Enabled getting an implicitly-created CCCD through GattCharacteristic::getDescriptor

Author: AGlass0fMilk

connectivity/FEATURE_BLE/include/ble/gatt/GattCharacteristic.h

@@ -1429,6 +1429,12 @@ class GattCharacteristic {
     GattCharacteristic(const GattCharacteristic &) = delete;
     GattCharacteristic& operator=(const GattCharacteristic &) = delete;
 
+    ~GattCharacteristic() {
+        if(_implicit_cccd != nullptr) {
+            delete _implicit_cccd;
+        }
+    }
+
 public:
 
     /**
@@ -1714,7 +1720,7 @@ class GattCharacteristic {
      */
     uint8_t getDescriptorCount() const
     {
-        return _descriptorCount;
+        return (_implicit_cccd == nullptr? _descriptorCount : _descriptorCount+1);
     }
 
     /**
@@ -1750,16 +1756,40 @@ class GattCharacteristic {
      *
      * @return A pointer the requested descriptor if @p index is within the
      * range of the descriptor array or nullptr otherwise.
+     *
+     * @note if this characteristic has an implicitly-created CCCD this
+     * descriptor will be available at the highest index
+     * (ie: return of getDescriptorCount() - 1)
      */
     GattAttribute *getDescriptor(uint8_t index)
     {
-        if (index >= _descriptorCount) {
+
+        if(index == _descriptorCount) {
+            // If _implicit_cccd is nullptr, we want to return that anyway
+            return _implicit_cccd;
+        }
+        else if (index > _descriptorCount) {
             return nullptr;
         }
 
         return _descriptors[index];
     }
 
+    /**
+     * Sets this GattCharacteristic's implicitly-created CCCD, if
+     * applicable.
+     *
+     * @note once this is called, the pointed-to GattAttribute
+     * is owned by this GattCharacteristic and will be deleted
+     * during this object's destructor
+     *
+     * @note this is an internal function and should not be called
+     * by the application
+     */
+    void _setImplicitCCCD(GattAttribute *implicit_cccd) {
+        _implicit_cccd = implicit_cccd;
+    }
+
 private:
 
     /**
@@ -1783,6 +1813,16 @@ class GattCharacteristic {
      */
     uint8_t _descriptorCount;
 
+    /**
+     * Pointer to characteristic's implicit CCCD, if applicable
+     *
+     * @note this is only populated if the stack creates an implicit CCCD
+     * for this GattCharacteristic. If the descriptors array passed into
+     * the constructor includes a CCCD this field is left as nullptr to
+     * indicate the CCCD was explicitly created.
+     */
+    GattAttribute* _implicit_cccd;
+
     /**
      * The registered callback handler for read authorization reply.
      */

connectivity/FEATURE_BLE/source/cordio/source/GattServerImpl.cpp

@@ -588,6 +588,23 @@ ble_error_t GattServer::insert_cccd(
     cccds[cccd_cnt].secLevel = characteristic->getUpdateSecurityRequirement().value();
     cccd_handles[cccd_cnt] = characteristic->getValueAttribute().getHandle();
 
+    /**
+     * Set the characteristic's implicitly-created CCCD
+     *
+     * Ownership is passed to the GattCharacteristic
+     */
+    GattAttribute* implicit_cccd = new GattAttribute(
+                                       CCCD_UUID,
+                                       attribute_it->pValue,
+                                       *attribute_it->pLen,
+                                       attribute_it->maxLen,
+                                       false);
+
+    implicit_cccd->setHandle(cccds[cccd_cnt].handle);
+    implicit_cccd->allowRead(true);
+    implicit_cccd->allowWrite(true);
+    characteristic->_setImplicitCCCD(implicit_cccd);
+
     cccd_cnt++;
     attribute_it++;