/*
 * Copyright (c) 2009, Raphael Manfredi
 *
 *----------------------------------------------------------------------
 * This file is part of gtk-gnutella.
 *
 *  gtk-gnutella 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.
 *
 *  gtk-gnutella 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 gtk-gnutella; if not, write to the Free Software
 *  Foundation, Inc.:
 *      51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *----------------------------------------------------------------------
 */

/**
 * @ingroup dht
 * @file
 *
 * Lookup / publish root node caching.
 *
 * Whenever a value lookup or a publish is made, the set of k-closest nodes
 * surrounding the target KUID (including the nodes which returned the values
 * for value lookups) are cached.  Upon the next value lookup or publish for
 * the same KUID, the lookup shortlist will be seeded with these previous
 * root nodes, on the grounds that it is most likely that these nodes will be
 * still around.  This ensures faster convergence for lookups.
 *
 * The set of cached root nodes is kept for some time and is then discarded.
 * We may not need to publish / lookup the KUID, and too many stale seeds are
 * going to rather slow lookups down, since we'll have to wait for more RPC
 * timeouts before moving forward.
 *
 * The cache is organized as two separate DBMW databases + one table kept in
 * memory:
 *
 * + The memory table maps a target KUID to a structure keeping track of the
 *   last updates made to the root nodes for this KUID.
 *
 * + The first DBMW maps a KUID target to KDA_K dbkeys.  The intent is NOT to
 *   be able to share contact information between targets (this would involve
 *   refcounting and more I/O load for bookkeeping) but rather to prevent
 *   any size limitation of SDBM and keep values short-enough.
 *
 * + The second DBMW maps each dbkey to a node contact.
 *
 * @author Raphael Manfredi
 * @date 2009
 */

#include "common.h"

#include "roots.h"
#include "keys.h"
#include "kuid.h"
#include "knode.h"

#include "core/gnet_stats.h"
#include "core/settings.h"

#include "if/gnet_property_priv.h"
#include "if/dht/kademlia.h"
#include "if/dht/dht.h"			/* For dht_is_active() */

#include "lib/atoms.h"
#include "lib/cq.h"
#include "lib/crash.h"
#include "lib/dbmw.h"
#include "lib/dbstore.h"
#include "lib/hset.h"
#include "lib/map.h"
#include "lib/patricia.h"
#include "lib/stringify.h"
#include "lib/tm.h"
#include "lib/unsigned.h"
#include "lib/vendors.h"
#include "lib/walloc.h"

#include "lib/override.h"		/* Must be the last header included */

#define ROOTS_CALLOUT		5000		/**< Heartbeat every 5 seconds */
#define ROOTKEY_LIFETIME	(2*3600*1000)	/**< 2 hours */
#define ROOTS_SYNC_PERIOD	60000		/**< Flush DB every minute */

#define ROOTKEYS_DB_CACHE_SIZE	512		/**< Cached amount of root keys */
#define CONTACT_DB_CACHE_SIZE	4096	/**< Cached amount of contacts */
#define CONTACT_MAP_CACHE_SIZE	128		/**< Amount of SDBM pages to cache */

/**
 * Private callout queue used to expire entries in the database that have
 * not been updated recently.
 */
static cqueue_t *roots_cq;

/**
 * Structure holding in-core information about all the target KUIDs we're
 * caching the roots for.
 *
 * We use a PATRICIA to be able to quickly locate roots close to a KUID.
 */
static patricia_t *roots;

/**
 * DBM wrapper to associate a target KUID with the set of KDA_K dbkeys.
 */
static dbmw_t *db_rootdata;
static char db_rootdata_base[] = "dht_roots";
static char db_rootdata_what[] = "DHT root node key datasets";

/**
 * DBM wrapper to associate a dbkey with the contact information.
 */
static dbmw_t *db_contact;
static char db_contact_base[] = "dht_root_contacts";
static char db_contact_what[] = "DHT root node contacts";

enum rootinfo_magic { ROOTINFO_MAGIC = 0x3320aefaU };

/**
 * Information about a target KUID that we're keeping in core.
 */
struct rootinfo {
	enum rootinfo_magic magic;
	kuid_t *kuid;				/**< The target key (atom) */
	cevent_t *expire_ev;		/**< The expire event for the key */
	time_t last_update;			/**< When we last updated the key set */
};

static inline void
rootinfo_check(const struct rootinfo *ri)
{
	g_assert(ri);
	g_assert(ROOTINFO_MAGIC == ri->magic);
}

#define ROOTDATA_STRUCT_VERSION	0

/**
 * Information about a target KUID that is stored to disk.
 * The structure is serialized first, not written as-is.
 */
struct rootdata {
	uint64 dbkeys[KDA_K];	/**< SDBM keys pointing to contact information */
	time_t last_update;		/**< When we last updated the key set */
	uint8 count;			/**< Amount of dbkeys contained */
};

/**
 * Internal counter used to assign DB keys to the contacts we're storing.
 */
static uint64 contactid = 1;		/* 0 is not a valid key (used as marker) */

#define CONTACT_STRUCT_VERSION	1

/**
 * Contact information.
 * The structure is serialized first, not written as-is.
 */
struct contact {
	kuid_t *id;				/**< KUID of the node (atom) */
	vendor_code_t vcode;	/**< Vendor code */
	time_t first_seen;		/**< First seen time */
	host_addr_t addr;		/**< IP of the node */
	uint16 port;			/**< Port of the node */
	uint8 major;			/**< Major version */
	uint8 minor;			/**< Minor version */
};

static unsigned targets_managed;	/**< Amount of targets held in database */
static unsigned contacts_managed;	/**< Amount of contacts held in database */

/**
 * Allocate a new rootinfo structure.
 */
static struct rootinfo *
allocate_rootinfo(const kuid_t *kuid)
{
	struct rootinfo *ri;

	WALLOC0(ri);
	ri->magic = ROOTINFO_MAGIC;
	ri->kuid = kuid_get_atom(kuid);

	return ri;
}

/**
 * Discard rootinfo structure.
 */
static void
free_rootinfo(struct rootinfo *ri)
{
	rootinfo_check(ri);

	cq_cancel(&ri->expire_ev);
	kuid_atom_free_null(&ri->kuid);
	WFREE(ri);
}

/**
 * Get rootdata from database.
 */
static struct rootdata *
get_rootdata(const kuid_t *id)
{
	struct rootdata *rd;

	rd = dbmw_read(db_rootdata, id, NULL);

	if (NULL == rd) {
		if (dbmw_has_ioerr(db_rootdata)) {
			s_warning_once_per(LOG_PERIOD_MINUTE,
				"DBMW \"%s\" I/O error, bad things could happen...",
				dbmw_name(db_rootdata));
		} else {
			s_warning_once_per(LOG_PERIOD_SECOND,
				"key %s exists but was not found in DBMW \"%s\"",
				kuid_to_hex_string(id), dbmw_name(db_rootdata));
		}
	}

	return rd;
}

/**
 * Get contact from database.
 */
static struct contact *
get_contact(uint64 dbkey, bool shout)
{
	struct contact *c;

	c = dbmw_read(db_contact, &dbkey, NULL);

	if (NULL == c) {
		if (dbmw_has_ioerr(db_contact)) {
			s_warning_once_per(LOG_PERIOD_MINUTE,
				"DBMW \"%s\" I/O error, bad things could happen...",
				dbmw_name(db_contact));
		} else if (shout) {
			s_warning_once_per(LOG_PERIOD_SECOND,
				"key %s exists but was not found in DBMW \"%s\"",
				uint64_to_string(dbkey), dbmw_name(db_contact));
		}
	}

	return c;
}

/**
 * Delete contact from database.
 */
static void
delete_contact(uint64 dbkey)
{
	g_assert(uint_is_positive(contacts_managed));

	contacts_managed--;
	gnet_stats_dec_general(GNR_DHT_CACHED_ROOTS_HELD);

	dbmw_delete(db_contact, &dbkey);

	if (GNET_PROPERTY(dht_roots_debug) > 2)
		g_debug("DHT contact DB-key %s reclaimed", uint64_to_string(dbkey));
}

/**
 * Delete rootdata from database.
 */
static void
delete_rootdata(const kuid_t *id)
{
	const struct rootdata *rd;
	unsigned i;

	rd = get_rootdata(id);
	if (NULL == rd)
		return;

	for (i = 0; i < rd->count; i++) {
		delete_contact(rd->dbkeys[i]);
	}

	dbmw_delete(db_rootdata, id);

	if (GNET_PROPERTY(dht_roots_debug) > 2)
		g_debug("DHT ROOTS k-closest nodes from %s reclaimed",
			kuid_to_hex_string(id));
}

/**
 * Map iterator callback to reclaim a DB-key value.
 */
static void
reclaim_dbkey(void *u_key, void *val, void *u_data)
{
	uint64 *dbkey = val;

	(void) u_key;
	(void) u_data;

	delete_contact(*dbkey);
}

/**
 * Callout queue callback to expire target.
 */
static void
roots_expire(cqueue_t *cq, void *obj)
{
	struct rootinfo *ri = obj;

	rootinfo_check(ri);
	g_assert(uint_is_positive(targets_managed));

	cq_zero(cq, &ri->expire_ev);		/* Event triggered */
	delete_rootdata(ri->kuid);
	patricia_remove(roots, ri->kuid);
	free_rootinfo(ri);
	targets_managed--;
	gnet_stats_dec_general(GNR_DHT_CACHED_KUID_TARGETS_HELD);
}

/**
 * Record k-closest roots we were able to locate around the specified KUID.
 *
 * @param nodes		the nodes that were successfully queried during lookup
 * @param kuid		the KUID target that was looked up
 */
void
roots_record(patricia_t *nodes, const kuid_t *kuid)
{
	struct rootinfo *ri;
	struct rootdata *rd;
	struct rootdata new_rd;
	struct {
		kuid_t id;
		uint64 dbkey;
	} previous[KDA_K];
	map_t *existing;
	patricia_iter_t *iter;
	unsigned i;
	unsigned new = 0, reused = 0;	/* For logging */
	bool existed = FALSE;			/* For logging */

	g_assert(nodes != NULL);
	g_assert(kuid != NULL);

	/*
	 * If KUID is within our k-ball, there's no need to cache the roots, as
	 * we routinely refresh our k-bucket and have normally a perfect knowledge
	 * of our KDA_K neighbours (if we are an active node).
	 */

	if (dht_is_active() && keys_within_kball(kuid))
		return;

	ri = patricia_lookup(roots, kuid);

	if (NULL == ri) {
		ri = allocate_rootinfo(kuid);
		patricia_insert(roots, ri->kuid, ri);
		rd = &new_rd;
		new_rd.count = 0;
		targets_managed++;
		gnet_stats_inc_general(GNR_DHT_CACHED_KUID_TARGETS_HELD);
	} else {
		rd = get_rootdata(kuid);
		if (NULL == rd) {
			if (dbmw_has_ioerr(db_rootdata))
				return;			/* I/O error */
			/* Key supposed to exist but not found -> DB was corrupted */
			rd = &new_rd;
			new_rd.count = 0;
		} else {
			existed = TRUE;
		}
	}

	/*
	 * To avoid having to create new (and then delete old) contacts, we
	 * retrieve all the known old roots and map their KUID to the existing
	 * DB key that was used to retrieve each of them.  To prevent atom
	 * creation, we take a copy of the KUIDs and dbkeys on the stack.
	 *
	 * Only truly new contacts will be created, and only old contacts that
	 * are no longer present among the k-closest roots will be deleted.
	 */

	STATIC_ASSERT(N_ITEMS(rd->dbkeys) == N_ITEMS(previous));

	existing = map_create_patricia(KUID_RAW_BITSIZE);

	for (i = 0; i < rd->count; i++) {
		struct contact *c = get_contact(rd->dbkeys[i], FALSE);

		/*
		 * It can happen that ``rd'' contains DB keys that no longer exist
		 * in the contact database.  At startup time, we clear orphaned keys,
		 * but we do nothing against "ghost" DB keys referenced by entries
		 * within db_rootdata.  These are harmless anyway and will disappear
		 * as we expire entries or update them after a lookup.
		 *
		 * That's why the above get_contact() call silences "key not found"
		 * type of warnings.
		 */

		if (NULL == c)
			continue;		/* I/O error or stale info in ``rd'' */

		previous[i].id = *c->id;		/* Struct copy */
		previous[i].dbkey = rd->dbkeys[i];
		map_insert(existing, &previous[i].id, &previous[i].dbkey);
	}

	/*
	 * Now fetch the k-closest roots from the target KUID.
	 */

	iter = patricia_metric_iterator_lazy(nodes, kuid, TRUE);
	i = 0;

	while (patricia_iter_has_next(iter) && i < N_ITEMS(rd->dbkeys)) {
		knode_t *kn = patricia_iter_next_value(iter);
		uint64 *dbkey_ptr;

		/*
		 * If entry existed in the previous set, we reuse the old contact.
		 *
		 * Note that presence in the ``existing'' map means that we were
		 * able to read the contact from the database earlier, so this time
		 * we issue a verbose get_contact() call to warn if we fail to
		 * retrieve the contact from the database again.
		 */

		dbkey_ptr = map_lookup(existing, kn->id);

		if (NULL != dbkey_ptr) {
			struct contact *c = get_contact(*dbkey_ptr, TRUE);

			if (NULL == c)
				continue;		/* I/O error, most probably */

			/* Update contact addr:port information, if stale */
			if (c->port != kn->port || !host_addr_equiv(c->addr, kn->addr)) {
				c->port = kn->port;
				c->addr = kn->addr;
				c->first_seen = tm_time();	/* New node address */
				dbmw_write(db_contact, dbkey_ptr, PTRLEN(c));
				gnet_stats_inc_general(GNR_DHT_CACHED_ROOTS_CONTACT_REFRESHED);
			}

			map_remove(existing, kn->id);	/* We reused it */
			rd->dbkeys[i++] = *dbkey_ptr;	/* Reuse existing contact */
			reused++;
		} else {
			struct contact nc;
			uint64 dbkey;

			nc.id = kuid_get_atom(kn->id);	/* Freed through free_contact() */
			nc.vcode = kn->vcode;	/* Struct copy */
			nc.addr = kn->addr;		/* Struct copy */
			nc.port = kn->port;
			nc.major = kn->major;
			nc.minor = kn->minor;
			nc.first_seen = kn->first_seen;
			dbkey = contactid++;
			contacts_managed++;
			gnet_stats_inc_general(GNR_DHT_CACHED_ROOTS_HELD);

			dbmw_write(db_contact, &dbkey, VARLEN(nc));

			rd->dbkeys[i++] = dbkey;
			new++;
		}
	}

	rd->count = i;
	patricia_iterator_release(&iter);

	/*
	 * Any remaining entry in ``existing'' was not reused and can be deleted.
	 */

	map_foreach(existing, reclaim_dbkey, NULL);
	map_destroy(existing);

	/*
	 * Persist rootdata and update rootinfo.
	 */

	rd->last_update = tm_time();
	dbmw_write(db_rootdata, kuid, PTRLEN(rd));

	if (ri->expire_ev) {
		cq_resched(ri->expire_ev, ROOTKEY_LIFETIME);
	} else {
		ri->expire_ev = cq_insert(roots_cq, ROOTKEY_LIFETIME, roots_expire, ri);
	}

	if (GNET_PROPERTY(dht_roots_debug) > 1) {
		g_debug("DHT ROOTS cached %u/%u k-closest node%s to %s target %s "
			"(new=%u, reused=%u, elapsed=%s)",
			rd->count, (unsigned) patricia_count(nodes), plural(rd->count),
			existed ? "existing" : "new",
			kuid_to_hex_string(kuid), new, reused,
			existed ?
				compact_time(delta_time(tm_time(), ri->last_update)) : "-");
	}

	ri->last_update = tm_time();
}

/*
 * Fill the supplied vector `kvec' whose size is `kcnt' with the knodes
 * that are the closest neighbours we have found.
 *
 * @param rd		the contact data we have found
 * @param kvec		base of the "knode_t *" vector
 * @param kcnt		size of the "knode_t *" vector
 * @param known		a PATRICIA containing known neighbours already.
 * @param furthest	if non-NULL, do not add nodes further away than this one
 * @param id		the target KUID, mandatory if furthest is non-NULL
 *
 * @return the amount of entries filled in the vector.  It will be up to the
 * caller to invoke knode_free() on the returned entries.
 */
static int
roots_fill_vector(struct rootdata *rd,
	knode_t **kvec, int kcnt, patricia_t *known,
	const knode_t *furthest, const kuid_t *id)
{
	int i;
	int j = 0;

	g_assert(NULL == furthest || id != NULL);

	for (i = 0; i < rd->count && i < kcnt; i++) {
		struct contact *c = get_contact(rd->dbkeys[i], FALSE);
		knode_t *kn;

		if (NULL == c)
			continue;		/* I/O error or corrupted database */

		if (patricia_contains(known, c->id))
			continue;

		/*
		 * If a furthest limit was given, skip nodes further away than
		 * that boundary.
		 */

		if (furthest != NULL && kuid_cmp3(id, c->id, furthest->id) >= 0)
			continue;

		kn = knode_new(c->id, 0,
			c->addr, c->port, c->vcode, c->major, c->minor);
		kn->flags |= KNODE_F_CACHED;
		kn->first_seen = c->first_seen;
		kvec[j++] = kn;
	}

	return j;	/* Amount filled */
}

/**
 * Fill the supplied vector `kvec' whose size is `kcnt' with the knodes
 * that are the closest neighbours we know about from our cached roots.
 *
 * @param id		the KUID target they want neighbours for
 * @param kvec		base of the "knode_t *" vector
 * @param kcnt		size of the "knode_t *" vector
 * @param known		a PATRICIA containing known neighbours already.
 *
 * @return the amount of entries filled in the vector.  It will be up to the
 * caller to invoke knode_free() on the returned entries.
 */
int
roots_fill_closest(const kuid_t *id,
	knode_t **kvec, int kcnt, patricia_t *known)
{
	struct rootinfo *ri;
	int filled = 0;
	bool approximate = TRUE;

	g_assert(id != NULL);
	g_assert(kcnt > 0);
	g_assert(kvec != NULL);
	g_assert(known != NULL);

	/*
	 * Do not count a cache miss if the lookup was for a key within
	 * our k-ball, since we do not cache roots for these keys (when we
	 * are an active node).
	 */

	if (dht_is_active() && keys_within_kball(id)) {
		gnet_stats_inc_general(GNR_DHT_CACHED_ROOTS_KBALL_LOOKUPS);
		return 0;
	}

	ri = patricia_lookup(roots, id);

	if (NULL != ri) {
		struct rootdata *rd = get_rootdata(id);

		if (NULL == rd)
			return 0;			/* I/O error or corrupted database */

		/*
		 * We have an exact target match: return the nodes we have
		 * that are not already known.
		 */

		filled = roots_fill_vector(rd, kvec, kcnt, known, NULL, NULL);
		gnet_stats_inc_general(GNR_DHT_CACHED_ROOTS_EXACT_HITS);

		if (GNET_PROPERTY(dht_roots_debug) > 1) {
			g_debug("DHT ROOTS exact match for %s (%s), filled %d new node%s",
				kuid_to_hex_string(id),
				compact_time(delta_time(tm_time(), ri->last_update)),
				PLURAL(filled));
		}

		/*
		 * If we had less than KDA_K nodes, then we probably never conducted
		 * a node search for this ID.  Rather this is the result of a value
		 * lookup.
		 */

		approximate = rd->count < KDA_K;
	}

	if (approximate) {
		knode_t *furthest = patricia_furthest(known, id);
		struct rootinfo *cri = NULL;
		patricia_t *aknown = known;

		/*
		 * We don't have an exact target match but maybe we known about
		 * another key which is going to be close enough: if we find another
		 * ID which is closer to the target than the furthest known node so
		 * far, it may be worth it.
		 */

		if (NULL == ri) {
			cri = patricia_closest(roots, id);
		} else {
			patricia_iter_t *iter;

			/*
			 * Since "ri" is not NULL, we got an exact match with a lookup
			 * on "id", so necessarily the closest node will again be the
			 * same set of nodes.
			 *
			 * If we come here, it's because we had less than KDA_K nodes
			 * to fill in from the closest ID so look for IDs further away
			 * but which are nonetheless closer that the furthest ID they
			 * know about...
			 */

			iter = patricia_metric_iterator(roots, id, TRUE);
			(void) patricia_iter_next_value(iter);	/* Skip exact match */

			while (patricia_iter_has_next(iter)) {
				struct rootdata *rd;

				cri = patricia_iter_next_value(iter);
				if (
					furthest != NULL &&
					kuid_cmp3(id, cri->kuid, furthest->id) >= 0
				) {
					cri = NULL;
					break;
				}

				rd = get_rootdata(cri->kuid);
				if (NULL == rd) {
					cri = NULL;		/* I/O error or corrupted database */
					break;
				}
				if (rd->count >= KDA_K)
					break;
			}

			patricia_iterator_release(&iter);

			if (NULL == cri) {
				if (GNET_PROPERTY(dht_roots_debug) > 1) {
					g_debug("DHT ROOTS no better approximate match for %s",
						kuid_to_hex_string(id));
				}
			} else {
				int i;

				if (GNET_PROPERTY(dht_roots_debug) > 1) {
					g_debug("DHT ROOTS trying to add from approximate match");
				}

				/*
				 * Since we partially added some nodes in the vector,
				 * we need to recompute the set of known KUID so that
				 * we do not attempt to insert duplicates again in the
				 * approximate matching step.
				 */

				aknown = patricia_create(KUID_RAW_BITSIZE);
				iter = patricia_tree_iterator(known, TRUE);
				while (patricia_iter_has_next(iter)) {
					knode_t *kn = patricia_iter_next_value(iter);
					patricia_insert(aknown, kn->id, kn);
				}
				patricia_iterator_release(&iter);
				for (i = 0; i < filled; i++) {
					knode_t *kn = kvec[i];
					patricia_insert(aknown, kn->id, kn);
				}
			}
		}

		if (
			cri != NULL &&
			(
				furthest == NULL ||			/* They have no known nodes */
				kuid_cmp3(id, cri->kuid, furthest->id) < 0
			)
		) {
			struct rootdata *rd = get_rootdata(cri->kuid);
			int added;

			if (NULL == rd)				/* I/O error or corrupted database */
				goto approximate_done;	/* May have filled some nodes above */

			added = roots_fill_vector(rd, &kvec[filled], kcnt - filled, aknown,
				furthest, id);
			filled += added;

			if (added > 0) {
				gnet_stats_inc_general(GNR_DHT_CACHED_ROOTS_APPROXIMATE_HITS);
			} else if (NULL == ri) {
				gnet_stats_inc_general(GNR_DHT_CACHED_ROOTS_MISSES);
			}

			if (GNET_PROPERTY(dht_roots_debug) > 1) {
				g_debug("DHT ROOTS approximate match of %s with %s (%s), "
					"filled %d new node%s",
					kuid_to_hex_string(id),
					kuid_to_hex_string2(cri->kuid),
					compact_time(delta_time(tm_time(), cri->last_update)),
					PLURAL(added));
			}
		} else if (NULL == ri) {
			gnet_stats_inc_general(GNR_DHT_CACHED_ROOTS_MISSES);

			if (GNET_PROPERTY(dht_roots_debug) > 1) {
				g_debug("DHT ROOTS no suitable cached entry for %s, "
					"closest was %s",
					kuid_to_hex_string(id),
					cri != NULL ?
						kuid_to_hex_string2(cri->kuid) : "<none>");
			}
		}

	approximate_done:

		if (aknown != known) {
			patricia_destroy(aknown);
		}
	}

	return filled;
}

/**
 * Serialization routine for rootdata.
 */
static void
serialize_rootdata(pmsg_t *mb, const void *data)
{
	const struct rootdata *rd = data;
	unsigned i;

	pmsg_write_u8(mb, rd->count);
	pmsg_write_time(mb, rd->last_update);
	for (i = 0; i < rd->count; i++) {
		pmsg_write_be64(mb, rd->dbkeys[i]);
	}

	/*
	 * Because this is persistent, version the structure so that changes
	 * can be processed efficiently after an upgrade.
	 *
	 * This is done here and not at the beginning of the serialized data
	 * because I forgot to plan for it before.
	 *		--RAM, 2009-10-18
	 */

	pmsg_write_u8(mb, ROOTDATA_STRUCT_VERSION);
}

/**
 * Deserialization routine for rootdata.
 */
static void
deserialize_rootdata(bstr_t *bs, void *valptr, size_t len)
{
	struct rootdata *rd = valptr;
	unsigned i;
	uint8 version;

	g_assert(sizeof *rd == len);

	bstr_read_u8(bs, &rd->count);
	bstr_read_time(bs, &rd->last_update);
	g_assert(rd->count <= N_ITEMS(rd->dbkeys));

	for (i = 0; i < rd->count; i++) {
		bstr_read_be64(bs, &rd->dbkeys[i]);
	}

	bstr_read_u8(bs, &version);
}

/**
 * Serialization routine for contacts.
 */
static void
serialize_contact(pmsg_t *mb, const void *data)
{
	const struct contact *c = data;

	pmsg_write(mb, c->id->v, KUID_RAW_SIZE);
	pmsg_write_be32(mb, c->vcode.u32);
	pmsg_write_ipv4_or_ipv6_addr(mb, c->addr);
	pmsg_write_be16(mb, c->port);
	pmsg_write_u8(mb, c->major);
	pmsg_write_u8(mb, c->minor);

	/*
	 * Because this is persistent, version the structure so that changes
	 * can be processed efficiently after an upgrade.
	 *
	 * This is done here and not at the beginning of the serialized data
	 * because I forgot to plan for it before.
	 *		--RAM, 2009-10-18
	 */

	pmsg_write_u8(mb, CONTACT_STRUCT_VERSION);
	pmsg_write_time(mb, c->first_seen);	/* Added at version 1 */
}

/**
 * Deserialization routine for contacts.
 */
static void
deserialize_contact(bstr_t *bs, void *valptr, size_t len)
{
	struct contact *c = valptr;
	kuid_t id;
	uint8 version;

	g_assert(sizeof *c == len);

	c->id = NULL;

	bstr_read(bs, id.v, KUID_RAW_SIZE);
	bstr_read_be32(bs, &c->vcode.u32);
	bstr_read_packed_ipv4_or_ipv6_addr(bs, &c->addr);
	bstr_read_be16(bs, &c->port);
	bstr_read_u8(bs, &c->major);
	bstr_read_u8(bs, &c->minor);
	bstr_read_u8(bs, &version);

	/*
	 * "first_seen" was added at version 1.
	 */

	if (version < 1)
		c->first_seen = tm_time();
	else
		bstr_read_time(bs, &c->first_seen);

	/*
	 * Only create the KUID atom if there was no error in the deserialization
	 * since the value free callbacks are not invoked by the DBMW layer when
	 * there is a deserialization error.
	 */

	if (bstr_ended(bs)) {
		c->id = kuid_get_atom(&id);
	}
}

/**
 * Free routine for contacts, to release internally allocated memory, not
 * the structure itself.
 */
static void
free_contact(void *valptr, size_t len)
{
	struct contact *c = valptr;

	g_assert(sizeof *c == len);

	kuid_atom_free_null(&c->id);
}

/**
 * Context for recreate_ri() and remove_orphan().
 */
struct recreate_context {
	hset_t *dbkeys;			/* Seen DB keys (atoms) */
	uint orphans;			/* Orphan keys found */
};

static void
free_dbkey_kv(const void *key, void *u_data)
{
	const uint64 *dbkey = key;

	(void) u_data;

	atom_uint64_free(dbkey);
}

/**
 * DBMW foreach iterator to recreate keyinfo if not too ancient.
 * @return TRUE if entry is too ancient and key must be deleted.
 */
static bool
recreate_ri(void *key, void *value, size_t u_len, void *data)
{
	struct recreate_context *ctx = data;
	const struct rootdata *rd = value;
	const kuid_t *id = key;
	struct rootinfo *ri;
	time_delta_t d;
	int i;

	(void) u_len;

	/*
	 * If cached roots are too ancient, drop them.
	 */

	d = delta_time(tm_time(), rd->last_update);

	if (GNET_PROPERTY(dht_roots_debug) > 4)
		g_debug("DHT ROOTS retrieved target %s (%s)",
			kuid_to_hex_string(id), compact_time(d));

	if (d >= ROOTKEY_LIFETIME / 1000) {
		for (i = 0; i < rd->count; i++) {
			dbmw_delete(db_contact, &rd->dbkeys[i]);
		}
		return TRUE;
	}

	/*
	 * OK, we can keep these roots.
	 *
	 * Be sure to remember the largest contact ID we keep, so that we can
	 * initialize our counter properly for creating new entries later on.
	 */

	for (i = 0; i < rd->count; i++) {
		uint64 dbkey = rd->dbkeys[i];

		if (dbkey >= contactid)
			contactid = dbkey + 1;

		if (!hset_contains(ctx->dbkeys, &dbkey)) {
			const uint64 *dbatom = atom_uint64_get(&dbkey);
			hset_insert(ctx->dbkeys, dbatom);
		}
	}

	ri = allocate_rootinfo(id);
	patricia_insert(roots, ri->kuid, ri);
	ri->last_update = rd->last_update;
	ri->expire_ev = cq_insert(roots_cq, ROOTKEY_LIFETIME - d * 1000,
		roots_expire, ri);

	/*
	 * Update stats.
	 */

	targets_managed++;
	gnet_stats_inc_general(GNR_DHT_CACHED_KUID_TARGETS_HELD);

	contacts_managed += rd->count;
	gnet_stats_count_general(GNR_DHT_CACHED_ROOTS_HELD, rd->count);

	if (GNET_PROPERTY(dht_roots_debug) > 3)
		g_debug("DHT ROOTS retrieved %u closest node%s from %s kept (for %s)",
			PLURAL(rd->count),
			kuid_to_hex_string(id), compact_time(ROOTKEY_LIFETIME / 1000 - d));

	return FALSE;
}

/**
 * DBMW foreach iterator to remove orphan DB keys.
 * @return TRUE if entry is an orphan and must be deleted.
 */
static bool
remove_orphan(void *key, void *u_value, size_t u_len, void *data)
{
	struct recreate_context *ctx = data;
	uint64 *dbkey = key;

	(void) u_value;
	(void) u_len;

	if (!hset_contains(ctx->dbkeys, dbkey)) {
		ctx->orphans++;
		return TRUE;
	}

	return FALSE;
}

/**
 * Periodic DB synchronization.
 */
static bool
roots_sync(void *unused_obj)
{
	(void) unused_obj;

	dbstore_sync(db_rootdata);
	dbstore_sync(db_contact);

	return TRUE;
}

/**
 * Recreate rootinfo data from persisted information.
 */
static void
roots_init_rootinfo(void)
{
	struct recreate_context ctx;
	size_t count;

	if (GNET_PROPERTY(dht_roots_debug)) {
		count = dbmw_count(db_rootdata);
		g_debug("DHT ROOTS scanning %u retrieved target KUID%s",
			(unsigned) PLURAL(count));
	}

	ctx.dbkeys = hset_create(HASH_KEY_FIXED, sizeof(uint64));
	ctx.orphans = 0;

	dbmw_foreach_remove(db_rootdata, recreate_ri, &ctx);
	dbmw_foreach_remove(db_contact, remove_orphan, &ctx);

	hset_foreach(ctx.dbkeys, free_dbkey_kv, NULL);
	hset_free_null(&ctx.dbkeys);

	count = dbmw_count(db_rootdata);

	if (GNET_PROPERTY(dht_roots_debug)) {
		g_debug("DHT ROOTS kept %u target KUID%s: targets=%u, contacts=%u",
			(unsigned) PLURAL(count),
			targets_managed, contacts_managed);
		g_debug("DHT ROOTS stripped %u orphan contact DB-key%s",
			PLURAL(ctx.orphans));
	}

	/*
	 * If we retained no entries, issue a dbmw_clear() to restore underlying
	 * SDBM files to their smallest possible value.  This is necessary because
	 * the database is persistent and it can grow very large on disk, but still
	 * holding only a few values per page.  Being able to get a fresh start
	 * occasionally is a plus.
	 */

	if (0 == count) {
		contactid = 1;
		targets_managed = contacts_managed = 0;
	}


	if (!crash_was_restarted()) {
		if (GNET_PROPERTY(dht_roots_debug)) {
			if (0 == count)
				g_debug("DHT ROOTS clearing database");
			else
				g_debug("DHT ROOTS shrinking database files");
		}

		dbstore_compact(db_rootdata);
		dbstore_compact(db_contact);
	}

	if (GNET_PROPERTY(dht_roots_debug)) {
		g_debug("DHT ROOTS first allocated contact DB-key will be %s",
			uint64_to_string(contactid));
	}
}

/**
 * Initialize root node caching.
 */
void G_COLD
roots_init(void)
{
	dbstore_kv_t root_kv = { KUID_RAW_SIZE, NULL, sizeof(struct rootdata), 0 };
	dbstore_kv_t contact_kv = { sizeof(uint64), NULL, sizeof(struct contact),
		sizeof(struct contact) + KUID_RAW_SIZE };
	dbstore_packing_t root_packing =
		{ serialize_rootdata, deserialize_rootdata, NULL };
	dbstore_packing_t contact_packing =
		{ serialize_contact, deserialize_contact, free_contact };

	g_assert(NULL == roots_cq);
	g_assert(NULL == roots);
	g_assert(NULL == db_rootdata);
	g_assert(NULL == db_contact);

	roots_cq = cq_main_submake("roots", ROOTS_CALLOUT);
	roots = patricia_create(KUID_RAW_BITSIZE);

	db_rootdata = dbstore_open(db_rootdata_what, settings_dht_db_dir(),
		db_rootdata_base, root_kv, root_packing,
		ROOTKEYS_DB_CACHE_SIZE, kuid_hash, kuid_eq,
		GNET_PROPERTY(dht_storage_in_memory));

	db_contact = dbstore_open(db_contact_what, settings_dht_db_dir(),
		db_contact_base, contact_kv, contact_packing,
		CONTACT_DB_CACHE_SIZE, uint64_mem_hash, uint64_mem_eq,
		GNET_PROPERTY(dht_storage_in_memory));

	dbmw_set_map_cache(db_contact, CONTACT_MAP_CACHE_SIZE);

	roots_init_rootinfo();
	cq_periodic_add(roots_cq, ROOTS_SYNC_PERIOD, roots_sync, NULL);
}

/**
 * Map iterator to free the items held in `roots'.
 */
static void
roots_free_kv(void *u_key, void *val, void *u_x)
{
	struct rootinfo *ri = val;

	(void) u_key;
	(void) u_x;

	free_rootinfo(ri);
}

/**
 * Close root node caching.
 */
void G_COLD
roots_close(void)
{
	if (roots) {
		map_t *mr = map_create_from_patricia(roots);
		map_foreach(mr, roots_free_kv, NULL);
		map_release(mr);
		patricia_destroy(roots);
		roots = NULL;
	}

	if (GNET_PROPERTY(dht_roots_debug)) {
		g_debug("DHT ROOTS shutdown with targets=%u, contacts=%u",
			targets_managed, contacts_managed);
	}

	dbstore_close(db_rootdata, settings_dht_db_dir(), db_rootdata_base);
	db_rootdata = NULL;

	dbstore_close(db_contact, settings_dht_db_dir(), db_contact_base);
	db_contact = NULL;

	cq_free_null(&roots_cq);
}

/* vi: set ts=4 sw=4 cindent: */
