Fix segfault when the handler is destructed from within a callback

include/libev.h

@@ -85,6 +85,14 @@ private:
             ev_io_start(_loop, &_io);
         }
 
+        /**
+         *  Watchers cannot be copied or moved
+         *
+         *  @param  that    The object to not move or copy
+         */
+        Watcher(Watcher &&that) = delete;
+        Watcher(const Watcher &that) = delete;
+
         /**
          *  Destructor
          */

include/tcpconnection.h

@@ -26,7 +26,9 @@ class TcpState;
 /**
  *  Class definition
  */
-class TcpConnection : private ConnectionHandler
+class TcpConnection :
+    private ConnectionHandler,
+    private Watchable
 {
 private:
     /**

src/tcpconnection.cpp

@@ -47,9 +47,15 @@ TcpConnection::~TcpConnection()
  */
 void TcpConnection::process(int fd, int flags)
 {
+    // monitor the object for destruction
+    Monitor monitor{ this };
+
     // pass on the the state, that returns a new impl
     auto *result = _state->process(fd, flags);
 
+    // are we still valid
+    if (!monitor.valid()) return;
+
     // skip if the same state is continued to be used, or when the process()
     // method returns nullptr (which only happens when the object is destructed,
     // and "this" is no longer valid)