[Server] Add callback for MTU change. (#265)

onMTUChange callback added that is called when a connection MTU is updated.

Author: h2zero

examples/NimBLE_Server/NimBLE_Server.ino

@@ -39,6 +39,9 @@ class ServerCallbacks: public NimBLEServerCallbacks {
         Serial.println("Client disconnected - start advertising");
         NimBLEDevice::startAdvertising();
     };
+    void onMTUChange(uint16_t MTU, ble_gap_conn_desc* desc) {
+        Serial.printf("MTU updated: %u for connection ID: %u\n", MTU, desc->conn_handle);
+    };
 
 /********************* Security handled here **********************
 ****** Note: these are the same return values as defaults ********/

src/NimBLEServer.cpp

@@ -416,6 +416,12 @@ NimBLEConnInfo NimBLEServer::getPeerIDInfo(uint16_t id) {
             NIMBLE_LOGI(LOG_TAG, "mtu update event; conn_handle=%d mtu=%d",
                         event->mtu.conn_handle,
                         event->mtu.value);
+            rc = ble_gap_conn_find(event->mtu.conn_handle, &desc);
+            if (rc != 0) {
+                return 0;
+            }
+
+            server->m_pServerCallbacks->onMTUChange(event->mtu.value, &desc);
             return 0;
         } // BLE_GAP_EVENT_MTU
 
@@ -809,6 +815,10 @@ void NimBLEServerCallbacks::onDisconnect(NimBLEServer* pServer, ble_gap_conn_des
     NIMBLE_LOGD("NimBLEServerCallbacks", "onDisconnect(): Default");
 } // onDisconnect
 
+void NimBLEServerCallbacks::onMTUChange(uint16_t MTU, ble_gap_conn_desc* desc) {
+    NIMBLE_LOGD("NimBLEServerCallbacks", "onMTUChange(): Default");
+} // onMTUChange
+
 uint32_t NimBLEServerCallbacks::onPassKeyRequest(){
     NIMBLE_LOGD("NimBLEServerCallbacks", "onPassKeyRequest: default: 123456");
     return 123456;

src/NimBLEServer.h

@@ -131,6 +131,14 @@ class NimBLEServerCallbacks {
      */
     virtual void onDisconnect(NimBLEServer* pServer, ble_gap_conn_desc* desc);
 
+     /**
+     * @brief Called when the connection MTU changes.
+     * @param [in] MTU The new MTU value.
+     * @param [in] desc A pointer to the connection description structure containig information
+     * about the connection.
+     */
+    virtual void onMTUChange(uint16_t MTU, ble_gap_conn_desc* desc);
+
     /**
      * @brief Called when a client requests a passkey for pairing.
      * @return The passkey to be sent to the client.