Fix descriptor search range in retrieveDescriptors()

The previous implementation incorrectly used the service's end handle
when searching for descriptors, which caused it to retrieve descriptors
from subsequent characteristics as well.

This fix calculates the correct end handle by finding the next
characteristic's handle and using (next_handle - 1) as the search limit.
This ensures only descriptors belonging to the current characteristic
are retrieved.

Fixes incorrect descriptor retrieval when multiple characteristics
exist in the same service.

Author: hjlee

src/NimBLERemoteCharacteristic.cpp

@@ -94,8 +94,24 @@ int NimBLERemoteCharacteristic::descriptorDiscCB(
 bool NimBLERemoteCharacteristic::retrieveDescriptors(NimBLEDescriptorFilter* pFilter) const {
     NIMBLE_LOGD(LOG_TAG, ">> retrieveDescriptors() for characteristic: %s", getUUID().toString().c_str());
 
+    const auto pSvc      = getRemoteService();
+    uint16_t   endHandle = pSvc->getEndHandle();
+
+    // Find the handle of the next characteristic to limit the descriptor search range.
+    const auto& chars = pSvc->getCharacteristics(false);
+    for (auto it = chars.begin(); it != chars.end(); ++it) {
+        if ((*it)->getHandle() == this->getHandle()) {
+            auto next_it = std::next(it);
+            if (next_it != chars.end()) {
+                endHandle = (*next_it)->getHandle() - 1;
+                NIMBLE_LOGD(LOG_TAG, "Search range limited to handle 0x%04X", endHandle);
+            }
+            break;
+        }
+    }
+
     // If this is the last handle then there are no descriptors
-    if (getHandle() == getRemoteService()->getEndHandle()) {
+    if (getHandle() == endHandle) {
         NIMBLE_LOGD(LOG_TAG, "<< retrieveDescriptors(): found 0 descriptors.");
         return true;
     }
@@ -108,7 +124,7 @@ bool NimBLERemoteCharacteristic::retrieveDescriptors(NimBLEDescriptorFilter* pFi
 
     int rc = ble_gattc_disc_all_dscs(getClient()->getConnHandle(),
                                      getHandle(),
-                                     getRemoteService()->getEndHandle(),
+                                     endHandle,
                                      NimBLERemoteCharacteristic::descriptorDiscCB,
                                      pFilter);
     if (rc != 0) {