Fix endless loop when calling scan start from scan end callback.

When attempting to connect and the scanner is running `NimBLEScan::stop` is called to stop it
which then calls the `onScanEnded` callback. If the app then starts the scan again in this
callback an endless loop will be created.

This change prevents the endless loop by setting a flag in `NimBLEDevice` that is checked before
starting a scan while a client is trying to connect.

* Adds `NimBLEDevice::setConnectionInProgress` and `NimBLEDevice::isConnectionInProgress` functions.

src/NimBLEClient.cpp

@@ -182,6 +182,9 @@ bool NimBLEClient::connect(const NimBLEAddress& address, bool deleteAttributes)
     m_pTaskData           = &taskData;
     int rc                = 0;
 
+    // Set the connection in progress flag to prevent a scan from starting while connecting.
+    NimBLEDevice::setConnectionInProgress(true);
+
     do {
 # if CONFIG_BT_NIMBLE_EXT_ADV
         rc = ble_gap_ext_connect(NimBLEDevice::m_ownAddrType,
@@ -207,7 +210,7 @@ bool NimBLEClient::connect(const NimBLEAddress& address, bool deleteAttributes)
                 break;
 
             case BLE_HS_EBUSY:
-                // Scan was still running, stop it and try again
+                // Scan was active, stop it through the NimBLEScan API to release any tasks and call the callback.
                 if (!NimBLEDevice::getScan()->stop()) {
                     rc = BLE_HS_EUNKNOWN;
                 }
@@ -236,8 +239,8 @@ bool NimBLEClient::connect(const NimBLEAddress& address, bool deleteAttributes)
 
     } while (rc == BLE_HS_EBUSY);
 
+    NimBLEDevice::setConnectionInProgress(false);
     m_lastErr = rc;
-
     if (rc != 0) {
         m_pTaskData = nullptr;
         return false;

src/NimBLEDevice.cpp

@@ -101,6 +101,10 @@ std::vector<NimBLEAddress> NimBLEDevice::m_ignoreList{};
 std::vector<NimBLEAddress> NimBLEDevice::m_whiteList{};
 uint8_t                    NimBLEDevice::m_ownAddrType{BLE_OWN_ADDR_PUBLIC};
 
+# if defined(CONFIG_BT_NIMBLE_ROLE_CENTRAL) || defined(CONFIG_BT_NIMBLE_ROLE_PERIPHERAL)
+bool NimBLEDevice::m_connectionInProgress{false};
+# endif
+
 # ifdef ESP_PLATFORM
 #  ifdef CONFIG_BTDM_BLE_SCAN_DUPL
 uint16_t NimBLEDevice::m_scanDuplicateSize{CONFIG_BTDM_SCAN_DUPL_CACHE_SIZE};
@@ -1232,6 +1236,23 @@ bool NimBLEDevice::setCustomGapHandler(gap_event_handler handler) {
     return rc == 0;
 } // setCustomGapHandler
 
+/**
+ * @brief Set the connection in progress flag.
+ * @param [in] inProgress The connection in progress flag.
+ * @details This is used to prevent a scan from starting while a connection is in progress.
+ */
+void NimBLEDevice::setConnectionInProgress(bool inProgress) {
+    m_connectionInProgress = inProgress;
+} // setConnectionInProgress
+
+/**
+ * @brief Check if a connection is in progress.
+ * @return True if a connection is in progress.
+ */
+bool NimBLEDevice::isConnectionInProgress() {
+    return m_connectionInProgress;
+} // isConnectionInProgress
+
 /**
  * @brief Return a string representation of the address of this device.
  * @return A string representation of this device address.

src/NimBLEDevice.h

@@ -183,6 +183,8 @@ class NimBLEDevice {
     static bool          isBonded(const NimBLEAddress& address);
     static bool          deleteAllBonds();
     static NimBLEAddress getBondedAddress(int index);
+    static void          setConnectionInProgress(bool inProgress);
+    static bool          isConnectionInProgress();
 # endif
 
   private:
@@ -194,6 +196,10 @@ class NimBLEDevice {
     static uint8_t                    m_ownAddrType;
     static std::vector<NimBLEAddress> m_whiteList;
 
+# if defined(CONFIG_BT_NIMBLE_ROLE_CENTRAL) || defined(CONFIG_BT_NIMBLE_ROLE_PERIPHERAL)
+    static bool m_connectionInProgress;
+# endif
+
 # if defined(CONFIG_BT_NIMBLE_ROLE_OBSERVER)
     static NimBLEScan* m_pScan;
 # endif

src/NimBLEScan.cpp

@@ -292,6 +292,11 @@ bool NimBLEScan::isScanning() {
 bool NimBLEScan::start(uint32_t duration, bool is_continue) {
     NIMBLE_LOGD(LOG_TAG, ">> start: duration=%" PRIu32, duration);
 
+    if (NimBLEDevice::isConnectionInProgress()) {
+        NIMBLE_LOGE(LOG_TAG, "Connection in progress, cannot start scan");
+        return false;
+    }
+
     // Save the duration in the case that the host is reset so we can reuse it.
     m_duration = duration;