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 the `NimBLEScan` that prevents the scan
from starting while a client is trying to connect.

Author: h2zero

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::getScan()->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::getScan()->setConnectionInProgress(false);
     m_lastErr = rc;
-
     if (rc != 0) {
         m_pTaskData = nullptr;
         return false;

src/NimBLEScan.cpp

@@ -40,6 +40,7 @@ NimBLEScan::NimBLEScan() {
     m_pTaskData                      = nullptr;
     m_duration                       = BLE_HS_FOREVER; // make sure this is non-zero in the event of a host reset
     m_maxResults                     = 0xFF;
+    m_connectionInProgress           = false;
 }
 
 
@@ -292,6 +293,11 @@ bool NimBLEScan::isScanning() {
 bool NimBLEScan::start(uint32_t duration, bool is_continue) {
     NIMBLE_LOGD(LOG_TAG, ">> start: duration=%" PRIu32, duration);
 
+    if (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;
 
@@ -444,6 +450,22 @@ void NimBLEScan::onHostSync() {
     }
 }
 
+/**
+ * @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 NimBLEScan::setConnectionInProgress(bool inProgress) {
+    m_connectionInProgress = inProgress;
+}
+
+/**
+ * @brief Get the connection in progress flag.
+ * @return True if a connection is in progress.
+ */
+bool NimBLEScan::isConnectionInProgress() {
+    return m_connectionInProgress;
+}
 
 /**
  * @brief Start scanning and block until scanning has been completed.

src/NimBLEScan.h

@@ -78,6 +78,8 @@ class NimBLEScan {
     NimBLEScanResults   getResults(uint32_t duration, bool is_continue = false);
     void                setMaxResults(uint8_t maxResults);
     void                erase(const NimBLEAddress &address);
+    void                setConnectionInProgress(bool inProgress);
+    bool                isConnectionInProgress();
 
 
 private:
@@ -96,6 +98,7 @@ class NimBLEScan {
     uint32_t              m_duration;
     BleTaskData           *m_pTaskData;
     uint8_t               m_maxResults;
+    bool                  m_connectionInProgress;
 };
 
 /**