/*
 * iterator/iterator.h - iterative resolver DNS query response module
 *
 * Copyright (c) 2007, NLnet Labs. All rights reserved.
 *
 * This software is open source.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 * 
 * Neither the name of the NLNET LABS nor the names of its contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * \file
 *
 * This file contains a module that performs recusive iterative DNS query
 * processing.
 */

#ifndef ITERATOR_ITERATOR_H
#define ITERATOR_ITERATOR_H
#include "services/outbound_list.h"
#include "util/data/msgreply.h"
struct module_func_block;
struct delegpt;
struct iter_hints;
struct iter_forwards;
struct iter_donotq;
struct iter_prep_list;

/** max number of query restarts. Determines max number of CNAME chain. */
#define MAX_RESTART_COUNT       8
/** max number of referrals. Makes sure resolver does not run away */
#define MAX_REFERRAL_COUNT	30
/** how nice is a server without further information, in msec 
 * Equals rtt initial timeout value.
 */
#define UNKNOWN_SERVER_NICENESS 3000
/** maximum timeout before a host is deemed unsuitable, in msec. 
 * After host_ttl this will be timed out and the host will be tried again. 
 * Equals RTT_MAX_TIMEOUT
 */
#define USEFUL_SERVER_TOP_TIMEOUT	120000

/**
 * Global state for the iterator. 
 */
struct iter_env {
	/** 
	 * The hints -- these aren't stored in the cache because they don't 
	 * expire. The hints are always used to "prime" the cache. Note 
	 * that both root hints and stub zone "hints" are stored in this 
	 * data structure.
	 */
	struct iter_hints* hints;

	/** A flag to indicate whether or not we have an IPv6 route */
	int supports_ipv6;

	/** Mapping of forwarding zones to targets. */
	struct iter_forwards* fwds;

	/** A set of inetaddrs that should never be queried. */
	struct iter_donotq* donotq;

	/** The maximum dependency depth that this resolver will pursue. */
	int max_dependency_depth;

	/**
	 * The target fetch policy for each dependency level. This is 
	 * described as a simple number (per dependency level): 
	 *	negative numbers (usually just -1) mean fetch-all, 
	 *	0 means only fetch on demand, and 
	 *	positive numbers mean to fetch at most that many targets.
	 * array of max_dependency_depth+1 size.
	 */
	int* target_fetch_policy;
};

/**
 * State of the iterator for a query.
 */
enum iter_state {
	/**
	 * Externally generated queries start at this state. Query restarts are
	 * reset to this state.
	 */
	INIT_REQUEST_STATE = 0,

	/**
	 * Root priming events reactivate here, most other events pass 
	 * through this naturally as the 2nd part of the INIT_REQUEST_STATE.
	 */
	INIT_REQUEST_2_STATE,

	/**
	 * Stub priming events reactivate here, most other events pass 
	 * through this naturally as the 3rd part of the INIT_REQUEST_STATE.
	 */
	INIT_REQUEST_3_STATE,

	/**
	 * Each time a delegation point changes for a given query or a 
	 * query times out and/or wakes up, this state is (re)visited. 
	 * This state is reponsible for iterating through a list of 
	 * nameserver targets.
	 */
	QUERYTARGETS_STATE,

	/**
	 * Responses to queries start at this state. This state handles 
	 * the decision tree associated with handling responses.
	 */
	QUERY_RESP_STATE,

	/** Responses to priming queries finish at this state. */
	PRIME_RESP_STATE,

	/** Responses that are to be returned upstream end at this state. 
	 * As well as responses to target queries. */
	FINISHED_STATE
};

/**
 * Per query state for the iterator module.
 */
struct iter_qstate {
	/** 
	 * State of the iterator module.
	 * This is the state that event is in or should sent to -- all 
	 * requests should start with the INIT_REQUEST_STATE. All 
	 * responses should start with QUERY_RESP_STATE. Subsequent 
	 * processing of the event will change this state.
	 */
	enum iter_state state;

	/** 
	 * Final state for the iterator module.
	 * This is the state that responses should be routed to once the 
	 * response is final. For externally initiated queries, this 
	 * will be FINISHED_STATE, locally initiated queries will have 
	 * different final states.
	 */
	enum iter_state final_state;

	/** 
	 * The depth of this query, this means the depth of recursion.
	 * This address is needed for another query, which is an address
	 * needed for another query, etc. Original client query has depth 0.
	 */
	int depth;

	/**
	 * The response
	 */
	struct dns_msg* response;

	/** 
	 * This is a list of RRsets that must be prepended to the 
	 * ANSWER section of a response before being sent upstream.
	 */
	struct iter_prep_list* prepend_list;
	/** Last element of the prepend list */
	struct iter_prep_list* prepend_last;

	/** query name used for chasing the results. Initially the same as
	 * the state qinfo, but after CNAMEs this will be different. 
	 * The query info used to elicit the results needed. */
	struct query_info qchase;
	/** query flags to use when chasing the answer (i.e. RD flag) */
	uint16_t chase_flags;

	/** 
	 * This is the current delegation point for an in-progress query. This
	 * object retains state as to which delegation targets need to be
	 * (sub)queried for vs which ones have already been visited.
	 */
	struct delegpt* dp;

	/** Current delegation message - returned for non-RD queries */
	struct dns_msg* deleg_msg;

	/** number of outstanding target sub queries */
	int num_target_queries;

	/** outstanding direct queries */
	int num_current_queries;

	/** the number of times this query has been restarted. */
	int query_restart_count;

	/** the number of times this query as followed a referral. */
	int referral_count;

	/**
	 * This flag, if true, means that this event is a priming query.
	 * In that case priming stub may be set as well.
	 */
	int priming;

	/**
	 * This is flag that, if true, means that this event is 
	 * representing a stub priming query. It is meaningless unless 
	 * the finalState is the PRIMING_RESP_STATE.
	 */
	int priming_stub;

	/** list of pending queries to authoritative servers. */
	struct outbound_list outlist;
};

/**
 * List of prepend items
 */
struct iter_prep_list {
	/** next in list */
	struct iter_prep_list* next;
	/** rrset */
	struct ub_packed_rrset_key* rrset;
};

/**
 * Get the iterator function block.
 * @return: function block with function pointers to iterator methods.
 */
struct module_func_block* iter_get_funcblock();

/**
 * Get iterator state as a string
 * @param state: to convert
 * @return constant string that is printable.
 */
const char* iter_state_to_string(enum iter_state state);

/**
 * See if iterator state is a response state
 * @param s: to inspect
 * @return true if response state.
 */
int iter_state_is_responsestate(enum iter_state s);

#endif /* ITERATOR_ITERATOR_H */