[Server] Add ability to create static attributes.

This allows creating instances of services/characteristics and decriptors without
needing to call the parent createX() methods. This allows creation of the attibutes
within a class or other structure and the attributes can be linked to the parent by
calling the parent addX() method.

Additonally this increases the backward compatibility with the original bluedroid library
to further support user migration.

src/NimBLEDescriptor.cpp

@@ -37,6 +37,7 @@ NimBLEDescriptor::NimBLEDescriptor(const char* uuid, uint16_t properties, uint16
 : NimBLEDescriptor(NimBLEUUID(uuid), max_len, properties, pCharacteristic) {
 }
 
+
 /**
  * @brief NimBLEDescriptor constructor.
  */
@@ -47,7 +48,7 @@ NimBLEDescriptor::NimBLEDescriptor(NimBLEUUID uuid, uint16_t properties, uint16_
     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    = nullptr;                     // No initial characteristic.
+    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_valMux             = portMUX_INITIALIZER_UNLOCKED;
@@ -122,6 +123,7 @@ uint8_t* NimBLEDescriptor::getValue() {
     return m_value.attr_value;
 } // getValue
 
+
 /**
  * @brief Get the value of this descriptor as a string.
  * @return A std::string instance containing a copy of the descriptor's value.
@@ -130,9 +132,18 @@ std::string NimBLEDescriptor::getStringValue() {
     return std::string((char *) m_value.attr_value, m_value.attr_len);
 }
 
+
+/**
+ * @brief Get the characteristic this descriptor belongs to.
+ * @return A pointer to the characteristic this descriptor belongs to.
+ */
+NimBLECharacteristic* NimBLEDescriptor::getCharacteristic() {
+    return m_pCharacteristic;
+} // getCharacteristic
+
+
 int NimBLEDescriptor::handleGapEvent(uint16_t conn_handle, uint16_t attr_handle,
-                             struct ble_gatt_access_ctxt *ctxt,
-                                     void *arg) {
+                                     struct ble_gatt_access_ctxt *ctxt, void *arg) {
     const ble_uuid_t *uuid;
     int rc;
     NimBLEDescriptor* pDescriptor = (NimBLEDescriptor*)arg;
@@ -237,6 +248,14 @@ void NimBLEDescriptor::setValue(const std::string &value) {
     setValue((uint8_t*) value.data(), value.length());
 } // setValue
 
+/**
+ * @brief Set the characteristic this descriptor belongs to.
+ * @param [in] pChar A pointer to the characteristic this descriptior belongs to.
+ */
+void NimBLEDescriptor::setCharacteristic(NimBLECharacteristic* pChar) {
+    m_pCharacteristic = pChar;
+} // setCharacteristic
+
 
 /**
  * @brief Return a string representation of the descriptor.