Merged in dstaesse/ouroboros/be-dht (pull request #529)

ipcpd: Add DHT as directory in normal IPCP

1 files changed, 2369 insertions, 0 deletions

diff --git a/src/ipcpd/normal/dht.c b/src/ipcpd/normal/dht.c
new file mode 100644
index 00000000..0b00e2f5
--- /dev/null
+++ b/src/ipcpd/normal/dht.c
@@ -0,0 +1,2369 @@
+/*
+ * Ouroboros - Copyright (C) 2016 - 2017
+ *
+ * Distributed Hash Table based on Kademlia
+ *
+ *    Dimitri Staessens <dimitri.staessens@ugent.be>
+ *    Sander Vrijders   <sander.vrijders@ugent.be>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * version 2.1 as published by the Free Software Foundation.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301 USA
+ */
+
+#define OUROBOROS_PREFIX "dht"
+
+#include <ouroboros/config.h>
+#include <ouroboros/hash.h>
+#include <ouroboros/bitmap.h>
+#include <ouroboros/errno.h>
+#include <ouroboros/logs.h>
+#include <ouroboros/list.h>
+#include <ouroboros/random.h>
+#include <ouroboros/time_utils.h>
+#include <ouroboros/utils.h>
+
+#include "dht.h"
+#include "dt.h"
+
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <inttypes.h>
+
+#include "kademlia.pb-c.h"
+typedef KadMsg kad_msg_t;
+typedef KadContactMsg kad_contact_msg_t;
+
+#define DHT_MAX_REQS  2048 /* KAD recommends rnd(), bmp can be changed.  */
+#define KAD_ALPHA     3    /* Parallel factor, proven optimal value.     */
+#define KAD_K         8    /* Replication factor, MDHT value.            */
+#define KAD_T_REPL    900  /* Replication time, tied to k. MDHT value.   */
+#define KAD_T_REFR    900  /* Refresh time stale bucket, MDHT value.     */
+#define KAD_T_JOIN    6    /* Response time to wait for a join.          */
+#define KAD_T_RESP    2    /* Response time to wait for a response.      */
+#define KAD_R_PING    2    /* Ping retries before declaring peer dead.   */
+#define KAD_QUEER     15   /* Time to declare peer questionable.         */
+#define KAD_BETA      8    /* Bucket split factor, must be 1, 2, 4 or 8. */
+
+enum dht_state {
+        DHT_INIT = 0,
+        DHT_RUNNING,
+        DHT_SHUTDOWN,
+};
+
+enum kad_code {
+        KAD_JOIN = 0,
+        KAD_FIND_NODE,
+        KAD_FIND_VALUE,
+        /* Messages without a response below. */
+        KAD_STORE,
+        KAD_RESPONSE
+};
+
+enum kad_req_state {
+        REQ_NULL = 0,
+        REQ_INIT,
+        REQ_PENDING,
+        REQ_RESPONSE,
+        REQ_DONE,
+        REQ_DESTROY
+};
+
+enum lookup_state {
+        LU_NULL = 0,
+        LU_INIT,
+        LU_PENDING,
+        LU_UPDATE,
+        LU_COMPLETE,
+        LU_DONE,
+        LU_DESTROY
+};
+
+struct kad_req {
+        struct list_head   next;
+
+        uint32_t           cookie;
+        enum kad_code      code;
+        uint8_t *          key;
+        uint64_t           addr;
+
+        enum kad_req_state state;
+        pthread_cond_t     cond;
+        pthread_mutex_t    lock;
+
+        time_t             t_exp;
+};
+
+struct lookup {
+        struct list_head  next;
+
+        uint8_t *         key;
+
+        struct list_head  contacts;
+        size_t            n_contacts;
+
+        uint64_t *        addrs;
+        size_t            n_addrs;
+
+        enum lookup_state state;
+        pthread_cond_t    cond;
+        pthread_mutex_t   lock;
+};
+
+struct val {
+        struct list_head next;
+
+        uint64_t         addr;
+
+        time_t           t_exp;
+        time_t           t_rep;
+};
+
+struct ref_entry {
+        struct list_head next;
+
+        uint8_t *        key;
+
+        time_t           t_rep;
+};
+
+struct dht_entry {
+        struct list_head next;
+
+        uint8_t *        key;
+        size_t           n_vals;
+        struct list_head vals;
+};
+
+struct contact {
+        struct list_head next;
+
+        uint8_t *        id;
+        uint64_t         addr;
+
+        size_t           fails;
+        time_t           t_seen;
+};
+
+struct bucket {
+        struct list_head contacts;
+        size_t           n_contacts;
+
+        struct list_head alts;
+        size_t           n_alts;
+
+        time_t           t_refr;
+
+        size_t           depth;
+        uint8_t          mask;
+
+        struct bucket *  parent;
+        struct bucket *  children[1L << KAD_BETA];
+};
+
+struct dht {
+        size_t           alpha;
+        size_t           b;
+        size_t           k;
+
+        time_t           t_expire;
+        time_t           t_refresh;
+        time_t           t_replic;
+        time_t           t_repub;
+
+        uint8_t *        id;
+        uint64_t         addr;
+
+        struct bucket *  buckets;
+
+        struct list_head entries;
+
+        struct list_head refs;
+
+        struct list_head lookups;
+
+        struct list_head requests;
+        struct bmp *     cookies;
+
+        enum dht_state   state;
+        pthread_mutex_t  mtx;
+
+        pthread_rwlock_t lock;
+
+        int              fd;
+
+        pthread_t        worker;
+};
+
+static uint8_t * dht_dup_key(const uint8_t * key,
+                             size_t          len)
+{
+        uint8_t * dup;
+
+        dup = malloc(sizeof(*dup) * len);
+        if (dup == NULL)
+                return NULL;
+
+        memcpy(dup, key, len);
+
+        return dup;
+}
+
+static enum dht_state dht_get_state(struct dht * dht)
+{
+        enum dht_state state;
+
+        pthread_mutex_lock(&dht->mtx);
+
+        state = dht->state;
+
+        pthread_mutex_unlock(&dht->mtx);
+
+        return state;
+}
+
+static void dht_set_state(struct dht *   dht,
+                          enum dht_state state)
+{
+        pthread_mutex_lock(&dht->mtx);
+
+        dht->state = state;
+
+        pthread_mutex_unlock(&dht->mtx);
+}
+
+static uint8_t * create_id(size_t len)
+{
+        uint8_t * id;
+
+        id = malloc(len);
+        if (id == NULL)
+                return NULL;
+
+        if (random_buffer(id, len) < 0) {
+                free(id);
+                return NULL;
+        }
+
+        return id;
+}
+
+static struct kad_req * kad_req_create(struct dht * dht,
+                                       kad_msg_t *  msg,
+                                       uint64_t     addr)
+{
+        struct kad_req *   req;
+        pthread_condattr_t cattr;
+        struct timespec    t;
+
+        req = malloc(sizeof(*req));
+        if (req == NULL)
+                return NULL;
+
+        list_head_init(&req->next);
+
+        clock_gettime(CLOCK_REALTIME_COARSE, &t);
+
+        req->t_exp  = t.tv_sec + KAD_T_RESP;
+        req->addr   = addr;
+        req->state  = REQ_INIT;
+        req->cookie = msg->cookie;
+        req->code   = msg->code;
+        req->key    = NULL;
+
+        if (msg->has_key) {
+                req->key = dht_dup_key(msg->key.data, dht->b);
+                if (req->key == NULL) {
+                        free(req);
+                        return NULL;
+                }
+        }
+
+        if (pthread_mutex_init(&req->lock, NULL)) {
+                free(req->key);
+                free(req);
+                return NULL;
+        }
+
+        pthread_condattr_init(&cattr);
+#ifndef __APPLE__
+        pthread_condattr_setclock(&cattr, PTHREAD_COND_CLOCK);
+#endif
+
+        if (pthread_cond_init(&req->cond, &cattr)) {
+                pthread_condattr_destroy(&cattr);
+                pthread_mutex_destroy(&req->lock);
+                free(req->key);
+                free(req);
+                return NULL;
+        }
+
+        pthread_condattr_destroy(&cattr);
+
+        return req;
+}
+
+static void kad_req_destroy(struct kad_req * req)
+{
+        assert(req);
+
+        if (req->key != NULL)
+                free(req->key);
+
+        pthread_mutex_lock(&req->lock);
+
+        switch (req->state) {
+        case REQ_DESTROY:
+                pthread_mutex_unlock(&req->lock);
+                return;
+        case REQ_PENDING:
+                req->state = REQ_DESTROY;
+                pthread_cond_signal(&req->cond);
+                break;
+        case REQ_INIT:
+        case REQ_DONE:
+                req->state = REQ_NULL;
+                break;
+        case REQ_RESPONSE:
+        case REQ_NULL:
+        default:
+                break;
+        }
+
+        while (req->state != REQ_NULL)
+                pthread_cond_wait(&req->cond, &req->lock);
+
+        pthread_mutex_unlock(&req->lock);
+
+        pthread_cond_destroy(&req->cond);
+        pthread_mutex_destroy(&req->lock);
+
+        free(req);
+}
+
+static int kad_req_wait(struct kad_req * req,
+                        time_t           t)
+{
+        struct timespec timeo = {t, 0};
+        struct timespec abs;
+        int ret = 0;
+
+        assert(req);
+
+        clock_gettime(PTHREAD_COND_CLOCK, &abs);
+
+        ts_add(&abs, &timeo, &abs);
+
+        pthread_mutex_lock(&req->lock);
+
+        req->state = REQ_PENDING;
+
+        while (req->state == REQ_PENDING && ret != -ETIMEDOUT)
+                ret = -pthread_cond_timedwait(&req->cond, &req->lock, &abs);
+
+        switch(req->state) {
+        case REQ_DESTROY:
+                ret = -1;
+                req->state = REQ_NULL;
+                pthread_cond_signal(&req->cond);
+                break;
+        case REQ_PENDING: /* ETIMEDOUT */
+        case REQ_RESPONSE:
+                req->state = REQ_DONE;
+                pthread_cond_signal(&req->cond);
+                break;
+        default:
+                break;
+        }
+
+        pthread_mutex_unlock(&req->lock);
+
+        return ret;
+}
+
+static void kad_req_respond(struct kad_req * req)
+{
+        pthread_mutex_lock(&req->lock);
+
+        req->state = REQ_RESPONSE;
+        pthread_cond_signal(&req->cond);
+
+        pthread_mutex_unlock(&req->lock);
+}
+
+static struct contact * contact_create(const uint8_t * id,
+                                       size_t          len,
+                                       uint64_t        addr)
+{
+        struct contact * c;
+        struct timespec  t;
+
+        c = malloc(sizeof(*c));
+        if (c == NULL)
+                return NULL;
+
+        list_head_init(&c->next);
+
+        clock_gettime(CLOCK_REALTIME_COARSE, &t);
+
+        c->addr   = addr;
+        c->fails  = 0;
+        c->t_seen = t.tv_sec;
+        c->id     = dht_dup_key(id, len);
+        if (c->id == NULL) {
+                free(c);
+                return NULL;
+        }
+
+        return c;
+}
+
+static void contact_destroy(struct contact * c)
+{
+        if (c != NULL)
+                free(c->id);
+
+        free(c);
+}
+
+static struct bucket * iter_bucket(struct bucket * b,
+                                   const uint8_t * id)
+{
+        uint8_t byte;
+        uint8_t mask;
+
+        assert(b);
+
+        if (b->children[0] == NULL)
+                return b;
+
+        byte = id[(b->depth * KAD_BETA) / CHAR_BIT];
+
+        mask = ((1L << KAD_BETA) - 1) & 0xFF;
+
+        byte >>= (CHAR_BIT - KAD_BETA) -
+                (((b->depth) * KAD_BETA) & (CHAR_BIT - 1));
+
+        return iter_bucket(b->children[(byte & mask)], id);
+}
+
+static struct bucket * dht_get_bucket(struct dht *    dht,
+                                      const uint8_t * id)
+{
+        assert(dht->buckets);
+
+        return iter_bucket(dht->buckets, id);
+}
+
+/*
+ * If someone builds a network where the n (n > k) closest nodes all
+ * have IDs starting with the same 64 bits: by all means, change this.
+ */
+static uint64_t dist(const uint8_t * src,
+                     const uint8_t * dst)
+{
+        return betoh64(*((uint64_t *) src) ^ *((uint64_t *) dst));
+}
+
+static size_t list_add_sorted(struct list_head * l,
+                              struct contact *   c,
+                              const uint8_t *    key)
+{
+        struct list_head * p;
+
+        assert(l);
+        assert(c);
+        assert(key);
+        assert(c->id);
+
+        list_for_each(p, l) {
+                struct contact * e = list_entry(p, struct contact, next);
+                if (dist(c->id, key) > dist(e->id, key))
+                        break;
+        }
+
+        list_add_tail(&c->next, p);
+
+        return 1;
+}
+
+static size_t dht_contact_list(struct dht *       dht,
+                               struct list_head * l,
+                               const uint8_t *    key)
+{
+        struct list_head * p;
+        struct bucket *    b;
+        size_t             len = 0;
+        size_t             i;
+        struct timespec    t;
+
+        assert(l);
+        assert(dht);
+        assert(key);
+        assert(list_is_empty(l));
+
+        clock_gettime(CLOCK_REALTIME_COARSE, &t);
+
+        b = dht_get_bucket(dht, key);
+        if (b == NULL)
+                return 0;
+
+        b->t_refr = t.tv_sec + KAD_T_REFR;
+
+        if (b->n_contacts == dht->k || b->parent == NULL) {
+                list_for_each(p, &b->contacts) {
+                        struct contact * c;
+                        c = list_entry(p, struct contact, next);
+                        c = contact_create(c->id, dht->b, c->addr);
+                        if (list_add_sorted(l, c, key) == 1)
+                                if (++len > dht->k)
+                                        break;
+                }
+        } else {
+                struct bucket * d = b->parent;
+                for (i = 0; i < (1L << KAD_BETA); ++i) {
+                        list_for_each(p, &d->children[i]->contacts) {
+                                struct contact * c;
+                                c = list_entry(p, struct contact, next);
+                                c = contact_create(c->id, dht->b, c->addr);
+                                if (c == NULL)
+                                        continue;
+                                if (list_add_sorted(l, c, key) == 1)
+                                        if (++len > dht->k)
+                                                break;
+                        }
+                }
+        }
+
+        assert(len == dht->k || b->parent == NULL);
+
+        return len;
+}
+
+static struct lookup * lookup_create(struct dht *    dht,
+                                     const uint8_t * id)
+{
+        struct lookup *    lu;
+        pthread_condattr_t cattr;
+
+        assert(dht);
+        assert(id);
+
+        lu = malloc(sizeof(*lu));
+        if (lu == NULL)
+                goto fail_malloc;
+
+        list_head_init(&lu->contacts);
+
+        lu->state   = LU_INIT;
+        lu->addrs   = NULL;
+        lu->n_addrs = 0;
+        lu->key     = dht_dup_key(id, dht->b);
+        if (lu->key == NULL)
+                goto fail_id;
+
+        if (pthread_mutex_init(&lu->lock, NULL))
+                goto fail_mutex;
+
+        pthread_condattr_init(&cattr);
+#ifndef __APPLE__
+        pthread_condattr_setclock(&cattr, PTHREAD_COND_CLOCK);
+#endif
+
+        if (pthread_cond_init(&lu->cond, &cattr))
+                goto fail_cond;
+
+        pthread_condattr_destroy(&cattr);
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        list_add(&lu->next, &dht->lookups);
+
+        lu->n_contacts = dht_contact_list(dht, &lu->contacts, id);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return lu;
+
+ fail_cond:
+        pthread_condattr_destroy(&cattr);
+        pthread_mutex_destroy(&lu->lock);
+ fail_mutex:
+        free(lu->key);
+ fail_id:
+        free(lu);
+ fail_malloc:
+        return NULL;
+}
+
+static void lookup_destroy(struct lookup * lu)
+{
+        struct list_head * p;
+        struct list_head * h;
+
+        assert(lu);
+
+        pthread_mutex_lock(&lu->lock);
+
+        switch (lu->state) {
+        case LU_DESTROY:
+                pthread_mutex_unlock(&lu->lock);
+                return;
+        case LU_PENDING:
+                lu->state = LU_DESTROY;
+                pthread_cond_signal(&lu->cond);
+                break;
+        case LU_INIT:
+        case LU_DONE:
+        case LU_UPDATE:
+        case LU_COMPLETE:
+                lu->state = REQ_NULL;
+                break;
+        case LU_NULL:
+        default:
+                break;
+        }
+
+        while (lu->state != LU_NULL)
+                pthread_cond_wait(&lu->cond, &lu->lock);
+
+        if (lu->key != NULL)
+                free(lu->key);
+        if (lu->addrs != NULL)
+                free(lu->addrs);
+
+        list_for_each_safe(p, h, &lu->contacts) {
+                struct contact * c = list_entry(p, struct contact, next);
+                list_del(&c->next);
+                contact_destroy(c);
+        }
+
+        pthread_mutex_unlock(&lu->lock);
+
+        pthread_cond_destroy(&lu->cond);
+        pthread_mutex_destroy(&lu->lock);
+
+        free(lu);
+}
+
+static void lookup_update(struct dht *    dht,
+                          struct lookup * lu,
+                          kad_msg_t *     msg)
+{
+        struct list_head * p = NULL;
+        struct contact *   c = NULL;
+        size_t             n;
+        size_t             pos = 0;
+
+        assert(lu);
+        assert(msg);
+
+        if (dht_get_state(dht) != DHT_RUNNING)
+                return;
+
+        pthread_mutex_lock(&lu->lock);
+
+        if (msg->n_addrs > 0) {
+                if (lu->addrs == NULL) {
+                        lu->addrs = malloc(sizeof(*lu->addrs) * msg->n_addrs);
+                        for (n = 0; n < msg->n_addrs; ++n)
+                                lu->addrs[n] = msg->addrs[n];
+                        lu->n_addrs = msg->n_addrs;
+                }
+                lu->state = LU_COMPLETE;
+                pthread_cond_signal(&lu->cond);
+                pthread_mutex_unlock(&lu->lock);
+                return;
+        }
+
+        while (lu->state == LU_INIT)
+                pthread_cond_wait(&lu->cond, &lu->lock);
+
+        for (n = 0; n < msg->n_contacts; ++n) {
+                c = contact_create(msg->contacts[n]->id.data,
+                                   dht->b, msg->contacts[n]->addr);
+                if (c == NULL)
+                        continue;
+
+                list_for_each(p, &lu->contacts) {
+                        struct contact * e;
+                        e = list_entry(p, struct contact, next);
+                        if (!memcmp(e->id, c->id, dht->b)) {
+                                contact_destroy(c);
+                                goto finish_node;
+                        }
+
+                        if (dist(c->id, lu->key) > dist(e->id, lu->key))
+                                break;
+                        pos++;
+                }
+
+        }
+
+        if (pos == dht->k) {
+                contact_destroy(c);
+                goto finish_node;
+        } else {
+                struct contact * d;
+                d = list_last_entry(&lu->contacts, struct contact, next);
+                list_del(&d->next);
+                list_add_tail(&c->next, p);
+                contact_destroy(d);
+        }
+
+ finish_node:
+        lu->state = LU_UPDATE;
+        pthread_cond_signal(&lu->cond);
+        pthread_mutex_unlock(&lu->lock);
+        return;
+}
+
+static ssize_t lookup_get_addrs(struct lookup * lu,
+                                uint64_t *      addrs)
+{
+        ssize_t n;
+
+        assert(lu);
+
+        pthread_mutex_lock(&lu->lock);
+
+        for (n = 0; (size_t) n < lu->n_addrs; ++n)
+                addrs[n] = lu->addrs[n];
+
+        assert((size_t) n == lu->n_addrs);
+
+        pthread_mutex_unlock(&lu->lock);
+
+        return n;
+}
+
+static ssize_t lookup_contact_addrs(struct lookup * lu,
+                                    uint64_t *      addrs)
+{
+        struct list_head * p;
+        ssize_t            n = 0;
+
+        assert(lu);
+        assert(addrs);
+
+        pthread_mutex_lock(&lu->lock);
+
+        list_for_each(p, &lu->contacts) {
+                struct contact * c = list_entry(p, struct contact, next);
+                addrs[n] = c->addr;
+                n++;
+        }
+
+        pthread_mutex_unlock(&lu->lock);
+
+        return n;
+}
+
+static ssize_t lookup_new_addrs(struct lookup * lu,
+                                uint64_t *      addrs)
+{
+        struct list_head * p;
+        ssize_t            n = 0;
+
+        assert(lu);
+        assert(addrs);
+
+        pthread_mutex_lock(&lu->lock);
+
+        /* Uses fails to check if the contact has been contacted. */
+        list_for_each(p, &lu->contacts) {
+                struct contact * c = list_entry(p, struct contact, next);
+                if (c->fails == 0) {
+                        c->fails = 1;
+                        addrs[n] = c->addr;
+                        n++;
+                }
+
+                if (n == KAD_ALPHA)
+                        break;
+        }
+
+        if (n == 0)
+                lu->state = LU_DONE;
+
+        pthread_mutex_unlock(&lu->lock);
+
+        assert(n <= KAD_ALPHA);
+
+        return n;
+}
+
+static enum lookup_state lookup_wait(struct lookup * lu)
+{
+        enum lookup_state state;
+
+        pthread_mutex_lock(&lu->lock);
+
+        lu->state = LU_PENDING;
+        pthread_cond_signal(&lu->cond);
+
+        pthread_cleanup_push((void (*)(void *)) lookup_destroy, (void *) lu);
+
+        while (lu->state == LU_PENDING)
+                pthread_cond_wait(&lu->cond, &lu->lock);
+
+        pthread_cleanup_pop(false);
+
+        if (lu->state == LU_DESTROY) {
+                lu->state = LU_NULL;
+                pthread_cond_signal(&lu->cond);
+                pthread_mutex_unlock(&lu->lock);
+                return -1;
+        }
+
+        state = lu->state;
+
+        pthread_mutex_unlock(&lu->lock);
+
+        return state;
+}
+
+static struct kad_req * dht_find_request(struct dht * dht,
+                                         kad_msg_t *  msg)
+{
+        struct list_head * p;
+
+        assert(dht);
+        assert(msg);
+
+        list_for_each(p, &dht->requests) {
+                struct kad_req * r = list_entry(p, struct kad_req, next);
+                if (r->cookie == msg->cookie)
+                        return r;
+        }
+
+        return NULL;
+}
+
+static struct lookup * dht_find_lookup(struct dht *    dht,
+                                       const uint8_t * key)
+{
+        struct list_head * p;
+
+        assert(dht);
+        assert(key);
+
+        list_for_each(p, &dht->lookups) {
+                struct lookup * l = list_entry(p, struct lookup, next);
+                if (!memcmp(l->key, key, dht->b))
+                        return l;
+        }
+
+        return NULL;
+}
+
+static struct val * val_create(uint64_t addr,
+                               time_t   exp)
+{
+        struct val *    v;
+        struct timespec t;
+
+        v = malloc(sizeof(*v));
+        if (v == NULL)
+                return NULL;
+
+        list_head_init(&v->next);
+        v->addr = addr;
+
+        clock_gettime(CLOCK_REALTIME_COARSE, &t);
+
+        v->t_exp = t.tv_sec + exp;
+        v->t_rep = t.tv_sec + KAD_T_REPL;
+
+        return v;
+}
+
+static void val_destroy(struct val * v)
+{
+        assert(v);
+
+        free(v);
+}
+
+static struct ref_entry * ref_entry_create(struct dht *    dht,
+                                           const uint8_t * key)
+{
+        struct ref_entry * e;
+        struct timespec    t;
+
+        assert(dht);
+        assert(key);
+
+        e = malloc(sizeof(*e));
+        if (e == NULL)
+                return NULL;
+
+        e->key = dht_dup_key(key, dht->b);
+        if (e->key == NULL) {
+                free(e);
+                return NULL;
+        }
+
+        clock_gettime(CLOCK_REALTIME_COARSE, &t);
+
+        e->t_rep = t.tv_sec + dht->t_repub;
+
+        return e;
+}
+
+static void ref_entry_destroy(struct ref_entry * e)
+{
+        free(e->key);
+        free(e);
+}
+
+static struct dht_entry * dht_entry_create(struct dht *    dht,
+                                           const uint8_t * key)
+{
+        struct dht_entry * e;
+
+        assert(dht);
+        assert(key);
+
+        e = malloc(sizeof(*e));
+        if (e == NULL)
+                return NULL;
+
+        list_head_init(&e->next);
+        list_head_init(&e->vals);
+
+        e->n_vals = 0;
+
+        e->key = dht_dup_key(key, dht->b);
+        if (e->key == NULL) {
+                free(e);
+                return NULL;
+        }
+
+        return e;
+}
+
+static void dht_entry_destroy(struct dht_entry * e)
+{
+        struct list_head * p;
+        struct list_head * h;
+
+        assert(e);
+
+        list_for_each_safe(p, h, &e->vals) {
+                struct val * v = list_entry(p, struct val, next);
+                list_del(&v->next);
+                val_destroy(v);
+        }
+
+        free(e->key);
+
+        free(e);
+}
+
+static int dht_entry_add_addr(struct dht_entry * e,
+                              uint64_t           addr,
+                              time_t             exp)
+{
+        struct list_head * p;
+        struct val * val;
+        struct timespec t;
+
+        clock_gettime(CLOCK_REALTIME_COARSE, &t);
+
+        list_for_each(p, &e->vals) {
+                struct val * v = list_entry(p, struct val, next);
+                if (v->addr == addr) {
+                        if (v->t_exp < t.tv_sec + exp) {
+                                v->t_exp = t.tv_sec + exp;
+                                v->t_rep = t.tv_sec + KAD_T_REPL;
+                        }
+
+                        return 0;
+                }
+        }
+
+        val = val_create(addr, exp);
+        if (val == NULL)
+                return -ENOMEM;
+
+        list_add(&val->next, &e->vals);
+        ++e->n_vals;
+
+        return 0;
+}
+
+
+static void dht_entry_del_addr(struct dht_entry * e,
+                               uint64_t           addr)
+{
+        struct list_head * p;
+        struct list_head * h;
+
+        assert(e);
+
+        list_for_each_safe(p, h, &e->vals) {
+                struct val * v = list_entry(p, struct val, next);
+                if (v->addr == addr) {
+                        list_del(&v->next);
+                        val_destroy(v);
+                        --e->n_vals;
+                }
+        }
+
+        if (e->n_vals == 0) {
+                list_del(&e->next);
+                dht_entry_destroy(e);
+        }
+}
+
+static uint64_t dht_entry_get_addr(struct dht *       dht,
+                                   struct dht_entry * e)
+{
+        struct list_head * p;
+
+        assert(e);
+        assert(!list_is_empty(&e->vals));
+
+        list_for_each(p, &e->vals) {
+                struct val * v = list_entry(p, struct val, next);
+                if (v->addr != dht->addr)
+                        return v->addr;
+        }
+
+        return 0;
+}
+
+/* Forward declaration. */
+static struct lookup * kad_lookup(struct dht *    dht,
+                                  const uint8_t * key,
+                                  enum kad_code   code);
+
+
+/* Build a refresh list. */
+static void bucket_refresh(struct dht *       dht,
+                           struct bucket *    b,
+                           time_t             t,
+                           struct list_head * r)
+{
+        size_t i;
+
+        if (*b->children != NULL)
+                for (i = 0; i < (1L << KAD_BETA); ++i)
+                        bucket_refresh(dht, b->children[i], t, r);
+
+        if (b->n_contacts == 0)
+                return;
+
+        if (t > b->t_refr) {
+                struct contact * c;
+                struct contact * d;
+                c = list_first_entry(&b->contacts, struct contact, next);
+                d = contact_create(c->id, dht->b, c->addr);
+                if (c != NULL)
+                        list_add(&d->next, r);
+                return;
+        }
+}
+
+
+static struct bucket * bucket_create(void)
+{
+        struct bucket * b;
+        struct timespec t;
+        size_t          i;
+
+        b = malloc(sizeof(*b));
+        if (b == NULL)
+                return NULL;
+
+        list_head_init(&b->contacts);
+        b->n_contacts = 0;
+
+        list_head_init(&b->alts);
+        b->n_alts = 0;
+
+        clock_gettime(CLOCK_REALTIME_COARSE, &t);
+        b->t_refr = t.tv_sec + KAD_T_REFR;
+
+        for (i = 0; i < (1L << KAD_BETA); ++i)
+                b->children[i]  = NULL;
+
+        b->parent = NULL;
+        b->depth = 0;
+
+        return b;
+}
+
+static void bucket_destroy(struct bucket * b)
+{
+        struct list_head * p;
+        struct list_head * h;
+        size_t             i;
+
+        assert(b);
+
+        for (i = 0; i < (1L << KAD_BETA); ++i)
+                if (b->children[i] != NULL)
+                        bucket_destroy(b->children[i]);
+
+        list_for_each_safe(p, h, &b->contacts) {
+                struct contact * c = list_entry(p, struct contact, next);
+                list_del(&c->next);
+                contact_destroy(c);
+                --b->n_contacts;
+        }
+
+        list_for_each_safe(p, h, &b->alts) {
+                struct contact * c = list_entry(p, struct contact, next);
+                list_del(&c->next);
+                contact_destroy(c);
+                --b->n_contacts;
+        }
+
+        free(b);
+}
+
+static bool bucket_has_id(struct bucket * b,
+                          const uint8_t * id)
+{
+        uint8_t mask;
+        uint8_t byte;
+
+        if (b->depth == 0)
+                return true;
+
+        byte = id[(b->depth * KAD_BETA) / CHAR_BIT];
+
+        mask = ((1L << KAD_BETA) - 1) & 0xFF;
+
+        byte >>= (CHAR_BIT - KAD_BETA) -
+                (((b->depth - 1) * KAD_BETA) & (CHAR_BIT - 1));
+
+        return ((byte & mask) == b->mask);
+}
+
+static int split_bucket(struct bucket * b)
+{
+        struct list_head * p;
+        struct list_head * h;
+        uint8_t mask = 0;
+        size_t i;
+        size_t c;
+
+        assert(b);
+        assert(b->n_alts == 0);
+        assert(b->n_contacts);
+        assert(b->children[0] == NULL);
+
+        c = b->n_contacts;
+
+        for (i = 0; i < (1L << KAD_BETA); ++i) {
+                b->children[i] = bucket_create();
+                if (b->children[i] == NULL) {
+                        size_t j;
+                        for (j = 0; j < i; ++j)
+                                bucket_destroy(b->children[j]);
+                        return -1;
+                }
+
+                b->children[i]->depth  = b->depth + 1;
+                b->children[i]->mask   = mask;
+                b->children[i]->parent = b;
+
+                list_for_each_safe(p, h, &b->contacts) {
+                        struct contact * c;
+                        c = list_entry(p, struct contact, next);
+                        if (bucket_has_id(b->children[i], c->id)) {
+                                list_del(&c->next);
+                                --b->n_contacts;
+                                list_add(&c->next, &b->children[i]->contacts);
+                                ++b->children[i]->n_contacts;
+                        }
+                }
+
+                mask++;
+        }
+
+        for (i = 0; i < (1L << KAD_BETA); ++i)
+                if (b->children[i]->n_contacts == c)
+                        split_bucket(b->children[i]);
+
+        return 0;
+}
+
+/* Locked externally to mandate update as (final) part of join transaction. */
+static int dht_update_bucket(struct dht *    dht,
+                             const uint8_t * id,
+                             uint64_t        addr)
+{
+        struct list_head * p;
+        struct list_head * h;
+        struct bucket *    b;
+        struct contact *   c;
+
+        assert(dht);
+
+        b = dht_get_bucket(dht, id);
+        if (b == NULL)
+                return -1;
+
+        c = contact_create(id, dht->b, addr);
+        if (c == NULL)
+                return -1;
+
+        list_for_each_safe(p, h, &b->contacts) {
+                struct contact * d = list_entry(p, struct contact, next);
+                if (d->addr == addr) {
+                        list_del(&d->next);
+                        contact_destroy(d);
+                        --b->n_contacts;
+                }
+        }
+
+        if (b->n_contacts == dht->k) {
+                if (bucket_has_id(b, dht->id)) {
+                        list_add_tail(&c->next, &b->contacts);
+                        ++b->n_contacts;
+                        if (split_bucket(b)) {
+                                list_del(&c->next);
+                                contact_destroy(c);
+                                --b->n_contacts;
+                        }
+                } else if (b->n_alts == dht->k) {
+                        struct contact * d;
+                        d = list_first_entry(&b->alts, struct contact, next);
+                        list_del(&d->next);
+                        contact_destroy(d);
+                        list_add_tail(&c->next, &b->alts);
+                } else {
+                        list_add_tail(&c->next, &b->alts);
+                        ++b->n_alts;
+                }
+        } else {
+                list_add_tail(&c->next, &b->contacts);
+                ++b->n_contacts;
+        }
+
+        return 0;
+}
+
+static int send_msg(struct dht * dht,
+                    kad_msg_t *  msg,
+                    uint64_t     addr)
+{
+        struct shm_du_buff * sdb;
+        struct kad_req *     req;
+        size_t               len;
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        if (dht->id != NULL) {
+                msg->has_s_id = true;
+                msg->s_id.data = dht->id;
+                msg->s_id.len  = dht->b;
+        }
+
+        msg->s_addr = dht->addr;
+
+        if (msg->code < KAD_STORE) {
+                msg->cookie = bmp_allocate(dht->cookies);
+                if (!bmp_is_id_valid(dht->cookies, msg->cookie))
+                        goto fail_bmp_alloc;
+        }
+
+        len = kad_msg__get_packed_size(msg);
+        if (len == 0)
+                goto fail_msg;
+
+        if (ipcp_sdb_reserve(&sdb, len))
+                goto fail_msg;
+
+        kad_msg__pack(msg, shm_du_buff_head(sdb));
+
+#ifndef __DHT_TEST__
+        if (dt_write_sdu(addr, QOS_CUBE_BE, dht->fd, sdb))
+                goto fail_write;
+#else
+        (void) addr;
+        ipcp_sdb_release(sdb);
+#endif /* __DHT_TEST__ */
+
+        if (msg->code < KAD_STORE) {
+                req = kad_req_create(dht, msg, addr);
+                if (req != NULL)
+                        list_add(&req->next, &dht->requests);
+        }
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return 0;
+
+#ifndef __DHT_TEST__
+ fail_write:
+        ipcp_sdb_release(sdb);
+#endif
+ fail_msg:
+        bmp_release(dht->cookies, msg->cookie);
+ fail_bmp_alloc:
+        pthread_rwlock_unlock(&dht->lock);
+        return -1;
+}
+
+static struct dht_entry * dht_find_entry(struct dht *    dht,
+                                         const uint8_t * key)
+{
+        struct list_head * p;
+
+        list_for_each(p, &dht->entries) {
+                struct dht_entry * e = list_entry(p, struct dht_entry, next);
+                if (!memcmp(key, e->key, dht->b))
+                        return e;
+        }
+
+        return NULL;
+}
+
+static int kad_add(struct dht *              dht,
+                   const kad_contact_msg_t * contacts,
+                   ssize_t                   n,
+                   time_t                    exp)
+{
+        struct dht_entry * e;
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        while (--n >= 0) {
+                if (contacts[n].id.len != dht->b)
+                        log_warn("Bad key length in contact data.");
+
+                e = dht_find_entry(dht, contacts[n].id.data);
+                if (e != NULL) {
+                        if (dht_entry_add_addr(e, contacts[n].addr, exp))
+                                goto fail;
+                } else {
+                        e = dht_entry_create(dht, contacts[n].id.data);
+                        if (e == NULL)
+                                goto fail;
+
+                        if (dht_entry_add_addr(e, contacts[n].addr, exp)) {
+                                dht_entry_destroy(e);
+                                goto fail;
+                        }
+
+                        list_add(&e->next, &dht->entries);
+                }
+        }
+
+        pthread_rwlock_unlock(&dht->lock);
+        return 0;
+
+ fail:
+        pthread_rwlock_unlock(&dht->lock);
+        return -ENOMEM;
+}
+
+static int wait_resp(struct dht * dht,
+                     kad_msg_t *  msg,
+                     time_t       timeo)
+{
+        struct kad_req * req;
+
+        assert(dht);
+        assert(msg);
+
+        pthread_rwlock_rdlock(&dht->lock);
+
+        req = dht_find_request(dht, msg);
+        if (req == NULL) {
+                pthread_rwlock_unlock(&dht->lock);
+                return -EPERM;
+        }
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return kad_req_wait(req, timeo);
+}
+
+static int kad_store(struct dht *    dht,
+                     const uint8_t * key,
+                     uint64_t        addr,
+                     uint64_t        r_addr,
+                     time_t          ttl)
+{
+        kad_msg_t msg = KAD_MSG__INIT;
+        kad_contact_msg_t cmsg = KAD_CONTACT_MSG__INIT;
+        kad_contact_msg_t * cmsgp[1];
+
+        cmsg.id.data = (uint8_t *) key;
+        cmsg.id.len  = dht->b;
+        cmsg.addr    = addr;
+
+        cmsgp[0] = &cmsg;
+
+        msg.code         = KAD_STORE;
+        msg.has_t_expire = true;
+        msg.t_expire     = ttl;
+        msg.n_contacts   = 1;
+        msg.contacts     = cmsgp;
+
+        if (send_msg(dht, &msg, r_addr))
+                return -1;
+
+        return 0;
+}
+
+static ssize_t kad_find(struct dht *     dht,
+                        const uint8_t *  key,
+                        const uint64_t * addrs,
+                        enum kad_code    code)
+{
+        kad_msg_t msg  = KAD_MSG__INIT;
+        ssize_t   sent = 0;
+
+        assert(dht);
+        assert(key);
+
+        msg.code = code;
+
+        msg.has_key       = true;
+        msg.key.data      = (uint8_t *) key;
+        msg.key.len       = dht->b;
+
+        while (*addrs != 0) {
+                if (*addrs != dht->addr) {
+                        send_msg(dht, &msg, *addrs);
+                        sent++;
+                }
+                ++addrs;
+        }
+
+        return sent;
+}
+
+static void lookup_set_state(struct lookup *   lu,
+                             enum lookup_state state)
+{
+        pthread_mutex_lock(&lu->lock);
+
+        lu->state = state;
+
+        pthread_mutex_unlock(&lu->lock);
+}
+
+static struct lookup * kad_lookup(struct dht *    dht,
+                                  const uint8_t * id,
+                                  enum kad_code   code)
+{
+        uint64_t          addrs[KAD_ALPHA + 1];
+        enum lookup_state state;
+        struct lookup *   lu;
+
+        lu = lookup_create(dht, id);
+        if (lu == NULL)
+                return NULL;
+
+        addrs[lookup_new_addrs(lu, addrs)] = 0;
+
+        if (addrs[0] == 0) {
+                pthread_rwlock_wrlock(&dht->lock);
+                list_del(&lu->next);
+                pthread_rwlock_unlock(&dht->lock);
+                lookup_destroy(lu);
+                return NULL;
+        }
+
+        if (kad_find(dht, id, addrs, code) == 0) {
+                pthread_rwlock_wrlock(&dht->lock);
+                list_del(&lu->next);
+                pthread_rwlock_unlock(&dht->lock);
+                lu->state = LU_COMPLETE;
+                return lu;
+        }
+
+        while ((state = lookup_wait(lu)) != LU_COMPLETE) {
+                switch (state) {
+                case LU_UPDATE:
+                        addrs[lookup_new_addrs(lu, addrs)] = 0;
+                        if (addrs[0] == 0) {
+                                pthread_rwlock_wrlock(&dht->lock);
+                                list_del(&lu->next);
+                                pthread_rwlock_unlock(&dht->lock);
+                                return lu;
+                        }
+
+                        kad_find(dht, id, addrs, code);
+                        break;
+                case LU_DESTROY:
+                        lookup_set_state(lu, LU_NULL);
+                        return NULL;
+                default:
+                        break;
+                };
+        }
+
+        assert(state = LU_COMPLETE);
+
+        pthread_rwlock_wrlock(&dht->lock);
+        list_del(&lu->next);
+        pthread_rwlock_unlock(&dht->lock);
+
+        return lu;
+}
+
+static void kad_publish(struct dht *    dht,
+                        const uint8_t * key,
+                        uint64_t        addr,
+                        time_t          exp)
+{
+        struct lookup * lu;
+        uint64_t        addrs[KAD_K];
+        ssize_t         n;
+
+        assert(dht);
+        assert(key);
+
+        lu = kad_lookup(dht, key, KAD_FIND_NODE);
+        if (lu == NULL)
+                return;
+
+        n = lookup_contact_addrs(lu, addrs);
+
+        while (--n > 0) {
+                if (addrs[n] == dht->addr) {
+                        kad_contact_msg_t msg = KAD_CONTACT_MSG__INIT;
+                        msg.id.data = (uint8_t *) key;
+                        msg.id.len  = dht->b;
+                        msg.addr    = addr;
+                        kad_add(dht, &msg, 1, exp);
+                } else {
+                        if (kad_store(dht, key, addr, addrs[n], dht->t_expire))
+                                log_warn("Failed to send store message.");
+                }
+        }
+
+        lookup_destroy(lu);
+}
+
+static int kad_join(struct dht * dht,
+                    uint64_t     addr)
+{
+        kad_msg_t       msg = KAD_MSG__INIT;
+        struct lookup * lu;
+
+        msg.code = KAD_JOIN;
+
+        msg.has_alpha       = true;
+        msg.has_b           = true;
+        msg.has_k           = true;
+        msg.has_t_refresh   = true;
+        msg.has_t_replicate = true;
+        msg.alpha           = KAD_ALPHA;
+        msg.b               = dht->b;
+        msg.k               = KAD_K;
+        msg.t_refresh       = KAD_T_REFR;
+        msg.t_replicate     = KAD_T_REPL;
+
+        if (send_msg(dht, &msg, addr))
+                return -1;
+
+        if (wait_resp(dht, &msg, KAD_T_JOIN) < 0)
+                return -1;
+
+        dht->id = create_id(dht->b);
+        if (dht->id == NULL)
+                return -1;
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        dht_update_bucket(dht, dht->id, dht->addr);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        lu = kad_lookup(dht, dht->id, KAD_FIND_NODE);
+        if (lu == NULL)
+                log_warn("Join response not yet added.");
+        else
+                lookup_destroy(lu);
+
+        return 0;
+}
+
+static void dht_dead_peer(struct dht * dht,
+                          uint8_t *    key,
+                          uint64_t     addr)
+{
+        struct list_head * p;
+        struct list_head * h;
+        struct bucket *    b;
+
+        b = dht_get_bucket(dht, key);
+
+        list_for_each_safe(p, h, &b->contacts) {
+                struct contact * c = list_entry(p, struct contact, next);
+                if (b->n_contacts + b->n_alts <= dht->k) {
+                        ++c->fails;
+                        return;
+                }
+
+                if (c->addr == addr) {
+                        list_del(&c->next);
+                        contact_destroy(c);
+                        --b->n_contacts;
+                        break;
+                }
+        }
+
+        while (b->n_contacts < dht->k && b->n_alts > 0) {
+                struct contact * c;
+                c = list_first_entry(&b->alts, struct contact, next);
+                list_del(&c->next);
+                --b->n_alts;
+                list_add(&c->next, &b->contacts);
+                ++b->n_contacts;
+        }
+}
+
+static int dht_del(struct dht *    dht,
+                   const uint8_t * key,
+                   uint64_t        addr)
+{
+        struct dht_entry * e;
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        e = dht_find_entry(dht, key);
+        if (e == NULL) {
+                pthread_rwlock_unlock(&dht->lock);
+                return -EPERM;
+        }
+
+        dht_entry_del_addr(e, addr);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return 0;
+}
+
+static buffer_t dht_retrieve(struct dht *    dht,
+                             const uint8_t * key)
+{
+        struct dht_entry * e;
+        struct list_head * p;
+        buffer_t           buf;
+        uint64_t *         pos;
+
+        buf.len = 0;
+
+        pthread_rwlock_rdlock(&dht->lock);
+
+        e = dht_find_entry(dht, key);
+        if (e == NULL) {
+                pthread_rwlock_unlock(&dht->lock);
+                return buf;
+        }
+
+        buf.data = malloc(sizeof(dht->addr) * e->n_vals);
+        if (buf.data == NULL) {
+                pthread_rwlock_unlock(&dht->lock);
+                return buf;
+        }
+
+        buf.len = e->n_vals;
+
+        pos = (uint64_t *) buf.data;;
+
+        list_for_each(p, &e->vals) {
+                struct val * v = list_entry(p, struct val, next);
+                *pos++ = v->addr;
+        }
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return buf;
+}
+
+static ssize_t dht_get_contacts(struct dht *          dht,
+                                const uint8_t *       key,
+                                kad_contact_msg_t *** msgs)
+{
+        struct list_head   l;
+        struct list_head * p;
+        struct list_head * h;
+        size_t             len;
+        size_t             i = 0;
+
+        list_head_init(&l);
+
+        pthread_rwlock_rdlock(&dht->lock);
+
+        len = dht_contact_list(dht, &l, key);
+        if (len == 0)
+                return 0;
+
+        *msgs = malloc(len * sizeof(**msgs));
+        if (*msgs == NULL)
+                return 0;
+
+        list_for_each_safe(p, h, &l) {
+                struct contact * c = list_entry(p, struct contact, next);
+                (*msgs)[i] = malloc(sizeof(***msgs));
+                if ((*msgs)[i] == NULL) {
+                        pthread_rwlock_unlock(&dht->lock);
+                        while (i > 0)
+                                free(*msgs[--i]);
+                        free(*msgs);
+                        return 0;
+                }
+
+                kad_contact_msg__init((*msgs)[i]);
+
+                (*msgs)[i]->id.data = c->id;
+                (*msgs)[i]->id.len  = dht->b;
+                (*msgs)[i++]->addr  = c->addr;
+                list_del(&c->next);
+                free(c);
+        }
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return i;
+}
+
+static time_t gcd(time_t a,
+                  time_t b)
+{
+        if (a == 0)
+                return b;
+
+        return gcd(b % a, a);
+}
+
+static void * work(void * o)
+{
+        struct dht *       dht;
+        struct timespec    now;
+        struct list_head * p;
+        struct list_head * h;
+        struct list_head   reflist;
+        time_t             intv;
+        struct lookup *    lu;
+
+        dht = (struct dht *) o;
+
+        intv = gcd(dht->t_expire, dht->t_repub);
+        intv = gcd(intv, gcd(KAD_T_REPL, KAD_T_REFR)) / 2;
+
+        list_head_init(&reflist);
+
+        while (true) {
+                clock_gettime(CLOCK_REALTIME_COARSE, &now);
+
+                pthread_rwlock_wrlock(&dht->lock);
+
+                /* Republish registered hashes. */
+                list_for_each_safe(p, h, &dht->refs) {
+                        struct ref_entry * e;
+                        e = list_entry(p, struct ref_entry, next);
+                        if (now.tv_sec > e->t_rep) {
+                                kad_publish(dht, e->key, dht->addr,
+                                            dht->t_expire);
+                                e->t_rep = now.tv_sec + dht->t_repub;
+                        }
+                }
+
+                /* Remove stale entries and republish if necessary. */
+                list_for_each_safe(p, h, &dht->entries) {
+                        struct list_head * p1;
+                        struct list_head * h1;
+                        struct dht_entry * e;
+                        e = list_entry (p, struct dht_entry, next);
+                        list_for_each_safe(p1, h1, &e->vals) {
+                                struct val * v;
+                                v = list_entry(p1, struct val, next);
+                                if (now.tv_sec > v->t_exp) {
+                                        list_del(&v->next);
+                                        val_destroy(v);
+                                 }
+
+                                if (now.tv_sec > v->t_rep) {
+                                        kad_publish(dht, e->key, v->addr,
+                                                    dht->t_expire - now.tv_sec);
+                                        v->t_rep = now.tv_sec + dht->t_replic;
+                                }
+                        }
+                }
+
+                /* Check the requests list for unresponsive nodes. */
+                list_for_each_safe(p, h, &dht->requests) {
+                        struct kad_req * r;
+                        r = list_entry(p, struct kad_req, next);
+                        if (now.tv_sec > r->t_exp) {
+                                list_del(&r->next);
+                                bmp_release(dht->cookies, r->cookie);
+                                dht_dead_peer(dht, r->key, r->addr);
+                                kad_req_destroy(r);
+                        }
+                }
+
+                /* Refresh unaccessed buckets. */
+                bucket_refresh(dht, dht->buckets, now.tv_sec, &reflist);
+
+                pthread_rwlock_unlock(&dht->lock);
+
+                list_for_each_safe(p, h, &reflist) {
+                        struct contact * c;
+                        c = list_entry(p, struct contact, next);
+                        lu = kad_lookup(dht, c->id, KAD_FIND_NODE);
+                        if (lu != NULL)
+                                lookup_destroy(lu);
+                        list_del(&c->next);
+                        contact_destroy(c);
+                }
+
+                sleep(intv);
+        }
+
+        return (void *) 0;
+}
+
+static int kad_handle_join_resp(struct dht *     dht,
+                                struct kad_req * req,
+                                kad_msg_t *      msg)
+{
+        assert(dht);
+        assert(req);
+        assert(msg);
+
+        /* We might send version numbers later to warn of updates if needed. */
+        if (!(msg->has_alpha && msg->has_b && msg->has_k && msg->has_t_expire &&
+              msg->has_t_refresh && msg->has_t_replicate)) {
+                log_warn("Join refused by remote.");
+                return -1;
+        }
+
+        if (msg->b < sizeof(uint64_t)) {
+                log_err("Hash sizes less than 8 bytes unsupported.");
+                return -1;
+        }
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        dht->buckets = bucket_create();
+        if (dht->buckets == NULL) {
+                pthread_rwlock_unlock(&dht->lock);
+                return -1;
+        }
+
+        /* Likely corrupt packet. The member will refuse, we might here too. */
+        if (msg->alpha != KAD_ALPHA || msg->k != KAD_K)
+                log_warn("Different kademlia parameters detected.");
+
+        if (msg->t_replicate != KAD_T_REPL)
+                log_warn("Different kademlia replication time detected.");
+
+        if (msg->t_refresh != KAD_T_REFR)
+                log_warn("Different kademlia refresh time detected.");
+
+        dht->k        = msg->k;
+        dht->b        = msg->b;
+        dht->t_expire = msg->t_expire;
+        dht->t_repub  = MAX(1, dht->t_expire - 10);
+
+        if (pthread_create(&dht->worker, NULL, work, dht)) {
+                bucket_destroy(dht->buckets);
+                pthread_rwlock_unlock(&dht->lock);
+                return -1;
+        }
+
+        dht->state = DHT_RUNNING;
+
+        kad_req_respond(req);
+
+        dht_update_bucket(dht, msg->s_id.data, msg->s_addr);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        log_dbg("Enrollment of DHT completed.");
+
+        return 0;
+}
+
+static int kad_handle_find_resp(struct dht *     dht,
+                                struct kad_req * req,
+                                kad_msg_t *      msg)
+{
+        struct lookup * lu;
+
+        assert(dht);
+        assert(req);
+        assert(msg);
+
+        pthread_rwlock_rdlock(&dht->lock);
+
+        lu = dht_find_lookup(dht, req->key);
+        if (lu == NULL) {
+                log_dbg("Response for unknown lookup.");
+                pthread_rwlock_unlock(&dht->lock);
+                return -1;
+        }
+
+        lookup_update(dht, lu, msg);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return 0;
+}
+
+static void kad_handle_response(struct dht * dht,
+                                kad_msg_t *  msg)
+{
+        struct kad_req * req;
+
+        assert(dht);
+        assert(msg);
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        req = dht_find_request(dht, msg);
+        if (req == NULL) {
+                pthread_rwlock_unlock(&dht->lock);
+                return;
+        }
+
+        bmp_release(dht->cookies, req->cookie);
+        list_del(&req->next);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        switch(req->code) {
+        case KAD_JOIN:
+                if (kad_handle_join_resp(dht, req, msg))
+                        log_err("Enrollment of DHT failed.");
+                break;
+        case KAD_FIND_VALUE:
+        case KAD_FIND_NODE:
+                if (dht_get_state(dht) != DHT_RUNNING)
+                        return;
+                if (kad_handle_find_resp(dht, req, msg))
+                        log_dbg("Invalid or outdated response.");
+                break;
+        default:
+                break;
+        }
+
+        kad_req_destroy(req);
+}
+
+int dht_bootstrap(struct dht * dht,
+                  size_t       b,
+                  time_t       t_expire)
+{
+        assert(dht);
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        dht->id = create_id(b);
+        if (dht->id == NULL)
+                goto fail_id;
+
+        dht->buckets = bucket_create();
+        if (dht->buckets == NULL)
+                goto fail_buckets;
+
+        dht->buckets->depth = 0;
+        dht->buckets->mask  = 0;
+
+        dht->b        = b / CHAR_BIT;
+        dht->t_expire = MAX(2, t_expire);
+        dht->t_repub  = MAX(1, t_expire - 10);
+        dht->k        = KAD_K;
+
+        if (pthread_create(&dht->worker, NULL, work, dht))
+                goto fail_pthread_create;
+
+        dht->state = DHT_RUNNING;
+
+        dht_update_bucket(dht, dht->id, dht->addr);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return 0;
+
+ fail_pthread_create:
+        bucket_destroy(dht->buckets);
+        dht->buckets = NULL;
+ fail_buckets:
+        free(dht->id);
+        dht->id = NULL;
+ fail_id:
+        pthread_rwlock_unlock(&dht->lock);
+        return -1;
+}
+
+int dht_enroll(struct dht * dht,
+               uint64_t     addr)
+{
+        assert(dht);
+
+        return kad_join(dht, addr);
+}
+
+int dht_reg(struct dht *    dht,
+            const uint8_t * key)
+{
+        struct ref_entry * e;
+
+        assert(dht);
+        assert(key);
+        assert(dht->addr != 0);
+
+        if (dht_get_state(dht) != DHT_RUNNING)
+                return -1;
+
+        e = ref_entry_create(dht, key);
+        if (e == NULL)
+                return -ENOMEM;
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        list_add(&e->next, &dht->refs);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        kad_publish(dht, key, dht->addr, dht->t_expire);
+
+        return 0;
+}
+
+int dht_unreg(struct dht *    dht,
+              const uint8_t * key)
+{
+        struct list_head * p;
+        struct list_head * h;
+
+        assert(dht);
+        assert(key);
+
+        if (dht_get_state(dht) != DHT_RUNNING)
+                return -1;
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        list_for_each_safe(p, h, &dht->refs) {
+                struct ref_entry * r = list_entry(p, struct ref_entry, next);
+                if (!memcmp(key, r->key, dht-> b) ) {
+                        list_del(&r->next);
+                        ref_entry_destroy(r);
+                }
+        }
+
+        dht_del(dht, key, dht->addr);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        return 0;
+}
+
+uint64_t dht_query(struct dht *    dht,
+                   const uint8_t * key)
+{
+        struct dht_entry * e;
+        struct lookup *    lu;
+        uint64_t           addrs[KAD_K];
+        size_t             n;
+
+        addrs[0] = 0;
+
+        pthread_rwlock_rdlock(&dht->lock);
+
+        e = dht_find_entry(dht, key);
+        if (e != NULL)
+                addrs[0] = dht_entry_get_addr(dht, e);
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        if (addrs[0] != 0 && addrs[0] != dht->addr)
+                return addrs[0];
+
+        lu = kad_lookup(dht, key, KAD_FIND_VALUE);
+        if (lu == NULL)
+                return 0;
+
+        n = lookup_get_addrs(lu, addrs);
+        if (n == 0) {
+                lookup_destroy(lu);
+                return 0;
+        }
+
+        lookup_destroy(lu);
+
+        /* Current behaviour is anycast and return the first peer address. */
+        if (addrs[0] != dht->addr)
+                return addrs[0];
+
+        if (n > 1)
+                return addrs[1];
+
+        return 0;
+}
+
+void dht_post_sdu(void *               ae,
+                  struct shm_du_buff * sdb)
+{
+        struct dht *         dht;
+        kad_msg_t *          msg;
+        kad_contact_msg_t ** cmsgs;
+        kad_msg_t            resp_msg = KAD_MSG__INIT;
+        uint64_t             addr;
+        buffer_t             buf;
+        size_t               i;
+
+        assert(ae);
+        assert(sdb);
+
+        memset(&buf, 0, sizeof(buf));
+
+        dht = (struct dht *) ae;
+
+        msg = kad_msg__unpack(NULL,
+                              shm_du_buff_tail(sdb) - shm_du_buff_head(sdb),
+                              shm_du_buff_head(sdb));
+
+        ipcp_sdb_release(sdb);
+
+        if (msg == NULL) {
+                log_err("Failed to unpack message.");
+                return;
+        }
+
+        if (msg->has_key && msg->key.len != dht->b) {
+                kad_msg__free_unpacked(msg, NULL);
+                log_warn("Bad key in message.");
+                return;
+        }
+
+        if (msg->has_s_id && !msg->has_b && msg->s_id.len != dht->b) {
+                kad_msg__free_unpacked(msg, NULL);
+                log_warn("Bad source ID in message of type %d.", msg->code);
+                return;
+        }
+
+        if (msg->code != KAD_RESPONSE && dht_get_state(dht) != DHT_RUNNING) {
+                kad_msg__free_unpacked(msg, NULL);
+                return;
+        }
+
+        addr = msg->s_addr;
+
+        resp_msg.code   = KAD_RESPONSE;
+        resp_msg.cookie = msg->cookie;
+
+        switch(msg->code) {
+        case KAD_JOIN:
+                /* Refuse enrollee on check fails. */
+                if (msg->alpha != KAD_ALPHA || msg->k != KAD_K) {
+                        log_warn("Parameter mismatch. "
+                                 "DHT enrolment refused.");
+                        break;
+                }
+
+                if (msg->t_replicate != KAD_T_REPL) {
+                        log_warn("Replication time mismatch. "
+                                 "DHT enrolment refused.");
+
+                        break;
+                }
+
+                if (msg->t_refresh != KAD_T_REFR) {
+                        log_warn("Refresh time mismatch. "
+                                 "DHT enrolment refused.");
+                        break;
+                }
+
+                resp_msg.has_alpha       = true;
+                resp_msg.has_b           = true;
+                resp_msg.has_k           = true;
+                resp_msg.has_t_expire    = true;
+                resp_msg.has_t_refresh   = true;
+                resp_msg.has_t_replicate = true;
+                resp_msg.alpha           = KAD_ALPHA;
+                resp_msg.b               = dht->b;
+                resp_msg.k               = KAD_K;
+                resp_msg.t_expire        = dht->t_expire;
+                resp_msg.t_refresh       = KAD_T_REFR;
+                resp_msg.t_replicate     = KAD_T_REPL;
+                break;
+        case KAD_FIND_VALUE:
+                buf = dht_retrieve(dht, msg->key.data);
+                if (buf.len != 0) {
+                        resp_msg.n_addrs = buf.len;
+                        resp_msg.addrs   = (uint64_t *) buf.data;
+                        break;
+                }
+                /* FALLTHRU */
+        case KAD_FIND_NODE:
+                /* Return k closest contacts. */
+                resp_msg.n_contacts =
+                        dht_get_contacts(dht, msg->key.data, &cmsgs);
+                resp_msg.contacts = cmsgs;
+                break;
+        case KAD_STORE:
+                if (msg->n_contacts < 1) {
+                        log_warn("No contacts in store message.");
+                        break;
+                }
+
+                if (!msg->has_t_expire) {
+                        log_warn("No expiry time in store message.");
+                        break;
+                }
+
+                kad_add(dht, *msg->contacts, msg->n_contacts, msg->t_expire);
+                break;
+        case KAD_RESPONSE:
+                kad_handle_response(dht, msg);
+                break;
+        default:
+                assert(false);
+                break;
+        }
+
+        if (msg->code != KAD_JOIN) {
+                pthread_rwlock_wrlock(&dht->lock);
+                if (dht_update_bucket(dht, msg->s_id.data, addr))
+                        log_warn("Failed to update bucket.");
+                pthread_rwlock_unlock(&dht->lock);
+        }
+
+        if (msg->code < KAD_STORE)
+                send_msg(dht, &resp_msg, addr);
+
+        kad_msg__free_unpacked(msg, NULL);
+
+        if (resp_msg.n_addrs > 0)
+                free(resp_msg.addrs);
+
+        if (resp_msg.n_contacts == 0)
+                return;
+
+        for (i = 0; i < resp_msg.n_contacts; ++i)
+                kad_contact_msg__free_unpacked(resp_msg.contacts[i], NULL);
+        free(resp_msg.contacts);
+}
+
+void dht_destroy(struct dht * dht)
+{
+        struct list_head * p;
+        struct list_head * h;
+
+        if (dht == NULL)
+                return;
+
+        if (dht_get_state(dht) == DHT_RUNNING)
+                dht_set_state(dht, DHT_SHUTDOWN);
+
+        pthread_rwlock_wrlock(&dht->lock);
+
+        list_for_each_safe(p, h, &dht->entries) {
+                struct dht_entry * e = list_entry(p, struct dht_entry, next);
+                list_del(&e->next);
+                dht_entry_destroy(e);
+        }
+
+        list_for_each_safe(p, h, &dht->requests) {
+                struct kad_req * r = list_entry(p, struct kad_req, next);
+                list_del(&r->next);
+                free(r);
+        }
+
+        list_for_each_safe(p, h, &dht->refs) {
+                struct ref_entry * e = list_entry(p, struct ref_entry, next);
+                list_del(&e->next);
+                ref_entry_destroy(e);
+        }
+
+        list_for_each_safe(p, h, &dht->lookups) {
+                struct lookup * l = list_entry(p, struct lookup, next);
+                list_del(&l->next);
+                lookup_destroy(l);
+        }
+
+        pthread_rwlock_unlock(&dht->lock);
+
+        if (dht_get_state(dht) == DHT_SHUTDOWN) {
+                pthread_cancel(dht->worker);
+                pthread_join(dht->worker, NULL);
+        }
+
+        if (dht->buckets != NULL)
+                bucket_destroy(dht->buckets);
+
+        bmp_destroy(dht->cookies);
+
+        pthread_mutex_destroy(&dht->mtx);
+
+        pthread_rwlock_destroy(&dht->lock);
+
+        free(dht->id);
+
+        free(dht);
+}
+
+struct dht * dht_create(uint64_t addr)
+{
+        struct dht * dht;
+
+        dht = malloc(sizeof(*dht));
+        if (dht == NULL)
+                goto fail_malloc;
+
+        dht->buckets = NULL;
+
+        list_head_init(&dht->entries);
+        list_head_init(&dht->requests);
+        list_head_init(&dht->refs);
+        list_head_init(&dht->lookups);
+
+        if (pthread_rwlock_init(&dht->lock, NULL))
+                goto fail_rwlock;
+
+        if (pthread_mutex_init(&dht->mtx, NULL))
+                goto fail_mutex;
+
+        dht->cookies = bmp_create(DHT_MAX_REQS, 1);
+        if (dht->cookies == NULL)
+                goto fail_bmp;
+
+        dht->b    = 0;
+        dht->addr = addr;
+        dht->id   = NULL;
+#ifndef __DHT_TEST__
+        dht->fd   = dt_reg_ae(dht, &dht_post_sdu);
+#endif /* __DHT_TEST__ */
+
+        dht->state = DHT_INIT;
+
+        return dht;
+
+ fail_bmp:
+        pthread_mutex_destroy(&dht->mtx);
+ fail_mutex:
+        pthread_rwlock_destroy(&dht->lock);
+ fail_rwlock:
+        free(dht);
+ fail_malloc:
+        return NULL;
+}