lpn.c

/*  Bluetooth Mesh */

/*
 * SPDX-FileCopyrightText: 2017 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <stdint.h>
#include <errno.h>

#include "crypto.h"
#include "adv.h"
#include "scan.h"
#include "mesh.h"
#include "transport.h"
#include "access.h"
#include "beacon.h"
#include "lpn.h"
#include "rpl.h"
#include "foundation.h"
#include "mesh/main.h"
#include "mesh/cfg_srv.h"
#include "heartbeat.h"

#include "mesh_v1.1/utils.h"

#ifdef CONFIG_BLE_MESH_LOW_POWER

#if CONFIG_BLE_MESH_LPN_AUTO
#define LPN_AUTO_TIMEOUT          K_SECONDS(CONFIG_BLE_MESH_LPN_AUTO_TIMEOUT)
#else
#define LPN_AUTO_TIMEOUT          0
#endif

#define LPN_RECV_DELAY            CONFIG_BLE_MESH_LPN_RECV_DELAY
#define SCAN_LATENCY              MIN(CONFIG_BLE_MESH_LPN_SCAN_LATENCY, LPN_RECV_DELAY)

#define FRIEND_REQ_RETRY_TIMEOUT  K_SECONDS(CONFIG_BLE_MESH_LPN_RETRY_TIMEOUT)

#define FRIEND_REQ_WAIT           K_MSEC(100)
#define FRIEND_REQ_SCAN           K_SECONDS(1)
#define FRIEND_REQ_TIMEOUT        (FRIEND_REQ_WAIT + FRIEND_REQ_SCAN)

#define POLL_RETRY_TIMEOUT        K_MSEC(100)

#define REQ_RETRY_DURATION(lpn)   (4 * (LPN_RECV_DELAY + (lpn)->adv_duration + \
                                   (lpn)->recv_win + POLL_RETRY_TIMEOUT))

#define POLL_TIMEOUT_INIT         (CONFIG_BLE_MESH_LPN_INIT_POLL_TIMEOUT * 100)
#define POLL_TIMEOUT_MAX(lpn)     ((CONFIG_BLE_MESH_LPN_POLL_TIMEOUT * 100) - \
                                   REQ_RETRY_DURATION(lpn))

/**
 * 1. Should use 20 attempts for BQB test case MESH/NODE/FRND/LPM/BI-02-C.
 * 2. We should use more specific value for each PollTimeout range.
 */
#define REQ_ATTEMPTS(lpn)         (POLL_TIMEOUT_MAX(lpn) < K_SECONDS(3) ? 2 : 6)

#define CLEAR_ATTEMPTS            2

#define LPN_CRITERIA              ((CONFIG_BLE_MESH_LPN_MIN_QUEUE_SIZE) | \
                                   (CONFIG_BLE_MESH_LPN_RSSI_FACTOR << 3) | \
                                   (CONFIG_BLE_MESH_LPN_RECV_WIN_FACTOR << 5))

#define POLL_TO(to)               { (uint8_t)((to) >> 16), (uint8_t)((to) >> 8), (uint8_t)(to) }
#define LPN_POLL_TO               POLL_TO(CONFIG_BLE_MESH_LPN_POLL_TIMEOUT)

/* 2 transmissions, 20ms interval */
#define POLL_XMIT                 BLE_MESH_TRANSMIT(1, 20)

#define FIRST_POLL_ATTEMPTS       6

static void (*lpn_cb)(uint16_t friend_addr, bool established);

#if !CONFIG_BLE_MESH_NO_LOG
static const char *state2str(int state)
{
    switch (state) {
    case BLE_MESH_LPN_DISABLED:
        return "disabled";
    case BLE_MESH_LPN_CLEAR:
        return "clear";
    case BLE_MESH_LPN_TIMER:
        return "timer";
    case BLE_MESH_LPN_ENABLED:
        return "enabled";
    case BLE_MESH_LPN_REQ_WAIT:
        return "req wait";
    case BLE_MESH_LPN_WAIT_OFFER:
        return "wait offer";
    case BLE_MESH_LPN_ESTABLISHED:
        return "established";
    case BLE_MESH_LPN_RECV_DELAY:
        return "recv delay";
    case BLE_MESH_LPN_WAIT_UPDATE:
        return "wait update";
    case BLE_MESH_LPN_OFFER_RECV:
        return "offer recv";
    default:
        return "(unknown)";
    }
}
#endif

static inline void lpn_set_state(int state)
{
    BT_DBG("%s -> %s", state2str(bt_mesh.lpn.state), state2str(state));
    bt_mesh.lpn.state = state;
}

static inline void group_zero(bt_mesh_atomic_t *target)
{
#if CONFIG_BLE_MESH_LPN_GROUPS > 32
    int i;

    for (i = 0; i < ARRAY_SIZE(bt_mesh.lpn.added); i++) {
        bt_mesh_atomic_set(&target[i], 0);
    }
#else
    bt_mesh_atomic_set(target, 0);
#endif
}

static inline void group_set(bt_mesh_atomic_t *target, bt_mesh_atomic_t *source)
{
#if CONFIG_BLE_MESH_LPN_GROUPS > 32
    int i;

    for (i = 0; i < ARRAY_SIZE(bt_mesh.lpn.added); i++) {
        (void)bt_mesh_atomic_or(&target[i], bt_mesh_atomic_get(&source[i]));
    }
#else
    (void)bt_mesh_atomic_or(target, bt_mesh_atomic_get(source));
#endif
}

static inline void group_clear(bt_mesh_atomic_t *target, bt_mesh_atomic_t *source)
{
#if CONFIG_BLE_MESH_LPN_GROUPS > 32
    int i;

    for (i = 0; i < ARRAY_SIZE(bt_mesh.lpn.added); i++) {
        (void)bt_mesh_atomic_and(&target[i], ~bt_mesh_atomic_get(&source[i]));
    }
#else
    (void)bt_mesh_atomic_and(target, ~bt_mesh_atomic_get(source));
#endif
}

static void clear_friendship(bool force, bool disable);

static bool scan_after_clear;

static void friend_clear_sent(int err, void *user_data)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    /* We're switching away from Low Power behavior, so permanently
     * enable scanning.
     */
    if (scan_after_clear == false) {
        bt_mesh_scan_enable();
        scan_after_clear = true;
    }

    lpn->req_attempts++;

    if (err) {
        BT_ERR("Sending Friend Clear failed (err %d)", err);
        lpn_set_state(BLE_MESH_LPN_ENABLED);
        clear_friendship(false, lpn->disable);
        return;
    }

    lpn_set_state(BLE_MESH_LPN_CLEAR);
    k_delayed_work_submit(&lpn->timer, FRIEND_REQ_TIMEOUT);
}

static const struct bt_mesh_send_cb clear_sent_cb = {
    .end = friend_clear_sent,
};

static int send_friend_clear(void)
{
    struct bt_mesh_msg_ctx ctx = {
        .net_idx   = bt_mesh.sub[0].net_idx,
        .app_idx   = BLE_MESH_KEY_UNUSED,
        .addr      = bt_mesh.lpn.frnd,
        .send_ttl  = 0,
        .send_cred = BLE_MESH_FLOODING_CRED,
        /* Tag with immutable-credentials */
        .send_tag  = BLE_MESH_TAG_IMMUTABLE_CRED,
    };
    struct bt_mesh_net_tx tx = {
        .sub  = &bt_mesh.sub[0],
        .ctx  = &ctx,
        .src  = bt_mesh_primary_addr(),
        .xmit = bt_mesh_net_transmit_get(),
    };
    struct bt_mesh_ctl_friend_clear req = {
        .lpn_addr    = sys_cpu_to_be16(tx.src),
        .lpn_counter = sys_cpu_to_be16(bt_mesh.lpn.counter),
    };

    return bt_mesh_ctl_send(&tx, TRANS_CTL_OP_FRIEND_CLEAR, &req,
                            sizeof(req), &clear_sent_cb, NULL);
}

static void clear_friendship(bool force, bool disable)
{
    struct bt_mesh_cfg_srv *cfg = bt_mesh_cfg_get();
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    BT_DBG("force %u disable %u", force, disable);

    if (!force && lpn->established && !lpn->clear_success &&
        lpn->req_attempts < CLEAR_ATTEMPTS) {
        send_friend_clear();
        lpn->disable = disable;
        return;
    }

    bt_mesh_rx_reset();
    bt_mesh_rpl_reset(true);

    k_delayed_work_cancel(&lpn->timer);

    friend_cred_del(bt_mesh.sub[0].net_idx, lpn->frnd);

    if (lpn->clear_success) {
        lpn->old_friend = BLE_MESH_ADDR_UNASSIGNED;
    } else {
        lpn->old_friend = lpn->frnd;
    }

    if (lpn_cb && lpn->frnd != BLE_MESH_ADDR_UNASSIGNED) {
        lpn_cb(lpn->frnd, false);
    }

    /* If the Low Power node supports directed forwarding functionality when
     * the friendship is established in a subnet, the Low Power node shall
     * store the current value of the Directed Forwarding state and shall set
     * the state to 0x00 for that subnet. When that friendship is terminated,
     * the Low Power node shall set the Directed Forwarding state to the stored
     * value.
     */
#if CONFIG_BLE_MESH_DF_SRV
    if (lpn->established) {
        bt_mesh_restore_directed_forwarding_state(bt_mesh.sub[0].net_idx,
                                                  lpn->old_directed_forwarding);
    }
#endif

    lpn->frnd = BLE_MESH_ADDR_UNASSIGNED;
    lpn->fsn = 0U;
    lpn->req_attempts = 0U;
    lpn->recv_win = 0U;
    lpn->queue_size = 0U;
    lpn->disable = 0U;
    lpn->sent_req = 0U;
    lpn->established = 0U;
    lpn->clear_success = 0U;

    group_zero(lpn->added);
    group_zero(lpn->pending);
    group_zero(lpn->to_remove);

    /* Set this to 1 to force group subscription when the next
     * Friendship is created, in case lpn->groups doesn't get
     * modified meanwhile.
     */
    lpn->groups_changed = 1U;

    if (cfg->hb_pub.feat & BLE_MESH_FEAT_LOW_POWER) {
        bt_mesh_heartbeat_send();
    }

    if (disable) {
        lpn_set_state(BLE_MESH_LPN_DISABLED);
        return;
    }

    lpn_set_state(BLE_MESH_LPN_ENABLED);
    k_delayed_work_submit(&lpn->timer, FRIEND_REQ_RETRY_TIMEOUT);

    scan_after_clear = false;
    if (IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
        bt_mesh_scan_disable();
    }
}

static void friend_req_sent(uint16_t duration, int err, void *user_data)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    if (err) {
        BT_ERR("Sending Friend Request failed (err %d)", err);

        if (IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
            bt_mesh_scan_enable();
        }
        return;
    }

    lpn->adv_duration = duration;

    if (IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
        k_delayed_work_submit(&lpn->timer, FRIEND_REQ_WAIT);
        lpn_set_state(BLE_MESH_LPN_REQ_WAIT);
    } else {
        k_delayed_work_submit(&lpn->timer,
                              duration + FRIEND_REQ_TIMEOUT);
        lpn_set_state(BLE_MESH_LPN_WAIT_OFFER);
    }
}

static const struct bt_mesh_send_cb friend_req_sent_cb = {
    .start = friend_req_sent,
};

static int send_friend_req(struct bt_mesh_lpn *lpn)
{
    const struct bt_mesh_comp *comp = bt_mesh_comp_get();
    struct bt_mesh_msg_ctx ctx = {
        .net_idx   = bt_mesh.sub[0].net_idx,
        .app_idx   = BLE_MESH_KEY_UNUSED,
        .addr      = BLE_MESH_ADDR_FRIENDS,
        .send_ttl  = 0,
        .send_cred = BLE_MESH_FLOODING_CRED,
        /* Tag with immutable-credentials and as a friendship PDU */
        .send_tag  = BLE_MESH_TAG_IMMUTABLE_CRED | BLE_MESH_TAG_FRIENDSHIP,
    };
    struct bt_mesh_net_tx tx = {
        .sub  = &bt_mesh.sub[0],
        .ctx  = &ctx,
        .src  = bt_mesh_primary_addr(),
        .xmit = POLL_XMIT,
    };
    struct bt_mesh_ctl_friend_req req = {
        .criteria    = LPN_CRITERIA,
        .recv_delay  = LPN_RECV_DELAY,
        .poll_to     = LPN_POLL_TO,
        .prev_addr   = sys_cpu_to_be16(lpn->old_friend),
        .num_elem    = comp->elem_count,
        .lpn_counter = sys_cpu_to_be16(lpn->counter),
    };

    return bt_mesh_ctl_send(&tx, TRANS_CTL_OP_FRIEND_REQ, &req,
                            sizeof(req), &friend_req_sent_cb, NULL);
}

static void req_sent(uint16_t duration, int err, void *user_data)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    BT_DBG("req 0x%02x duration %u err %d state %s",
           lpn->sent_req, duration, err, state2str(lpn->state));

    if (err) {
        BT_ERR("Sending request failed (err %d)", err);
        lpn->sent_req = 0U;
        group_zero(lpn->pending);
        return;
    }

    lpn->req_attempts++;
    lpn->adv_duration = duration;

    if (lpn->established || IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
        lpn_set_state(BLE_MESH_LPN_RECV_DELAY);
        /* We start scanning a bit early to eliminate risk of missing
         * response data due to HCI and other latencies.
         */
        k_delayed_work_submit(&lpn->timer,
                              LPN_RECV_DELAY - SCAN_LATENCY);
    } else {
        lpn_set_state(BLE_MESH_LPN_OFFER_RECV);
        /**
         * Friend Update is replied by Friend Node with TTL set to 0 and Network
         * Transmit set to 30ms which will cause the packet easy to be missed.
         * Regarding this situation, here we can reduce the duration of receiving
         * the first Friend Update.
         */
        k_delayed_work_submit(&lpn->timer,
                              LPN_RECV_DELAY + duration +
                              lpn->recv_win);
    }
}

static const struct bt_mesh_send_cb req_sent_cb = {
    .start = req_sent,
};

static int send_friend_poll(void)
{
    struct bt_mesh_msg_ctx ctx = {
        .net_idx   = bt_mesh.sub[0].net_idx,
        .app_idx   = BLE_MESH_KEY_UNUSED,
        .addr      = bt_mesh.lpn.frnd,
        .send_ttl  = 0,
        .send_cred = BLE_MESH_FRIENDSHIP_CRED,
        /* Tag with immutable-credentials and as a friendship PDU */
        .send_tag  = BLE_MESH_TAG_IMMUTABLE_CRED | BLE_MESH_TAG_FRIENDSHIP,
    };
    struct bt_mesh_net_tx tx = {
        .sub  = &bt_mesh.sub[0],
        .ctx  = &ctx,
        .src  = bt_mesh_primary_addr(),
        .xmit = POLL_XMIT,
    };
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;
    uint8_t fsn = lpn->fsn;
    int err = 0;

    BT_DBG("lpn->sent_req 0x%02x", lpn->sent_req);

    if (lpn->sent_req) {
        if (lpn->sent_req != TRANS_CTL_OP_FRIEND_POLL) {
            lpn->pending_poll = 1U;
        }

        return 0;
    }

    err = bt_mesh_ctl_send(&tx, TRANS_CTL_OP_FRIEND_POLL, &fsn, 1,
                           &req_sent_cb, NULL);
    if (err == 0) {
        lpn->pending_poll = 0U;
        lpn->sent_req = TRANS_CTL_OP_FRIEND_POLL;
    }

    return err;
}

void bt_mesh_lpn_disable(bool force)
{
    if (bt_mesh.lpn.state == BLE_MESH_LPN_DISABLED) {
        return;
    }

    clear_friendship(force, true);
}

int bt_mesh_lpn_set(bool enable, bool force)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    if (enable) {
        if (lpn->state != BLE_MESH_LPN_DISABLED) {
            return 0;
        }
    } else {
        if (lpn->state == BLE_MESH_LPN_DISABLED) {
            return 0;
        }
    }

    if (!bt_mesh_is_provisioned()) {
        if (enable) {
            lpn_set_state(BLE_MESH_LPN_ENABLED);
        } else {
            lpn_set_state(BLE_MESH_LPN_DISABLED);
        }

        return 0;
    }

    if (enable) {
        lpn_set_state(BLE_MESH_LPN_ENABLED);

        if (IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
            bt_mesh_scan_disable();
        }

        send_friend_req(lpn);
    } else {
        if (IS_ENABLED(CONFIG_BLE_MESH_LPN_AUTO) &&
                lpn->state == BLE_MESH_LPN_TIMER) {
            k_delayed_work_cancel(&lpn->timer);
            lpn_set_state(BLE_MESH_LPN_DISABLED);
        } else {
            bt_mesh_lpn_disable(force);
        }
    }

    return 0;
}

static void friend_response_received(struct bt_mesh_lpn *lpn)
{
    BT_DBG("lpn->sent_req 0x%02x", lpn->sent_req);

    if (lpn->sent_req == TRANS_CTL_OP_FRIEND_POLL) {
        lpn->fsn++;
    }

    k_delayed_work_cancel(&lpn->timer);
    bt_mesh_scan_disable();
    lpn_set_state(BLE_MESH_LPN_ESTABLISHED);
    lpn->req_attempts = 0U;
    lpn->sent_req = 0U;
}

void bt_mesh_lpn_msg_received(struct bt_mesh_net_rx *rx)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    if (lpn->state == BLE_MESH_LPN_TIMER) {
        BT_DBG("Restarting establishment timer");
        k_delayed_work_submit(&lpn->timer, LPN_AUTO_TIMEOUT);
        return;
    }

    if (lpn->sent_req != TRANS_CTL_OP_FRIEND_POLL) {
        BT_WARN("Unexpected message without a preceding Poll");
        return;
    }

    friend_response_received(lpn);

    BT_DBG("Requesting more messages from Friend");

    send_friend_poll();
}

int bt_mesh_lpn_friend_offer(struct bt_mesh_net_rx *rx,
                             struct net_buf_simple *buf)
{
    struct bt_mesh_ctl_friend_offer *msg = (void *)buf->data;
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;
    struct bt_mesh_subnet *sub = rx->sub;
    struct friend_cred *cred = NULL;
    uint16_t frnd_counter = 0U;
    int err = 0;

    if (buf->len < sizeof(*msg)) {
        BT_WARN("Too short Friend Offer");
        return -EINVAL;
    }

    if (lpn->state != BLE_MESH_LPN_WAIT_OFFER) {
        BT_WARN("Ignoring unexpected Friend Offer");
        return 0;
    }

    if (!msg->recv_win) {
        BT_WARN("Prohibited ReceiveWindow value");
        return -EINVAL;
    }

    frnd_counter = sys_be16_to_cpu(msg->frnd_counter);

    BT_INFO("recv_win %u queue_size %u sub_list_size %u rssi %d counter %u",
           msg->recv_win, msg->queue_size, msg->sub_list_size, msg->rssi,
           frnd_counter);

    lpn->frnd = rx->ctx.addr;

    cred = friend_cred_create(sub, lpn->frnd, lpn->counter, frnd_counter);
    if (!cred) {
        lpn->frnd = BLE_MESH_ADDR_UNASSIGNED;
        return -ENOMEM;
    }

    /* TODO: Add offer acceptance criteria check */

    k_delayed_work_cancel(&lpn->timer);

    lpn->recv_win = msg->recv_win;
    lpn->queue_size = msg->queue_size;

    err = send_friend_poll();
    if (err) {
        friend_cred_clear(cred);
        lpn->frnd = BLE_MESH_ADDR_UNASSIGNED;
        lpn->recv_win = 0U;
        lpn->queue_size = 0U;
        return err;
    }

    lpn->counter++;

    if (IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
        bt_mesh_scan_disable();
    }

    return 0;
}

int bt_mesh_lpn_friend_clear_cfm(struct bt_mesh_net_rx *rx,
                                 struct net_buf_simple *buf)
{
    struct bt_mesh_ctl_friend_clear_confirm *msg = (void *)buf->data;
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;
    uint16_t addr = 0U, counter = 0U;

    if (buf->len < sizeof(*msg)) {
        BT_WARN("Too short Friend Clear Confirm");
        return -EINVAL;
    }

    if (lpn->state != BLE_MESH_LPN_CLEAR) {
        BT_WARN("Ignoring unexpected Friend Clear Confirm");
        return 0;
    }

    addr = sys_be16_to_cpu(msg->lpn_addr);
    counter = sys_be16_to_cpu(msg->lpn_counter);

    BT_DBG("LPNAddress 0x%04x LPNCounter 0x%04x", addr, counter);

    if (addr != bt_mesh_primary_addr() || counter != lpn->counter) {
        BT_WARN("Invalid parameters in Friend Clear Confirm");
        return 0;
    }

    lpn->clear_success = 1U;
    clear_friendship(false, lpn->disable);

    return 0;
}

static void lpn_group_add(uint16_t group)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;
    uint16_t *free_slot = NULL;
    int i;

    for (i = 0; i < ARRAY_SIZE(lpn->groups); i++) {
        if (lpn->groups[i] == group) {
            bt_mesh_atomic_clear_bit(lpn->to_remove, i);
            return;
        }

        if (!free_slot && lpn->groups[i] == BLE_MESH_ADDR_UNASSIGNED) {
            free_slot = &lpn->groups[i];
        }
    }

    if (!free_slot) {
        BT_WARN("Friend Subscription List exceeded!");
        return;
    }

    *free_slot = group;
    lpn->groups_changed = 1U;
}

static void lpn_group_del(uint16_t group)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;
    int i;

    for (i = 0; i < ARRAY_SIZE(lpn->groups); i++) {
        if (lpn->groups[i] == group) {
            if (bt_mesh_atomic_test_bit(lpn->added, i) ||
                bt_mesh_atomic_test_bit(lpn->pending, i)) {
                bt_mesh_atomic_set_bit(lpn->to_remove, i);
                lpn->groups_changed = 1U;
            } else {
                lpn->groups[i] = BLE_MESH_ADDR_UNASSIGNED;
            }
        }
    }
}

static inline int group_popcount(bt_mesh_atomic_t *target)
{
#if CONFIG_BLE_MESH_LPN_GROUPS > 32
    int i, count = 0;

    for (i = 0; i < ARRAY_SIZE(bt_mesh.lpn.added); i++) {
        count += popcount(bt_mesh_atomic_get(&target[i]));
    }
#else
    return popcount(bt_mesh_atomic_get(target));
#endif
}

static bool sub_update(uint8_t op)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;
    int added_count = group_popcount(lpn->added);
    struct bt_mesh_msg_ctx ctx = {
        .net_idx   = bt_mesh.sub[0].net_idx,
        .app_idx   = BLE_MESH_KEY_UNUSED,
        .addr      = lpn->frnd,
        .send_ttl  = 0,
        .send_cred = BLE_MESH_FRIENDSHIP_CRED,
        /* Tag with immutable-credentials and as a friendship PDU */
        .send_tag  = BLE_MESH_TAG_IMMUTABLE_CRED | BLE_MESH_TAG_FRIENDSHIP,
    };
    struct bt_mesh_net_tx tx = {
        .sub  = &bt_mesh.sub[0],
        .ctx  = &ctx,
        .src  = bt_mesh_primary_addr(),
        .xmit = POLL_XMIT,
    };
    struct bt_mesh_ctl_friend_sub req = {0};
    size_t i = 0U, g = 0U;

    BT_DBG("op 0x%02x sent_req 0x%02x", op, lpn->sent_req);

    if (lpn->sent_req) {
        return false;
    }

    for (i = 0U, g = 0U; i < ARRAY_SIZE(lpn->groups); i++) {
        if (lpn->groups[i] == BLE_MESH_ADDR_UNASSIGNED) {
            continue;
        }

        if (op == TRANS_CTL_OP_FRIEND_SUB_ADD) {
            if (bt_mesh_atomic_test_bit(lpn->added, i)) {
                continue;
            }
        } else {
            if (!bt_mesh_atomic_test_bit(lpn->to_remove, i)) {
                continue;
            }
        }

        if (added_count + g >= lpn->queue_size) {
            BT_WARN("Friend Queue Size exceeded");
            break;
        }

        req.addr_list[g++] = sys_cpu_to_be16(lpn->groups[i]);
        bt_mesh_atomic_set_bit(lpn->pending, i);

        if (g == ARRAY_SIZE(req.addr_list)) {
            break;
        }
    }

    if (g == 0U) {
        group_zero(lpn->pending);
        return false;
    }

    req.xact = lpn->xact_next++;

    if (bt_mesh_ctl_send(&tx, op, &req, 1 + g * 2,
                         &req_sent_cb, NULL) < 0) {
        group_zero(lpn->pending);
        return false;
    }

    lpn->xact_pending = req.xact;
    lpn->sent_req = op;
    return true;
}

static void update_timeout(struct bt_mesh_lpn *lpn)
{
    if (lpn->established) {
        BT_WARN("No response from Friend during ReceiveWindow");
        bt_mesh_scan_disable();
        lpn_set_state(BLE_MESH_LPN_ESTABLISHED);
        k_delayed_work_submit(&lpn->timer, POLL_RETRY_TIMEOUT);
    } else {
        if (IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
            bt_mesh_scan_disable();
        }

        if (lpn->req_attempts < FIRST_POLL_ATTEMPTS) {
            BT_WARN("Retrying first Friend Poll");
            lpn->sent_req = 0U;
            if (send_friend_poll() == 0) {
                return;
            }
        }

        BT_ERR("Timed out waiting for first Friend Update");
        clear_friendship(false, false);
    }
}

static void lpn_timeout(struct k_work *work)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    BT_DBG("state: %s", state2str(lpn->state));

    switch (lpn->state) {
    case BLE_MESH_LPN_DISABLED:
        break;
    case BLE_MESH_LPN_CLEAR:
        clear_friendship(false, bt_mesh.lpn.disable);
        break;
    case BLE_MESH_LPN_TIMER:
        BT_DBG("Starting to look for Friend nodes");
        lpn_set_state(BLE_MESH_LPN_ENABLED);
        if (IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
            bt_mesh_scan_disable();
        }
    /* fall through */
    case BLE_MESH_LPN_ENABLED:
        send_friend_req(lpn);
        break;
    case BLE_MESH_LPN_REQ_WAIT:
        bt_mesh_scan_enable();
        k_delayed_work_submit(&lpn->timer,
                              lpn->adv_duration + FRIEND_REQ_SCAN);
        lpn_set_state(BLE_MESH_LPN_WAIT_OFFER);
        break;
    case BLE_MESH_LPN_WAIT_OFFER:
        BT_WARN("No acceptable Friend Offers received");
        if (IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
            bt_mesh_scan_disable();
        }
        lpn->counter++;
        lpn_set_state(BLE_MESH_LPN_ENABLED);
        lpn->sent_req = 0U;
        k_delayed_work_submit(&lpn->timer, FRIEND_REQ_RETRY_TIMEOUT);
        break;
    case BLE_MESH_LPN_OFFER_RECV:
        if (lpn->req_attempts < FIRST_POLL_ATTEMPTS) {
            BT_WARN("Retrying the first Friend Poll, %d attempts", lpn->req_attempts);
            lpn->sent_req = 0U;
            send_friend_poll();
            break;
        }

        BT_ERR("Timeout waiting for the first Friend Update");
        clear_friendship(true, false);
        break;
    case BLE_MESH_LPN_ESTABLISHED:
        if (lpn->req_attempts < REQ_ATTEMPTS(lpn)) {
            uint8_t req = lpn->sent_req;

            lpn->sent_req = 0U;

            if (!req || req == TRANS_CTL_OP_FRIEND_POLL) {
                send_friend_poll();
            } else {
                sub_update(req);
            }

            break;
        }

        BT_ERR("No response from Friend after %u retries",
               lpn->req_attempts);
        lpn->req_attempts = 0U;
        clear_friendship(false, false);
        break;
    case BLE_MESH_LPN_RECV_DELAY:
        k_delayed_work_submit(&lpn->timer,
                              lpn->adv_duration + SCAN_LATENCY +
                              lpn->recv_win);
        bt_mesh_scan_enable();
        lpn_set_state(BLE_MESH_LPN_WAIT_UPDATE);
        break;
    case BLE_MESH_LPN_WAIT_UPDATE:
        update_timeout(lpn);
        break;
    default:
        BT_ERR("Unhandled LPN state");
        break;
    }
}

void bt_mesh_lpn_group_add(uint16_t group)
{
    BT_DBG("group 0x%04x", group);

    lpn_group_add(group);

    if (!bt_mesh_lpn_established() || bt_mesh.lpn.sent_req) {
        return;
    }

    sub_update(TRANS_CTL_OP_FRIEND_SUB_ADD);
}

void bt_mesh_lpn_group_del(uint16_t *groups, size_t group_count)
{
    int i;

    for (i = 0; i < group_count; i++) {
        if (groups[i] != BLE_MESH_ADDR_UNASSIGNED) {
            BT_DBG("group 0x%04x", groups[i]);
            lpn_group_del(groups[i]);
        }
    }

    if (!bt_mesh_lpn_established() || bt_mesh.lpn.sent_req) {
        return;
    }

    sub_update(TRANS_CTL_OP_FRIEND_SUB_REM);
}

static int32_t poll_timeout(struct bt_mesh_lpn *lpn)
{
    /* If we're waiting for segment acks keep polling at high freq */
    if (bt_mesh_tx_in_progress()) {
        return MIN(POLL_TIMEOUT_MAX(lpn), K_SECONDS(1));
    }

    if (lpn->poll_timeout < POLL_TIMEOUT_MAX(lpn)) {
        lpn->poll_timeout *= 2;
        lpn->poll_timeout = MIN(lpn->poll_timeout,
                                POLL_TIMEOUT_MAX(lpn));
    }

    BT_DBG("Poll Timeout is %ums", lpn->poll_timeout);

    return lpn->poll_timeout;
}

int bt_mesh_lpn_friend_sub_cfm(struct bt_mesh_net_rx *rx,
                               struct net_buf_simple *buf)
{
    struct bt_mesh_ctl_friend_sub_confirm *msg = (void *)buf->data;
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    if (buf->len < sizeof(*msg)) {
        BT_WARN("Too short Friend Subscription Confirm");
        return -EINVAL;
    }

    BT_DBG("xact 0x%02x", msg->xact);

    if (!lpn->sent_req) {
        BT_WARN("No pending subscription list message");
        return 0;
    }

    if (msg->xact != lpn->xact_pending) {
        BT_WARN("Transaction mismatch (0x%02x != 0x%02x)",
                msg->xact, lpn->xact_pending);
        return 0;
    }

    if (lpn->sent_req == TRANS_CTL_OP_FRIEND_SUB_ADD) {
        group_set(lpn->added, lpn->pending);
        group_zero(lpn->pending);
    } else if (lpn->sent_req == TRANS_CTL_OP_FRIEND_SUB_REM) {
        int i;

        group_clear(lpn->added, lpn->pending);

        for (i = 0; i < ARRAY_SIZE(lpn->groups); i++) {
            if (bt_mesh_atomic_test_and_clear_bit(lpn->pending, i) &&
                bt_mesh_atomic_test_and_clear_bit(lpn->to_remove, i)) {
                lpn->groups[i] = BLE_MESH_ADDR_UNASSIGNED;
            }
        }
    } else {
        BT_WARN("Unexpected Friend Subscription Confirm");
        return 0;
    }

    friend_response_received(lpn);

    if (lpn->groups_changed) {
        sub_update(TRANS_CTL_OP_FRIEND_SUB_ADD);
        sub_update(TRANS_CTL_OP_FRIEND_SUB_REM);

        if (!lpn->sent_req) {
            lpn->groups_changed = 0U;
        }
    }

    if (lpn->pending_poll) {
        send_friend_poll();
    }

    if (!lpn->sent_req) {
        k_delayed_work_submit(&lpn->timer, poll_timeout(lpn));
    }

    return 0;
}

int bt_mesh_lpn_friend_update(struct bt_mesh_net_rx *rx,
                              struct net_buf_simple *buf)
{
    struct bt_mesh_ctl_friend_update *msg = (void *)buf->data;
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;
    struct bt_mesh_subnet *sub = rx->sub;
    uint32_t iv_index = 0U;

    if (buf->len < sizeof(*msg)) {
        BT_WARN("Too short Friend Update");
        return -EINVAL;
    }

    if (lpn->sent_req != TRANS_CTL_OP_FRIEND_POLL) {
        BT_WARN("Unexpected friend update");
        return 0;
    }

    if (sub->kr_phase == BLE_MESH_KR_PHASE_2 && !rx->new_key) {
        BT_WARN("Ignoring Phase 2 KR Update secured using old key");
        return 0;
    }

    if (bt_mesh_atomic_test_bit(bt_mesh.flags, BLE_MESH_IVU_INITIATOR) &&
        (bt_mesh_atomic_test_bit(bt_mesh.flags, BLE_MESH_IVU_IN_PROGRESS) ==
         BLE_MESH_IV_UPDATE(msg->flags))) {
        bt_mesh_beacon_ivu_initiator(false);
    }

    if (!lpn->established) {
        struct bt_mesh_cfg_srv *cfg = bt_mesh_cfg_get();

        /* This is normally checked on the transport layer, however
         * in this state we're also still accepting master
         * credentials so we need to ensure the right ones (Friend
         * Credentials) were used for this message.
         */
        if (rx->ctx.recv_cred != BLE_MESH_FRIENDSHIP_CRED) {
            BT_WARN("Friend Update with wrong credentials");
            return -EINVAL;
        }

        lpn->established = 1U;

        BT_INFO("Friendship established with 0x%04x", lpn->frnd);

        if (cfg->hb_pub.feat & BLE_MESH_FEAT_LOW_POWER) {
            bt_mesh_heartbeat_send();
        }

        if (lpn_cb) {
            lpn_cb(lpn->frnd, true);
        }

        /* Set initial poll timeout */
        lpn->poll_timeout = MIN(POLL_TIMEOUT_MAX(lpn),
                                POLL_TIMEOUT_INIT);

        /* If the Low Power node supports directed forwarding functionality when
         * the friendship is established in a subnet, the Low Power node shall
         * store the current value of the Directed Forwarding state and shall set
         * the state to 0x00 for that subnet. When that friendship is terminated,
         * the Low Power node shall set the Directed Forwarding state to the stored
         * value.
         */
#if CONFIG_BLE_MESH_DF_SRV
        lpn->old_directed_forwarding = bt_mesh_get_and_disable_directed_forwarding_state(sub);
#endif
    }

    friend_response_received(lpn);

    iv_index = sys_be32_to_cpu(msg->iv_index);

    BT_INFO("flags 0x%02x iv_index 0x%08x md %u", msg->flags, iv_index,
           msg->md);

    if (bt_mesh_kr_update(sub, BLE_MESH_KEY_REFRESH(msg->flags),
                          rx->new_key)) {
        bt_mesh_net_secure_beacon_update(sub);
    }

    bt_mesh_net_iv_update(iv_index, BLE_MESH_IV_UPDATE(msg->flags));

    if (lpn->groups_changed) {
        sub_update(TRANS_CTL_OP_FRIEND_SUB_ADD);
        sub_update(TRANS_CTL_OP_FRIEND_SUB_REM);

        if (!lpn->sent_req) {
            lpn->groups_changed = 0U;
        }
    }

    if (msg->md) {
        BT_DBG("Requesting for more messages");
        send_friend_poll();
    }

    if (!lpn->sent_req) {
        k_delayed_work_submit(&lpn->timer, poll_timeout(lpn));
    }

    return 0;
}

int bt_mesh_lpn_poll(void)
{
    if (!bt_mesh.lpn.established) {
        return -EAGAIN;
    }

    BT_DBG("Requesting more messages");

    return send_friend_poll();
}

void bt_mesh_lpn_set_cb(void (*cb)(uint16_t friend_addr, bool established))
{
    lpn_cb = cb;
}

int bt_mesh_lpn_init(void)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    k_delayed_work_init(&lpn->timer, lpn_timeout);

    if (lpn->state == BLE_MESH_LPN_ENABLED) {
        if (!IS_ENABLED(CONFIG_BLE_MESH_LPN_ESTABLISHMENT)) {
            bt_mesh_scan_enable();
        }

        send_friend_req(lpn);
    } else {
        bt_mesh_scan_enable();

        if (IS_ENABLED(CONFIG_BLE_MESH_LPN_AUTO)) {
            BT_DBG("Waiting %u ms for messages", LPN_AUTO_TIMEOUT);
            lpn_set_state(BLE_MESH_LPN_TIMER);
            k_delayed_work_submit(&lpn->timer, LPN_AUTO_TIMEOUT);
        }
    }

    return 0;
}

#if CONFIG_BLE_MESH_DEINIT
int bt_mesh_lpn_deinit(void)
{
    struct bt_mesh_lpn *lpn = &bt_mesh.lpn;

    bt_mesh_lpn_disable(true);

    k_delayed_work_free(&lpn->timer);

    return 0;
}
#endif /* CONFIG_BLE_MESH_DEINIT */

#endif /* CONFIG_BLE_MESH_LOW_POWER */