subsys/bluetooth/audio/ccid.c

/*  Bluetooth Audio Content Control */

/*
 * Copyright (c) 2020 Bose Corporation
 * Copyright (c) 2021-2024 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: Apache-2.0
 */
#include <errno.h>
#include <stddef.h>
#include <stdint.h>
#include <sys/types.h>

#include <zephyr/bluetooth/att.h>
#include <zephyr/bluetooth/audio/ccid.h>
#include <zephyr/bluetooth/gatt.h>
#include <zephyr/bluetooth/uuid.h>
#include <zephyr/sys/__assert.h>

struct ccid_search_param {
	const struct bt_gatt_attr *attr;
	uint8_t ccid;
};

static uint8_t ccid_attr_cb(const struct bt_gatt_attr *attr, uint16_t handle, void *user_data)
{
	struct ccid_search_param *search_param = user_data;

	if (attr->read != NULL) {
		uint8_t ccid = 0U;
		ssize_t res;

		res = attr->read(NULL, attr, &ccid, sizeof(ccid), 0);

		if (res == sizeof(ccid) && search_param->ccid == ccid) {
			search_param->attr = attr;

			return BT_GATT_ITER_STOP;
		}
	}

	return BT_GATT_ITER_CONTINUE;
}

const struct bt_gatt_attr *bt_ccid_find_attr(uint8_t ccid)
{
	struct ccid_search_param search_param = {
		.attr = NULL,
		.ccid = ccid,
	};

	bt_gatt_foreach_attr_type(BT_ATT_FIRST_ATTRIBUTE_HANDLE, BT_ATT_LAST_ATTRIBUTE_HANDLE,
				  BT_UUID_CCID, NULL, 0, ccid_attr_cb, &search_param);

	return search_param.attr;
}

int bt_ccid_alloc_value(void)
{
	static uint8_t next_ccid_value;
	const uint8_t tmp = next_ccid_value;

	/* Verify that the CCID is unused and increment until we reach an unused value or until we
	 * reach our starting point
	 * This is not a perfect check as there may be services that are not registered that have
	 * allocated a CCID.
	 * Implementing a perfect solution would require a alloc and free API where we need to
	 * keep track of all allocated CCIDs, which requires additional memory for something that's
	 * very unlikely to be an issue.
	 */
	while (bt_ccid_find_attr(next_ccid_value) != NULL) {
		next_ccid_value++;
		if (tmp == next_ccid_value) {
			return -ENOMEM;
		}
	}

	return next_ccid_value++;
}