replace deprecated GnuTLS functions with newer ones if available

closes https://github.com/rsyslog/rsyslog/issues/302

Upstream fix https://github.com/rsyslog/rsyslog/commit/b34c35e38f258935c0e92ca754da097d7f3f0f58

Upstream-Status: Backport
Signed-off-by: Tudor Florea  <tudor.florea@enea.com>

---
 configure.ac       |  2 ++
 runtime/nsd_gtls.c | 21 ++++++++++++++++++---
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/configure.ac b/configure.ac
index 643fc94..56835fb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -763,6 +763,8 @@ AC_ARG_ENABLE(gnutls,
 if test "x$enable_gnutls" = "xyes"; then
 	PKG_CHECK_MODULES(GNUTLS, gnutls >= 1.4.0)
 	AC_DEFINE([ENABLE_GNUTLS], [1], [Indicator that GnuTLS is present])
+        AC_CHECK_LIB(gnutls, gnutls_global_init)
+	AC_CHECK_FUNCS(gnutls_certificate_set_retrieve_function,,)
 fi
 AM_CONDITIONAL(ENABLE_GNUTLS, test x$enable_gnutls = xyes)
 
diff --git a/runtime/nsd_gtls.c b/runtime/nsd_gtls.c
index a763e4b..e127834 100644
--- a/runtime/nsd_gtls.c
+++ b/runtime/nsd_gtls.c
@@ -232,15 +232,26 @@ gtlsLoadOurCertKey(nsd_gtls_t *pThis)
  */
 static int
 gtlsClientCertCallback(gnutls_session session,
-              __attribute__((unused)) const gnutls_datum* req_ca_rdn, int __attribute__((unused)) nreqs,
-              __attribute__((unused)) const gnutls_pk_algorithm* sign_algos, int __attribute__((unused)) sign_algos_length,
-              gnutls_retr_st *st)
+        __attribute__((unused)) const gnutls_datum* req_ca_rdn,
+	int __attribute__((unused)) nreqs,
+        __attribute__((unused)) const gnutls_pk_algorithm* sign_algos,
+	int __attribute__((unused)) sign_algos_length,
+#if HAVE_GNUTLS_CERTIFICATE_SET_RETRIEVE_FUNCTION
+	gnutls_retr2_st* st
+#else
+        gnutls_retr_st *st
+#endif
+	)
 {
 	nsd_gtls_t *pThis;
 
 	pThis = (nsd_gtls_t*) gnutls_session_get_ptr(session);
 
+#if HAVE_GNUTLS_CERTIFICATE_SET_RETRIEVE_FUNCTION
+	st->cert_type = GNUTLS_CRT_X509;
+#else
 	st->type = GNUTLS_CRT_X509;
+#endif
 	st->ncerts = 1;
 	st->cert.x509 = &pThis->ourCert;
 	st->key.x509 = pThis->ourKey;
@@ -1625,7 +1625,11 @@ Connect(nsd_t *pNsd, int family, uchar *port, uchar *host)
 	gnutls_session_set_ptr(pThis->sess, (void*)pThis);
 	iRet = gtlsLoadOurCertKey(pThis); /* first load .pem files */
 	if(iRet == RS_RET_OK) {
+#		if HAVE_GNUTLS_CERTIFICATE_SET_RETRIEVE_FUNCTION 
+		gnutls_certificate_set_retrieve_function(xcred, gtlsClientCertCallback);
+#		else
 		gnutls_certificate_client_set_retrieve_function(xcred, gtlsClientCertCallback);
+#	endif
 	} else if(iRet != RS_RET_CERTLESS) {
 		FINALIZE; /* we have an error case! */
 	}