esp-idf/components/nvs_flash/include/nvs_handle.hpp

#ifndef NVS_HANDLE_HPP_
#define NVS_HANDLE_HPP_

#include <string>
#include <memory>
#include <type_traits>

#include "nvs.h"

namespace nvs {

/**
 * The possible blob types. This is a helper definition for template functions.
 */
enum class ItemType : uint8_t {
    U8   = NVS_TYPE_U8,
    I8   = NVS_TYPE_I8,
    U16  = NVS_TYPE_U16,
    I16  = NVS_TYPE_I16,
    U32  = NVS_TYPE_U32,
    I32  = NVS_TYPE_I32,
    U64  = NVS_TYPE_U64,
    I64  = NVS_TYPE_I64,
    SZ   = NVS_TYPE_STR,
    BLOB = 0x41,
    BLOB_DATA = NVS_TYPE_BLOB,
    BLOB_IDX  = 0x48,
    ANY  = NVS_TYPE_ANY
};


/**
 * @brief A handle allowing nvs-entry related operations on the NVS.
 *
 * @note The scope of this handle may vary depending on the implementation, but normally would be the namespace of
 * a particular partition. Outside that scope, nvs entries can't be accessed/altered.
 */
class NVSHandle {
public:
    virtual ~NVSHandle() { }

    /**
     * @brief      set value for given key
     *
     * Sets value for key. Note that physical storage will not be updated until nvs_commit function is called.
     *
     * @param[in]  key     Key name. Maximal length is (NVS_KEY_NAME_MAX_SIZE-1) characters. Shouldn't be empty.
     * @param[in]  value   The value to set. Allowed types are the ones declared in ItemType as well as enums.
     *                     For strings, the maximum length (including null character) is
     *                     4000 bytes, if there is one complete page free for writing.
     *                     This decreases, however, if the free space is fragmented.
     *                     Note that enums loose their type information when stored in NVS. Ensure that the correct
     *                     enum type is used during retrieval with \ref get_item!
     *
     * @return
     *             - ESP_OK if value was set successfully
     *             - ESP_ERR_NVS_READ_ONLY if storage handle was opened as read only
     *             - ESP_ERR_NVS_INVALID_NAME if key name doesn't satisfy constraints
     *             - ESP_ERR_NVS_NOT_ENOUGH_SPACE if there is not enough space in the
     *               underlying storage to save the value
     *             - ESP_ERR_NVS_REMOVE_FAILED if the value wasn't updated because flash
     *               write operation has failed. The value was written however, and
     *               update will be finished after re-initialization of nvs, provided that
     *               flash operation doesn't fail again.
     *             - ESP_ERR_NVS_VALUE_TOO_LONG if the string value is too long
     */
    template<typename T>
    esp_err_t set_item(const char *key, T value);
    virtual
    esp_err_t set_string(const char *key, const char* value) = 0;

    /**
     * @brief      get value for given key
     *
     * These functions retrieve value for the key, given its name. If key does not
     * exist, or the requested variable type doesn't match the type which was used
     * when setting a value, an error is returned.
     *
     * In case of any error, out_value is not modified.
     *
     * @param[in]     key        Key name. Maximal length is (NVS_KEY_NAME_MAX_SIZE-1) characters. Shouldn't be empty.
     * @param         value      The output value. All integral types which are declared in ItemType as well as enums
     *                           are allowed. Note however that enums lost their type information when stored in NVS.
     *                           Ensure that the correct enum type is used during retrieval with \ref get_item!
     *
     * @return
     *             - ESP_OK if the value was retrieved successfully
     *             - ESP_ERR_NVS_NOT_FOUND if the requested key doesn't exist
     *             - ESP_ERR_NVS_INVALID_NAME if key name doesn't satisfy constraints
     *             - ESP_ERR_NVS_INVALID_LENGTH if length is not sufficient to store data
     */
    template<typename T>
    esp_err_t get_item(const char *key, T &value);

    /**
     * @brief       set variable length binary value for given key
     *
     * This family of functions set value for the key, given its name. Note that
     * actual storage will not be updated until nvs_commit function is called.
     *
     * @param[in]  key     Key name. Maximal length is (NVS_KEY_NAME_MAX_SIZE-1) characters. Shouldn't be empty.
     * @param[in]  blob    The blob value to set.
     * @param[in]  len     length of binary value to set, in bytes; Maximum length is
     *                     508000 bytes or (97.6% of the partition size - 4000) bytes
     *                     whichever is lower.
     *
     * @return
     *             - ESP_OK if value was set successfully
     *             - ESP_ERR_NVS_READ_ONLY if storage handle was opened as read only
     *             - ESP_ERR_NVS_INVALID_NAME if key name doesn't satisfy constraints
     *             - ESP_ERR_NVS_NOT_ENOUGH_SPACE if there is not enough space in the
     *               underlying storage to save the value
     *             - ESP_ERR_NVS_REMOVE_FAILED if the value wasn't updated because flash
     *               write operation has failed. The value was written however, and
     *               update will be finished after re-initialization of nvs, provided that
     *               flash operation doesn't fail again.
     *             - ESP_ERR_NVS_VALUE_TOO_LONG if the value is too long
     *
     * @note compare to \ref nvs_set_blob in nvs.h
     */
    virtual esp_err_t set_blob(const char *key, const void* blob, size_t len) = 0;

    /**
     * @brief      get value for given key
     *
     * These functions retrieve the data of an entry, given its key. If key does not
     * exist, or the requested variable type doesn't match the type which was used
     * when setting a value, an error is returned.
     *
     * In case of any error, out_value is not modified.
     *
     * Both functions expect out_value to be a pointer to an already allocated variable
     * of the given type.
     *
     * It is suggested that nvs_get/set_str is used for zero-terminated short C strings, and
     * nvs_get/set_blob is used for arbitrary data structures and long C strings.
     *
     * @param[in]     key        Key name. Maximum length is (NVS_KEY_NAME_MAX_SIZE-1) characters. Shouldn't be empty.
     * @param         out_str/   Pointer to the output value.
     *                out_blob
     * @param[inout]  len        The length of the output buffer pointed to by out_str/out_blob.
     *                           Use \c get_item_size to query the size of the item beforehand.
     *
     * @return
     *             - ESP_OK if the value was retrieved successfully
     *             - ESP_ERR_NVS_NOT_FOUND if the requested key doesn't exist
     *             - ESP_ERR_NVS_INVALID_NAME if key name doesn't satisfy constraints
     *             - ESP_ERR_NVS_INVALID_LENGTH if length is not sufficient to store data
     */
    virtual esp_err_t get_string(const char *key, char* out_str, size_t len) = 0;
    virtual esp_err_t get_blob(const char *key, void* out_blob, size_t len) = 0;

    /**
     * @brief Look up the size of an entry's data.
     *
     * @param[in]     datatype   Data type to search for.
     * @param[in]     key        Key name. Maximum length is (NVS_KEY_NAME_MAX_SIZE-1) characters. Shouldn't be empty.
     * @param[out]    size       Size of the item, if it exists.
     *                           For strings, this size includes the zero terminator.
     *
     * @return     - ESP_OK if the item with specified type and key exists. Its size will be returned via \c size.
     *             - ESP_ERR_NVS_NOT_FOUND if an item with the requested key and type doesn't exist or any other
     *               error occurs.
     */
    virtual esp_err_t get_item_size(ItemType datatype, const char *key, size_t &size) = 0;

    /**
     * @brief Erases an entry.
     */
    virtual esp_err_t erase_item(const char* key) = 0;

    /**
     * Erases all entries in the scope of this handle. The scope may vary, depending on the implementation.
     *
     * @not If you want to erase the whole nvs flash (partition), refer to \ref
     */
    virtual esp_err_t erase_all() = 0;

    /**
     * Commits all changes done through this handle so far.
     * Currently, NVS writes to storage right after the set and get functions,
     * but this is not guaranteed.
     */
    virtual esp_err_t commit() = 0;

    /**
     * @brief      Calculate all entries in the scope of the handle.
     *
     * @param[out]  used_entries Returns amount of used entries from a namespace on success.
     *
     *
     * @return
     *             - ESP_OK if the changes have been written successfully.
     *               Return param used_entries will be filled valid value.
     *             - ESP_ERR_NVS_NOT_INITIALIZED if the storage driver is not initialized.
     *               Return param used_entries will be filled 0.
     *             - ESP_ERR_INVALID_ARG if nvs_stats equal to NULL.
     *             - Other error codes from the underlying storage driver.
     *               Return param used_entries will be filled 0.
     */
    virtual esp_err_t get_used_entry_count(size_t& usedEntries) = 0;

protected:
    virtual esp_err_t set_typed_item(ItemType datatype, const char *key, const void* data, size_t dataSize) = 0;

    virtual esp_err_t get_typed_item(ItemType datatype, const char *key, void* data, size_t dataSize) = 0;
};

/**
 * @brief Opens non-volatile storage and returns a handle object.
 *
 * The handle is automatically closed on desctruction. The scope of the handle is the namespace ns_name
 * in a particular partition partition_name.
 * The parameters partition_name, ns_name and open_mode have the same meaning and restrictions as the parameters
 * part_name, name and open_mode in \ref nvs_open_from_partition, respectively.
 *
 * @param err an optional pointer to an esp_err_t result of the open operation, having the same meaning as the return
 * value in \ref nvs_open_from_partition:
 *             - ESP_OK if storage handle was opened successfully
 *             - ESP_ERR_NVS_NOT_INITIALIZED if the storage driver is not initialized
 *             - ESP_ERR_NVS_PART_NOT_FOUND if the partition with label "nvs" is not found
 *             - ESP_ERR_NVS_NOT_FOUND id namespace doesn't exist yet and
 *               mode is NVS_READONLY
 *             - ESP_ERR_NVS_INVALID_NAME if namespace name doesn't satisfy constraints
 *             - ESP_ERR_NOT_ALLOWED if the NVS partition is read-only and mode is NVS_READWRITE
 *             - other error codes from the underlying storage driver
 *
 * @return unique pointer of an nvs handle on success, an empty unique pointer otherwise
 */
std::unique_ptr<NVSHandle> open_nvs_handle_from_partition(const char *partition_name,
        const char *ns_name,
        nvs_open_mode_t open_mode,
        esp_err_t *err = nullptr);

/**
 * @brief This function does the same as \ref open_nvs_handle_from_partition but uses the default nvs partition
 * instead of a partition_name parameter.
 */
std::unique_ptr<NVSHandle> open_nvs_handle(const char *ns_name,
        nvs_open_mode_t open_mode,
        esp_err_t *err = nullptr);

// Helper functions for template usage
/**
 * Help to translate all integral types into ItemType.
 */
template<typename T, typename std::enable_if<std::is_integral<T>::value, void*>::type = nullptr>
constexpr ItemType itemTypeOf()
{
    return static_cast<ItemType>(((std::is_signed<T>::value)?0x10:0x00) | sizeof(T));
}

/**
 * Help to translate all enum types into integral ItemType.
 */
template<typename T, typename std::enable_if<std::is_enum<T>::value, int>::type = 0>
constexpr ItemType itemTypeOf()
{
    return static_cast<ItemType>(((std::is_signed<T>::value)?0x10:0x00) | sizeof(T));
}

template<typename T>
constexpr ItemType itemTypeOf(const T&)
{
    return itemTypeOf<T>();
}

// Template Implementations
template<typename T>
esp_err_t NVSHandle::set_item(const char *key, T value) {
    return set_typed_item(itemTypeOf(value), key, &value, sizeof(value));
}

template<typename T>
esp_err_t NVSHandle::get_item(const char *key, T &value) {
    return get_typed_item(itemTypeOf(value), key, &value, sizeof(value));
}

} // nvs

#endif // NVS_HANDLE_HPP_