curl/docs/libcurl/opts/CURLINFO_TLS_SSL_PTR.3

.\" **************************************************************************
.\" *                                  _   _ ____  _
.\" *  Project                     ___| | | |  _ \| |
.\" *                             / __| | | | |_) | |
.\" *                            | (__| |_| |  _ <| |___
.\" *                             \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
.\" * are also available at https://curl.se/docs/copyright.html.
.\" *
.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
.\" * copies of the Software, and permit persons to whom the Software is
.\" * furnished to do so, under the terms of the COPYING file.
.\" *
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
.\" * KIND, either express or implied.
.\" *
.\" **************************************************************************
.\"
.TH CURLINFO_TLS_SSL_PTR 3 "23 Feb 2016" "libcurl 7.48.0" "curl_easy_getinfo options"
.SH NAME
CURLINFO_TLS_SESSION, CURLINFO_TLS_SSL_PTR \- get TLS session info
.SH SYNOPSIS
.nf
#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);
.SH 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 \fBLIMITATIONS\fP section.

.nf
struct curl_tlssessioninfo {
  curl_sslbackend backend;
  void *internals;
};
.fi

The \fIbackend\fP 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 \fIinternals\fP struct member will point to a TLS library specific pointer
for the active ("in use") SSL connection, with the following underlying types:
.RS
.IP GnuTLS
gnutls_session_t
.IP gskit
gsk_handle
.IP NSS
PRFileDesc *
.IP OpenSSL
CURLINFO_TLS_SESSION: SSL_CTX *

CURLINFO_TLS_SSL_PTR: SSL *
.RE
Since 7.48.0 the \fIinternals\fP member can point to these other SSL backends
as well:
.RS
.IP mbedTLS
mbedtls_ssl_context *
.IP "Secure Channel"
CtxtHandle *
.IP "Secure Transport"
SSLContext *
.IP "wolfSSL"
SSL *
.IP "MesaLink"
SSL *
.RE

If the \fIinternals\fP 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).
.SH 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
\fICURLOPT_USE_SSL(3)\fP. 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 \fICURLOPT_SSL_CTX_FUNCTION(3)\fP 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
.SH PROTOCOLS
All TLS-based
.SH EXAMPLE
.nf
#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;
}
.fi
.SH AVAILABILITY
Added in 7.48.0.

This option supersedes \fICURLINFO_TLS_SESSION(3)\fP which was added in 7.34.0.
This option is exactly the same as that option except in the case of OpenSSL.
.SH RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR curl_easy_getinfo "(3), " curl_easy_setopt "(3), "
.BR CURLINFO_TLS_SESSION "(3), "