[BREAKING] Refactor attributes

Refactor attributes to reduce code duplication and improve maintainability.

* Add attribute base classes to provide common code.
* Add const where possible to functions and parameters.
* `NimBLECharacteristic::notify` no longer takes a `bool is_notification` parameter, instead `indicate()` should be called to send indications.
* `NimBLECharacteristic::indicate` now takes the same parameters as `notify`.
* `NimBLECharacteristicCallbacks` and `NimBLEDescriptorCallbacks` methods now take `const NimBLEConnInfo&` instead of non-const.
* `NimBLECharacteristic::onNotify` callback removed as unnecessary, the library does not call notify without app input.
* Add NimBLEUUID constructor that takes a reference to `ble_uuid_any_t`.
* `NimBLERemoteService::getCharacteristics` now returns a `const std::vector<NimBLERemoteCharacteristic*>&` instead of non-const `std::vector<NimBLERemoteCharacteristic*>*`
* `NimBLERemoteService::getValue` now returns `NimBLEAttValue` instead of `std::string`
* `NimBLEService::getCharacteristics` now returns a `const std::vector<NimBLECharacteristic*>&` instead of a copy of std::vector<NimBLECharacteristic *>.

examples/NimBLE_Client/NimBLE_Client.ino

@@ -112,7 +112,7 @@ void notifyCB(NimBLERemoteCharacteristic* pRemoteCharacteristic, uint8_t* pData,
     std::string str = (isNotify == true) ? "Notification" : "Indication";
     str += " from ";
     /** NimBLEAddress and NimBLEUUID have std::string operators */
-    str += std::string(pRemoteCharacteristic->getRemoteService()->getClient()->getPeerAddress());
+    str += std::string(pRemoteCharacteristic->getClient()->getPeerAddress());
     str += ": Service = " + std::string(pRemoteCharacteristic->getRemoteService()->getUUID());
     str += ", Characteristic = " + std::string(pRemoteCharacteristic->getUUID());
     str += ", Value = " + std::string((char*)pData, length);

examples/NimBLE_Server/NimBLE_Server.ino

@@ -241,7 +241,7 @@ void loop() {
         if(pSvc) {
             NimBLECharacteristic* pChr = pSvc->getCharacteristic("F00D");
             if(pChr) {
-                pChr->notify(true);
+                pChr->notify();
             }
         }
     }

src/NimBLEAttValue.h

@@ -192,20 +192,15 @@ class NimBLEAttValue {
         return setValue(reinterpret_cast<const uint8_t*>(s), len);
     }
 
-    /**
-     * @brief Get a pointer to the value buffer with timestamp.
-     * @param[in] timestamp A pointer to a time_t variable to store the timestamp.
-     * @returns A pointer to the internal value buffer.
-     */
-    const uint8_t* getValue(time_t* timestamp = nullptr) const {
+    const NimBLEAttValue& getValue(time_t* timestamp = nullptr) const {
         if (timestamp != nullptr) {
 # if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
             *timestamp = m_timestamp;
 # else
             *timestamp = 0;
 # endif
         }
-        return m_attr_value;
+        return *this;
     }
 
     /**
@@ -271,7 +266,15 @@ class NimBLEAttValue {
         if (!skipSizeCheck && size() < sizeof(T)) {
             return T();
         }
-        return *(reinterpret_cast<const T*>(getValue(timestamp)));
+        if (timestamp != nullptr) {
+# if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+            *timestamp = m_timestamp;
+# else
+            *timestamp = 0;
+# endif
+        }
+
+        return *(reinterpret_cast<const T*>(m_attr_value));
     }
 
     /*********************** Operators ************************/

src/NimBLEAttribute.h

@@ -0,0 +1,50 @@
+/*
+ * NimBLEAttribute.h
+ *
+ *  Created: on July 28 2024
+ *      Author H2zero
+ */
+
+#ifndef NIMBLE_CPP_ATTRIBUTE_H_
+#define NIMBLE_CPP_ATTRIBUTE_H_
+
+#include "nimconfig.h"
+#if defined(CONFIG_BT_ENABLED) && (defined(CONFIG_BT_NIMBLE_ROLE_PERIPHERAL) || defined(CONFIG_BT_NIMBLE_ROLE_CENTRAL))
+
+# include "NimBLEUUID.h"
+
+/**
+ * @brief A base class for BLE attributes.
+ */
+class NimBLEAttribute {
+  public:
+    /**
+     * @brief Get the UUID of the attribute.
+     * @return The UUID.
+     */
+    const NimBLEUUID& getUUID() const { return m_uuid; }
+
+    /**
+     * @brief Get the handle of the attribute.
+     */
+    uint16_t getHandle() const { return m_handle; };
+
+  protected:
+    /**
+     * @brief Construct a new NimBLEAttribute object.
+     * @param [in] handle The handle of the attribute.
+     * @param [in] uuid The UUID of the attribute.
+     */
+    NimBLEAttribute(const NimBLEUUID& uuid, uint16_t handle) : m_uuid{uuid}, m_handle{handle} {}
+
+    /**
+     * @brief Destroy the NimBLEAttribute object.
+     */
+    ~NimBLEAttribute() = default;
+
+    const NimBLEUUID m_uuid{};
+    uint16_t   m_handle{0};
+};
+
+#endif // CONFIG_BT_ENABLED && (CONFIG_BT_NIMBLE_ROLE_PERIPHERAL || CONFIG_BT_NIMBLE_ROLE_CENTRAL)
+#endif // NIMBLE_CPP_ATTRIBUTE_H_