgraded/downgraded to/from SSL: FTP, SMTP, POP3, IMAP when
used with _USE_SSL§ion=3">CURLOPT_USE_SSL(3). Though you will be able to retrieve the
SSL pointer, it's 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.
If you are using OpenSSL or wolfSSL then _SSL_CTX_FUNCTION§ion=3">CURLOPT_SSL_CTX_FUNCTION(3)
can be used to set a certificate verification callback in the CTX. That
is safer than using this option to poll for certificate changes and
doesn't suffer from any of the problems above. There is currently no
way in libcurl to set a verification callback for the other SSL
backends.
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
All TLS-based
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;
}
AVAILABILITY
Added in 7.48.0.
This option supersedes _TLS_SESSION§ion=3">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.
RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION
if not.
SEE ALSO
curl_easy_getinfo(3), curl_easy_setopt(3), CURLINFO_TLS_SESSION(3),
libcurl 7.77.0 November 4, 2020 CURLINFO_TLS_SSL_PTR(3)
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