more elegant close procedure for tcp connections

src/linux_tcp/tcpconnected.h

@@ -54,8 +54,36 @@ private:
      *  @var size_t
      */
     size_t _reallocate = 0;
+    
+    /**
+     *  Have we already made the last report to the user (about an error or closed connection?)
+     *  @var bool
+     */
+    bool _finalized = false;
 
     
+    /**
+     *  Close the connection
+     *  @return bool
+     */
+    bool close()
+    {
+        // do nothing if already closed
+        if (_socket < 0) return false;
+        
+        // and stop monitoring it
+        _handler->monitor(_connection, _socket, 0);
+
+        // close the socket
+        ::close(_socket);
+        
+        // forget filedescriptor
+        _socket = -1;
+        
+        // done
+        return true;
+    }
+    
     /**
      *  Helper method to report an error
      *  @return bool        Was an error reported?
@@ -65,6 +93,16 @@ private:
         // some errors are ok and do not (necessarily) mean that we're disconnected
         if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR) return false;
         
+        // connection can be closed now
+        close();
+        
+        // if the user has already been notified, we do not have to do anything else
+        if (_finalized) return true;
+        
+        // update the _finalized member before we make the call to user space because
+        // the user space may destruct this object
+        _finalized = true;
+        
         // we have an error - report this to the user
         _handler->onError(_connection, strerror(errno));
         
@@ -110,14 +148,8 @@ public:
      */
     virtual ~TcpConnected() noexcept
     {
-        // skip if handler is already forgotten
-        if (_handler == nullptr) return;
-        
-        // we no longer have to monitor the socket
-        _handler->monitor(_connection, _socket, 0);
-        
         // close the socket
-        close(_socket);
+        close();
     }
 
     /**
@@ -145,7 +177,7 @@ public:
             auto result = _out.sendto(_socket);
             
             // are we in an error state?
-            if (result <  0 && reportError()) return nextState(monitor);
+            if (result < 0 && reportError()) return nextState(monitor);
             
             // if buffer is empty by now, we no longer have to check for 
             // writability, but only for readability
@@ -255,28 +287,47 @@ public:
         return TcpState::reportNegotiate(heartbeat);
     }
 
+    /**
+     *  Report to the handler that the object is in an error state.
+     *  @param  error
+     */
+    virtual void reportError(const char *error)
+    {
+        // close the socket
+        close();
+        
+        // if the user was already notified of an final state, we do not have to proceed
+        if (_finalized) return;
+        
+        // remember that this is the final call to user space
+        _finalized = true;
+        
+        // pass to handler
+        _handler->onError(_connection, error);
+    }
+
     /**
      *  Report to the handler that the connection was nicely closed
+     *  This is the counter-part of the connection->close() call.
      */
     virtual void reportClosed() override
     {
-        // we no longer have to monitor the socket
-        _handler->monitor(_connection, _socket, 0);
+        // we will shutdown the socket in a very elegant way, we notify the peer 
+        // that we will not be sending out more write operations
+        shutdown(_socket, SHUT_WR);
+        
+        // we still monitor the socket for readability to see if our close call was
+        // confirmed by the peer
+        _handler->monitor(_connection, _socket, readable);
 
-        // close the socket
-        close(_socket);
+        // if the user was already notified of an final state, we do not have to proceed
+        if (_finalized) return;
         
-        // socket is closed now
-        _socket = -1;
+        // remember that this is the final call to user space
+        _finalized = true;
         
-        // copy the handler (if might destruct this object)
-        auto *handler = _handler;
-        
-        // reset member before the handler can make a mess of it
-        _handler = nullptr;
-        
-        // notify to handler
-        handler->onClosed(_connection);
+        // pass to handler
+        _handler->onClosed(_connection);
     }
 };
     

src/linux_tcp/tcpresolver.h

@@ -194,7 +194,7 @@ public:
         if (_socket >= 0) 
         {
             // if we need a secure connection, we move to the tls handshake
-            // @todo catch exception
+            // @todo catch possible exception
             if (_secure) return new SslHandshake(_connection, _socket, _hostname, std::move(_buffer), _handler);
             
             // otherwise we have a valid regular tcp connection

src/linux_tcp/tcpstate.h

@@ -36,22 +36,6 @@ protected:
     TcpHandler *_handler;
 
 protected:
-    /**
-     *  Helper function to reset the handler, and to return the old handler object
-     *  @return TcpHandler* User-supplied handler that was just reset
-     */
-    TcpHandler *reset(TcpHandler *handler)
-    {
-        // remember old handler
-        auto *oldhandler = _handler;
-        
-        // install the new handler
-        _handler = handler;
-        
-        // return the old handler
-        return oldhandler;
-    }
-
     /**
      *  Protected constructor
      *  @param  connection  Original TCP connection object
@@ -150,7 +134,7 @@ public:
     virtual void reportError(const char *error)
     {
         // pass to handler
-        reset(nullptr)->onError(_connection, error);
+        _handler->onError(_connection, error);
     }
 
     /**
@@ -182,7 +166,7 @@ public:
     virtual void reportClosed()
     {
         // pass to handler
-        reset(nullptr)->onClosed(_connection);
+        _handler->onClosed(_connection);
     }
 };