/*
 * iterator/iterator.c - 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.
 */

#include "config.h"
#include "iterator/iterator.h"
#include "iterator/iter_utils.h"
#include "iterator/iter_hints.h"
#include "services/cache/dns.h"
#include "util/module.h"
#include "util/netevent.h"
#include "util/net_help.h"
#include "util/region-allocator.h"

/** iterator init */
static int 
iter_init(struct module_env* env, int id)
{
	struct iter_env* iter_env = (struct iter_env*)calloc(1,
		sizeof(struct iter_env));
	if(!iter_env) {
		log_err("malloc failure");
		return 0;
	}
	env->modinfo[id] = (void*)iter_env;
	if(!iter_apply_cfg(iter_env, env->cfg)) {
		log_err("iterator: could not apply configuration settings.");
		return 0;
	}
	return 1;
}

/** iterator deinit */
static void 
iter_deinit(struct module_env* env, int id)
{
	struct iter_env* iter_env;
	if(!env || !env->modinfo)
		return;
	iter_env = (struct iter_env*)env->modinfo[id];
	free(iter_env->target_fetch_policy);
	hints_delete(iter_env->hints);
	if(iter_env)
		free(iter_env);
}

/** new query for iterator */
static int
iter_new(struct module_qstate* qstate, int id)
{
	struct iter_qstate* iq = (struct iter_qstate*)region_alloc(
		qstate->region, sizeof(struct iter_qstate));
	qstate->minfo[id] = iq;
	if(!iq) 
		return 0;
	memset(iq, 0, sizeof(*iq));
	iq->state = INIT_REQUEST_STATE;
	iq->final_state = FINISHED_STATE;
	iq->prepend_list = NULL;
	iq->prepend_last = NULL;
	iq->dp = NULL;
	iq->current_target = NULL;
	iq->num_target_queries = -1; /* default our targetQueries counter. */
	iq->num_current_queries = 0;
	iq->query_restart_count = 0;
	iq->referral_count = 0;
	iq->priming_stub = 0;
	outbound_list_init(&iq->outlist);
	return 1;
}

/** new query for iterator in forward mode */
static int
fwd_new(struct module_qstate* qstate, int id)
{
	struct iter_qstate* iq = (struct iter_qstate*)region_alloc(
		qstate->region, sizeof(struct iter_qstate));
	struct module_env* env = qstate->env;
	struct iter_env* ie = (struct iter_env*)env->modinfo[id];
	struct outbound_entry* e;
	uint16_t flags = 0; /* opcode=query, no flags */
	int dnssec = 1; /* always get dnssec info */
	qstate->minfo[id] = iq;
	if(!iq) 
		return 0;
	memset(iq, 0, sizeof(*iq));
	outbound_list_init(&iq->outlist);
	if(qstate->qinfo.has_cd)
		flags |= BIT_CD;
	e = (*env->send_query)(qstate->qinfo.qname, qstate->qinfo.qname_len,
		qstate->qinfo.qtype, qstate->qinfo.qclass, flags, dnssec, 
		&ie->fwd_addr, ie->fwd_addrlen, qstate);
	if(!e) 
		return 0;
	outbound_list_insert(&iq->outlist, e);
	qstate->ext_state[id] = module_wait_reply;
	return 1;
}

/** iterator handle reply from authoritative server */
static int
iter_handlereply(struct module_qstate* qstate, int id,
        struct outbound_entry* ATTR_UNUSED(outbound))
{
	struct module_env* env = qstate->env;
	uint16_t us = qstate->edns.udp_size;
	struct query_info reply_qinfo;
	struct reply_info* reply_msg;
	struct edns_data reply_edns;
	int r;
	if((r=reply_info_parse(qstate->reply->c->buffer, env->alloc, 
		&reply_qinfo, &reply_msg, qstate->scratch, 
		&reply_edns))!=0)
		return 0;

	qstate->edns.edns_version = EDNS_ADVERTISED_VERSION;
	qstate->edns.udp_size = EDNS_ADVERTISED_SIZE;
	qstate->edns.ext_rcode = 0;
	qstate->edns.bits &= EDNS_DO;
	if(!reply_info_answer_encode(&reply_qinfo, reply_msg, 0, 
		qstate->query_flags, qstate->buf, 0, 0, 
		qstate->scratch, us, &qstate->edns))
		return 0;
	dns_cache_store_msg(qstate->env, &reply_qinfo, qstate->query_hash, 
		reply_msg);
	qstate->ext_state[id] = module_finished;
	return 1;
}

/** perform forwarder functionality */
static void 
perform_forward(struct module_qstate* qstate, enum module_ev event, int id,
	struct outbound_entry* outbound)
{
	verbose(VERB_ALGO, "iterator: forwarding");
	if(event == module_event_new) {
		if(!fwd_new(qstate, id))
			qstate->ext_state[id] = module_error;
		return;
	}
	/* it must be a query reply */
	if(!outbound) {
		verbose(VERB_ALGO, "query reply was not serviced");
		qstate->ext_state[id] = module_error;
		return;
	}
	if(event == module_event_timeout || event == module_event_error) {
		qstate->ext_state[id] = module_error;
		return;
	}
	if(event == module_event_reply) {
		if(!iter_handlereply(qstate, id, outbound))
			qstate->ext_state[id] = module_error;
		return;
	}
	log_err("bad event for iterator[forwarding]");
	qstate->ext_state[id] = module_error;
}

/**
 * Transition to the next state. This can be used to advance a currently
 * processing event. It cannot be used to reactivate a forEvent.
 *
 * @param qstate: query state
 * @param iq: iterator query state
 * @param nextstate The state to transition to.
 * @return true. This is so this can be called as the return value for the
 *         actual process*State() methods. (Transitioning to the next state
 *         implies further processing).
 */
static int
next_state(struct module_qstate* qstate, struct iter_qstate* iq, 
	enum iter_state nextstate)
{
	/* If transitioning to a "response" state, make sure that there is a
	 * response */
	if(iter_state_is_responsestate(nextstate)) {
		if(qstate->reply == NULL) {
			log_err("transitioning to response state sans "
				"response.");
		}
	}
	iq->state = nextstate;
	return 1;
}

/**
 * Transition an event to its final state. Final states always either return
 * a result up the module chain, or reactivate a dependent event. Which
 * final state to transtion to is set in the module state for the event when
 * it was created, and depends on the original purpose of the event.
 *
 * The response is stored in the qstate->buf buffer.
 *
 * @param qstate: query state
 * @param iq: iterator query state
 * @return false. This is so this method can be used as the return value for
 *         the processState methods. (Transitioning to the final state
 */
static int
final_state(struct module_qstate* qstate, struct iter_qstate* iq)
{
	return next_state(qstate, iq, iq->final_state);
}

/**
 * Return an error to the client
 */
static int
error_response(struct module_qstate* qstate, struct iter_qstate* iq, int rcode)
{
	log_info("err response %s", ldns_lookup_by_id(ldns_rcodes, rcode)?
		ldns_lookup_by_id(ldns_rcodes, rcode)->name:"??");
	qinfo_query_encode(qstate->buf, &qstate->qinfo);
	LDNS_RCODE_SET(ldns_buffer_begin(qstate->buf), rcode);
	LDNS_QR_SET(ldns_buffer_begin(qstate->buf));
	return final_state(qstate, iq);
}

/** 
 * Process the initial part of the request handling. This state roughly
 * corresponds to resolver algorithms steps 1 (find answer in cache) and 2
 * (find the best servers to ask).
 *
 * Note that all requests start here, and query restarts revisit this state.
 *
 * This state either generates: 1) a response, from cache or error, 2) a
 * priming event, or 3) forwards the request to the next state (init2,
 * generally).
 *
 * @param qstate: query state.
 * @param iq: iterator query state.
 * @param ie: iterator shared global environment.
 * @return true if the event needs more request processing immediately,
 *         false if not.
 */
static int
processInitRequest(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	int d;
	uint8_t* delname;
	size_t delnamelen;
	log_nametypeclass("resolving", qstate->qinfo.qname, 
		qstate->qinfo.qtype, qstate->qinfo.qclass);
	/* check effort */

	/* We enforce a maximum number of query restarts. This is primarily a
	 * cheap way to prevent CNAME loops. */
	if(iq->query_restart_count > MAX_RESTART_COUNT) {
		verbose(VERB_DETAIL, "request has exceeded the maximum number"
			" of query restarts with %d", iq->query_restart_count);
		return error_response(qstate, iq, LDNS_RCODE_SERVFAIL);
	}

	/* We enforce a maximum recursion/dependency depth -- in general, 
	 * this is unnecessary for dependency loops (although it will 
	 * catch those), but it provides a sensible limit to the amount 
	 * of work required to answer a given query. */
	d = module_subreq_depth(qstate);
	verbose(VERB_ALGO, "request has dependency depth of %d", d);
	if(d > ie->max_dependency_depth) {
		verbose(VERB_DETAIL, "request has exceeded the maximum "
			"dependency depth with depth of %d", d);
		return error_response(qstate, iq, LDNS_RCODE_SERVFAIL);
	}

	/* Resolver Algorithm Step 1 -- Look for the answer in local data. */

	/* This either results in a query restart (CNAME cache response), a
	 * terminating response (ANSWER), or a cache miss (null). */
	
	/* TODO: cache lookup */
	/* lookup qname, qtype qclass */

	/* TODO: handle positive cache response */
		/* calc response type (from cache msg) */
		/* if cname */
			/* handle cname, overwrite qname, restart */
		/* it is an answer, response, to final state */
	
	/* TODO attempt to forward the request */

	/* TODO attempt to find a covering DNAME in the cache */

	/* Resolver Algorithm Step 2 -- find the "best" servers. */

	/* first, adjust for DS queries. To avoid the grandparent problem, 
	 * we just look for the closest set of server to the parent of qname.
	 */
	delname = qstate->qinfo.qname;
	delnamelen = qstate->qinfo.qname_len;
	if(qstate->qinfo.qtype == LDNS_RR_TYPE_DS && delname[0] != 0) {
		/* do not adjust root label */
		size_t lablen = delname[0] + 1;
		delname += lablen;
		delnamelen -= lablen;
	}
	
	/* Lookup the delegation in the cache. If null, then the cache needs 
	 * to be primed for the qclass. */
	iq->dp = dns_cache_find_delegation(qstate->env, delname, delnamelen,
		qstate->qinfo.qclass, qstate->region);

	/* If the cache has returned nothing, then we have a root priming
	 * situation. */
	if(iq->dp == NULL) {
		/* Note that the result of this will set a new
		 * DelegationPoint based on the result of priming. */

		 /* TODO
		if(!prime_root(qstate, iq, ie, qstate->qinfo.qclass))
			return error_response(qstate, iq, LDNS_RCODE_SERVFAIL);
			*/

		/* priming creates an sends a subordinate query, with 
		 * this query as the parent. So further processing for 
		 * this event will stop until reactivated by the results 
		 * of priming. */
		return false;
	}

	/* Reset the RD flag. If this is a query restart, then the RD 
	 * will have been turned off. */
	 /*
	 TODO store original flags and original qinfo 
	qstate->query_flags |= (qstate->orig_query_flags & BIT_RD);
	*/

	/* Otherwise, set the current delegation point and move on to the 
	 * next state. */
	return next_state(qstate, iq, INIT_REQUEST_2_STATE);
}

#if 0
/** TODO */
static int
processInitRequest2(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	return 0;
}

/** TODO */
static int
processInitRequest3(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	return 0;
}

/** TODO */
static int
processQueryTargets(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	return 0;
}

/** TODO */
static int
processQueryResponse(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	return 0;
}

/** TODO */
static int
processPrimeResponse(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	return 0;
}

/** TODO */
static int
processTargetResponse(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	return 0;
}

/** TODO */
static int
processFinished(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	return 0;
}
#endif

/**
 * Handle iterator state.
 * Handle events. This is the real processing loop for events, responsible
 * for moving events through the various states. If a processing method
 * returns true, then it will be advanced to the next state. If false, then
 * processing will stop.
 *
 * @param qstate: query state.
 * @param ie: iterator shared global environment.
 * @param iq: iterator query state.
 */
static void
iter_handle(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	int cont = 1;
	while(cont) {
		verbose(VERB_ALGO, "iter_handle processing q with state %s",
			iter_state_to_string(iq->state));
		switch(iq->state) {
			case INIT_REQUEST_STATE:
				cont = processInitRequest(qstate, iq, ie);
				break;
#if 0
			case INIT_REQUEST_2_STATE:
				cont = processInitRequest2(qstate, iq, ie);
				break;
			case INIT_REQUEST_3_STATE:
				cont = processInitRequest3(qstate, iq, ie);
				break;
			case QUERYTARGETS_STATE:
				cont = processQueryTargets(qstate, iq, ie);
				break;
			case QUERY_RESP_STATE:
				cont = processQueryResponse(qstate, iq, ie);
				break;
			case PRIME_RESP_STATE:
				cont = processPrimeResponse(qstate, iq, ie);
				break;
			case TARGET_RESP_STATE:
				cont = processTargetResponse(qstate, iq, ie);
				break;
			case FINISHED_STATE:
				cont = processFinished(qstate, iq, ie);
				break;
#endif
			default:
				log_warn("iterator: invalid state: %d",
					iq->state);
				cont = 0;
				break;
		}
	}
}

/** 
 * This is the primary entry point for processing request events. Note that
 * this method should only be used by external modules.
 * @param qstate: query state.
 * @param ie: iterator shared global environment.
 * @param iq: iterator query state.
 */
static void
process_request(struct module_qstate* qstate, struct iter_qstate* iq,
	struct iter_env* ie)
{
	/* external requests start in the INIT state, and finish using the
	 * FINISHED state. */
	iq->state = INIT_REQUEST_STATE;
	iq->final_state = FINISHED_STATE;
	verbose(VERB_ALGO, "process_request: new external request event");
	iter_handle(qstate, iq, ie);
}

/** process authoritative server reply */
static void
process_response(struct module_qstate* qstate, struct iter_qstate* iq, 
	struct iter_env* ie, struct outbound_entry* outbound)
{
	verbose(VERB_ALGO, "process_response: new external response event");
	/* TODO outbound: use it for scrubbing and so on */
	iq->state = QUERY_RESP_STATE;
	iter_handle(qstate, iq, ie);
}

/** iterator operate on a query */
static void 
iter_operate(struct module_qstate* qstate, enum module_ev event, int id,
	struct outbound_entry* outbound)
{
	struct iter_env* ie = (struct iter_env*)qstate->env->modinfo[id];
	struct iter_qstate* iq;
	verbose(VERB_ALGO, "iterator[module %d] operate: extstate:%s event:%s", 
		id, strextstate(qstate->ext_state[id]), strmodulevent(event));
	if(ie->fwd_addrlen != 0) {
		perform_forward(qstate, event, id, outbound);
		return;
	}
	/* perform iterator state machine */
	if(event == module_event_new) {
		log_info("iter state machine");
		if(!iter_new(qstate, id)) {
			qstate->ext_state[id] = module_error;
			return;
		}
		iq = (struct iter_qstate*)qstate->minfo[id];
		process_request(qstate, iq, ie);
		return;
	}
	iq = (struct iter_qstate*)qstate->minfo[id];
	if(event == module_event_reply) {
		process_response(qstate, iq, ie, outbound);
		return;
	}
	/* TODO: uhh */

	log_err("bad event for iterator");
	qstate->ext_state[id] = module_error;
}

/** iterator cleanup query state */
static void 
iter_clear(struct module_qstate* qstate, int id)
{
	struct iter_qstate* iq;
	if(!qstate)
		return;
	iq = (struct iter_qstate*)qstate->minfo[id];
	outbound_list_clear(&iq->outlist);
	qstate->minfo[id] = NULL;
}

/**
 * The iterator function block 
 */
static struct module_func_block iter_block = {
	"iterator",
	&iter_init, &iter_deinit, &iter_operate, &iter_clear
};

struct module_func_block* 
iter_get_funcblock()
{
	return &iter_block;
}

const char* 
iter_state_to_string(enum iter_state state)
{
	switch (state)
	{
	case INIT_REQUEST_STATE :
		return "INIT REQUEST STATE";
	case INIT_REQUEST_2_STATE :
		return "INIT REQUEST STATE (stage 2)";
	case INIT_REQUEST_3_STATE:
		return "INIT REQUEST STATE (stage 3)";
	case QUERYTARGETS_STATE :
		return "QUERY TARGETS STATE";
	case PRIME_RESP_STATE :
		return "PRIME RESPONSE STATE";
	case QUERY_RESP_STATE :
		return "QUERY RESPONSE STATE";
	case TARGET_RESP_STATE :
		return "TARGET RESPONSE STATE";
	case FINISHED_STATE :
		return "FINISHED RESPONSE STATE";
	default :
		return "UNKNOWN ITER STATE";
	}
}

int 
iter_state_is_responsestate(enum iter_state s)
{
	switch(s) {
		case INIT_REQUEST_STATE :
		case INIT_REQUEST_2_STATE :
		case INIT_REQUEST_3_STATE :
		case QUERYTARGETS_STATE :
			return 0;
		default:
			break;
	}
	return 1;
}