Initial draft of a TLS abstraction layer based on GNU TLS.

This adds a tls_t that looks a bit like a socket, but can turn
on and off tls. The idea would be to plug this into the xmpp_conn_t
and use it iff the connection is in TLS mode.

src/tls.h

@@ -0,0 +1,40 @@
+/* tls.h
+** libstrophe XMPP client library -- TLS abstraction header
+**
+** Copyright (C) 2005 OGG, LCC. All rights reserved.
+**
+**  This software is provided AS-IS with no warranty, either express
+**  or implied.
+**
+**  This software is distributed under license and may not be copied,
+**  modified or distributed except as expressly authorized under the
+**  terms of the license contained in the file LICENSE.txt in this
+**  distribution.
+*/
+
+#ifndef __LIBSTROPHE_TLS_H__
+#define __LIBSTROPHE_TLS_H__
+
+#include <gnutls/gnutls.h>
+#include "common.h"
+#include "sock.h"
+
+typedef struct _tls tls_t;
+
+void tls_initialize(void);
+void tls_shutdown(void);
+
+tls_t *tls_new(xmpp_ctx_t *ctx, sock_t sock);
+void tls_free(tls_t *tls);
+
+int tls_setcredentials(tls_t *tls, const char *cafilename);
+
+int tls_start(tls_t *tls);
+int tls_stop(tls_t *tls);
+
+int tls_error(tls_t *tls);
+
+int tls_read(tls_t *tls, void * const buff, const size_t len);
+int tls_write(tls_t *tls, const void * const buff, const size_t len);
+
+#endif /* __LIBSTROPHE_TLS_H__ */