/*
 * $Id: peer_select.c,v 1.134.2.4 2008/07/10 09:48:41 hno Exp $
 *
 * DEBUG: section 44    Peer Selection Algorithm
 * AUTHOR: Duane Wessels
 *
 * SQUID Web Proxy Cache          http://www.squid-cache.org/
 * ----------------------------------------------------------
 *
 *  Squid is the result of efforts by numerous individuals from
 *  the Internet community; see the CONTRIBUTORS file for full
 *  details.   Many organizations have provided support for Squid's
 *  development; see the SPONSORS file for full details.  Squid is
 *  Copyrighted (C) 2001 by the Regents of the University of
 *  California; see the COPYRIGHT file for full details.  Squid
 *  incorporates software developed and/or copyrighted by other
 *  sources; see the CREDITS file for full details.
 *
 *  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.
 *  
 *  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.
 *  
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
 *
 */

#include "squid.h"

const char *hier_strings[] =
{
    "NONE",
    "DIRECT",
    "SIBLING_HIT",
    "PARENT_HIT",
    "DEFAULT_PARENT",
    "SINGLE_PARENT",
    "FIRST_UP_PARENT",
    "FIRST_PARENT_MISS",
    "CLOSEST_PARENT_MISS",
    "CLOSEST_PARENT",
    "CLOSEST_DIRECT",
    "NO_DIRECT_FAIL",
    "SOURCE_FASTEST",
    "ROUNDROBIN_PARENT",
#if USE_CACHE_DIGESTS
    "CD_PARENT_HIT",
    "CD_SIBLING_HIT",
#endif
#if USE_CARP
    "CARP",
#endif
    "ANY_PARENT",
    "USERHASH_PARENT",
    "SOURCEHASH_PARENT",
    "PINNED",
    "INVALID CODE"
};

static struct {
    int timeouts;
} PeerStats;

static const char *DirectStr[] =
{
    "DIRECT_UNKNOWN",
    "DIRECT_NO",
    "DIRECT_MAYBE",
    "DIRECT_YES"
};

static void peerSelectFoo(ps_state *);
static void peerPingTimeout(void *data);
static void peerSelectCallback(ps_state * psstate);
static IRCB peerHandlePingReply;
static void peerSelectStateFree(ps_state * psstate);
static void peerIcpParentMiss(peer *, icp_common_t *, ps_state *);
#if USE_HTCP
static void peerHtcpParentMiss(peer *, htcpReplyData *, ps_state *);
static void peerHandleHtcpReply(peer *, peer_t, htcpReplyData *, void *);
#endif
static int peerCheckNetdbDirect(ps_state * psstate);
static void peerGetPinned(ps_state * ps);
static void peerGetSomeNeighbor(ps_state *);
static void peerGetSomeNeighborReplies(ps_state *);
static void peerGetSomeDirect(ps_state *);
static void peerGetSomeParent(ps_state *);
static void peerGetAllParents(ps_state *);

static void
peerSelectStateFree(ps_state * psstate)
{
    if (psstate->acl_checklist) {
	debug(44, 1) ("calling aclChecklistFree() from peerSelectStateFree\n");
	aclChecklistFree(psstate->acl_checklist);
    }
    requestUnlink(psstate->request);
    psstate->request = NULL;
    if (psstate->entry) {
	assert(psstate->entry->ping_status != PING_WAITING);
	storeUnlockObject(psstate->entry);
	psstate->entry = NULL;
    }
    cbdataFree(psstate);
}

static int
peerSelectIcpPing(request_t * request, int direct, StoreEntry * entry)
{
    int n;
    assert(entry);
    assert(entry->ping_status == PING_NONE);
    assert(direct != DIRECT_YES);
    debug(44, 3) ("peerSelectIcpPing: %s\n", storeUrl(entry));
    if (!request->flags.hierarchical && direct != DIRECT_NO)
	return 0;
    if (EBIT_TEST(entry->flags, KEY_PRIVATE) && !neighbors_do_private_keys)
	if (direct != DIRECT_NO)
	    return 0;
    n = neighborsCount(request);
    debug(44, 3) ("peerSelectIcpPing: counted %d neighbors\n", n);
    return n;
}


void
peerSelect(request_t * request,
    StoreEntry * entry,
    PSC * callback,
    void *callback_data)
{
    ps_state *psstate;
    if (entry)
	debug(44, 3) ("peerSelect: %s\n", storeUrl(entry));
    else
	debug(44, 3) ("peerSelect: %s\n", RequestMethods[request->method].str);
    psstate = cbdataAlloc(ps_state);
    psstate->request = requestLink(request);
    psstate->entry = entry;
    psstate->callback = callback;
    psstate->callback_data = callback_data;
    psstate->direct = DIRECT_UNKNOWN;
#if USE_CACHE_DIGESTS
    request->hier.peer_select_start = current_time;
#endif
    if (psstate->entry)
	storeLockObject(psstate->entry);
    cbdataLock(callback_data);
    peerSelectFoo(psstate);
}

static void
peerCheckNeverDirectDone(int answer, void *data)
{
    ps_state *psstate = data;
    psstate->acl_checklist = NULL;
    debug(44, 3) ("peerCheckNeverDirectDone: %d\n", answer);
    psstate->never_direct = answer ? 1 : -1;
    peerSelectFoo(psstate);
}

static void
peerCheckAlwaysDirectDone(int answer, void *data)
{
    ps_state *psstate = data;
    psstate->acl_checklist = NULL;
    debug(44, 3) ("peerCheckAlwaysDirectDone: %d\n", answer);
    psstate->always_direct = answer ? 1 : -1;
    peerSelectFoo(psstate);
}

static void
peerSelectCallback(ps_state * psstate)
{
    StoreEntry *entry = psstate->entry;
    FwdServer *fs = psstate->servers;
    void *data = psstate->callback_data;
    if (entry) {
	debug(44, 3) ("peerSelectCallback: %s\n", storeUrl(entry));
	if (entry->ping_status == PING_WAITING)
	    eventDelete(peerPingTimeout, psstate);
	entry->ping_status = PING_DONE;
    }
    if (fs == NULL) {
	debug(44, 1) ("Failed to select source for '%s'\n", storeUrl(entry));
	debug(44, 1) ("  always_direct = %d\n", psstate->always_direct);
	debug(44, 1) ("   never_direct = %d\n", psstate->never_direct);
	debug(44, 1) ("       timedout = %d\n", psstate->ping.timedout);
    }
    psstate->ping.stop = current_time;
    psstate->request->hier.ping = psstate->ping;
    if (cbdataValid(data)) {
	psstate->servers = NULL;
	psstate->callback(fs, data);
    }
    cbdataUnlock(data);
    peerSelectStateFree(psstate);
}

static int
peerCheckNetdbDirect(ps_state * psstate)
{
    peer *p;
    int myrtt;
    int myhops;
    if (psstate->direct == DIRECT_NO)
	return 0;
    myrtt = netdbHostRtt(psstate->request->host);
    debug(44, 3) ("peerCheckNetdbDirect: MY RTT = %d msec\n", myrtt);
    debug(44, 3) ("peerCheckNetdbDirect: minimum_direct_rtt = %d msec\n",
	Config.minDirectRtt);
    if (myrtt && myrtt <= Config.minDirectRtt)
	return 1;
    myhops = netdbHostHops(psstate->request->host);
    debug(44, 3) ("peerCheckNetdbDirect: MY hops = %d\n", myhops);
    debug(44, 3) ("peerCheckNetdbDirect: minimum_direct_hops = %d\n",
	Config.minDirectHops);
    if (myhops && myhops <= Config.minDirectHops)
	return 1;
    p = whichPeer(&psstate->closest_parent_miss);
    if (p == NULL)
	return 0;
    debug(44, 3) ("peerCheckNetdbDirect: closest_parent_miss RTT = %d msec\n",
	psstate->ping.p_rtt);
    if (myrtt && myrtt <= psstate->ping.p_rtt)
	return 1;
    return 0;
}

static void
peerSelectFoo(ps_state * ps)
{
    StoreEntry *entry = ps->entry;
    request_t *request = ps->request;
    debug(44, 3) ("peerSelectFoo: '%s %s'\n",
	RequestMethods[request->method].str,
	request->host);
    if (ps->direct == DIRECT_UNKNOWN) {
	if (ps->always_direct == 0 && Config.accessList.AlwaysDirect) {
	    ps->acl_checklist = aclChecklistCreate(
		Config.accessList.AlwaysDirect,
		request,
		NULL);		/* ident */
	    aclNBCheck(ps->acl_checklist,
		peerCheckAlwaysDirectDone,
		ps);
	    return;
	} else if (ps->always_direct > 0) {
	    ps->direct = DIRECT_YES;
	} else if (ps->never_direct == 0 && Config.accessList.NeverDirect) {
	    ps->acl_checklist = aclChecklistCreate(
		Config.accessList.NeverDirect,
		request,
		NULL);		/* ident */
	    aclNBCheck(ps->acl_checklist,
		peerCheckNeverDirectDone,
		ps);
	    return;
	} else if (ps->never_direct > 0) {
	    ps->direct = DIRECT_NO;
	} else if (request->flags.no_direct) {
	    ps->direct = DIRECT_NO;
	} else if (request->flags.loopdetect) {
	    ps->direct = DIRECT_YES;
	} else if (peerCheckNetdbDirect(ps)) {
	    ps->direct = DIRECT_YES;
	} else {
	    ps->direct = DIRECT_MAYBE;
	}
	debug(44, 3) ("peerSelectFoo: direct = %s\n",
	    DirectStr[ps->direct]);
    }
    if (!entry || entry->ping_status == PING_NONE)
	peerGetPinned(ps);
    if (entry == NULL) {
	(void) 0;
    } else if (entry->ping_status == PING_NONE) {
	peerGetSomeNeighbor(ps);
	if (entry->ping_status == PING_WAITING)
	    return;
    } else if (entry->ping_status == PING_WAITING) {
	peerGetSomeNeighborReplies(ps);
	entry->ping_status = PING_DONE;
    }
    switch (ps->direct) {
    case DIRECT_YES:
	peerGetSomeDirect(ps);
	break;
    case DIRECT_NO:
	peerGetSomeParent(ps);
	peerGetAllParents(ps);
	break;
    default:
	if (Config.onoff.prefer_direct)
	    peerGetSomeDirect(ps);
	if (request->flags.hierarchical || !Config.onoff.nonhierarchical_direct)
	    peerGetSomeParent(ps);
	if (!Config.onoff.prefer_direct)
	    peerGetSomeDirect(ps);
	break;
    }
    peerSelectCallback(ps);
}

/*
 * peerGetPinned
 *
 * Selects a pinned connection
 */
static void
peerGetPinned(ps_state * ps)
{
    request_t *request = ps->request;
    peer *peer;
    if (!request->pinned_connection)
	return;
    if (clientGetPinnedInfo(request->pinned_connection, request, &peer) != -1) {
	if (peer && peerAllowedToUse(peer, request)) {
	    peerAddFwdServer(&ps->servers, peer, PINNED);
	    if (ps->entry)
		ps->entry->ping_status = PING_DONE;	/* Skip ICP */
	} else if (!peer && ps->direct != DIRECT_NO) {
	    peerAddFwdServer(&ps->servers, NULL, PINNED);
	    if (ps->entry)
		ps->entry->ping_status = PING_DONE;	/* Skip ICP */
	}
    }
}

/*
 * peerGetSomeNeighbor
 * 
 * Selects a neighbor (parent or sibling) based on one of the
 * following methods:
 *      Cache Digests
 *      CARP
 *      Netdb RTT estimates
 *      ICP/HTCP queries
 */
static void
peerGetSomeNeighbor(ps_state * ps)
{
    StoreEntry *entry = ps->entry;
    request_t *request = ps->request;
    peer *p;
    hier_code code = HIER_NONE;
    assert(entry->ping_status == PING_NONE);
    if (ps->direct == DIRECT_YES) {
	entry->ping_status = PING_DONE;
	return;
    }
#if USE_CACHE_DIGESTS
    if ((p = neighborsDigestSelect(request))) {
	if (neighborType(p, request) == PEER_PARENT)
	    code = CD_PARENT_HIT;
	else
	    code = CD_SIBLING_HIT;
    } else
#endif
    if ((p = netdbClosestParent(request))) {
	code = CLOSEST_PARENT;
    } else if (peerSelectIcpPing(request, ps->direct, entry)) {
	debug(44, 3) ("peerGetSomeNeighbor: Doing ICP pings\n");
	ps->ping.start = current_time;
	ps->ping.n_sent = neighborsUdpPing(request,
	    entry,
	    peerHandlePingReply,
	    ps,
	    &ps->ping.n_replies_expected,
	    &ps->ping.timeout);
	if (ps->ping.n_sent == 0)
	    debug(44, 0) ("WARNING: neighborsUdpPing returned 0\n");
	debug(44, 3) ("peerGetSomeNeighbor: %d ICP replies expected, RTT %d msec\n",
	    ps->ping.n_replies_expected, ps->ping.timeout);
	if (ps->ping.n_replies_expected > 0) {
	    entry->ping_status = PING_WAITING;
	    eventAdd("peerPingTimeout",
		peerPingTimeout,
		ps,
		0.001 * ps->ping.timeout,
		0);
	    return;
	}
    }
    if (code != HIER_NONE) {
	assert(p);
	debug(44, 3) ("peerGetSomeNeighbor: %s/%s\n", hier_strings[code], p->name);
	peerAddFwdServer(&ps->servers, p, code);
    }
    entry->ping_status = PING_DONE;
}

/*
 * peerGetSomeNeighborReplies
 * 
 * Selects a neighbor (parent or sibling) based on ICP/HTCP replies.
 */
static void
peerGetSomeNeighborReplies(ps_state * ps)
{
    request_t *request = ps->request;
    peer *p = NULL;
    hier_code code = HIER_NONE;
    assert(ps->entry->ping_status == PING_WAITING);
    assert(ps->direct != DIRECT_YES);
    if (peerCheckNetdbDirect(ps)) {
	code = CLOSEST_DIRECT;
	debug(44, 3) ("peerGetSomeNeighborReplies: %s/%s\n", hier_strings[code], request->host);
	peerAddFwdServer(&ps->servers, NULL, code);
	return;
    }
    if ((p = ps->hit)) {
	code = ps->hit_type == PEER_PARENT ? PARENT_HIT : SIBLING_HIT;
    } else
#if ALLOW_SOURCE_PING
    if ((p = ps->secho)) {
	code = SOURCE_FASTEST;
    } else
#endif
    if (ps->closest_parent_miss.sin_addr.s_addr != any_addr.s_addr) {
	p = whichPeer(&ps->closest_parent_miss);
	code = CLOSEST_PARENT_MISS;
    } else if (ps->first_parent_miss.sin_addr.s_addr != any_addr.s_addr) {
	p = whichPeer(&ps->first_parent_miss);
	code = FIRST_PARENT_MISS;
    }
    if (p && code != HIER_NONE) {
	debug(44, 3) ("peerGetSomeNeighborReplies: %s/%s\n", hier_strings[code], p->name);
	peerAddFwdServer(&ps->servers, p, code);
    }
}


/*
 * peerGetSomeDirect
 * 
 * Simply adds a 'direct' entry to the FwdServers list if this
 * request can be forwarded directly to the origin server
 */
static void
peerGetSomeDirect(ps_state * ps)
{
    if (ps->direct == DIRECT_NO)
	return;
    if (ps->request->protocol == PROTO_WAIS)
	return;			/* No server-side implemented, can't go direct */
    peerAddFwdServer(&ps->servers, NULL, HIER_DIRECT);
}

static void
peerGetSomeParent(ps_state * ps)
{
    peer *p;
    request_t *request = ps->request;
    hier_code code = HIER_NONE;
    debug(44, 3) ("peerGetSomeParent: %s %s\n",
	RequestMethods[request->method].str,
	request->host);
    if (ps->direct == DIRECT_YES)
	return;
    if ((p = getDefaultParent(request))) {
	code = DEFAULT_PARENT;
    } else if ((p = peerUserHashSelectParent(request))) {
	code = USERHASH_PARENT;
    } else if ((p = peerSourceHashSelectParent(request))) {
	code = SOURCEHASH_PARENT;
#if USE_CARP
    } else if ((p = carpSelectParent(request))) {
	code = CARP;
#endif
    } else if ((p = getRoundRobinParent(request))) {
	code = ROUNDROBIN_PARENT;
    } else if ((p = getFirstUpParent(request))) {
	code = FIRSTUP_PARENT;
    } else if ((p = getAnyParent(request))) {
	code = ANY_OLD_PARENT;
    }
    if (code != HIER_NONE) {
	debug(44, 3) ("peerGetSomeParent: %s/%s\n", hier_strings[code], p->name);
	peerAddFwdServer(&ps->servers, p, code);
    }
}

/* Adds alive parents. Used as a last resort for never_direct.
 */
static void
peerGetAllParents(ps_state * ps)
{
    peer *p;
    request_t *request = ps->request;
    /* Add all alive parents */
    for (p = Config.peers; p; p = p->next) {
	/* XXX: neighbors.c lacks a public interface for enumerating
	 * parents to a request so we have to dig some here..
	 */
	if (neighborType(p, request) != PEER_PARENT)
	    continue;
	if (!peerHTTPOkay(p, request))
	    continue;
	debug(15, 3) ("peerGetAllParents: adding alive parent %s\n", p->name);
	peerAddFwdServer(&ps->servers, p, ANY_OLD_PARENT);
    }
    /* XXX: should add dead parents here, but it is currently
     * not possible to find out which parents are dead or which
     * simply are not configured to handle the request.
     */
    /* Add default parent as a last resort */
    if ((p = getDefaultParent(request))) {
	peerAddFwdServer(&ps->servers, p, DEFAULT_PARENT);
    }
}

static void
peerPingTimeout(void *data)
{
    ps_state *psstate = data;
    StoreEntry *entry = psstate->entry;
    if (entry)
	debug(44, 3) ("peerPingTimeout: '%s'\n", storeUrl(entry));
    if (!cbdataValid(psstate->callback_data)) {
	/* request aborted */
	entry->ping_status = PING_DONE;
	cbdataUnlock(psstate->callback_data);
	peerSelectStateFree(psstate);
	return;
    }
    PeerStats.timeouts++;
    psstate->ping.timedout = 1;
    peerSelectFoo(psstate);
}

void
peerSelectInit(void)
{
    memset(&PeerStats, '\0', sizeof(PeerStats));
    assert(sizeof(hier_strings) == (HIER_MAX + 1) * sizeof(char *));
}

static void
peerIcpParentMiss(peer * p, icp_common_t * header, ps_state * ps)
{
    int rtt;
    int hops;
    if (Config.onoff.query_icmp) {
	if (header->flags & ICP_FLAG_SRC_RTT) {
	    rtt = header->pad & 0xFFFF;
	    hops = (header->pad >> 16) & 0xFFFF;
	    if (rtt > 0 && rtt < 0xFFFF)
		netdbUpdatePeer(ps->request, p, rtt, hops);
	    if (rtt && (ps->ping.p_rtt == 0 || rtt < ps->ping.p_rtt)) {
		ps->closest_parent_miss = p->in_addr;
		ps->ping.p_rtt = rtt;
	    }
	}
    }
    /* if closest-only is set, then don't allow FIRST_PARENT_MISS */
    if (p->options.closest_only)
	return;
    /* set FIRST_MISS if there is no CLOSEST parent */
    if (ps->closest_parent_miss.sin_addr.s_addr != any_addr.s_addr)
	return;
    rtt = tvSubMsec(ps->ping.start, current_time) / p->weight;
    if (ps->first_parent_miss.sin_addr.s_addr == any_addr.s_addr ||
	rtt < ps->ping.w_rtt) {
	ps->first_parent_miss = p->in_addr;
	ps->ping.w_rtt = rtt;
    }
}

static void
peerHandleIcpReply(peer * p, peer_t type, icp_common_t * header, void *data)
{
    ps_state *psstate = data;
    icp_opcode op = header->opcode;
    debug(44, 3) ("peerHandleIcpReply: %s %s\n",
	icp_opcode_str[op],
	storeUrl(psstate->entry));
#if USE_CACHE_DIGESTS && 0
    /* do cd lookup to count false misses */
    if (p && request)
	peerNoteDigestLookup(request, p,
	    peerDigestLookup(p, request, psstate->entry));
#endif
    psstate->ping.n_recv++;
    if (op == ICP_MISS || op == ICP_DECHO) {
	if (type == PEER_PARENT)
	    peerIcpParentMiss(p, header, psstate);
    } else if (op == ICP_HIT) {
	psstate->hit = p;
	psstate->hit_type = type;
	peerSelectFoo(psstate);
	return;
    }
#if ALLOW_SOURCE_PING
    else if (op == ICP_SECHO) {
	psstate->secho = p;
	peerSelectFoo(psstate);
	return;
    }
#endif
    if (psstate->ping.n_recv < psstate->ping.n_replies_expected)
	return;
    peerSelectFoo(psstate);
}

#if USE_HTCP
static void
peerHandleHtcpReply(peer * p, peer_t type, htcpReplyData * htcp, void *data)
{
    ps_state *psstate = data;
    debug(44, 3) ("peerHandleHtcpReply: %s %s\n",
	htcp->hit ? "HIT" : "MISS",
	storeUrl(psstate->entry));
    psstate->ping.n_recv++;
    if (htcp->hit) {
	psstate->hit = p;
	psstate->hit_type = type;
	peerSelectFoo(psstate);
	return;
    }
    if (type == PEER_PARENT)
	peerHtcpParentMiss(p, htcp, psstate);
    if (psstate->ping.n_recv < psstate->ping.n_replies_expected)
	return;
    peerSelectFoo(psstate);
}

static void
peerHtcpParentMiss(peer * p, htcpReplyData * htcp, ps_state * ps)
{
    int rtt;
    int hops;
    if (Config.onoff.query_icmp) {
	if (htcp->cto.rtt > 0) {
	    rtt = (int) htcp->cto.rtt * 1000;
	    hops = (int) htcp->cto.hops * 1000;
	    netdbUpdatePeer(ps->request, p, rtt, hops);
	    if (rtt && (ps->ping.p_rtt == 0 || rtt < ps->ping.p_rtt)) {
		ps->closest_parent_miss = p->in_addr;
		ps->ping.p_rtt = rtt;
	    }
	}
    }
    /* if closest-only is set, then don't allow FIRST_PARENT_MISS */
    if (p->options.closest_only)
	return;
    /* set FIRST_MISS if there is no CLOSEST parent */
    if (ps->closest_parent_miss.sin_addr.s_addr != any_addr.s_addr)
	return;
    rtt = tvSubMsec(ps->ping.start, current_time) / p->weight;
    if (ps->first_parent_miss.sin_addr.s_addr == any_addr.s_addr ||
	rtt < ps->ping.w_rtt) {
	ps->first_parent_miss = p->in_addr;
	ps->ping.w_rtt = rtt;
    }
}
#endif

static void
peerHandlePingReply(peer * p, peer_t type, protocol_t proto, void *pingdata, void *data)
{
    if (proto == PROTO_ICP)
	peerHandleIcpReply(p, type, pingdata, data);
#if USE_HTCP
    else if (proto == PROTO_HTCP)
	peerHandleHtcpReply(p, type, pingdata, data);
#endif
    else
	debug(44, 1) ("peerHandlePingReply: unknown protocol_t %d\n", (int) proto);
}

void
peerAddFwdServer(FwdServer ** FS, peer * p, hier_code code)
{
    FwdServer *fs;
    debug(44, 5) ("peerAddFwdServer: adding %s %s\n",
	p ? p->name : "DIRECT",
	hier_strings[code]);
    while (*FS) {
	if ((*FS)->peer == p && (*FS)->code != PINNED) {
	    debug(44, 5) ("peerAddFwdServer: Skipping duplicate registration of %s\n", p ? p->name : "DIRECT");
	    return;
	}
	FS = &(*FS)->next;
    }
    fs = memAllocate(MEM_FWD_SERVER);
    fs->peer = p;
    fs->code = code;
    cbdataLock(fs->peer);
    *FS = fs;
}