/*
 * \brief  Utilities for handling server-side session policies
 * \author Norman Feske
 * \date   2011-09-13
 */

/*
 * Copyright (C) 2011-2013 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU General Public License version 2.
 */

#ifndef _INCLUDE__OS__SESSION_POLICY_H_
#define _INCLUDE__OS__SESSION_POLICY_H_

#include <util/arg_string.h>
#include <os/config.h>

namespace Genode {
	
	class Session_label;
	class Session_policy;
}


class Genode::Session_label
{
	public:

		enum { MAX_LEN = 128 };

	private:

		char _buf[MAX_LEN];

	public:

		Session_label() { _buf[0] = 0; }

		/**
		 * Constructor
		 *
		 * \param args  session arguments as null-terminated string
		 */
		explicit Session_label(char const *args)
		{
			Arg_string::find_arg(args, "label").string(_buf, sizeof(_buf),
			                                           "<undefined>");
		}

		char const *string() const { return _buf; }
};


/**
 * Query server-side policy for a session request
 */
class Genode::Session_policy : public Xml_node
{
	public:

		/**
		 * Exception type
		 */
		class No_policy_defined { };

	private:

		/**
		 * Returns true if the start of the label matches the specified
		 * match string
		 */
		static bool _label_matches(Session_label const &label, char const *match) {
			return strcmp(label.string(), match, strlen(match)) == 0; }

		/**
		 * Query session policy from session label
		 */
		static Xml_node _query_policy(Session_label const &label)
		{
			/* find index of policy node that matches best */
			int best_match = -1;
			try {
				unsigned label_len = 0;
				Xml_node policy = config()->xml_node().sub_node();

				for (int i = 0;; i++, policy = policy.next()) {

					if (!policy.has_type("policy"))
						continue;

					/* label attribute from policy node */
					char policy_label[Session_label::MAX_LEN];
					policy.attribute("label").value(policy_label,
					                                sizeof(policy_label));

					if (!_label_matches(label, policy_label)
					 || strlen(policy_label) < label_len)
						continue;

					label_len = strlen(policy_label);
					best_match = i;
				}
			} catch (...) { }

			if (best_match != -1)
				return config()->xml_node().sub_node(best_match);

			throw No_policy_defined();
		}

	public:

		/**
		 * Constructor
		 *
		 * \param args  session arguments
		 *
		 * \throw No_policy_defined  if the server configuration has no
		 *                           policy defined for the session
		 *                           request
		 *
		 * On construction, the 'Session_policy' looks up the 'policy' XML
		 * node that matches the label provided as argument. The
		 * server-side policies are defined in one or more policy subnodes
		 * of the server's 'config' node. Each policy node has a label
		 * attribute. If the policy label matches the first part of the
		 * label delivered as session argument, the policy matches. If
		 * multiple policies match, the one with the largest label is
		 * selected.
		 */
		explicit Session_policy(Session_label const &label)
		: Xml_node(_query_policy(label)) { }
};

#endif /* _INCLUDE__OS__SESSION_POLICY_H_ */