Add NimBLEAttValue class. (#67)

This is a specialized container class to hold BLE attribute values.

- Removes the use of std::string previously used to store the values.
- Allows for setting/getting/notifying values from std::string, std::vector<uint8_t>, Arduino String, const char*, and uint8_t buffers.
- Has operators retrieve the value as std::string, Arduino String, std::vector<uint8_t>, uint8_t* or char pointers.
- Includes iterators and subscript/random access operator.
- Introduces a max length parameter to the creation of server characteristics/descriptors to limit the size of the memory footprint.
- Nearly Seamless integration with existing code.
- Adds a config option to enable/disable timestamp storage when the value is updated.
- Adds a config option to specify the initial size of the value container if not specified in the constructor.

src/NimBLEAttValue.h

@@ -0,0 +1,447 @@
+/*
+ * NimBLEAttValue.h
+ *
+ *  Created: on March 18, 2021
+ *      Author H2zero
+ *
+ */
+
+#ifndef MAIN_NIMBLEATTVALUE_H_
+#define MAIN_NIMBLEATTVALUE_H_
+#include "nimconfig.h"
+#if defined(CONFIG_BT_ENABLED)
+
+#ifdef NIMBLE_CPP_ARDUINO_STRING_AVAILABLE
+#include <Arduino.h>
+#endif
+
+#include "NimBLELog.h"
+
+/****  FIX COMPILATION ****/
+#undef min
+#undef max
+/**************************/
+
+#include <string>
+#include <vector>
+
+#ifndef CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+#    define CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED 0
+#endif
+
+#if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+#    include <time.h>
+#endif
+
+#if !defined(CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH)
+#    define CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH 20
+#elif CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH > BLE_ATT_ATTR_MAX_LEN
+#    error CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH cannot be larger than 512 (BLE_ATT_ATTR_MAX_LEN)
+#elif CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH < 1
+#    error CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH cannot be less than 1; Range = 1 : 512
+#endif
+
+
+/* Used to determine if the type passed to a template has a c_str() and length() method. */
+template <typename T, typename = void, typename = void>
+struct Has_c_str_len : std::false_type {};
+
+template <typename T>
+struct Has_c_str_len<T, decltype(void(std::declval<T &>().c_str())),
+                     decltype(void(std::declval<T &>().length()))> : std::true_type {};
+
+
+/**
+ * @brief A specialized container class to hold BLE attribute values.
+ * @details This class is designed to be more memory efficient than using\n
+ * standard container types for value storage, while being convertable to\n
+ * many different container classes.
+ */
+class NimBLEAttValue
+{
+    uint8_t*     m_attr_value = nullptr;
+    uint16_t     m_attr_max_len = 0;
+    uint16_t     m_attr_len = 0;
+    uint16_t     m_capacity = 0;
+#if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+    time_t       m_timestamp = 0;
+#endif
+    void         deepCopy(const NimBLEAttValue & source);
+
+public:
+    /**
+     * @brief Default constructor.
+     * @param[in] init_len The initial size in bytes.
+     * @param[in] max_len The max size in bytes that the value can be.
+     */
+    NimBLEAttValue(uint16_t init_len = CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH,
+                   uint16_t max_len = BLE_ATT_ATTR_MAX_LEN);
+
+    /**
+     * @brief Construct with an initial value from a buffer.
+     * @param value A pointer to the initial value to set.
+     * @param[in] len The size in bytes of the value to set.
+     * @param[in] max_len The max size in bytes that the value can be.
+     */
+    NimBLEAttValue(const uint8_t *value, uint16_t len,
+                   uint16_t max_len = BLE_ATT_ATTR_MAX_LEN);
+
+    /**
+     * @brief Construct with an initializer list.
+     * @param list An initializer list containing the initial value to set.
+     * @param[in] max_len The max size in bytes that the value can be.
+     */
+    NimBLEAttValue(std::initializer_list<uint8_t> list,
+                   uint16_t max_len = BLE_ATT_ATTR_MAX_LEN)
+                   :NimBLEAttValue(list.begin(), (uint16_t)list.size(), max_len){}
+
+    /**
+     * @brief Construct with an initial value from a const char string.
+     * @param value A pointer to the initial value to set.
+     * @param[in] max_len The max size in bytes that the value can be.
+     */
+    NimBLEAttValue(const char *value, uint16_t max_len = BLE_ATT_ATTR_MAX_LEN)
+                   :NimBLEAttValue((uint8_t*)value, (uint16_t)strlen(value), max_len){}
+
+    /**
+     * @brief Construct with an initial value from a std::string.
+     * @param str A std::string containing to the initial value to set.
+     * @param[in] max_len The max size in bytes that the value can be.
+     */
+    NimBLEAttValue(const std::string str, uint16_t max_len = BLE_ATT_ATTR_MAX_LEN)
+                   :NimBLEAttValue((uint8_t*)str.data(), (uint16_t)str.length(), max_len){}
+
+    /**
+     * @brief Construct with an initial value from a std::vector<uint8_t>.
+     * @param vec A std::vector<uint8_t> containing to the initial value to set.
+     * @param[in] max_len The max size in bytes that the value can be.
+     */
+    NimBLEAttValue(const std::vector<uint8_t> vec, uint16_t max_len = BLE_ATT_ATTR_MAX_LEN)
+                   :NimBLEAttValue(&vec[0], (uint16_t)vec.size(), max_len){}
+
+#ifdef NIMBLE_CPP_ARDUINO_STRING_AVAILABLE
+    /**
+     * @brief Construct with an initial value from an Arduino String.
+     * @param str An Arduino String containing to the initial value to set.
+     * @param[in] max_len The max size in bytes that the value can be.
+     */
+    NimBLEAttValue(const String str, uint16_t max_len = BLE_ATT_ATTR_MAX_LEN)
+                   :NimBLEAttValue((uint8_t*)str.c_str(), str.length(), max_len){}
+#endif
+
+    /** @brief Copy constructor */
+    NimBLEAttValue(const NimBLEAttValue & source) { deepCopy(source); }
+
+    /** @brief Move constructor */
+    NimBLEAttValue(NimBLEAttValue && source) { *this = std::move(source); }
+
+    /** @brief Destructor */
+    ~NimBLEAttValue();
+
+    /** @brief Returns the max size in bytes */
+    uint16_t        max_size()     const   { return m_attr_max_len; }
+
+    /** @brief Returns the currently allocated capacity in bytes */
+    uint16_t        capacity()     const   { return m_capacity; }
+
+    /** @brief Returns the current length of the value in bytes */
+    uint16_t        length()       const   { return m_attr_len; }
+
+    /** @brief Returns the current size of the value in bytes */
+    uint16_t        size()         const   { return m_attr_len; }
+
+    /** @brief Returns a pointer to the internal buffer of the value */
+    const uint8_t*  data()         const   { return m_attr_value; }
+
+    /** @brief Returns a pointer to the internal buffer of the value as a const char* */
+    const char*     c_str()        const   { return (const char*)m_attr_value; }
+
+    /** @brief Iterator begin */
+    const uint8_t*  begin()        const   { return m_attr_value; }
+
+    /** @brief Iterator end */
+    const uint8_t*  end()          const   { return m_attr_value + m_attr_len; }
+
+#if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+    /** @brief Returns a timestamp of when the value was last updated */
+    time_t          getTimeStamp() const   { return m_timestamp; }
+
+    /** @brief Set the timestamp to the current time */
+    void            setTimeStamp()         { m_timestamp = time(nullptr); }
+
+    /**
+     * @brief Set the timestamp to the specified time
+     * @param[in] t The timestamp value to set
+     */
+    void            setTimeStamp(time_t t) { m_timestamp = t; }
+#else
+    time_t          getTimeStamp() const   { return 0; }
+    void            setTimeStamp()         { }
+    void            setTimeStamp(time_t t) { }
+#endif
+
+    /**
+     * @brief Set the value from a buffer
+     * @param[in] value A ponter to a buffer containing the value.
+     * @param[in] len The length of the value in bytes.
+     * @returns True if successful.
+     */
+    bool            setValue(const uint8_t *value, uint16_t len);
+
+    /**
+     * @brief Set value to the value of const char*.
+     * @param [in] s A ponter to a const char value to set.
+     */
+    bool            setValue(const char* s) {
+                         return setValue((uint8_t*)s, (uint16_t)strlen(s)); }
+
+    /**
+     * @brief Get a pointer to the value buffer with timestamp.
+     * @param[in] timestamp A ponter to a time_t variable to store the timestamp.
+     * @returns A pointer to the internal value buffer.
+     */
+    const uint8_t*  getValue(time_t *timestamp);
+
+    /**
+     * @brief Append data to the value.
+     * @param[in] value A ponter to a data buffer with the value to append.
+     * @param[in] len The length of the value to append in bytes.
+     * @returns A reference to the appended NimBLEAttValue.
+     */
+    NimBLEAttValue& append(const uint8_t *value, uint16_t len);
+
+
+    /*********************** Template Functions ************************/
+
+    /**
+     * @brief Template to set value to the value of <type\>val.
+     * @param [in] s The <type\>value to set.
+     * @details Only used for types without a `c_str()` method.
+     */
+    template<typename T>
+#ifdef _DOXYGEN_
+    bool
+#else
+    typename std::enable_if<!Has_c_str_len<T>::value, bool>::type
+#endif
+    setValue(const T &s) {
+        return setValue((uint8_t*)&s, sizeof(T));
+    }
+
+    /**
+     * @brief Template to set value to the value of <type\>val.
+     * @param [in] s The <type\>value to set.
+     * @details Only used if the <type\> has a `c_str()` method.
+     */
+    template<typename T>
+#ifdef _DOXYGEN_
+    bool
+#else
+    typename std::enable_if<Has_c_str_len<T>::value, bool>::type
+#endif
+    setValue(const T & s) {
+        return setValue((uint8_t*)s.c_str(), (uint16_t)s.length());
+    }
+
+    /**
+     * @brief Template to return the value as a <type\>.
+     * @tparam T The type to convert the data to.
+     * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
+     * @param [in] skipSizeCheck If true it will skip checking if the data size is less than\n
+     * <tt>sizeof(<type\>)</tt>.
+     * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is\n
+     * less than <tt>sizeof(<type\>)</tt>.
+     * @details <b>Use:</b> <tt>getValue<type>(&timestamp, skipSizeCheck);</tt>
+     */
+    template<typename T>
+    T   getValue(time_t *timestamp = nullptr, bool skipSizeCheck = false) {
+            if(!skipSizeCheck && size() < sizeof(T)) {
+                return T();
+            }
+            return *((T *)getValue(timestamp));
+    }
+
+
+    /*********************** Operators ************************/
+
+    /** @brief Subscript operator */
+    uint8_t operator [](int pos) const {
+        assert(pos < m_attr_len && "out of range"); return m_attr_value[pos]; }
+
+    /** @brief Operator; Get the value as a std::vector<uint8_t>. */
+    operator std::vector<uint8_t>() const {
+        return std::vector<uint8_t>(m_attr_value, m_attr_value + m_attr_len); }
+
+    /** @brief Operator; Get the value as a std::string. */
+    operator std::string() const {
+        return std::string((char*)m_attr_value, m_attr_len); }
+
+    /** @brief Operator; Get the value as a const uint8_t*. */
+    operator const uint8_t*() const { return m_attr_value; }
+
+    /** @brief Operator; Append another NimBLEAttValue. */
+    NimBLEAttValue& operator  +=(const NimBLEAttValue & source) {
+        return append(source.data(), source.size()); }
+
+    /** @brief Operator; Set the value from a std::string source. */
+    NimBLEAttValue& operator  =(const std::string & source) {
+        setValue((uint8_t*)source.data(), (uint16_t)source.size()); return *this; }
+
+    /** @brief Move assignment operator */
+    NimBLEAttValue& operator  =(NimBLEAttValue && source);
+
+    /** @brief Copy assignment operator */
+    NimBLEAttValue& operator  =(const NimBLEAttValue & source);
+
+    /** @brief Equality operator */
+    bool operator  ==(const NimBLEAttValue & source) {
+        return (m_attr_len == source.size()) ?
+                memcmp(m_attr_value, source.data(), m_attr_len) == 0 : false; }
+
+    /** @brief Inequality operator */
+    bool operator  !=(const NimBLEAttValue & source){ return !(*this == source); }
+
+#ifdef NIMBLE_CPP_ARDUINO_STRING_AVAILABLE
+    /** @brief Operator; Get the value as an Arduino String value. */
+    operator String() const { return String((char*)m_attr_value); }
+#endif
+
+};
+
+
+inline NimBLEAttValue::NimBLEAttValue(uint16_t init_len, uint16_t max_len) {
+    m_attr_value   = (uint8_t*)calloc(init_len + 1, 1);
+    assert(m_attr_value && "No Mem");
+    m_attr_max_len = std::min(BLE_ATT_ATTR_MAX_LEN, (int)max_len);
+    m_attr_len     = 0;
+    m_capacity     = init_len;
+    setTimeStamp(0);
+}
+
+inline NimBLEAttValue::NimBLEAttValue(const uint8_t *value, uint16_t len, uint16_t max_len)
+: NimBLEAttValue(len, max_len) {
+    memcpy(m_attr_value, value, len);
+    m_attr_value[len] = '\0';
+    m_attr_len        = len;
+}
+
+inline NimBLEAttValue::~NimBLEAttValue() {
+    if(m_attr_value != nullptr) {
+        free(m_attr_value);
+    }
+}
+
+inline NimBLEAttValue& NimBLEAttValue::operator =(NimBLEAttValue && source) {
+    if (this != &source){
+        free(m_attr_value);
+
+        m_attr_value   = source.m_attr_value;
+        m_attr_max_len = source.m_attr_max_len;
+        m_attr_len     = source.m_attr_len;
+        m_capacity     = source.m_capacity;
+        setTimeStamp(source.getTimeStamp());
+        source.m_attr_value = nullptr;
+    }
+    return *this;
+}
+
+inline NimBLEAttValue& NimBLEAttValue::operator =(const NimBLEAttValue & source) {
+    if (this != &source) {
+        deepCopy(source);
+    }
+    return *this;
+}
+
+inline void NimBLEAttValue::deepCopy(const NimBLEAttValue & source) {
+    uint8_t* res = (uint8_t*)realloc( m_attr_value, source.m_capacity + 1);
+    assert(res && "deepCopy: realloc failed");
+
+    ble_npl_hw_enter_critical();
+    m_attr_value   = res;
+    m_attr_max_len = source.m_attr_max_len;
+    m_attr_len     = source.m_attr_len;
+    m_capacity     = source.m_capacity;
+    setTimeStamp(source.getTimeStamp());
+    memcpy(m_attr_value, source.m_attr_value, m_attr_len + 1);
+    ble_npl_hw_exit_critical(0);
+}
+
+inline const uint8_t*  NimBLEAttValue::getValue(time_t *timestamp) {
+    if(timestamp != nullptr) {
+#if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+        *timestamp = m_timestamp;
+#else
+        *timestamp = 0;
+#endif
+    }
+    return m_attr_value;
+}
+
+inline bool NimBLEAttValue::setValue(const uint8_t *value, uint16_t len) {
+    if (len > m_attr_max_len) {
+        NIMBLE_LOGE("NimBLEAttValue", "value exceeds max, len=%u, max=%u",
+                     len, m_attr_max_len);
+        return false;
+    }
+
+    uint8_t *res = m_attr_value;
+    if (len > m_capacity) {
+        res = (uint8_t*)realloc(m_attr_value, (len + 1));
+        m_capacity = len;
+    }
+    assert(res && "setValue: realloc failed");
+
+#if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+    time_t t = time(nullptr);
+#else
+    time_t t = 0;
+#endif
+
+    ble_npl_hw_enter_critical();
+    m_attr_value = res;
+    memcpy(m_attr_value, value, len);
+    m_attr_value[len] = '\0';
+    m_attr_len = len;
+    setTimeStamp(t);
+    ble_npl_hw_exit_critical(0);
+    return true;
+}
+
+inline NimBLEAttValue& NimBLEAttValue::append(const uint8_t *value, uint16_t len) {
+    if (len < 1) {
+        return *this;
+    }
+
+    if ((m_attr_len + len) > m_attr_max_len) {
+        NIMBLE_LOGE("NimBLEAttValue", "val > max, len=%u, max=%u",
+                    len, m_attr_max_len);
+        return *this;
+    }
+
+    uint8_t* res = m_attr_value;
+    uint16_t new_len = m_attr_len + len;
+    if (new_len > m_capacity) {
+        res = (uint8_t*)realloc(m_attr_value, (new_len + 1));
+        m_capacity = new_len;
+    }
+    assert(res && "append: realloc failed");
+
+#if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+    time_t t = time(nullptr);
+#else
+    time_t t = 0;
+#endif
+
+    ble_npl_hw_enter_critical();
+    m_attr_value = res;
+    memcpy(m_attr_value + m_attr_len, value, len);
+    m_attr_len = new_len;
+    m_attr_value[m_attr_len] = '\0';
+    setTimeStamp(t);
+    ble_npl_hw_exit_critical(0);
+
+    return *this;
+}
+
+#endif /*(CONFIG_BT_ENABLED) */
+#endif /* MAIN_NIMBLEATTVALUE_H_ */

src/NimBLECharacteristic.cpp

@@ -30,26 +30,29 @@ static const char* LOG_TAG = "NimBLECharacteristic";
  * @brief Construct a characteristic
  * @param [in] uuid - UUID (const char*) for the characteristic.
  * @param [in] properties - Properties for the characteristic.
+ * @param [in] max_len - The maximum length in bytes that the characteristic value can hold. (Default: 512 bytes for esp32, 20 for all others).
  * @param [in] pService - pointer to the service instance this characteristic belongs to.
  */
-NimBLECharacteristic::NimBLECharacteristic(const char* uuid, uint16_t properties, NimBLEService* pService)
-: NimBLECharacteristic(NimBLEUUID(uuid), properties, pService) {
+NimBLECharacteristic::NimBLECharacteristic(const char* uuid, uint16_t properties,
+                                           uint16_t max_len, NimBLEService* pService)
+: NimBLECharacteristic(NimBLEUUID(uuid), properties, max_len, pService) {
 }
 
 /**
  * @brief Construct a characteristic
  * @param [in] uuid - UUID for the characteristic.
  * @param [in] properties - Properties for the characteristic.
+ * @param [in] max_len - The maximum length in bytes that the characteristic value can hold. (Default: 512 bytes for esp32, 20 for all others).
  * @param [in] pService - pointer to the service instance this characteristic belongs to.
  */
-NimBLECharacteristic::NimBLECharacteristic(const NimBLEUUID &uuid, uint16_t properties, NimBLEService* pService) {
+NimBLECharacteristic::NimBLECharacteristic(const NimBLEUUID &uuid, uint16_t properties,
+                                           uint16_t max_len, NimBLEService* pService)
+:   m_value(std::min(CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH , (int)max_len), max_len) {
     m_uuid        = uuid;
     m_handle      = NULL_HANDLE;
     m_properties  = properties;
     m_pCallbacks  = &defaultCallback;
     m_pService    = pService;
-    m_value       = "";
-    m_timestamp   = 0;
     m_removed     = 0;
 } // NimBLECharacteristic
 
@@ -231,17 +234,14 @@ NimBLEUUID NimBLECharacteristic::getUUID() {
 
 /**
  * @brief Retrieve the current value of the characteristic.
- * @return A std::string containing the current characteristic value.
+ * @return The NimBLEAttValue containing the current characteristic value.
  */
-std::string NimBLECharacteristic::getValue(time_t *timestamp) {
-    ble_npl_hw_enter_critical();
-    std::string retVal = m_value;
+NimBLEAttValue NimBLECharacteristic::getValue(time_t *timestamp) {
     if(timestamp != nullptr) {
-        *timestamp = m_timestamp;
+        m_value.getValue(timestamp);
     }
-    ble_npl_hw_exit_critical(0);
 
-    return retVal;
+    return m_value;
 } // getValue
 
 
@@ -250,10 +250,7 @@ std::string NimBLECharacteristic::getValue(time_t *timestamp) {
  * @return The length of the current characteristic data.
  */
 size_t NimBLECharacteristic::getDataLength() {
-    ble_npl_hw_enter_critical();
-    size_t len = m_value.length();
-    ble_npl_hw_exit_critical(0);
-    return len;
+    return m_value.size();
 }
 
 
@@ -286,25 +283,26 @@ int NimBLECharacteristic::handleGapEvent(uint16_t conn_handle, uint16_t attr_han
                 }
 
                 ble_npl_hw_enter_critical();
-                rc = os_mbuf_append(ctxt->om, (uint8_t*)pCharacteristic->m_value.data(),
-                                    pCharacteristic->m_value.length());
+                rc = os_mbuf_append(ctxt->om, pCharacteristic->m_value.data(), pCharacteristic->m_value.size());
                 ble_npl_hw_exit_critical(0);
                 return rc == 0 ? 0 : BLE_ATT_ERR_INSUFFICIENT_RES;
             }
 
             case BLE_GATT_ACCESS_OP_WRITE_CHR: {
-                if (ctxt->om->om_len > BLE_ATT_ATTR_MAX_LEN) {
+                uint16_t att_max_len = pCharacteristic->m_value.max_size();
+
+                if (ctxt->om->om_len > att_max_len) {
                     return BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN;
                 }
 
-                uint8_t buf[BLE_ATT_ATTR_MAX_LEN];
+                uint8_t buf[att_max_len];
                 size_t len = ctxt->om->om_len;
                 memcpy(buf, ctxt->om->om_data,len);
 
                 os_mbuf *next;
                 next = SLIST_NEXT(ctxt->om, om_next);
                 while(next != NULL){
-                    if((len + next->om_len) > BLE_ATT_ATTR_MAX_LEN) {
+                    if((len + next->om_len) > att_max_len) {
                         return BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN;
                     }
                     memcpy(&buf[len], next->om_data, next->om_len);
@@ -384,36 +382,58 @@ void NimBLECharacteristic::setSubscribe(struct ble_gap_event *event) {
 
 
 /**
- * @brief Send an indication.\n
- * An indication is a transmission of up to the first 20 bytes of the characteristic value.\n
- * An indication will block waiting for a positive confirmation from the client.
+ * @brief Send an indication.
  */
 void NimBLECharacteristic::indicate() {
-    NIMBLE_LOGD(LOG_TAG, ">> indicate: length: %d", getDataLength());
     notify(false);
-    NIMBLE_LOGD(LOG_TAG, "<< indicate");
 } // indicate
 
 
 /**
- * @brief Send a notification.\n
- * A notification is a transmission of up to the first 20 bytes of the characteristic value.\n
- * A notification will not block; it is a fire and forget.
+ * @brief Send an indication.
+ * @param[in] value A pointer to the data to send.
+ * @param[in] length The length of the data to send.
+ */
+void NimBLECharacteristic::indicate(const uint8_t* value, size_t length) {
+    notify(value, length, false);
+} // indicate
+
+
+/**
+ * @brief Send an indication.
+ * @param[in] value A std::vector<uint8_t> containing the value to send as the notification value.
+ */
+void NimBLECharacteristic::indicate(const std::vector<uint8_t>& value) {
+    notify(value.data(), value.size(), false);
+} // indicate
+
+
+/**
+ * @brief Send a notification or indication.
  * @param[in] is_notification if true sends a notification, false sends an indication.
  */
 void NimBLECharacteristic::notify(bool is_notification) {
-    notify(getValue(), is_notification);
-}
+    notify(m_value.data(), m_value.length(), is_notification);
+} // notify
+
 
 /**
- * @brief Send a notification.\n
- * A notification is a transmission of up to the first 20 bytes of the characteristic value.\n
- * A notification will not block; it is a fire and forget.
- * @param[in] value An optional value to send as the notification, else the current characteristic value is used.
+ * @brief Send a notification or indication.
+ * @param[in] value A std::vector<uint8_t> containing the value to send as the notification value.
  * @param[in] is_notification if true sends a notification, false sends an indication.
  */
-void NimBLECharacteristic::notify(std::string value, bool is_notification) {
-    size_t length = value.length();
+void NimBLECharacteristic::notify(const std::vector<uint8_t>& value, bool is_notification) {
+    notify(value.data(), value.size(), is_notification);
+} // notify
+
+
+/**
+ * @brief Send a notification or indication.
+ * @param[in] value A pointer to the data to send.
+ * @param[in] length The length of the data to send.
+ * @param[in] is_notification if true sends a notification, false sends an indication.
+ */
+void NimBLECharacteristic::notify(const uint8_t* value, size_t length, bool is_notification) {
     NIMBLE_LOGD(LOG_TAG, ">> notify: length: %d", length);
 
     if(!(m_properties & NIMBLE_PROPERTY::NOTIFY) &&
@@ -472,7 +492,7 @@ void NimBLECharacteristic::notify(std::string value, bool is_notification) {
         // don't create the m_buf until we are sure to send the data or else
         // we could be allocating a buffer that doesn't get released.
         // We also must create it in each loop iteration because it is consumed with each host call.
-        os_mbuf *om = ble_hs_mbuf_from_flat((uint8_t*)value.data(), length);
+        os_mbuf *om = ble_hs_mbuf_from_flat(value, length);
 
         if(!is_notification && (m_properties & NIMBLE_PROPERTY::INDICATE)) {
             if(!NimBLEDevice::getServer()->setIndicateWait(it.first)) {
@@ -516,40 +536,30 @@ NimBLECharacteristicCallbacks* NimBLECharacteristic::getCallbacks() {
 
 
 /**
- * @brief Set the value of the characteristic.
- * @param [in] data The data to set for the characteristic.
- * @param [in] length The length of the data in bytes.
+ * @brief Set the value of the characteristic from a data buffer .
+ * @param [in] data The data buffer to set for the characteristic.
+ * @param [in] length The number of bytes in the data buffer.
  */
 void NimBLECharacteristic::setValue(const uint8_t* data, size_t length) {
 #if CONFIG_NIMBLE_CPP_LOG_LEVEL >= 4
     char* pHex = NimBLEUtils::buildHexData(nullptr, data, length);
-    NIMBLE_LOGD(LOG_TAG, ">> setValue: length=%d, data=%s, characteristic UUID=%s", length, pHex, getUUID().toString().c_str());
+    NIMBLE_LOGD(LOG_TAG, ">> setValue: length=%d, data=%s, characteristic UUID=%s",
+                length, pHex, getUUID().toString().c_str());
     free(pHex);
 #endif
 
-    if (length > BLE_ATT_ATTR_MAX_LEN) {
-        NIMBLE_LOGE(LOG_TAG, "Size %d too large, must be no bigger than %d", length, BLE_ATT_ATTR_MAX_LEN);
-        return;
-    }
-
-    time_t t = time(nullptr);
-    ble_npl_hw_enter_critical();
-    m_value = std::string((char*)data, length);
-    m_timestamp = t;
-    ble_npl_hw_exit_critical(0);
-
+    m_value.setValue(data, length);
     NIMBLE_LOGD(LOG_TAG, "<< setValue");
 } // setValue
 
 
 /**
- * @brief Set the value of the characteristic from string data.\n
- * We set the value of the characteristic from the bytes contained in the string.
- * @param [in] value the std::string value of the characteristic.
+ * @brief Set the value of the characteristic from a `std::vector<uint8_t>`.\n
+ * @param [in] vec The std::vector<uint8_t> reference to set the characteristic value from.
  */
-void NimBLECharacteristic::setValue(const std::string &value) {
-    setValue((uint8_t*)(value.data()), value.length());
-} // setValue
+void NimBLECharacteristic::setValue(const std::vector<uint8_t>& vec) {
+    return setValue((uint8_t*)&vec[0], vec.size());
+}// setValue
 
 
 /**

src/NimBLECharacteristic.h

@@ -44,6 +44,7 @@ typedef enum {
 
 #include "NimBLEService.h"
 #include "NimBLEDescriptor.h"
+#include "NimBLEAttValue.h"
 
 #include <string>
 #include <vector>
@@ -65,11 +66,13 @@ public:
                          uint16_t properties =
                          NIMBLE_PROPERTY::READ |
                          NIMBLE_PROPERTY::WRITE,
+                         uint16_t max_len = BLE_ATT_ATTR_MAX_LEN,
                          NimBLEService* pService = nullptr);
     NimBLECharacteristic(const NimBLEUUID &uuid,
                          uint16_t properties =
                          NIMBLE_PROPERTY::READ |
                          NIMBLE_PROPERTY::WRITE,
+                         uint16_t max_len = BLE_ATT_ATTR_MAX_LEN,
                          NimBLEService* pService = nullptr);
 
     ~NimBLECharacteristic();
@@ -77,66 +80,93 @@ public:
     uint16_t          getHandle();
     NimBLEUUID        getUUID();
     std::string       toString();
-
-    void              setCallbacks(NimBLECharacteristicCallbacks* pCallbacks);
-    NimBLECharacteristicCallbacks*
-                      getCallbacks();
-
     void              indicate();
+    void              indicate(const uint8_t* value, size_t length);
+    void              indicate(const std::vector<uint8_t>& value);
     void              notify(bool is_notification = true);
-    void              notify(std::string value, bool is_notification = true);
-
+    void              notify(const uint8_t* value, size_t length, bool is_notification = true);
+    void              notify(const std::vector<uint8_t>& value, bool is_notification = true);
     size_t            getSubscribedCount();
-
-    NimBLEDescriptor* createDescriptor(const char* uuid,
-                                       uint32_t properties =
-                                       NIMBLE_PROPERTY::READ |
-                                       NIMBLE_PROPERTY::WRITE,
-                                       uint16_t max_len = 100);
-    NimBLEDescriptor* createDescriptor(const NimBLEUUID &uuid,
-                                       uint32_t properties =
-                                       NIMBLE_PROPERTY::READ |
-                                       NIMBLE_PROPERTY::WRITE,
-                                       uint16_t max_len = 100);
-
     void              addDescriptor(NimBLEDescriptor *pDescriptor);
     NimBLEDescriptor* getDescriptorByUUID(const char* uuid);
     NimBLEDescriptor* getDescriptorByUUID(const NimBLEUUID &uuid);
     NimBLEDescriptor* getDescriptorByHandle(uint16_t handle);
     void              removeDescriptor(NimBLEDescriptor *pDescriptor, bool deleteDsc = false);
-
-    std::string       getValue(time_t *timestamp = nullptr);
+    NimBLEService*    getService();
+    uint16_t          getProperties();
+    NimBLEAttValue    getValue(time_t *timestamp = nullptr);
     size_t            getDataLength();
-    /**
-     * @brief A template to convert the characteristic data to <type\>.
-     * @tparam T The type to convert the data to.
-     * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
-     * @param [in] skipSizeCheck If true it will skip checking if the data size is less than <tt>sizeof(<type\>)</tt>.
-     * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is
-     * less than <tt>sizeof(<type\>)</tt>.
-     * @details <b>Use:</b> <tt>getValue<type>(&timestamp, skipSizeCheck);</tt>
-     */
-    template<typename T>
-    T                 getValue(time_t *timestamp = nullptr, bool skipSizeCheck = false) {
-        std::string value = getValue();
-        if(!skipSizeCheck && value.size() < sizeof(T)) return T();
-        const char *pData = value.data();
-        return *((T *)pData);
-    }
-
     void              setValue(const uint8_t* data, size_t size);
-    void              setValue(const std::string &value);
+    void              setValue(const std::vector<uint8_t>& vec);
+    void              setCallbacks(NimBLECharacteristicCallbacks* pCallbacks);
+    NimBLEDescriptor* createDescriptor(const char* uuid,
+                                       uint32_t properties =
+                                       NIMBLE_PROPERTY::READ |
+                                       NIMBLE_PROPERTY::WRITE,
+                                       uint16_t max_len = BLE_ATT_ATTR_MAX_LEN);;
+    NimBLEDescriptor* createDescriptor(const NimBLEUUID &uuid,
+                                       uint32_t properties =
+                                       NIMBLE_PROPERTY::READ |
+                                       NIMBLE_PROPERTY::WRITE,
+                                       uint16_t max_len = BLE_ATT_ATTR_MAX_LEN);
+
+    NimBLECharacteristicCallbacks* getCallbacks();
+
+
+    /*********************** Template Functions ************************/
+
     /**
-     * @brief Convenience template to set the characteristic value to <type\>val.
+     * @brief Template to set the characteristic value to <type\>val.
      * @param [in] s The value to set.
      */
     template<typename T>
-    void              setValue(const T &s) {
-        setValue((uint8_t*)&s, sizeof(T));
+    void              setValue(const T &s) { m_value.setValue<T>(s); }
+
+    /**
+     * @brief Template to convert the characteristic data to <type\>.
+     * @tparam T The type to convert the data to.
+     * @param [in] timestamp (Optional) A pointer to a time_t struct to store the time the value was read.
+     * @param [in] skipSizeCheck (Optional) If true it will skip checking if the data size is less than <tt>sizeof(<type\>)</tt>.
+     * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is less than <tt>sizeof(<type\>)</tt>.
+     * @details <b>Use:</b> <tt>getValue<type>(&timestamp, skipSizeCheck);</tt>
+     */
+    template<typename T>
+    T   getValue(time_t *timestamp = nullptr, bool skipSizeCheck = false) {
+        return m_value.getValue<T>(timestamp, skipSizeCheck);
     }
 
-    NimBLEService*    getService();
-    uint16_t          getProperties();
+    /**
+     * @brief Template to send a notification from a class type that has a c_str() and length() method.
+     * @tparam T The a reference to a class containing the data to send.
+     * @param[in] value The <type\>value to set.
+     * @param[in] is_notification if true sends a notification, false sends an indication.
+     * @details Only used if the <type\> has a `c_str()` method.
+     */
+    template<typename T>
+#ifdef _DOXYGEN_
+    void
+#else
+    typename std::enable_if<Has_c_str_len<T>::value, void>::type
+#endif
+    notify(const T& value, bool is_notification = true) {
+        notify((uint8_t*)value.c_str(), value.length(), is_notification);
+    }
+
+    /**
+     * @brief Template to send an indication from a class type that has a c_str() and length() method.
+     * @tparam T The a reference to a class containing the data to send.
+     * @param[in] value The <type\>value to set.
+     * @details Only used if the <type\> has a `c_str()` method.
+     */
+    template<typename T>
+#ifdef _DOXYGEN_
+    void
+#else
+    typename std::enable_if<Has_c_str_len<T>::value, void>::type
+#endif
+    indicate(const T& value) {
+        indicate((uint8_t*)value.c_str(), value.length());
+    }
 
 private:
 
@@ -153,9 +183,8 @@ private:
     uint16_t                       m_properties;
     NimBLECharacteristicCallbacks* m_pCallbacks;
     NimBLEService*                 m_pService;
-    std::string                    m_value;
+    NimBLEAttValue                 m_value;
     std::vector<NimBLEDescriptor*> m_dscVec;
-    time_t                         m_timestamp;
     uint8_t                        m_removed;
 
     std::vector<std::pair<uint16_t, uint16_t>>  m_subscribedVec;
@@ -188,7 +217,7 @@ public:
         ERROR_INDICATE_FAILURE
     }Status;
 
-    virtual ~NimBLECharacteristicCallbacks();
+    virtual      ~NimBLECharacteristicCallbacks();
     virtual void onRead(NimBLECharacteristic* pCharacteristic);
     virtual void onRead(NimBLECharacteristic* pCharacteristic, ble_gap_conn_desc* desc);
     virtual void onWrite(NimBLECharacteristic* pCharacteristic);

src/NimBLEClient.cpp

@@ -768,11 +768,11 @@ int NimBLEClient::serviceDiscoveredCB(
  * @param [in] characteristicUUID The characteristic whose value we wish to read.
  * @returns characteristic value or an empty string if not found
  */
-std::string NimBLEClient::getValue(const NimBLEUUID &serviceUUID, const NimBLEUUID &characteristicUUID) {
+NimBLEAttValue NimBLEClient::getValue(const NimBLEUUID &serviceUUID, const NimBLEUUID &characteristicUUID) {
     NIMBLE_LOGD(LOG_TAG, ">> getValue: serviceUUID: %s, characteristicUUID: %s",
                          serviceUUID.toString().c_str(), characteristicUUID.toString().c_str());
 
-    std::string ret = "";
+    NimBLEAttValue ret;
     NimBLERemoteService* pService = getService(serviceUUID);
 
     if(pService != nullptr) {
@@ -796,7 +796,7 @@ std::string NimBLEClient::getValue(const NimBLEUUID &serviceUUID, const NimBLEUU
  * @returns true if successful otherwise false
  */
 bool NimBLEClient::setValue(const NimBLEUUID &serviceUUID, const NimBLEUUID &characteristicUUID,
-                            const std::string &value, bool response)
+                            const NimBLEAttValue &value, bool response)
 {
     NIMBLE_LOGD(LOG_TAG, ">> setValue: serviceUUID: %s, characteristicUUID: %s",
                          serviceUUID.toString().c_str(), characteristicUUID.toString().c_str());
@@ -857,7 +857,7 @@ uint16_t NimBLEClient::getMTU() {
  * @param [in] arg A pointer to the client instance that registered for this callback.
  */
  /*STATIC*/
- int NimBLEClient::handleGapEvent(struct ble_gap_event *event, void *arg) {
+int NimBLEClient::handleGapEvent(struct ble_gap_event *event, void *arg) {
     NimBLEClient* client = (NimBLEClient*)arg;
     int rc;
 
@@ -976,11 +976,7 @@ uint16_t NimBLEClient::getMTU() {
                                 (*characteristic)->toString().c_str());
 
                     uint32_t data_len = OS_MBUF_PKTLEN(event->notify_rx.om);
-                    time_t t = time(nullptr);
-                    ble_npl_hw_enter_critical();
-                    (*characteristic)->m_value = std::string((char *)event->notify_rx.om->om_data, data_len);
-                    (*characteristic)->m_timestamp = t;
-                    ble_npl_hw_exit_critical(0);
+                    (*characteristic)->m_value.setValue(event->notify_rx.om->om_data, data_len);
 
                     if ((*characteristic)->m_notifyCallback != nullptr) {
                         NIMBLE_LOGD(LOG_TAG, "Invoking callback for notification on characteristic %s",

src/NimBLEClient.h

@@ -21,6 +21,7 @@
 #include "NimBLEUUID.h"
 #include "NimBLEUtils.h"
 #include "NimBLEConnInfo.h"
+#include "NimBLEAttValue.h"
 #include "NimBLEAdvertisedDevice.h"
 #include "NimBLERemoteService.h"
 
@@ -51,9 +52,9 @@ public:
     NimBLERemoteService*                        getService(const NimBLEUUID &uuid);
     void                                        deleteServices();
     size_t                                      deleteService(const NimBLEUUID &uuid);
-    std::string                                 getValue(const NimBLEUUID &serviceUUID, const NimBLEUUID &characteristicUUID);
+    NimBLEAttValue                              getValue(const NimBLEUUID &serviceUUID, const NimBLEUUID &characteristicUUID);
     bool                                        setValue(const NimBLEUUID &serviceUUID, const NimBLEUUID &characteristicUUID,
-                                                         const std::string &value, bool response = false);
+                                                         const NimBLEAttValue &value, bool response = false);
     NimBLERemoteCharacteristic*                 getCharacteristic(const uint16_t handle);
     bool                                        isConnected();
     void                                        setClientCallbacks(NimBLEClientCallbacks *pClientCallbacks,

src/NimBLEDescriptor.cpp

@@ -28,27 +28,32 @@ static NimBLEDescriptorCallbacks defaultCallbacks;
 
 
 /**
- * @brief NimBLEDescriptor constructor.
+ * @brief Construct a descriptor
+ * @param [in] uuid - UUID (const char*) for the descriptor.
+ * @param [in] properties - Properties for the descriptor.
+ * @param [in] max_len - The maximum length in bytes that the descriptor value can hold. (Default: 512 bytes for esp32, 20 for all others).
+ * @param [in] pCharacteristic - pointer to the characteristic instance this descriptor belongs to.
  */
 NimBLEDescriptor::NimBLEDescriptor(const char* uuid, uint16_t properties, uint16_t max_len,
-                                    NimBLECharacteristic* pCharacteristic)
-: NimBLEDescriptor(NimBLEUUID(uuid), max_len, properties, pCharacteristic) {
+                                   NimBLECharacteristic* pCharacteristic)
+: NimBLEDescriptor(NimBLEUUID(uuid), properties, max_len, pCharacteristic) {
 }
 
 
 /**
- * @brief NimBLEDescriptor constructor.
+ * @brief Construct a descriptor
+ * @param [in] uuid - UUID (const char*) for the descriptor.
+ * @param [in] properties - Properties for the descriptor.
+ * @param [in] max_len - The maximum length in bytes that the descriptor value can hold. (Default: 512 bytes for esp32, 20 for all others).
+ * @param [in] pCharacteristic - pointer to the characteristic instance this descriptor belongs to.
  */
 NimBLEDescriptor::NimBLEDescriptor(NimBLEUUID uuid, uint16_t properties, uint16_t max_len,
                                     NimBLECharacteristic* pCharacteristic)
-{
+:   m_value(std::min(CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH , (int)max_len), max_len) {
     m_uuid               = uuid;
-    m_value.attr_len     = 0;                           // Initial length is 0.
-    m_value.attr_max_len = max_len;                     // Maximum length of the data.
     m_handle             = NULL_HANDLE;                 // Handle is initially unknown.
     m_pCharacteristic    = pCharacteristic;
     m_pCallbacks         = &defaultCallbacks;           // No initial callback.
-    m_value.attr_value   = (uint8_t*) calloc(max_len,1);  // Allocate storage for the value.
     m_properties         = 0;
     m_removed            = 0;
 
@@ -84,7 +89,6 @@ NimBLEDescriptor::NimBLEDescriptor(NimBLEUUID uuid, uint16_t properties, uint16_
  * @brief NimBLEDescriptor destructor.
  */
 NimBLEDescriptor::~NimBLEDescriptor() {
-    free(m_value.attr_value);   // Release the storage we created in the constructor.
 } // ~NimBLEDescriptor
 
 /**
@@ -101,7 +105,7 @@ uint16_t NimBLEDescriptor::getHandle() {
  * @return The length (in bytes) of the value of this descriptor.
  */
 size_t NimBLEDescriptor::getLength() {
-    return m_value.attr_len;
+    return m_value.size();
 } // getLength
 
 
@@ -115,10 +119,14 @@ NimBLEUUID NimBLEDescriptor::getUUID() {
 
 /**
  * @brief Get the value of this descriptor.
- * @return A pointer to the value of this descriptor.
+ * @return The NimBLEAttValue of this descriptor.
  */
-uint8_t* NimBLEDescriptor::getValue() {
-    return m_value.attr_value;
+NimBLEAttValue NimBLEDescriptor::getValue(time_t *timestamp) {
+    if (timestamp != nullptr) {
+        m_value.getValue(timestamp);
+    }
+
+    return m_value;
 } // getValue
 
 
@@ -127,7 +135,7 @@ uint8_t* NimBLEDescriptor::getValue() {
  * @return A std::string instance containing a copy of the descriptor's value.
  */
 std::string NimBLEDescriptor::getStringValue() {
-    return std::string((char *) m_value.attr_value, m_value.attr_len);
+    return std::string(m_value);
 }
 
 
@@ -163,23 +171,25 @@ int NimBLEDescriptor::handleGapEvent(uint16_t conn_handle, uint16_t attr_handle,
                 }
 
                 ble_npl_hw_enter_critical();
-                rc = os_mbuf_append(ctxt->om, pDescriptor->getValue(), pDescriptor->getLength());
+                rc = os_mbuf_append(ctxt->om, pDescriptor->m_value.data(), pDescriptor->m_value.size());
                 ble_npl_hw_exit_critical(0);
                 return rc == 0 ? 0 : BLE_ATT_ERR_INSUFFICIENT_RES;
             }
 
             case BLE_GATT_ACCESS_OP_WRITE_DSC: {
-                if (ctxt->om->om_len > pDescriptor->m_value.attr_max_len) {
+                uint16_t att_max_len = pDescriptor->m_value.max_size();
+
+                if (ctxt->om->om_len > att_max_len) {
                     return BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN;
                 }
 
-                uint8_t buf[pDescriptor->m_value.attr_max_len];
+                uint8_t buf[att_max_len];
                 size_t len = ctxt->om->om_len;
                 memcpy(buf, ctxt->om->om_data,len);
                 os_mbuf *next;
                 next = SLIST_NEXT(ctxt->om, om_next);
                 while(next != NULL){
-                    if((len + next->om_len) > pDescriptor->m_value.attr_max_len) {
+                    if((len + next->om_len) > att_max_len) {
                         return BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN;
                     }
                     memcpy(&buf[len], next->om_data, next->om_len);
@@ -231,27 +241,19 @@ void NimBLEDescriptor::setHandle(uint16_t handle) {
  * @param [in] length The length of the data in bytes.
  */
 void NimBLEDescriptor::setValue(const uint8_t* data, size_t length) {
-    if (length > m_value.attr_max_len) {
-        NIMBLE_LOGE(LOG_TAG, "Size %d too large, must be no bigger than %d", length, m_value.attr_max_len);
-        return;
-    }
-
-    ble_npl_hw_enter_critical();
-    m_value.attr_len = length;
-    memcpy(m_value.attr_value, data, length);
-    ble_npl_hw_exit_critical(0);
-
+    m_value.setValue(data, length);
 } // setValue
 
 
 /**
- * @brief Set the value of the descriptor.
- * @param [in] value The value of the descriptor in string form.
+ * @brief Set the value of the descriptor from a `std::vector<uint8_t>`.\n
+ * @param [in] vec The std::vector<uint8_t> reference to set the descriptor value from.
  */
-void NimBLEDescriptor::setValue(const std::string &value) {
-    setValue((uint8_t*) value.data(), value.length());
+void NimBLEDescriptor::setValue(const std::vector<uint8_t>& vec) {
+    return setValue((uint8_t*)&vec[0], vec.size());
 } // setValue
 
+
 /**
  * @brief Set the characteristic this descriptor belongs to.
  * @param [in] pChar A pointer to the characteristic this descriptior belongs to.

src/NimBLEDescriptor.h

@@ -20,17 +20,10 @@
 
 #include "NimBLECharacteristic.h"
 #include "NimBLEUUID.h"
+#include "NimBLEAttValue.h"
 
 #include <string>
 
-
-typedef struct
-{
-    uint16_t attr_max_len;  /*!<  attribute max value length */
-    uint16_t attr_len;      /*!<  attribute current value length */
-    uint8_t  *attr_value;    /*!<  the pointer to attribute value */
-} attr_value_t;
-
 class NimBLEService;
 class NimBLECharacteristic;
 class NimBLEDescriptorCallbacks;
@@ -54,24 +47,36 @@ public:
     uint16_t              getHandle();
     NimBLEUUID            getUUID();
     std::string           toString();
-
     void                  setCallbacks(NimBLEDescriptorCallbacks* pCallbacks);
+    NimBLECharacteristic* getCharacteristic();
 
     size_t                getLength();
-    uint8_t*              getValue();
+    NimBLEAttValue        getValue(time_t *timestamp = nullptr);
     std::string           getStringValue();
 
     void                  setValue(const uint8_t* data, size_t size);
-    void                  setValue(const std::string &value);
-    NimBLECharacteristic* getCharacteristic();
+    void                  setValue(const std::vector<uint8_t>& vec);
+
+    /*********************** Template Functions ************************/
 
     /**
-     * @brief Convenience template to set the descriptor value to <type\>val.
+     * @brief Template to set the characteristic value to <type\>val.
      * @param [in] s The value to set.
      */
     template<typename T>
-    void setValue(const T &s) {
-        setValue((uint8_t*)&s, sizeof(T));
+    void setValue(const T &s) { m_value.setValue<T>(s); }
+
+    /**
+     * @brief Template to convert the descriptor data to <type\>.
+     * @tparam T The type to convert the data to.
+     * @param [in] timestamp (Optional) A pointer to a time_t struct to store the time the value was read.
+     * @param [in] skipSizeCheck (Optional) If true it will skip checking if the data size is less than <tt>sizeof(<type\>)</tt>.
+     * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is less than <tt>sizeof(<type\>)</tt>.
+     * @details <b>Use:</b> <tt>getValue<type>(&timestamp, skipSizeCheck);</tt>
+     */
+    template<typename T>
+    T getValue(time_t *timestamp = nullptr, bool skipSizeCheck = false) {
+        return m_value.getValue<T>(timestamp, skipSizeCheck);
     }
 
 private:
@@ -89,7 +94,7 @@ private:
     NimBLEDescriptorCallbacks* m_pCallbacks;
     NimBLECharacteristic*      m_pCharacteristic;
     uint8_t                    m_properties;
-    attr_value_t               m_value;
+    NimBLEAttValue             m_value;
     uint8_t                    m_removed;
 }; // NimBLEDescriptor
 

src/NimBLERemoteCharacteristic.cpp

@@ -58,7 +58,6 @@ static const char* LOG_TAG = "NimBLERemoteCharacteristic";
     m_charProp           = chr->properties;
     m_pRemoteService     = pRemoteService;
     m_notifyCallback     = nullptr;
-    m_timestamp          = 0;
 
     NIMBLE_LOGD(LOG_TAG, "<< NimBLERemoteCharacteristic(): %s", m_uuid.toString().c_str());
  } // NimBLERemoteCharacteristic
@@ -414,15 +413,12 @@ NimBLEUUID NimBLERemoteCharacteristic::getUUID() {
  * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
  * @return The value of the remote characteristic.
  */
-std::string NimBLERemoteCharacteristic::getValue(time_t *timestamp) {
-    ble_npl_hw_enter_critical();
-    std::string value = m_value;
+NimBLEAttValue NimBLERemoteCharacteristic::getValue(time_t *timestamp) {
     if(timestamp != nullptr) {
-        *timestamp = m_timestamp;
+        *timestamp = m_value.getTimeStamp();
     }
-    ble_npl_hw_exit_critical(0);
 
-    return value;
+    return m_value;
 }
 
 
@@ -470,12 +466,12 @@ float NimBLERemoteCharacteristic::readFloat() {
  * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
  * @return The value of the remote characteristic.
  */
-std::string NimBLERemoteCharacteristic::readValue(time_t *timestamp) {
+NimBLEAttValue NimBLERemoteCharacteristic::readValue(time_t *timestamp) {
     NIMBLE_LOGD(LOG_TAG, ">> readValue(): uuid: %s, handle: %d 0x%.2x",
                          getUUID().toString().c_str(), getHandle(), getHandle());
 
     NimBLEClient* pClient = getRemoteService()->getClient();
-    std::string value;
+    NimBLEAttValue value;
 
     if (!pClient->isConnected()) {
         NIMBLE_LOGE(LOG_TAG, "Disconnected");
@@ -526,14 +522,11 @@ std::string NimBLERemoteCharacteristic::readValue(time_t *timestamp) {
         }
     } while(rc != 0 && retryCount--);
 
-    time_t t = time(nullptr);
-    ble_npl_hw_enter_critical();
+    value.setTimeStamp();
     m_value = value;
-    m_timestamp = t;
     if(timestamp != nullptr) {
-        *timestamp = m_timestamp;
+        *timestamp = value.getTimeStamp();
     }
-    ble_npl_hw_exit_critical(0);
 
     NIMBLE_LOGD(LOG_TAG, "<< readValue length: %d rc=%d", value.length(), rc);
     return value;
@@ -558,17 +551,17 @@ int NimBLERemoteCharacteristic::onReadCB(uint16_t conn_handle,
 
     NIMBLE_LOGI(LOG_TAG, "Read complete; status=%d conn_handle=%d", error->status, conn_handle);
 
-    std::string *strBuf = (std::string*)pTaskData->buf;
+    NimBLEAttValue *valBuf = (NimBLEAttValue*)pTaskData->buf;
     int rc = error->status;
 
     if(rc == 0) {
         if(attr) {
             uint16_t data_len = OS_MBUF_PKTLEN(attr->om);
-            if(((*strBuf).length() + data_len) > BLE_ATT_ATTR_MAX_LEN) {
+            if((valBuf->size() + data_len) > BLE_ATT_ATTR_MAX_LEN) {
                 rc = BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN;
             } else {
                 NIMBLE_LOGD(LOG_TAG, "Got %u bytes", data_len);
-                (*strBuf) += std::string((char*) attr->om->om_data, data_len);
+                valBuf->append(attr->om->om_data, data_len);
                 return 0;
             }
         }
@@ -719,22 +712,33 @@ std::string NimBLERemoteCharacteristic::toString() {
 
 
 /**
- * @brief Write the new value for the characteristic.
- * @param [in] newValue The new value to write.
- * @param [in] response Do we expect a response?
- * @return false if not connected or cant perform write for some reason.
+ * @brief Write a new value to the remote characteristic from a std::vector<uint8_t>.
+ * @param [in] vec A std::vector<uint8_t> value to write to the remote characteristic.
+ * @param [in] response Whether we require a response from the write.
+ * @return false if not connected or otherwise cannot perform write.
  */
-bool NimBLERemoteCharacteristic::writeValue(const std::string &newValue, bool response) {
-    return writeValue((uint8_t*)newValue.c_str(), newValue.length(), response);
+bool NimBLERemoteCharacteristic::writeValue(const std::vector<uint8_t>& vec, bool response) {
+    return writeValue((uint8_t*)&vec[0], vec.size(), response);
 } // writeValue
 
 
 /**
- * @brief Write the new value for the characteristic from a data buffer.
+ * @brief Write a new value to the remote characteristic from a const char*.
+ * @param [in] char_s A character string to write to the remote characteristic.
+ * @param [in] response Whether we require a response from the write.
+ * @return false if not connected or otherwise cannot perform write.
+ */
+bool NimBLERemoteCharacteristic::writeValue(const char* char_s, bool response) {
+    return writeValue((uint8_t*)char_s, strlen(char_s), response);
+} // writeValue
+
+
+/**
+ * @brief Write a new value to the remote characteristic from a data buffer.
  * @param [in] data A pointer to a data buffer.
  * @param [in] length The length of the data in the data buffer.
  * @param [in] response Whether we require a response from the write.
- * @return false if not connected or cant perform write for some reason.
+ * @return false if not connected or otherwise cannot perform write.
  */
 bool NimBLERemoteCharacteristic::writeValue(const uint8_t* data, size_t length, bool response) {
 

src/NimBLERemoteCharacteristic.h

@@ -23,6 +23,7 @@
 
 #include <vector>
 #include <functional>
+#include "NimBLELog.h"
 
 class NimBLERemoteService;
 class NimBLERemoteDescriptor;
@@ -60,47 +61,15 @@ public:
     uint16_t                                       getHandle();
     uint16_t                                       getDefHandle();
     NimBLEUUID                                     getUUID();
-    std::string                                    readValue(time_t *timestamp = nullptr);
-
-    /**
-     * @brief A template to convert the remote characteristic data to <type\>.
-     * @tparam T The type to convert the data to.
-     * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
-     * @param [in] skipSizeCheck If true it will skip checking if the data size is less than <tt>sizeof(<type\>)</tt>.
-     * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is
-     * less than <tt>sizeof(<type\>)</tt>.
-     * @details <b>Use:</b> <tt>readValue<type>(&timestamp, skipSizeCheck);</tt>
-     */
-    template<typename T>
-    T                                              readValue(time_t *timestamp = nullptr, bool skipSizeCheck = false) {
-        std::string value = readValue(timestamp);
-        if(!skipSizeCheck && value.size() < sizeof(T)) return T();
-        const char *pData = value.data();
-        return *((T *)pData);
-    }
+    NimBLEAttValue                                 readValue(time_t *timestamp = nullptr);
+    std::string                                    toString();
+    NimBLERemoteService*                           getRemoteService();
 
     uint8_t                                        readUInt8()  __attribute__ ((deprecated("Use template readValue<uint8_t>()")));
     uint16_t                                       readUInt16() __attribute__ ((deprecated("Use template readValue<uint16_t>()")));
     uint32_t                                       readUInt32() __attribute__ ((deprecated("Use template readValue<uint32_t>()")));
     float                                          readFloat()  __attribute__ ((deprecated("Use template readValue<float>()")));
-    std::string                                    getValue(time_t *timestamp = nullptr);
-
-    /**
-     * @brief A template to convert the remote characteristic data to <type\>.
-     * @tparam T The type to convert the data to.
-     * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
-     * @param [in] skipSizeCheck If true it will skip checking if the data size is less than <tt>sizeof(<type\>)</tt>.
-     * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is
-     * less than <tt>sizeof(<type\>)</tt>.
-     * @details <b>Use:</b> <tt>getValue<type>(&timestamp, skipSizeCheck);</tt>
-     */
-    template<typename T>
-    T                                              getValue(time_t *timestamp = nullptr, bool skipSizeCheck = false) {
-        std::string value = getValue(timestamp);
-        if(!skipSizeCheck && value.size() < sizeof(T)) return T();
-        const char *pData = value.data();
-        return *((T *)pData);
-    }
+    NimBLEAttValue                                 getValue(time_t *timestamp = nullptr);
 
     bool                                           subscribe(bool notifications = true,
                                                              notify_callback notifyCallback = nullptr,
@@ -113,20 +82,74 @@ public:
     bool                                           writeValue(const uint8_t* data,
                                                               size_t length,
                                                               bool response = false);
-    bool                                           writeValue(const std::string &newValue,
-                                                              bool response = false);
+    bool                                           writeValue(const std::vector<uint8_t>& v, bool response = false);
+    bool                                           writeValue(const char* s, bool response = false);
+
+
+    /*********************** Template Functions ************************/
+
     /**
-     * @brief Convenience template to set the remote characteristic value to <type\>val.
+     * @brief Template to set the remote characteristic value to <type\>val.
      * @param [in] s The value to write.
      * @param [in] response True == request write response.
+     * @details Only used for non-arrays and types without a `c_str()` method.
      */
     template<typename T>
-    bool writeValue(const T &s, bool response = false) {
+#ifdef _DOXYGEN_
+    bool
+#else
+    typename std::enable_if<!std::is_array<T>::value && !Has_c_str_len<T>::value, bool>::type
+#endif
+    writeValue(const T& s, bool response = false) {
         return writeValue((uint8_t*)&s, sizeof(T), response);
     }
 
-    std::string                                    toString();
-    NimBLERemoteService*                           getRemoteService();
+    /**
+     * @brief Template to set the remote characteristic value to <type\>val.
+     * @param [in] s The value to write.
+     * @param [in] response True == request write response.
+     * @details Only used if the <type\> has a `c_str()` method.
+     */
+    template<typename T>
+#ifdef _DOXYGEN_
+    bool
+#else
+    typename std::enable_if<Has_c_str_len<T>::value, bool>::type
+#endif
+    writeValue(const T& s, bool response = false) {
+        return writeValue((uint8_t*)s.c_str(), s.length(), response);
+    }
+
+    /**
+     * @brief Template to convert the remote characteristic data to <type\>.
+     * @tparam T The type to convert the data to.
+     * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
+     * @param [in] skipSizeCheck If true it will skip checking if the data size is less than <tt>sizeof(<type\>)</tt>.
+     * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is
+     * less than <tt>sizeof(<type\>)</tt>.
+     * @details <b>Use:</b> <tt>getValue<type>(&timestamp, skipSizeCheck);</tt>
+     */
+    template<typename T>
+    T getValue(time_t *timestamp = nullptr, bool skipSizeCheck = false) {
+        if(!skipSizeCheck && m_value.size() < sizeof(T)) return T();
+        return *((T *)m_value.getValue(timestamp));
+    }
+
+    /**
+     * @brief Template to convert the remote characteristic data to <type\>.
+     * @tparam T The type to convert the data to.
+     * @param [in] timestamp A pointer to a time_t struct to store the time the value was read.
+     * @param [in] skipSizeCheck If true it will skip checking if the data size is less than <tt>sizeof(<type\>)</tt>.
+     * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is
+     * less than <tt>sizeof(<type\>)</tt>.
+     * @details <b>Use:</b> <tt>readValue<type>(&timestamp, skipSizeCheck);</tt>
+     */
+    template<typename T>
+    T readValue(time_t *timestamp = nullptr, bool skipSizeCheck = false) {
+        NimBLEAttValue value = readValue();
+        if(!skipSizeCheck && value.size() < sizeof(T)) return T();
+        return *((T *)value.getValue(timestamp));
+    }
 
 private:
 
@@ -156,9 +179,8 @@ private:
     uint16_t                m_defHandle;
     uint16_t                m_endHandle;
     NimBLERemoteService*    m_pRemoteService;
-    std::string             m_value;
+    NimBLEAttValue          m_value;
     notify_callback         m_notifyCallback;
-    time_t                  m_timestamp;
 
     // We maintain a vector of descriptors owned by this characteristic.
     std::vector<NimBLERemoteDescriptor*> m_descriptorVector;

src/NimBLERemoteDescriptor.cpp

@@ -86,11 +86,7 @@ NimBLEUUID NimBLERemoteDescriptor::getUUID() {
  * @deprecated Use readValue<uint8_t>().
  */
 uint8_t NimBLERemoteDescriptor::readUInt8() {
-    std::string value = readValue();
-    if (value.length() >= 1) {
-        return (uint8_t) value[0];
-    }
-    return 0;
+    return readValue<uint8_t>();
 } // readUInt8
 
 
@@ -100,11 +96,7 @@ uint8_t NimBLERemoteDescriptor::readUInt8() {
  * @deprecated Use readValue<uint16_t>().
  */
 uint16_t NimBLERemoteDescriptor::readUInt16() {
-    std::string value = readValue();
-    if (value.length() >= 2) {
-        return *(uint16_t*) value.data();
-    }
-    return 0;
+    return readValue<uint16_t>();
 } // readUInt16
 
 
@@ -114,11 +106,7 @@ uint16_t NimBLERemoteDescriptor::readUInt16() {
  * @deprecated Use readValue<uint32_t>().
  */
 uint32_t NimBLERemoteDescriptor::readUInt32() {
-    std::string value = readValue();
-    if (value.length() >= 4) {
-        return *(uint32_t*) value.data();
-    }
-    return 0;
+    return readValue<uint32_t>();
 } // readUInt32
 
 
@@ -126,11 +114,11 @@ uint32_t NimBLERemoteDescriptor::readUInt32() {
  * @brief Read the value of the remote descriptor.
  * @return The value of the remote descriptor.
  */
-std::string NimBLERemoteDescriptor::readValue() {
+NimBLEAttValue NimBLERemoteDescriptor::readValue() {
     NIMBLE_LOGD(LOG_TAG, ">> Descriptor readValue: %s", toString().c_str());
 
     NimBLEClient* pClient = getRemoteCharacteristic()->getRemoteService()->getClient();
-    std::string value;
+    NimBLEAttValue value;
 
     if (!pClient->isConnected()) {
         NIMBLE_LOGE(LOG_TAG, "Disconnected");
@@ -204,17 +192,17 @@ int NimBLERemoteDescriptor::onReadCB(uint16_t conn_handle,
 
     NIMBLE_LOGD(LOG_TAG, "Read complete; status=%d conn_handle=%d", error->status, conn_handle);
 
-    std::string *strBuf = (std::string*)pTaskData->buf;
+    NimBLEAttValue *valBuf = (NimBLEAttValue*)pTaskData->buf;
     int rc = error->status;
 
     if(rc == 0) {
         if(attr) {
             uint16_t data_len = OS_MBUF_PKTLEN(attr->om);
-            if(((*strBuf).length() + data_len) > BLE_ATT_ATTR_MAX_LEN) {
+            if((valBuf->size() + data_len) > BLE_ATT_ATTR_MAX_LEN) {
                 rc = BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN;
             } else {
                 NIMBLE_LOGD(LOG_TAG, "Got %u bytes", data_len);
-                (*strBuf) += std::string((char*) attr->om->om_data, data_len);
+                valBuf->append(attr->om->om_data, data_len);
                 return 0;
             }
         }
@@ -267,11 +255,33 @@ int NimBLERemoteDescriptor::onWriteCB(uint16_t conn_handle,
 
 
 /**
- * @brief Write data to the BLE Remote Descriptor.
+ * @brief Write a new value to a remote descriptor from a std::vector<uint8_t>.
+ * @param [in] vec A std::vector<uint8_t> value to write to the remote descriptor.
+ * @param [in] response Whether we require a response from the write.
+ * @return false if not connected or otherwise cannot perform write.
+ */
+bool NimBLERemoteDescriptor::writeValue(const std::vector<uint8_t>& vec, bool response) {
+    return writeValue((uint8_t*)&vec[0], vec.size(), response);
+} // writeValue
+
+
+/**
+ * @brief Write a new value to the remote descriptor from a const char*.
+ * @param [in] char_s A character string to write to the remote descriptor.
+ * @param [in] response Whether we require a response from the write.
+ * @return false if not connected or otherwise cannot perform write.
+ */
+bool NimBLERemoteDescriptor::writeValue(const char* char_s, bool response) {
+    return writeValue((uint8_t*)char_s, strlen(char_s), response);
+} // writeValue
+
+
+/**
+ * @brief Write a new value to a remote descriptor.
  * @param [in] data The data to send to the remote descriptor.
  * @param [in] length The length of the data to send.
  * @param [in] response True if we expect a write response.
- * @return True if successful
+ * @return false if not connected or otherwise cannot perform write.
  */
 bool NimBLERemoteDescriptor::writeValue(const uint8_t* data, size_t length, bool response) {
 
@@ -352,14 +362,4 @@ bool NimBLERemoteDescriptor::writeValue(const uint8_t* data, size_t length, bool
 } // writeValue
 
 
-/**
- * @brief Write data represented as a string to the BLE Remote Descriptor.
- * @param [in] newValue The data to send to the remote descriptor.
- * @param [in] response True if we expect a response.
- * @return True if successful
- */
-bool NimBLERemoteDescriptor::writeValue(const std::string &newValue, bool response) {
-    return writeValue((uint8_t*) newValue.data(), newValue.length(), response);
-} // writeValue
-
 #endif /* CONFIG_BT_ENABLED && CONFIG_BT_NIMBLE_ROLE_CENTRAL */

src/NimBLERemoteDescriptor.h

@@ -29,10 +29,53 @@ public:
     uint16_t                    getHandle();
     NimBLERemoteCharacteristic* getRemoteCharacteristic();
     NimBLEUUID                  getUUID();
-    std::string                 readValue();
+    NimBLEAttValue              readValue();
+
+    uint8_t                     readUInt8()  __attribute__ ((deprecated("Use template readValue<uint8_t>()")));
+    uint16_t                    readUInt16() __attribute__ ((deprecated("Use template readValue<uint16_t>()")));
+    uint32_t                    readUInt32() __attribute__ ((deprecated("Use template readValue<uint32_t>()")));
+    std::string                 toString(void);
+    bool                        writeValue(const uint8_t* data, size_t length, bool response = false);
+    bool                        writeValue(const std::vector<uint8_t>& v, bool response = false);
+    bool                        writeValue(const char* s, bool response = false);
+
+
+    /*********************** Template Functions ************************/
 
     /**
-     * @brief A template to convert the remote descriptor data to <type\>.
+     * @brief Template to set the remote descriptor value to <type\>val.
+     * @param [in] s The value to write.
+     * @param [in] response True == request write response.
+     * @details Only used for non-arrays and types without a `c_str()` method.
+     */
+    template<typename T>
+#ifdef _DOXYGEN_
+    bool
+#else
+    typename std::enable_if<!std::is_array<T>::value && !Has_c_str_len<T>::value, bool>::type
+#endif
+    writeValue(const T& s, bool response = false) {
+        return writeValue((uint8_t*)&s, sizeof(T), response);
+    }
+
+    /**
+     * @brief Template to set the remote descriptor value to <type\>val.
+     * @param [in] s The value to write.
+     * @param [in] response True == request write response.
+     * @details Only used if the <type\> has a `c_str()` method.
+     */
+    template<typename T>
+#ifdef _DOXYGEN_
+    bool
+#else
+    typename std::enable_if<Has_c_str_len<T>::value, bool>::type
+#endif
+    writeValue(const T& s, bool response = false) {
+        return writeValue((uint8_t*)s.c_str(), s.length(), response);
+    }
+
+    /**
+     * @brief Template to convert the remote descriptor data to <type\>.
      * @tparam T The type to convert the data to.
      * @param [in] skipSizeCheck If true it will skip checking if the data size is less than <tt>sizeof(<type\>)</tt>.
      * @return The data converted to <type\> or NULL if skipSizeCheck is false and the data is
@@ -40,28 +83,10 @@ public:
      * @details <b>Use:</b> <tt>readValue<type>(skipSizeCheck);</tt>
      */
     template<typename T>
-    T                           readValue(bool skipSizeCheck = false) {
-        std::string value = readValue();
+    T readValue(bool skipSizeCheck = false) {
+        NimBLEAttValue value = readValue();
         if(!skipSizeCheck && value.size() < sizeof(T)) return T();
-        const char *pData = value.data();
-        return *((T *)pData);
-    }
-
-    uint8_t                     readUInt8()  __attribute__ ((deprecated("Use template readValue<uint8_t>()")));
-    uint16_t                    readUInt16() __attribute__ ((deprecated("Use template readValue<uint16_t>()")));
-    uint32_t                    readUInt32() __attribute__ ((deprecated("Use template readValue<uint32_t>()")));
-    std::string                 toString(void);
-    bool                        writeValue(const uint8_t* data, size_t length, bool response = false);
-    bool                        writeValue(const std::string &newValue, bool response = false);
-    
-    /**
-     * @brief Convenience template to set the remote descriptor value to <type\>val.
-     * @param [in] s The value to write.
-     * @param [in] response True == request write response.
-     */
-    template<typename T>
-    bool writeValue(const T &s, bool response = false) {
-        return writeValue((uint8_t*)&s, sizeof(T), response);
+        return *((T *)value.data());
     }
 
 private:

src/NimBLEService.cpp

@@ -250,10 +250,11 @@ uint16_t NimBLEService::getHandle() {
  * @brief Create a new BLE Characteristic associated with this service.
  * @param [in] uuid - The UUID of the characteristic.
  * @param [in] properties - The properties of the characteristic.
+ * @param [in] max_len - The maximum length in bytes that the characteristic value can hold.
  * @return The new BLE characteristic.
  */
-NimBLECharacteristic* NimBLEService::createCharacteristic(const char* uuid, uint32_t properties) {
-    return createCharacteristic(NimBLEUUID(uuid), properties);
+NimBLECharacteristic* NimBLEService::createCharacteristic(const char* uuid, uint32_t properties, uint16_t max_len) {
+    return createCharacteristic(NimBLEUUID(uuid), properties, max_len);
 }
 
 
@@ -261,10 +262,11 @@ NimBLECharacteristic* NimBLEService::createCharacteristic(const char* uuid, uint
  * @brief Create a new BLE Characteristic associated with this service.
  * @param [in] uuid - The UUID of the characteristic.
  * @param [in] properties - The properties of the characteristic.
+ * @param [in] max_len - The maximum length in bytes that the characteristic value can hold.
  * @return The new BLE characteristic.
  */
-NimBLECharacteristic* NimBLEService::createCharacteristic(const NimBLEUUID &uuid, uint32_t properties) {
-    NimBLECharacteristic* pCharacteristic = new NimBLECharacteristic(uuid, properties, this);
+NimBLECharacteristic* NimBLEService::createCharacteristic(const NimBLEUUID &uuid, uint32_t properties, uint16_t max_len) {
+    NimBLECharacteristic* pCharacteristic = new NimBLECharacteristic(uuid, properties, max_len, this);
 
     if (getCharacteristic(uuid) != nullptr) {
         NIMBLE_LOGD(LOG_TAG, "<< Adding a duplicate characteristic with UUID: %s",

src/NimBLEService.h

@@ -50,12 +50,14 @@ public:
     NimBLECharacteristic* createCharacteristic(const char* uuid,
                                               uint32_t properties =
                                               NIMBLE_PROPERTY::READ |
-                                              NIMBLE_PROPERTY::WRITE);
+                                              NIMBLE_PROPERTY::WRITE,
+                                              uint16_t max_len = BLE_ATT_ATTR_MAX_LEN);
 
     NimBLECharacteristic* createCharacteristic(const NimBLEUUID &uuid,
                                                uint32_t properties =
                                                NIMBLE_PROPERTY::READ |
-                                               NIMBLE_PROPERTY::WRITE);
+                                               NIMBLE_PROPERTY::WRITE,
+                                               uint16_t max_len = BLE_ATT_ATTR_MAX_LEN);
 
     void                  addCharacteristic(NimBLECharacteristic* pCharacteristic);
     void                  removeCharacteristic(NimBLECharacteristic* pCharacteristic, bool deleteChr = false);

src/NimBLEUtils.h

@@ -29,7 +29,7 @@ typedef struct {
     void *pATT;
     TaskHandle_t task;
     int rc;
-    std::string *buf;
+    void *buf;
 } ble_task_data_t;
 
 

src/nimconfig.h

@@ -25,6 +25,13 @@
 #define CONFIG_BT_NIMBLE_ROLE_BROADCASTER
 #endif
 
+/* Enables the use of Arduino String class for attribute values */
+#if defined __has_include
+#  if __has_include (<Arduino.h>)
+#    define NIMBLE_CPP_ARDUINO_STRING_AVAILABLE
+#  endif
+#endif
+
 #endif /* CONFIG_BT_ENABLED */
 
 #ifdef _DOXYGEN_
@@ -32,6 +39,22 @@
 /** @brief Un-comment to change the number of simultaneous connections (esp controller max is 9) */
 #define CONFIG_BT_NIMBLE_MAX_CONNECTIONS 3
 
+/** @brief Un-comment to enable storing the timestamp when an attribute value is updated\n
+ *  This allows for checking the last update time using getTimeStamp() or getValue(time_t*)\n
+ *  If disabled, the timestamp returned from these functions will be 0.\n
+ *  Disabling timestamps will reduce the memory used for each value.\n
+ *  1 = Enabled, 0 = Disabled; Default = Disabled
+ */
+#define CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED 0
+
+/** @brief Uncomment to set the default allocation size (bytes) for each attribute if\n
+ *  not specified when the constructor is called. This is also the size used when a remote\n
+ *  characteristic or descriptor is constructed before a value is read/notifed.\n
+ *  Increasing this will reduce reallocations but increase memory footprint.\n
+ *  Default value is 20. Range: 1 : 512 (BLE_ATT_ATTR_MAX_LEN)
+ */
+#define CONFIG_NIMBLE_CPP_ATT_VALUE_INIT_LENGTH 20
+
 /** @brief Un-comment to change the default MTU size */
 #define CONFIG_BT_NIMBLE_ATT_PREFERRED_MTU 255