attribute_manager supports attribute_handler's to handle configuration attributes via plugins

moved resolv.conf editing to a separate plugin (resolv_conf)
extended attribute_provider interface to hand out arbitrary attributes
  moved strongswan.conf based dns/nbns configuration to a plugin (attr)

src/charon/config/attributes/attribute_handler.h

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2009 Martin Willi
+ * Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ *
+ * $Id$
+ */
+
+/**
+ * @defgroup attribute_handler attribute_handler
+ * @{ @ingroup attributes
+ */
+
+#ifndef ATTRIBUTE_HANDLER_H_
+#define ATTRIBUTE_HANDLER_H_
+
+#include <sa/ike_sa.h>
+#include <encoding/payloads/configuration_attribute.h>
+
+typedef struct attribute_handler_t attribute_handler_t;
+
+/**
+ * Interface to handle configuration payload attributes.
+ */
+struct attribute_handler_t {
+	
+	/**
+	 * Handle a configuration attribute.
+	 *
+	 * After receiving a configuration attriubte, it is passed to each
+	 * attribute handler until it is handled.
+	 *
+	 * @param type		type of configuration attribute to handle
+	 * @param data		associated attribute data
+	 * @return			TRUE if attribute handled
+	 */
+	bool (*handle)(attribute_handler_t *this, ike_sa_t *ike_sa,
+				   configuration_attribute_type_t type, chunk_t data);
+	
+	/**
+	 * Release an attribute handled during handle().
+	 *
+	 * A handler that handle()d an attribute gets a call to release() when the
+	 * IKE_SA gets closed. Depending on the implementation, this is required
+	 * to remove the attribute.
+	 */
+	void (*release)(attribute_handler_t *this, ike_sa_t *ike_sa,
+					configuration_attribute_type_t type, chunk_t data);
+};
+
+#endif /* ATTRIBUTE_HANDLER_ @}*/