/*
 * util/rtt.c - UDP round trip time estimator for resend timeouts.
 *
 * 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 COPYRIGHT
 * HOLDER 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 data type and functions to help estimate good
 * round trip times for UDP resend timeout values.
 */
#include "config.h"
#include "util/rtt.h"
#include "iterator/iterator.h"

/* overwritten by config: infra_cache_min_rtt: */
int RTT_MIN_TIMEOUT = 50;
/* overwritten by config: infra_cache_max_rtt: */
int RTT_MAX_TIMEOUT = 120000;

/** calculate RTO from rtt information */
static int
calc_rto(const struct rtt_info* rtt)
{
        /* From Stevens, Unix Network Programming, Vol1, 3rd ed., p.598 */
        int rto = rtt->srtt + 4*rtt->rttvar;
        if(rto < RTT_MIN_TIMEOUT)
                rto = RTT_MIN_TIMEOUT;
        if(rto > RTT_MAX_TIMEOUT)
                rto = RTT_MAX_TIMEOUT;
        return rto;
}

void 
rtt_init(struct rtt_info* rtt)
{
        rtt->srtt = 0;
        rtt->rttvar = UNKNOWN_SERVER_NICENESS/4;
        rtt->rto = calc_rto(rtt);
        /* default value from the book is 0 + 4*0.75 = 3 seconds */
        /* first RTO is 0 + 4*0.094 = 0.376 seconds */
}

int 
rtt_timeout(const struct rtt_info* rtt)
{
        return rtt->rto;
}

int 
rtt_unclamped(const struct rtt_info* rtt)
{
        if(calc_rto(rtt) != rtt->rto) {
                /* timeout fallback has happened */
                return rtt->rto;
        }
        /* return unclamped value */
        return rtt->srtt + 4*rtt->rttvar;
}

void 
rtt_update(struct rtt_info* rtt, int ms)
{
        int delta = ms - rtt->srtt;
        rtt->srtt += delta / 8; /* g = 1/8 */
        if(delta < 0)
                delta = -delta; /* |delta| */
        rtt->rttvar += (delta - rtt->rttvar) / 4; /* h = 1/4 */
        rtt->rto = calc_rto(rtt);
}

void 
rtt_lost(struct rtt_info* rtt, int orig)
{
        /* exponential backoff */

        /* if a query succeeded and put down the rto meanwhile, ignore this */
        if(rtt->rto < orig)
                return;

        /* the original rto is doubled, not the current one to make sure
         * that the values in the cache are not increased by lots of
         * queries simultaneously as they time out at the same time */
        orig *= 2;
        if(rtt->rto <= orig) {
                rtt->rto = orig;
                if(rtt->rto > RTT_MAX_TIMEOUT)
                        rtt->rto = RTT_MAX_TIMEOUT;
        }
}

int rtt_notimeout(const struct rtt_info* rtt)
{
        return calc_rto(rtt);
}