friend.c

/*  Bluetooth Mesh */

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

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

#include "crypto.h"
#include "adv.h"
#include "mesh.h"
#include "transport.h"
#include "access.h"
#include "friend.h"
#include "foundation.h"
#include "mesh/main.h"
#include "mesh/common.h"
#include "pvnr_mgmt.h"

#include "mesh_v1.1/utils.h"

#ifdef CONFIG_BLE_MESH_FRIEND

/* We reserve one extra buffer for each friendship, since we need to be able
 * to resend the last sent PDU, which sits separately outside of the queue.
 */
#define FRIEND_BUF_COUNT    ((CONFIG_BLE_MESH_FRIEND_QUEUE_SIZE + 1) * \
                              CONFIG_BLE_MESH_FRIEND_LPN_COUNT)

#define FRIEND_ADV(buf)     CONTAINER_OF(BLE_MESH_ADV(buf), struct friend_adv, adv)

/* PDUs from Friend to the LPN should only be transmitted once with the
 * smallest possible interval (20ms).
 *
 * Spec v1.1, Section 3.4.6:
 * When transmitting a Network PDU that is tagged as friendship, the
 * Advertising Bearer Network Interface shall transmit the Network PDU
 * over the advertising bearer only once.
 */
#define FRIEND_XMIT         BLE_MESH_TRANSMIT(0, 20)

struct friend_pdu_info {
    uint16_t src;
    uint16_t dst;

    uint8_t  seq[3];

    uint8_t  ttl:7,
             ctl:1;

    uint32_t iv_index;
};

NET_BUF_POOL_FIXED_DEFINE(friend_buf_pool, FRIEND_BUF_COUNT,
                          BLE_MESH_ADV_DATA_SIZE, NULL);

static struct friend_adv {
    struct bt_mesh_adv adv;
    uint16_t app_idx;
} adv_pool[FRIEND_BUF_COUNT];

enum {
    BLE_MESH_FRIENDSHIP_TERMINATE_ESTABLISH_FAIL,
    BLE_MESH_FRIENDSHIP_TERMINATE_POLL_TIMEOUT,
    BLE_MESH_FRIENDSHIP_TERMINATE_RECV_FRND_REQ,
    BLE_MESH_FRIENDSHIP_TERMINATE_RECV_FRND_CLEAR,
    BLE_MESH_FRIENDSHIP_TERMINATE_DISABLE,
};

static void (*friend_cb)(bool establish, uint16_t lpn_addr, uint8_t reason);
static void enqueue_update(struct bt_mesh_friend *frnd, uint8_t md);

static bool friend_init = false;

static struct bt_mesh_subnet *friend_subnet_get(uint16_t net_idx)
{
    return bt_mesh_subnet_get(net_idx);
}

static struct bt_mesh_adv *adv_alloc(int id)
{
    adv_pool[id].app_idx = BLE_MESH_KEY_UNUSED;
    return &adv_pool[id].adv;
}

static bool is_lpn_unicast(struct bt_mesh_friend *frnd, uint16_t addr)
{
    if (frnd->lpn == BLE_MESH_ADDR_UNASSIGNED) {
        return false;
    }

    return (addr >= frnd->lpn && addr < (frnd->lpn + frnd->num_elem));
}

struct bt_mesh_friend *bt_mesh_friend_find(uint16_t net_idx, uint16_t lpn_addr,
                                           bool valid, bool established)
{
    int i;

    BT_DBG("net_idx 0x%04x lpn_addr 0x%04x", net_idx, lpn_addr);

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (valid && !frnd->valid) {
            continue;
        }

        if (established && !frnd->established) {
            continue;
        }

        if (net_idx != BLE_MESH_KEY_ANY && frnd->net_idx != net_idx) {
            continue;
        }

        if (is_lpn_unicast(frnd, lpn_addr)) {
            return frnd;
        }
    }

    return NULL;
}

static void purge_buffers(sys_slist_t *list)
{
    while (!sys_slist_is_empty(list)) {
        struct net_buf *buf = NULL;

        buf = (void *)sys_slist_get_not_empty(list);

        buf->frags = NULL;
        buf->flags &= ~NET_BUF_FRAGS;

        net_buf_unref(buf);
    }
}

/* Intentionally start a little bit late into the ReceiveWindow when
 * it's large enough. This may improve reliability with some platforms,
 * like the PTS, where the receiver might not have sufficiently compensated
 * for internal latencies required to start scanning.
 */
static int32_t recv_delay(struct bt_mesh_friend *frnd)
{
#if CONFIG_BLE_MESH_FRIEND_RECV_WIN > 50
    return (int32_t)frnd->recv_delay + (CONFIG_BLE_MESH_FRIEND_RECV_WIN / 5);
#else
    return frnd->recv_delay;
#endif
}

static void friend_clear(struct bt_mesh_friend *frnd, uint8_t reason)
{
    int i;

    BT_DBG("LPN 0x%04x", frnd->lpn);

    k_delayed_work_cancel(&frnd->timer);

    if (frnd->established) {
        if (friend_cb) {
            friend_cb(false, frnd->lpn, reason);
        }

#if CONFIG_BLE_MESH_DF_SRV
        struct bt_mesh_subnet *sub = friend_subnet_get(frnd->net_idx);
        if (sub && sub->directed_friend == BLE_MESH_DIRECTED_FRIEND_ENABLED) {
            if (bt_mesh_directed_update_dependent_node(sub, 0, frnd->lpn, frnd->num_elem)) {
                BT_ERR("Friend failed to update dependent node");
            }
        }
#endif /* CONFIG_BLE_MESH_DF_SRV */
    }

    friend_cred_del(frnd->net_idx, frnd->lpn);

    if (frnd->last) {
        /* Cancel the sending if necessary */
        if (frnd->pending_buf) {
            bt_mesh_adv_buf_ref_debug(__func__, frnd->last, 2U, BLE_MESH_BUF_REF_EQUAL);
            BLE_MESH_ADV(frnd->last)->busy = 0U;
        } else {
            bt_mesh_adv_buf_ref_debug(__func__, frnd->last, 1U, BLE_MESH_BUF_REF_EQUAL);
        }

        net_buf_unref(frnd->last);
        frnd->last = NULL;
    }

    purge_buffers(&frnd->queue);

    for (i = 0; i < ARRAY_SIZE(frnd->seg); i++) {
        struct bt_mesh_friend_seg *seg = &frnd->seg[i];

        purge_buffers(&seg->queue);
        seg->seg_count = 0U;
    }

    frnd->valid = 0U;
    frnd->established = 0U;
    frnd->pending_buf = 0U;
    frnd->fsn = 0U;
    frnd->queue_size = 0U;
    frnd->pending_req = 0U;
    (void)memset(frnd->sub_list, 0, sizeof(frnd->sub_list));
}

void bt_mesh_friend_clear_net_idx(uint16_t net_idx)
{
    int i;

    BT_DBG("net_idx 0x%04x", net_idx);

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (frnd->net_idx == BLE_MESH_KEY_UNUSED) {
            continue;
        }

        if (net_idx == BLE_MESH_KEY_ANY || frnd->net_idx == net_idx) {
            friend_clear(frnd, BLE_MESH_FRIENDSHIP_TERMINATE_DISABLE);
        }
    }
}

void bt_mesh_friend_sec_update(uint16_t net_idx)
{
    int i;

    BT_DBG("net_idx 0x%04x", net_idx);

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (frnd->net_idx == BLE_MESH_KEY_UNUSED) {
            continue;
        }

        if (net_idx == BLE_MESH_KEY_ANY || frnd->net_idx == net_idx) {
            /* For case MESH/NODE/FRND/FN/BV-20-C.
             * A situation is:
             * The friend node may receive more than one different secure updates
             * consecutively. And using the previous approach will cause only the
             * latest Friend Update message been enqueued.
             * So we update the implementation here to enqueue the Friend Update
             * message immediately once a different secure beacon is received.
             *
             * A disadvantage of the change is:
             * A friend node may receive different secure beacons. Then the
             * beacon_cache mechanism will not work. This will cause the friend
             * message queue been full of these secure beacons. So before enqueuing
             * the secure updates, we should check if the currently received one
             * is already exists in the message queue. Or enhance the beacon cache
             * filtering mechanism.
             */
            enqueue_update(frnd, 1);
        }
    }
}

int bt_mesh_friend_clear(struct bt_mesh_net_rx *rx, struct net_buf_simple *buf)
{
    struct bt_mesh_ctl_friend_clear *msg = (void *)buf->data;
    struct bt_mesh_friend *frnd = NULL;
    uint16_t lpn_addr = 0U, lpn_counter = 0U;
    struct bt_mesh_net_tx tx = {
        .sub  = rx->sub,
        .ctx  = &rx->ctx,
        .src  = bt_mesh_primary_addr(),
        .xmit = bt_mesh_net_transmit_get(),
    };
    struct bt_mesh_ctl_friend_clear_confirm cfm = {0};

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

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

    BT_DBG("LPN addr 0x%04x counter 0x%04x", lpn_addr, lpn_counter);

    frnd = bt_mesh_friend_find(rx->sub->net_idx, lpn_addr, false, false);
    if (!frnd) {
        BT_WARN("No matching LPN addr 0x%04x", lpn_addr);
        return 0;
    }

    /* A Friend Clear message is considered valid if the result of the
     * subtraction of the value of the LPNCounter field of the Friend
     * Request message (the one that initiated the friendship) from the
     * value of the LPNCounter field of the Friend Clear message, modulo
     * 65536, is in the range 0 to 255 inclusive.
     */
    if (lpn_counter - frnd->lpn_counter > 255) {
        BT_WARN("LPN Counter out of range (old %u new %u)",
                frnd->lpn_counter, lpn_counter);
        return 0;
    }

    tx.ctx->send_ttl  = BLE_MESH_TTL_MAX;
    tx.ctx->send_cred = BLE_MESH_FLOODING_CRED;
    /* Tag with immutable-credentials */
    tx.ctx->send_tag  = BLE_MESH_TAG_IMMUTABLE_CRED;

    cfm.lpn_addr    = msg->lpn_addr;
    cfm.lpn_counter = msg->lpn_counter;

    bt_mesh_ctl_send(&tx, TRANS_CTL_OP_FRIEND_CLEAR_CFM, &cfm,
                     sizeof(cfm), NULL, NULL);

    friend_clear(frnd, BLE_MESH_FRIENDSHIP_TERMINATE_RECV_FRND_CLEAR);

    return 0;
}

static bool friend_sub_exist(struct bt_mesh_friend *frnd, uint16_t addr)
{
    int i;

    for (i = 0; i < ARRAY_SIZE(frnd->sub_list); i++) {
        if (frnd->sub_list[i] == addr) {
            return true;
        }
    }

    return false;
}

static void friend_sub_add(struct bt_mesh_friend *frnd, uint16_t addr)
{
    int i;

    for (i = 0; i < ARRAY_SIZE(frnd->sub_list); i++) {
        if (frnd->sub_list[i] == BLE_MESH_ADDR_UNASSIGNED) {
            frnd->sub_list[i] = addr;
            return;
        }
    }

    BT_WARN("No space in friend subscription list");
}

static void friend_sub_rem(struct bt_mesh_friend *frnd, uint16_t addr)
{
    int i;

    for (i = 0; i < ARRAY_SIZE(frnd->sub_list); i++) {
        if (frnd->sub_list[i] == addr) {
            frnd->sub_list[i] = BLE_MESH_ADDR_UNASSIGNED;
            return;
        }
    }
}

static struct net_buf *create_friend_pdu(struct bt_mesh_friend *frnd,
                                         struct friend_pdu_info *info,
                                         struct net_buf_simple *sdu)
{
    struct net_buf *buf = NULL;

    buf = bt_mesh_adv_create_from_pool(&friend_buf_pool, adv_alloc,
                                       BLE_MESH_ADV_DATA, K_NO_WAIT);
    if (!buf) {
        return NULL;
    }

    net_buf_add_u8(buf, (info->iv_index & 1) << 7); /* Will be reset in encryption */

    if (info->ctl) {
        net_buf_add_u8(buf, info->ttl | 0x80);
    } else {
        net_buf_add_u8(buf, info->ttl);
    }

    net_buf_add_mem(buf, info->seq, sizeof(info->seq));

    net_buf_add_be16(buf, info->src);
    net_buf_add_be16(buf, info->dst);

    net_buf_add_mem(buf, sdu->data, sdu->len);

    return buf;
}

struct unseg_app_sdu_meta {
    struct bt_mesh_net_rx net;
    const uint8_t *key;
    struct bt_mesh_subnet *subnet;
    bool is_dev_key;
    uint8_t aid;
    uint8_t *ad;
};

static int unseg_app_sdu_unpack(struct bt_mesh_friend *frnd,
                                struct net_buf *buf,
                                struct unseg_app_sdu_meta *meta)
{
    uint16_t app_idx = FRIEND_ADV(buf)->app_idx;
    int err = 0;

    meta->subnet = friend_subnet_get(frnd->net_idx);
    if (!meta->subnet) {
        BT_ERR("Invalid subnet for unseg app sdu");
        return -EINVAL;
    }

    meta->is_dev_key = (app_idx == BLE_MESH_KEY_DEV);
    bt_mesh_net_header_parse(&buf->b, &meta->net);
    err = bt_mesh_upper_key_get(meta->subnet, app_idx, &meta->key,
                                &meta->aid, meta->net.ctx.addr);
    if (err) {
        BT_ERR("Failed to get AppKey");
        return err;
    }

    if (BLE_MESH_ADDR_IS_VIRTUAL(meta->net.ctx.recv_dst)) {
        meta->ad = bt_mesh_label_uuid_get(meta->net.ctx.recv_dst);
        if (!meta->ad) {
            BT_ERR("Failed to get label uuid");
            return -ENOENT;
        }
    } else {
        meta->ad = NULL;
    }

    return 0;
}

static int unseg_app_sdu_decrypt(struct bt_mesh_friend *frnd,
                                 struct net_buf *buf,
                                 const struct unseg_app_sdu_meta *meta)
{
    struct net_buf_simple sdu = {0};

    net_buf_simple_clone(&buf->b, &sdu);
    net_buf_simple_pull(&sdu, 10);
    sdu.len -= 4;

    return bt_mesh_app_decrypt(meta->key, meta->is_dev_key, 0, &sdu, &sdu,
                               meta->ad, meta->net.ctx.addr,
                               meta->net.ctx.recv_dst, meta->net.seq,
                               BLE_MESH_NET_IVI_TX);
}

static int unseg_app_sdu_encrypt(struct bt_mesh_friend *frnd,
                                 struct net_buf *buf,
                                 const struct unseg_app_sdu_meta *meta)
{
    struct net_buf_simple sdu = {0};

    net_buf_simple_clone(&buf->b, &sdu);
    net_buf_simple_pull(&sdu, 10);
    sdu.len -= 4;

    return bt_mesh_app_encrypt(meta->key, meta->is_dev_key, 0, &sdu,
                               meta->ad, meta->net.ctx.addr,
                               meta->net.ctx.recv_dst, bt_mesh.seq,
                               BLE_MESH_NET_IVI_TX);
}

static int unseg_app_sdu_prepare(struct bt_mesh_friend *frnd,
                                 struct net_buf *buf)
{
    struct unseg_app_sdu_meta meta = {0};
    int err = 0;

    if (FRIEND_ADV(buf)->app_idx == BLE_MESH_KEY_UNUSED) {
        return 0;
    }

    err = unseg_app_sdu_unpack(frnd, buf, &meta);
    if (err) {
        return err;
    }

    /* No need to re-encrypt the message if the sequence number is
     * unchanged.
     */
    if (meta.net.seq == bt_mesh.seq) {
        return 0;
    }

    err = unseg_app_sdu_decrypt(frnd, buf, &meta);
    if (err) {
        BT_WARN("Decryption failed! %d", err);
        return err;
    }

    err = unseg_app_sdu_encrypt(frnd, buf, &meta);
    if (err) {
        BT_WARN("Re-encryption failed! %d", err);
    }

    return err;
}

static int encrypt_friend_pdu(struct bt_mesh_friend *frnd, struct net_buf *buf,
                              bool master_cred)
{
    struct bt_mesh_subnet *sub = friend_subnet_get(frnd->net_idx);
    const uint8_t *enc = NULL, *priv = NULL;
    uint32_t iv_index = 0U;
    uint16_t src = 0U;
    uint8_t nid = 0U;
    int err = 0;

    if (!sub) {
        BT_ERR("Invalid subnet to encrypt friend pdu");
        return -EINVAL;
    }

    if (master_cred) {
        enc = sub->keys[sub->kr_flag].enc;
        priv = sub->keys[sub->kr_flag].privacy;
        nid = sub->keys[sub->kr_flag].nid;
    } else {
        if (friend_cred_get(sub, frnd->lpn, &nid, &enc, &priv)) {
            BT_ERR("friend_cred_get failed");
            return -ENOENT;
        }
    }

    src = sys_get_be16(&buf->data[5]);

    if (bt_mesh_elem_find(src)) {
        uint32_t seq;

        if (FRIEND_ADV(buf)->app_idx != BLE_MESH_KEY_UNUSED) {
            err = unseg_app_sdu_prepare(frnd, buf);
            if (err) {
                return err;
            }
        }

        seq = bt_mesh_next_seq();
        sys_put_be24(seq, &buf->data[2]);

        iv_index = BLE_MESH_NET_IVI_TX;
        FRIEND_ADV(buf)->app_idx = BLE_MESH_KEY_UNUSED;
    } else {
        uint8_t ivi = (buf->data[0] >> 7);
        iv_index = (bt_mesh.iv_index - ((bt_mesh.iv_index & 1) != ivi));
    }

    buf->data[0] = (nid | (iv_index & 1) << 7);

    if (bt_mesh_net_encrypt(enc, &buf->b, iv_index, false, false)) {
        BT_ERR("Encrypting failed");
        return -EINVAL;
    }

    if (bt_mesh_net_obfuscate(buf->data, iv_index, priv)) {
        BT_ERR("Obfuscating failed");
        return -EINVAL;
    }

    return 0;
}

static struct net_buf *encode_friend_ctl(struct bt_mesh_friend *frnd,
                                         uint8_t ctl_op,
                                         struct net_buf_simple *sdu)
{
    struct friend_pdu_info info = {0};

    BT_DBG("LPN 0x%04x", frnd->lpn);

    net_buf_simple_push_u8(sdu, TRANS_CTL_HDR(ctl_op, 0));

    info.src = bt_mesh_primary_addr();
    info.dst = frnd->lpn;

    info.ctl = 1U;
    info.ttl = 0U;

    memset(info.seq, 0, sizeof(info.seq));

    info.iv_index = BLE_MESH_NET_IVI_TX;

    return create_friend_pdu(frnd, &info, sdu);
}

static struct net_buf *encode_update(struct bt_mesh_friend *frnd, uint8_t md)
{
    struct bt_mesh_ctl_friend_update *upd = NULL;
    NET_BUF_SIMPLE_DEFINE(sdu, 1 + sizeof(*upd));
    struct bt_mesh_subnet *sub = friend_subnet_get(frnd->net_idx);

    if (!sub) {
        BT_ERR("Friend subnet 0x%04x not found", frnd->net_idx);
        return NULL;
    }

    BT_DBG("lpn 0x%04x md 0x%02x", frnd->lpn, md);

    net_buf_simple_reserve(&sdu, 1);

    upd = net_buf_simple_add(&sdu, sizeof(*upd));
    upd->flags = bt_mesh_net_flags(sub);
    upd->iv_index = sys_cpu_to_be32(bt_mesh.iv_index);
    upd->md = md;

    return encode_friend_ctl(frnd, TRANS_CTL_OP_FRIEND_UPDATE, &sdu);
}

static void enqueue_sub_cfm(struct bt_mesh_friend *frnd, uint8_t xact)
{
    struct bt_mesh_ctl_friend_sub_confirm *cfm = NULL;
    NET_BUF_SIMPLE_DEFINE(sdu, 1 + sizeof(*cfm));
    struct net_buf *buf = NULL;

    BT_DBG("lpn 0x%04x xact 0x%02x", frnd->lpn, xact);

    net_buf_simple_reserve(&sdu, 1);

    cfm = net_buf_simple_add(&sdu, sizeof(*cfm));
    cfm->xact = xact;

    buf = encode_friend_ctl(frnd, TRANS_CTL_OP_FRIEND_SUB_CFM, &sdu);
    if (!buf) {
        BT_ERR("Unable to encode Subscription List Confirmation");
        return;
    }

    if (encrypt_friend_pdu(frnd, buf, false)) {
        return;
    }

    if (frnd->last) {
        BT_DBG("Discarding last PDU");
        net_buf_unref(frnd->last);
    }

    frnd->last = buf;
    frnd->send_last = 1U;
}

static void friend_recv_delay(struct bt_mesh_friend *frnd)
{
    frnd->pending_req = 1U;
    k_delayed_work_submit(&frnd->timer, recv_delay(frnd));
    BT_INFO("Waiting RecvDelay of %d ms", recv_delay(frnd));
}

int bt_mesh_friend_sub_add(struct bt_mesh_net_rx *rx,
                           struct net_buf_simple *buf)
{
    struct bt_mesh_friend *frnd = NULL;
    uint8_t xact = 0U;

    if (buf->len < BLE_MESH_FRIEND_SUB_MIN_LEN) {
        BT_WARN("Too short Friend Subscription Add (len %d)", buf->len);
        return -EINVAL;
    }

    frnd = bt_mesh_friend_find(rx->sub->net_idx, rx->ctx.addr, true, true);
    if (!frnd) {
        BT_WARN("No matching LPN addr 0x%04x", rx->ctx.addr);
        return 0;
    }

    if (frnd->pending_buf) {
        BT_WARN("Previous buffer not yet sent!");
        return 0;
    }

    friend_recv_delay(frnd);

    xact = net_buf_simple_pull_u8(buf);

    while (buf->len >= 2U) {
        uint16_t addr = net_buf_simple_pull_be16(buf);

        if (!BLE_MESH_ADDR_IS_GROUP(addr) &&
            !BLE_MESH_ADDR_IS_VIRTUAL(addr) &&
            !BLE_MESH_ADDR_IS_FIXED_GROUP(addr)) {
            BT_WARN("Invalid friend sub addr 0x%04x to add", addr);
            continue;
        }

        if (friend_sub_exist(frnd, addr)) {
            continue;
        }

        friend_sub_add(frnd, addr);
    }

    enqueue_sub_cfm(frnd, xact);

#if CONFIG_BLE_MESH_DF_SRV
    return bt_mesh_directed_friend_solicitation(frnd, rx->sub);
#else
    return 0;
#endif
}

int bt_mesh_friend_sub_rem(struct bt_mesh_net_rx *rx,
                           struct net_buf_simple *buf)
{
    struct bt_mesh_friend *frnd = NULL;
    uint8_t xact = 0U;

    if (buf->len < BLE_MESH_FRIEND_SUB_MIN_LEN) {
        BT_WARN("Too short Friend Subscription Remove (len %d)", buf->len);
        return -EINVAL;
    }

    frnd = bt_mesh_friend_find(rx->sub->net_idx, rx->ctx.addr, true, true);
    if (!frnd) {
        BT_WARN("No matching LPN addr 0x%04x", rx->ctx.addr);
        return 0;
    }

    if (frnd->pending_buf) {
        BT_WARN("Previous buffer not yet sent!");
        return 0;
    }

    friend_recv_delay(frnd);

    xact = net_buf_simple_pull_u8(buf);

    while (buf->len >= 2U) {
        uint16_t addr = net_buf_simple_pull_be16(buf);

        if (!BLE_MESH_ADDR_IS_GROUP(addr) &&
            !BLE_MESH_ADDR_IS_VIRTUAL(addr) &&
            !BLE_MESH_ADDR_IS_FIXED_GROUP(addr)) {
            BT_WARN("Invalid friend sub addr 0x%04x to remove", addr);
            continue;
        }

        friend_sub_rem(frnd, addr);
    }

    enqueue_sub_cfm(frnd, xact);

    return 0;
}

static void enqueue_buf(struct bt_mesh_friend *frnd, struct net_buf *buf)
{
    net_buf_slist_put(&frnd->queue, buf);
    frnd->queue_size++;
}

static void enqueue_update(struct bt_mesh_friend *frnd, uint8_t md)
{
    struct net_buf *buf = NULL;

    buf = encode_update(frnd, md);
    if (!buf) {
        BT_ERR("Unable to encode Friend Update");
        return;
    }

    enqueue_buf(frnd, buf);
}

int bt_mesh_friend_poll(struct bt_mesh_net_rx *rx, struct net_buf_simple *buf)
{
    struct bt_mesh_ctl_friend_poll *msg = (void *)buf->data;
    struct bt_mesh_friend *frnd = NULL;

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

    frnd = bt_mesh_friend_find(rx->sub->net_idx, rx->ctx.addr, true, false);
    if (!frnd) {
        BT_WARN("No matching LPN addr 0x%04x", rx->ctx.addr);
        return 0;
    }

    if (msg->fsn & ~1) {
        BT_WARN("Prohibited (non-zero) padding bits");
        return -EINVAL;
    }

    if (frnd->pending_buf) {
        BT_WARN("Previous buffer not yet sent!");
        return 0;
    }

    BT_DBG("msg->fsn %u frnd->fsn %u", (msg->fsn & 1), frnd->fsn);

    friend_recv_delay(frnd);

    if (!frnd->established) {
        BT_INFO("Friendship established with 0x%04x", frnd->lpn);
        frnd->established = 1U;
        if (friend_cb) {
            friend_cb(true, frnd->lpn, 0);
        }
    }

    if (msg->fsn == frnd->fsn && frnd->last) {
        BT_DBG("Re-sending last PDU");
        frnd->send_last = 1U;
    } else {
        if (frnd->last) {
            net_buf_unref(frnd->last);
            frnd->last = NULL;
        }

        frnd->fsn = msg->fsn;

        if (sys_slist_is_empty(&frnd->queue)) {
            enqueue_update(frnd, 0);
            BT_DBG("Enqueued Friend Update to empty queue");
        }
    }

    return 0;
}

static struct bt_mesh_friend *find_clear(uint16_t prev_friend)
{
    int i;

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (frnd->clear.frnd == prev_friend) {
            return frnd;
        }
    }

    return NULL;
}

static void friend_clear_sent(int err, void *user_data)
{
    struct bt_mesh_friend *frnd = user_data;

    k_delayed_work_submit(&frnd->clear.timer,
                          K_SECONDS(frnd->clear.repeat_sec));
    frnd->clear.repeat_sec *= 2U;
}

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

static void send_friend_clear(struct bt_mesh_friend *frnd)
{
    struct bt_mesh_msg_ctx ctx = {
        .net_idx   = frnd->net_idx,
        .app_idx   = BLE_MESH_KEY_UNUSED,
        .addr      = frnd->clear.frnd,
        .send_ttl  = BLE_MESH_TTL_MAX,
        .send_cred = BLE_MESH_FLOODING_CRED,
        /* Tag with immutable-credentials */
        .send_tag  = BLE_MESH_TAG_IMMUTABLE_CRED,
    };
    struct bt_mesh_net_tx tx = {
        .sub  = friend_subnet_get(frnd->net_idx),
        .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(frnd->lpn),
        .lpn_counter = sys_cpu_to_be16(frnd->lpn_counter),
    };

    if (!tx.sub) {
        BT_ERR("Invalid subnet for Friend Clear");
        return;
    }

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

static void clear_timeout(struct k_work *work)
{
    struct bt_mesh_friend *frnd = CONTAINER_OF(work, struct bt_mesh_friend,
                                  clear.timer.work);
    uint32_t duration = 0U;

    BT_DBG("LPN 0x%04x (old) Friend 0x%04x", frnd->lpn, frnd->clear.frnd);

    duration = k_uptime_get_32() - frnd->clear.start;
    if (duration > 2 * frnd->poll_to) {
        BT_DBG("Clear Procedure timer expired");
        frnd->clear.frnd = BLE_MESH_ADDR_UNASSIGNED;
        return;
    }

    send_friend_clear(frnd);
}

static void clear_procedure_start(struct bt_mesh_friend *frnd)
{
    BT_DBG("LPN 0x%04x (old) Friend 0x%04x", frnd->lpn, frnd->clear.frnd);

    frnd->clear.start = k_uptime_get_32();
    frnd->clear.repeat_sec = 1U;

    send_friend_clear(frnd);
}

int bt_mesh_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_friend *frnd = NULL;
    uint16_t lpn_addr = 0U, lpn_counter = 0U;

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

    frnd = find_clear(rx->ctx.addr);
    if (!frnd) {
        BT_WARN("No pending clear procedure for 0x%02x", rx->ctx.addr);
        return 0;
    }

    lpn_addr = sys_be16_to_cpu(msg->lpn_addr);
    if (lpn_addr != frnd->lpn) {
        BT_WARN("LPN address mismatch (0x%04x != 0x%04x)",
                lpn_addr, frnd->lpn);
        return 0;
    }

    lpn_counter = sys_be16_to_cpu(msg->lpn_counter);
    if (lpn_counter != frnd->lpn_counter) {
        BT_WARN("LPN counter mismatch (0x%04x != 0x%04x)",
                lpn_counter, frnd->lpn_counter);
        return 0;
    }

    k_delayed_work_cancel(&frnd->clear.timer);
    frnd->clear.frnd = BLE_MESH_ADDR_UNASSIGNED;

    return 0;
}

static void enqueue_offer(struct bt_mesh_friend *frnd, int8_t rssi)
{
    struct bt_mesh_ctl_friend_offer *off = NULL;
    NET_BUF_SIMPLE_DEFINE(sdu, 1 + sizeof(*off));
    struct net_buf *buf = NULL;

    net_buf_simple_reserve(&sdu, 1);

    off = net_buf_simple_add(&sdu, sizeof(*off));

    off->recv_win = CONFIG_BLE_MESH_FRIEND_RECV_WIN;
    off->queue_size = CONFIG_BLE_MESH_FRIEND_QUEUE_SIZE;
    off->sub_list_size = ARRAY_SIZE(frnd->sub_list);
    off->rssi = rssi;
    off->frnd_counter = sys_cpu_to_be16(frnd->counter);

    buf = encode_friend_ctl(frnd, TRANS_CTL_OP_FRIEND_OFFER, &sdu);
    if (!buf) {
        BT_ERR("Unable to encode Friend Offer");
        return;
    }

    if (encrypt_friend_pdu(frnd, buf, true)) {
        return;
    }

    frnd->counter++;

    if (frnd->last) {
        net_buf_unref(frnd->last);
    }

    frnd->last = buf;
    frnd->send_last = 1U;
}

#define RECV_WIN                  CONFIG_BLE_MESH_FRIEND_RECV_WIN
#define RSSI_FACT(crit)           (((crit) >> 5) & (uint8_t)BIT_MASK(2))
#define RECV_WIN_FACT(crit)       (((crit) >> 3) & (uint8_t)BIT_MASK(2))
#define MIN_QUEUE_SIZE_LOG(crit)  ((crit) & (uint8_t)BIT_MASK(3))
#define MIN_QUEUE_SIZE(crit)      ((uint32_t)BIT(MIN_QUEUE_SIZE_LOG(crit)))

static int32_t offer_delay(struct bt_mesh_friend *frnd, int8_t rssi, uint8_t crit)
{
    /* Scaling factors. The actual values are 1, 1.5, 2 & 2.5, but we
     * want to avoid floating-point arithmetic.
     */
    static const uint8_t fact[] = { 10, 15, 20, 25 };
    int32_t delay = 0;

    BT_INFO("ReceiveWindowFactor %u ReceiveWindow %u RSSIFactor %u RSSI %d",
            fact[RECV_WIN_FACT(crit)], RECV_WIN,
            fact[RSSI_FACT(crit)], rssi);

    /* Delay = ReceiveWindowFactor * ReceiveWindow - RSSIFactor * RSSI */
    delay = (int32_t)fact[RECV_WIN_FACT(crit)] * RECV_WIN;
    delay -= (int32_t)fact[RSSI_FACT(crit)] * rssi;
    delay /= 10;

    BT_DBG("Local Delay calculated as %d ms", delay);

    if (delay < 100) {
        return K_MSEC(100);
    }

    return K_MSEC(delay);
}

int bt_mesh_friend_req(struct bt_mesh_net_rx *rx, struct net_buf_simple *buf)
{
    struct bt_mesh_ctl_friend_req *msg = (void *)buf->data;
    struct bt_mesh_friend *frnd = NULL;
    uint32_t poll_to = 0U;
    int i;

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

    if (msg->recv_delay <= 0x09) {
        BT_WARN("Prohibited ReceiveDelay (0x%02x)", msg->recv_delay);
        return -EINVAL;
    }

    poll_to = sys_get_be24(msg->poll_to);

    if (poll_to <= 0x000009 || poll_to >= 0x34bc00) {
        BT_WARN("Prohibited PollTimeout (0x%06x)", poll_to);
        return -EINVAL;
    }

    if (msg->num_elem == 0x00) {
        BT_WARN("Prohibited NumElements value (0x00)");
        return -EINVAL;
    }

    if (!BLE_MESH_ADDR_IS_UNICAST(rx->ctx.addr + msg->num_elem - 1)) {
        BT_WARN("LPN elements stretch outside of unicast range");
        return -EINVAL;
    }

    if (!MIN_QUEUE_SIZE_LOG(msg->criteria)) {
        BT_WARN("Prohibited Minimum Queue Size in Friend Request");
        return -EINVAL;
    }

    if (CONFIG_BLE_MESH_FRIEND_QUEUE_SIZE < MIN_QUEUE_SIZE(msg->criteria)) {
        BT_WARN("We have a too small Friend Queue size (%u < %u)",
                CONFIG_BLE_MESH_FRIEND_QUEUE_SIZE,
                MIN_QUEUE_SIZE(msg->criteria));
        return 0;
    }

    frnd = bt_mesh_friend_find(rx->sub->net_idx, rx->ctx.addr, true, false);
    if (frnd) {
        BT_WARN("Existing LPN re-requesting Friendship");
        friend_clear(frnd, BLE_MESH_FRIENDSHIP_TERMINATE_RECV_FRND_REQ);
        goto init_friend;
    }

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        if (!bt_mesh.frnd[i].valid) {
            frnd = &bt_mesh.frnd[i];
            frnd->valid = 1U;
            break;
        }
    }

    if (!frnd) {
        BT_WARN("No free Friend contexts for new LPN");
        return -ENOMEM;
    }

init_friend:
    frnd->lpn = rx->ctx.addr;
    frnd->num_elem = msg->num_elem;
    frnd->net_idx = rx->sub->net_idx;
    frnd->recv_delay = msg->recv_delay;
    frnd->poll_to = poll_to * 100U;
    frnd->lpn_counter = sys_be16_to_cpu(msg->lpn_counter);
    frnd->clear.frnd = sys_be16_to_cpu(msg->prev_addr);

    BT_INFO("LPN 0x%04x rssi %d recv_delay %u poll_to %ums",
           frnd->lpn, rx->ctx.recv_rssi, frnd->recv_delay, frnd->poll_to);

    /**
     * Spec says:
     * After a friendship has been established, if the PreviousAddress field
     * of the Friend Request message contains a valid unicast address that is
     * not the Friend node’s own unicast address, then the Friend node shall
     * begin sending Friend Clear messages to that unicast address.
     */
    if (BLE_MESH_ADDR_IS_UNICAST(frnd->clear.frnd) &&
        !bt_mesh_elem_find(frnd->clear.frnd)) {
        clear_procedure_start(frnd);
    }

    k_delayed_work_submit(&frnd->timer,
                          offer_delay(frnd, rx->ctx.recv_rssi,
                                      msg->criteria));

    friend_cred_create(rx->sub, frnd->lpn, frnd->lpn_counter,
                       frnd->counter);

    enqueue_offer(frnd, rx->ctx.recv_rssi);

    return 0;
}

static bool is_seg(struct bt_mesh_friend_seg *seg, uint16_t src, uint16_t seq_zero)
{
    struct net_buf *buf = (void *)sys_slist_peek_head(&seg->queue);
    struct net_buf_simple_state state = {0};
    uint16_t buf_seq_zero = 0U;
    uint16_t buf_src = 0U;

    if (!buf) {
        return false;
    }

    net_buf_simple_save(&buf->b, &state);
    net_buf_skip(buf, 5);   /* skip IVI, NID, CTL, TTL, SEQ */
    buf_src = net_buf_pull_be16(buf);
    net_buf_skip(buf, 3);   /* skip DST, OP/AID */
    buf_seq_zero = ((net_buf_pull_be16(buf) >> 2) & TRANS_SEQ_ZERO_MASK);
    net_buf_simple_restore(&buf->b, &state);

    return ((src == buf_src) && (seq_zero == buf_seq_zero));
}

static struct bt_mesh_friend_seg *get_seg(struct bt_mesh_friend *frnd,
                                          uint16_t src, uint16_t seq_zero,
                                          uint8_t seg_count)
{
    struct bt_mesh_friend_seg *unassigned = NULL;
    int i;

    for (i = 0; i < ARRAY_SIZE(frnd->seg); i++) {
        struct bt_mesh_friend_seg *seg = &frnd->seg[i];

        if (is_seg(seg, src, seq_zero)) {
            return seg;
        }

        if (!unassigned && !sys_slist_peek_head(&seg->queue)) {
            unassigned = seg;
        }
    }

    if (unassigned) {
        unassigned->seg_count = seg_count;
    }

    return unassigned;
}

static void enqueue_friend_pdu(struct bt_mesh_friend *frnd,
                               enum bt_mesh_friend_pdu_type type,
                               uint16_t src, uint8_t seg_count,
                               struct net_buf *buf)
{
    struct bt_mesh_friend_seg *seg = NULL;

    BT_DBG("type %u", type);

    if (type == BLE_MESH_FRIEND_PDU_SINGLE) {
        enqueue_buf(frnd, buf);
        return;
    }

    uint16_t seq_zero = (((buf->data[10] << 8 | buf->data[11]) >> 2) & TRANS_SEQ_ZERO_MASK);

    seg = get_seg(frnd, src, seq_zero, seg_count);
    if (!seg) {
        BT_ERR("No free friend segment RX contexts for 0x%04x", src);
        net_buf_unref(buf);
        return;
    }

    net_buf_slist_put(&seg->queue, buf);

    if (type == BLE_MESH_FRIEND_PDU_COMPLETE) {
        sys_slist_merge_slist(&frnd->queue, &seg->queue);

        frnd->queue_size += seg->seg_count;
        seg->seg_count = 0U;
    } else {
        /* Mark the buffer as having more to come after it */
        buf->flags |= NET_BUF_FRAGS;
    }
}

static void buf_send_start(uint16_t duration, int err, void *user_data)
{
    struct bt_mesh_friend *frnd = user_data;

    BT_DBG("err %d", err);

    frnd->pending_buf = 0U;

    /* Friend Offer doesn't follow the re-sending semantics */
    if (!frnd->established) {
        net_buf_unref(frnd->last);
        frnd->last = NULL;
    }
}

static void buf_send_end(int err, void *user_data)
{
    struct bt_mesh_friend *frnd = user_data;

    BT_DBG("err %d", err);

    if (frnd->pending_req) {
        BT_WARN("Another request before previous completed sending");
        return;
    }

    if (frnd->established) {
        k_delayed_work_submit(&frnd->timer, frnd->poll_to);
        BT_DBG("Waiting %u ms for next poll", frnd->poll_to);
    } else {
        /* Friend offer timeout is 1 second */
        k_delayed_work_submit(&frnd->timer, K_SECONDS(1));
        BT_DBG("Waiting for first poll");
    }
}

static void friend_timeout(struct k_work *work)
{
    struct bt_mesh_friend *frnd = CONTAINER_OF(work, struct bt_mesh_friend,
                                  timer.work);
    static const struct bt_mesh_send_cb buf_sent_cb = {
        .start = buf_send_start,
        .end = buf_send_end,
    };

    if (frnd->pending_buf != 0U) {
        BT_ERR("Previous buffer not yet sent!");
        return;
    }

    BT_DBG("lpn 0x%04x send_last %u last %p", frnd->lpn,
           frnd->send_last, frnd->last);

    if (frnd->send_last && frnd->last) {
        BT_DBG("Sending frnd->last %p", frnd->last);
        frnd->send_last = 0U;
        goto send_last;
    }

    if (frnd->established && !frnd->pending_req) {
        BT_WARN("Friendship lost with 0x%04x", frnd->lpn);
        friend_clear(frnd, BLE_MESH_FRIENDSHIP_TERMINATE_POLL_TIMEOUT);
        return;
    }

    frnd->last = (void *)sys_slist_get(&frnd->queue);
    if (!frnd->last) {
        BT_WARN("Friendship not established with 0x%04x", frnd->lpn);
        friend_clear(frnd, BLE_MESH_FRIENDSHIP_TERMINATE_ESTABLISH_FAIL);
        return;
    }

    if (encrypt_friend_pdu(frnd, frnd->last, false)) {
        return;
    }

    /* Clear the flag we use for segment tracking */
    frnd->last->flags &= ~NET_BUF_FRAGS;
    frnd->last->frags = NULL;

    BT_DBG("Sending buf %p from Friend Queue of LPN 0x%04x",
           frnd->last, frnd->lpn);
    frnd->queue_size--;

send_last:
    frnd->pending_req = 0U;
    frnd->pending_buf = 1U;
    bt_mesh_adv_send(frnd->last, FRIEND_XMIT, &buf_sent_cb, frnd);
}

void bt_mesh_friend_set_cb(void (*cb)(bool establish, uint16_t lpn_addr, uint8_t reason))
{
    friend_cb = cb;
}

int bt_mesh_friend_init(void)
{
    int i;

    if (friend_init == true) {
        BT_WARN("%s, Already", __func__);
        return -EALREADY;
    }

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];
        int j;

        frnd->net_idx = BLE_MESH_KEY_UNUSED;

        sys_slist_init(&frnd->queue);

        k_delayed_work_init(&frnd->timer, friend_timeout);
        k_delayed_work_init(&frnd->clear.timer, clear_timeout);

        for (j = 0; j < ARRAY_SIZE(frnd->seg); j++) {
            sys_slist_init(&frnd->seg[j].queue);
        }
    }

    friend_init = true;

    return 0;
}

#if CONFIG_BLE_MESH_DEINIT
int bt_mesh_friend_deinit(void)
{
    int i;

    if (friend_init == false) {
        BT_WARN("%s, Already", __func__);
        return -EALREADY;
    }

    bt_mesh_friend_clear_net_idx(BLE_MESH_KEY_ANY);

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        frnd->net_idx = BLE_MESH_KEY_UNUSED;

        k_delayed_work_free(&frnd->timer);
        k_delayed_work_free(&frnd->clear.timer);
    }

    bt_mesh_unref_buf_from_pool(&friend_buf_pool);
    memset(adv_pool, 0, sizeof(adv_pool));

    friend_init = false;

    return 0;
}
#endif /* CONFIG_BLE_MESH_DEINIT */

static bool is_segack(struct net_buf *buf, const uint64_t *seqauth, uint16_t src)
{
    struct net_buf_simple_state state = {0};
    bool found = false;

    if (buf->len != 16) {
        return false;
    }

    net_buf_simple_save(&buf->b, &state);

    net_buf_skip(buf, 1); /* skip IVI, NID */

    if (!(net_buf_pull_u8(buf) >> 7)) {
        goto end;
    }

    net_buf_pull(buf, 3); /* skip SEQNUM */

    if (src != net_buf_pull_be16(buf)) {
        goto end;
    }

    net_buf_skip(buf, 2); /* skip dst */

    if (TRANS_CTL_OP((uint8_t *) net_buf_pull_mem(buf, 1)) != TRANS_CTL_OP_ACK) {
        goto end;
    }

    found = ((net_buf_pull_be16(buf) >> 2) & TRANS_SEQ_ZERO_MASK) ==
        (*seqauth & TRANS_SEQ_ZERO_MASK);
end:
    net_buf_simple_restore(&buf->b, &state);
    return found;
}

static void friend_purge_old_ack(struct bt_mesh_friend *frnd,
                                 const uint64_t *seq_auth, uint16_t src)
{
    sys_snode_t *cur = NULL, *prev = NULL;

    BT_DBG("SeqAuth %llx src 0x%04x", *seq_auth, src);

    for (cur = sys_slist_peek_head(&frnd->queue);
            cur != NULL; prev = cur, cur = sys_slist_peek_next(cur)) {
        struct net_buf *buf = (void *)cur;

        if (is_segack(buf, seq_auth, src)) {
            BT_DBG("Removing old ack from Friend Queue");

            sys_slist_remove(&frnd->queue, prev, cur);
            frnd->queue_size--;
            /* Make sure old slist entry state doesn't remain */
            buf->frags = NULL;

            net_buf_unref(buf);
            break;
        }
    }
}

static void friend_lpn_enqueue_rx(struct bt_mesh_friend *frnd,
                                  struct bt_mesh_net_rx *rx,
                                  enum bt_mesh_friend_pdu_type type,
                                  const uint64_t *seq_auth, uint8_t seg_count,
                                  struct net_buf_simple *sbuf)
{
    struct friend_pdu_info info = {0};
    struct net_buf *buf = NULL;

    /* Because of network loopback, tx packets will also be passed into
     * this rx function. These packets have already been added to the
     * queue, and should be ignored.
     */
    if (bt_mesh_elem_find(rx->ctx.addr)) {
        return;
    }

    BT_DBG("LPN 0x%04x queue_size %u", frnd->lpn, frnd->queue_size);

    if (type == BLE_MESH_FRIEND_PDU_SINGLE && seq_auth) {
        friend_purge_old_ack(frnd, seq_auth, rx->ctx.addr);
    }

    info.src = rx->ctx.addr;
    info.dst = rx->ctx.recv_dst;

    if (rx->net_if == BLE_MESH_NET_IF_LOCAL) {
        info.ttl = rx->ctx.recv_ttl;
    } else {
        info.ttl = rx->ctx.recv_ttl - 1U;
    }

    info.ctl = rx->ctl;

    sys_put_be24(rx->seq, info.seq);

    info.iv_index = BLE_MESH_NET_IVI_RX(rx);

    buf = create_friend_pdu(frnd, &info, sbuf);
    if (!buf) {
        BT_ERR("Failed to encode Friend buffer");
        return;
    }

    enqueue_friend_pdu(frnd, type, info.src, seg_count, buf);

    BT_DBG("Queued message for LPN 0x%04x, queue_size %u",
           frnd->lpn, frnd->queue_size);
}

static void friend_lpn_enqueue_tx(struct bt_mesh_friend *frnd,
                                  struct bt_mesh_net_tx *tx,
                                  enum bt_mesh_friend_pdu_type type,
                                  const uint64_t *seq_auth, uint8_t seg_count,
                                  struct net_buf_simple *sbuf)
{
    struct friend_pdu_info info = {0};
    struct net_buf *buf = NULL;

    BT_DBG("LPN 0x%04x", frnd->lpn);

    if (type == BLE_MESH_FRIEND_PDU_SINGLE && seq_auth) {
        friend_purge_old_ack(frnd, seq_auth, tx->src);
    }

    info.src = tx->src;
    info.dst = tx->ctx->addr;

    info.ttl = tx->ctx->send_ttl;
    info.ctl = (tx->ctx->app_idx == BLE_MESH_KEY_UNUSED);

    sys_put_be24(bt_mesh.seq, info.seq);

    info.iv_index = BLE_MESH_NET_IVI_TX;

    buf = create_friend_pdu(frnd, &info, sbuf);
    if (!buf) {
        BT_ERR("Failed to encode Friend buffer");
        return;
    }

    if (type == BLE_MESH_FRIEND_PDU_SINGLE && !info.ctl) {
        /* Unsegmented application packets may be re-encrypted later,
         * as they depend on the the sequence number being the same
         * when encrypting in transport and network.
         */
        FRIEND_ADV(buf)->app_idx = tx->ctx->app_idx;
    }

    enqueue_friend_pdu(frnd, type, info.src, seg_count, buf);

    BT_DBG("Queued message for LPN 0x%04x", frnd->lpn);
}

static bool friend_lpn_matches(struct bt_mesh_friend *frnd, uint16_t net_idx,
                               uint16_t addr)
{
    int i;

    if (!frnd->established) {
        return false;
    }

    if (net_idx != frnd->net_idx) {
        return false;
    }

    if (BLE_MESH_ADDR_IS_UNICAST(addr)) {
        return is_lpn_unicast(frnd, addr);
    }

    for (i = 0; i < ARRAY_SIZE(frnd->sub_list); i++) {
        if (frnd->sub_list[i] == addr) {
            return true;
        }
    }

    return false;
}

bool bt_mesh_friend_match(uint16_t net_idx, uint16_t addr)
{
    int i;

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (friend_lpn_matches(frnd, net_idx, addr)) {
            BT_DBG("LPN 0x%04x matched address 0x%04x",
                   frnd->lpn, addr);
            return true;
        }
    }

    BT_DBG("No matching LPN for address 0x%04x", addr);

    return false;
}

bool bt_mesh_friend_unicast_match(uint16_t net_idx, uint16_t addr, uint8_t *selem)
{
    int i;

    if (!BLE_MESH_ADDR_IS_UNICAST(addr) || selem == NULL) {
        BT_ERR("%s, Invalid parameter", __func__);
        return false;
    }

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (frnd->established && net_idx == frnd->net_idx &&
            BLE_MESH_ADDR_IS_UNICAST(frnd->lpn) &&
            (addr >= frnd->lpn && addr < (frnd->lpn + frnd->num_elem))) {
            *selem = frnd->num_elem - 1;
            return true;
        }
    }

    return false;
}

static bool friend_queue_has_space(struct bt_mesh_friend *frnd, uint16_t addr,
                                   const uint64_t *seq_auth, uint8_t seg_count)
{
    uint32_t total = 0U;
    int i;

    if (seg_count > CONFIG_BLE_MESH_FRIEND_QUEUE_SIZE) {
        return false;
    }

    for (i = 0; i < ARRAY_SIZE(frnd->seg); i++) {
        struct bt_mesh_friend_seg *seg = &frnd->seg[i];

        if (seq_auth && is_seg(seg, addr, *seq_auth & TRANS_SEQ_ZERO_MASK)) {
            /* If there's a segment queue for this message then the
             * space verification has already happened.
             */
            return true;
        }

        total += seg->seg_count;
    }

    /* If currently pending segments combined with this segmented message
     * are more than the Friend Queue Size, then there's no space. This
     * is because we don't have a mechanism of aborting already pending
     * segmented messages to free up buffers.
     */
    return (CONFIG_BLE_MESH_FRIEND_QUEUE_SIZE - total) > seg_count;
}

bool bt_mesh_friend_queue_has_space(uint16_t net_idx, uint16_t src, uint16_t dst,
                                    const uint64_t *seq_auth, uint8_t seg_count)
{
    bool someone_has_space = false, friend_match = false;
    int i;

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (!friend_lpn_matches(frnd, net_idx, dst)) {
            continue;
        }

        friend_match = true;

        if (friend_queue_has_space(frnd, src, seq_auth, seg_count)) {
            someone_has_space = true;
        }
    }

    /* If there were no matched LPNs treat this as success, so the
     * transport layer can continue its work.
     */
    if (!friend_match) {
        return true;
    }

    /* From the transport layers perspective it's good enough that at
     * least one Friend Queue has space. If there were multiple Friend
     * matches then the destination must be a group address, in which
     * case e.g. segment acks are not sent.
     */
    return someone_has_space;
}

static bool friend_queue_prepare_space(struct bt_mesh_friend *frnd, uint16_t addr,
                                       const uint64_t *seq_auth, uint8_t seg_count)
{
    bool pending_segments = false;
    uint8_t avail_space = 0U;

    if (!friend_queue_has_space(frnd, addr, seq_auth, seg_count)) {
        return false;
    }

    avail_space = CONFIG_BLE_MESH_FRIEND_QUEUE_SIZE - frnd->queue_size;
    pending_segments = false;

    while (pending_segments || avail_space < seg_count) {
        struct net_buf *buf = (void *)sys_slist_get(&frnd->queue);

        if (!buf) {
            BT_ERR("Unable to free up enough buffers");
            return false;
        }

        frnd->queue_size--;
        avail_space++;

        pending_segments = (buf->flags & NET_BUF_FRAGS);

        /* Make sure old slist entry state doesn't remain */
        buf->frags = NULL;
        buf->flags &= ~NET_BUF_FRAGS;

        net_buf_unref(buf);
    }

    return true;
}

void bt_mesh_friend_enqueue_rx(struct bt_mesh_net_rx *rx,
                               enum bt_mesh_friend_pdu_type type,
                               const uint64_t *seq_auth, uint8_t seg_count,
                               struct net_buf_simple *sbuf)
{
    int i;

    if (!rx->friend_match ||
        (rx->ctx.recv_ttl <= 1U && rx->net_if != BLE_MESH_NET_IF_LOCAL) ||
        bt_mesh_friend_get() != BLE_MESH_FRIEND_ENABLED) {
        return;
    }

    BT_DBG("recv_ttl %u net_idx 0x%04x src 0x%04x dst 0x%04x",
           rx->ctx.recv_ttl, rx->sub->net_idx, rx->ctx.addr,
           rx->ctx.recv_dst);

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (!friend_lpn_matches(frnd, rx->sub->net_idx,
                                rx->ctx.recv_dst)) {
            continue;
        }

        if (!friend_queue_prepare_space(frnd, rx->ctx.addr, seq_auth,
                                        seg_count)) {
            continue;
        }

        friend_lpn_enqueue_rx(frnd, rx, type, seq_auth, seg_count,
                              sbuf);
    }
}

bool bt_mesh_friend_enqueue_tx(struct bt_mesh_net_tx *tx,
                               enum bt_mesh_friend_pdu_type type,
                               const uint64_t *seq_auth, uint8_t seg_count,
                               struct net_buf_simple *sbuf)
{
    bool matched = false;
    int i;

    if (!bt_mesh_friend_match(tx->sub->net_idx, tx->ctx->addr) ||
        bt_mesh_friend_get() != BLE_MESH_FRIEND_ENABLED) {
        return matched;
    }

    BT_DBG("net_idx 0x%04x dst 0x%04x src 0x%04x", tx->sub->net_idx,
           tx->ctx->addr, tx->src);

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];

        if (!friend_lpn_matches(frnd, tx->sub->net_idx,
                                tx->ctx->addr)) {
            continue;
        }

        if (!friend_queue_prepare_space(frnd, tx->src, seq_auth,
                                        seg_count)) {
            continue;
        }

        friend_lpn_enqueue_tx(frnd, tx, type, seq_auth, seg_count,
                              sbuf);
        matched = true;
    }

    return matched;
}

void bt_mesh_friend_clear_incomplete(struct bt_mesh_subnet *sub, uint16_t src,
                                     uint16_t dst, const uint64_t *seq_auth)
{
    int i;

    for (i = 0; i < ARRAY_SIZE(bt_mesh.frnd); i++) {
        struct bt_mesh_friend *frnd = &bt_mesh.frnd[i];
        int j;

        if (!friend_lpn_matches(frnd, sub->net_idx, dst)) {
            continue;
        }

        for (j = 0; j < ARRAY_SIZE(frnd->seg); j++) {
            struct bt_mesh_friend_seg *seg = &frnd->seg[j];

            if (!is_seg(seg, src, *seq_auth & TRANS_SEQ_ZERO_MASK)) {
                continue;
            }

            BT_WARN("Clearing incomplete segments for 0x%04x", src);

            purge_buffers(&seg->queue);
            seg->seg_count = 0U;
            break;
        }
    }
}

void bt_mesh_friend_remove_lpn(uint16_t lpn_addr)
{
    struct bt_mesh_friend *frnd = NULL;

    frnd = bt_mesh_friend_find(BLE_MESH_KEY_ANY, lpn_addr, false, false);
    if (frnd) {
        friend_clear(frnd, BLE_MESH_FRIENDSHIP_TERMINATE_DISABLE);
    }
}

#endif /* CONFIG_BLE_MESH_FRIEND */