Fix https://github.com/zerotier/libzt/issues/244:

Memory leak if libzt events aren't consumed by user app
If arg is not enqueued by Events, then treat as if ownership has NOT
been transferred and caller of Events->enqueue is responsible for freeing

src/Events.cpp

@@ -93,11 +93,18 @@ void Events::run()
     }
 }
 
-void Events::enqueue(unsigned int event_code, const void* arg, int len)
+bool Events::enqueue(unsigned int event_code, const void* arg, int len)
 {
     if (! _enabled) {
-        return;
+        return false;
     }
+    if (_callbackMsgQueue.size_approx() > 1024) {
+        /* Rate-limit number of events. This value should only grow if the
+        user application isn't returning from the event handler in a timely manner.
+        For most applications it should hover around 1 to 2 */
+        return false;
+    }
+    
     zts_event_msg_t* msg = new zts_event_msg_t();
     msg->event_code = event_code;
 
@@ -132,15 +139,12 @@ void Events::enqueue(unsigned int event_code, const void* arg, int len)
         msg->cache = (void*)arg;
         msg->len = len;
     }
-    if (msg && _callbackMsgQueue.size_approx() > 1024) {
+
-        /* Rate-limit number of events. This value should only grow if the
+    //
-        user application isn't returning from the event handler in a timely manner.
+    // ownership of arg is now transferred
-        For most applications it should hover around 1 to 2 */
+    //
-        destroy(msg);
-    }
-    else {
     _callbackMsgQueue.enqueue(msg);
-    }
+    return true;
 }
 
 void Events::destroy(zts_event_msg_t* msg)

src/Events.hpp

@@ -115,8 +115,12 @@ class Events {
 
     /**
      * Enqueue an event to be sent to the user application
+     * 
+     * Returns true if arg was enqueued.
+     * If enqueued, then ownership of arg has been transferred.
+     * If NOT enqueued, then ownership of arg has NOT been transferred.
      */
-    void enqueue(unsigned int event_code, const void* arg, int len = 0);
+    bool enqueue(unsigned int event_code, const void* arg, int len = 0);
 
     /**
      * Send callback message to user application

src/NodeService.cpp

@@ -957,13 +957,17 @@ void NodeService::sendEventToUser(unsigned int zt_event_code, const void* obj, u
 
     void* objptr = NULL;
 
+    zts_node_info_t* nd;
+    zts_net_info_t* nt;
+    zts_peer_info_t* pr;
+    
     switch (zt_event_code) {
         case ZTS_EVENT_NODE_UP:
         case ZTS_EVENT_NODE_ONLINE:
         case ZTS_EVENT_NODE_OFFLINE:
         case ZTS_EVENT_NODE_DOWN:
         case ZTS_EVENT_NODE_FATAL_ERROR: {
-            zts_node_info_t* nd = new zts_node_info_t;
+            nd = new zts_node_info_t;
             nd->node_id = _nodeId;
             nd->ver_major = ZEROTIER_ONE_VERSION_MAJOR;
             nd->ver_minor = ZEROTIER_ONE_VERSION_MINOR;
@@ -980,7 +984,7 @@ void NodeService::sendEventToUser(unsigned int zt_event_code, const void* obj, u
         case ZTS_EVENT_NETWORK_ACCESS_DENIED:
         case ZTS_EVENT_NETWORK_DOWN: {
             NetworkState* ns = (NetworkState*)obj;
-            zts_net_info_t* nt = new zts_net_info_t();
+            nt = new zts_net_info_t();
             nt->net_id = ns->config.nwid;
             objptr = (void*)nt;
             break;
@@ -990,7 +994,7 @@ void NodeService::sendEventToUser(unsigned int zt_event_code, const void* obj, u
         case ZTS_EVENT_NETWORK_READY_IP6:
         case ZTS_EVENT_NETWORK_OK: {
             NetworkState* ns = (NetworkState*)obj;
-            zts_net_info_t* nt = new zts_net_info_t();
+            nt = new zts_net_info_t();
             nt->net_id = ns->config.nwid;
             nt->mac = ns->config.mac;
             strncpy(nt->name, ns->config.name, sizeof(ns->config.name));
@@ -1051,7 +1055,7 @@ void NodeService::sendEventToUser(unsigned int zt_event_code, const void* obj, u
         case ZTS_EVENT_PEER_UNREACHABLE:
         case ZTS_EVENT_PEER_PATH_DISCOVERED:
         case ZTS_EVENT_PEER_PATH_DEAD: {
-            zts_peer_info_t* pr = new zts_peer_info_t();
+            pr = new zts_peer_info_t();
             ZT_Peer* peer = (ZT_Peer*)obj;
             memcpy(pr, peer, sizeof(zts_peer_info_t));
             for (unsigned int j = 0; j < peer->pathCount; j++) {
@@ -1067,7 +1071,64 @@ void NodeService::sendEventToUser(unsigned int zt_event_code, const void* obj, u
     // Send event
 
     if (objptr) {
-        _events->enqueue(zt_event_code, objptr, len);
+        if (!_events->enqueue(zt_event_code, objptr, len)) {
+            //
+            // ownership of objptr was NOT transferred, so delete any news from above
+            //
+            switch (zt_event_code) {
+                case ZTS_EVENT_NODE_UP:
+                case ZTS_EVENT_NODE_ONLINE:
+                case ZTS_EVENT_NODE_OFFLINE:
+                case ZTS_EVENT_NODE_DOWN:
+                case ZTS_EVENT_NODE_FATAL_ERROR: {
+                    delete nd;
+                    break;
+                }
+                case ZTS_EVENT_NETWORK_NOT_FOUND:
+                case ZTS_EVENT_NETWORK_CLIENT_TOO_OLD:
+                case ZTS_EVENT_NETWORK_REQ_CONFIG:
+                case ZTS_EVENT_NETWORK_ACCESS_DENIED:
+                case ZTS_EVENT_NETWORK_DOWN: {
+                    delete nt;
+                    break;
+                }
+                case ZTS_EVENT_NETWORK_UPDATE:
+                case ZTS_EVENT_NETWORK_READY_IP4:
+                case ZTS_EVENT_NETWORK_READY_IP6:
+                case ZTS_EVENT_NETWORK_OK: {
+                    delete nt;
+                    break;
+                }
+                case ZTS_EVENT_ADDR_ADDED_IP4:
+                    break;
+                case ZTS_EVENT_ADDR_ADDED_IP6:
+                    break;
+                case ZTS_EVENT_ADDR_REMOVED_IP4:
+                    break;
+                case ZTS_EVENT_ADDR_REMOVED_IP6:
+                    break;
+                case ZTS_EVENT_STORE_IDENTITY_PUBLIC:
+                    break;
+                case ZTS_EVENT_STORE_IDENTITY_SECRET:
+                    break;
+                case ZTS_EVENT_STORE_PLANET:
+                    break;
+                case ZTS_EVENT_STORE_PEER:
+                    break;
+                case ZTS_EVENT_STORE_NETWORK:
+                    break;
+                case ZTS_EVENT_PEER_DIRECT:
+                case ZTS_EVENT_PEER_RELAY:
+                case ZTS_EVENT_PEER_UNREACHABLE:
+                case ZTS_EVENT_PEER_PATH_DISCOVERED:
+                case ZTS_EVENT_PEER_PATH_DEAD: {
+                    delete pr;
+                    break;
+                }
+                default:
+                    break;
+            }
+        }
     }
 }
 

src/VirtualTap.cpp

@@ -312,6 +312,10 @@ static void zts_main_lwip_driver_loop(void* arg)
         zts_util_delay(LWIP_DRIVER_LOOP_INTERVAL);
     }
     _has_exited = true;
+    
+    //
+    // no need to check if event was enqueued since NULL is being passed
+    //
     zts_events->enqueue(ZTS_EVENT_STACK_DOWN, NULL);
 }