Find characteristic end handle using the next characterisic handle.

On some devices, searching for descriptors using the service end handle would return an invalid error.
This patch instead uses the handle of the next characteristic as the end handle (if available).

src/NimBLERemoteCharacteristic.cpp

@@ -209,15 +209,21 @@ int NimBLERemoteCharacteristic::descriptorDiscCB(uint16_t conn_handle,
 bool NimBLERemoteCharacteristic::retrieveDescriptors(const NimBLEUUID *uuid_filter) {
     NIMBLE_LOGD(LOG_TAG, ">> retrieveDescriptors() for characteristic: %s", getUUID().toString().c_str());
 
+    uint16_t endHandle = getRemoteService()->getEndHandle(this);
+    if(m_handle >= endHandle) {
+        return false;
+    }
+
     int rc = 0;
     ble_task_data_t taskData = {this, xTaskGetCurrentTaskHandle(), 0, nullptr};
     desc_filter_t filter = {uuid_filter, &taskData};
 
     rc = ble_gattc_disc_all_dscs(getRemoteService()->getClient()->getConnId(),
                                  m_handle,
-                                 getRemoteService()->getEndHandle(),
+                                 endHandle,
                                  NimBLERemoteCharacteristic::descriptorDiscCB,
                                  &filter);
+
     if (rc != 0) {
         NIMBLE_LOGE(LOG_TAG, "ble_gattc_disc_all_chrs: rc=%d %s", rc, NimBLEUtils::returnCodeToString(rc));
         return false;
@@ -226,12 +232,13 @@ bool NimBLERemoteCharacteristic::retrieveDescriptors(const NimBLEUUID *uuid_filt
     ulTaskNotifyTake(pdTRUE, portMAX_DELAY);
 
     if(taskData.rc != 0) {
+        NIMBLE_LOGE(LOG_TAG, "ble_gattc_disc_all_chrs: startHandle:%d endHandle:%d taskData.rc=%d %s", m_handle, endHandle, taskData.rc, NimBLEUtils::returnCodeToString(0x0100+taskData.rc));
         return false;
     }
 
     return true;
     NIMBLE_LOGD(LOG_TAG, "<< retrieveDescriptors(): Found %d descriptors.", m_descriptorVector.size());
-} // getDescriptors
+} // retrieveDescriptors
 
 
 /**

src/NimBLERemoteService.cpp

@@ -249,6 +249,23 @@ uint16_t NimBLERemoteService::getEndHandle() {
     return m_endHandle;
 } // getEndHandle
 
+/**
+ * @brief Get the end handle of specified NimBLERemoteCharacteristic.
+ */
+
+uint16_t NimBLERemoteService::getEndHandle(NimBLERemoteCharacteristic *pCharacteristic) {
+    uint16_t endHandle = m_endHandle;
+    
+    for(auto &it: m_characteristicVector) {
+        uint16_t defHandle = it->getDefHandle() - 1;
+        if(defHandle > pCharacteristic->getDefHandle() && endHandle > defHandle) {
+            endHandle = defHandle;
+        }
+    }
+
+    return endHandle;
+} // getEndHandle
+
 
 /**
  * @brief Get the service start handle.

src/NimBLERemoteService.h

@@ -70,6 +70,7 @@ private:
 
     uint16_t            getStartHandle();
     uint16_t            getEndHandle();
+    uint16_t            getEndHandle(NimBLERemoteCharacteristic *pCharacteristic);
     void                releaseSemaphores();
 
     // Properties