netplay: force safe disposal pattern for IClientConnection:s

Mark `IClientConnection` destructor as `protected`, so that
external code cannot accidentally invoke `delete` on a connection
object directly, and thus is forced to call `close()` method on
it for safe disposal.

Signed-off-by: Pavel Solodovnikov <pavel.al.solodovnikov@gmail.com>

lib/netplay/client_connection.h

@@ -55,8 +55,6 @@ class IClientConnection
 {
 public:
 
-	virtual ~IClientConnection() = default;
-
 	/// <summary>
 	/// Read exactly `size` bytes into `buf` buffer.
 	/// Supports setting a timeout value in milliseconds.
@@ -219,7 +217,16 @@ class IClientConnection
 
 protected:
 
+	// Allow `PendingWritesManager` to access hidden destructor
+	// since this class ultimately does the final cleanup of
+	// disposed connections.
+	friend class PendingWritesManager;
+
 	IClientConnection(WzConnectionProvider& connProvider);
+	// Hide the destructor so that external code cannot accidentally
+	// `delete` the connection directly and has to use `close()` method
+	// to dispose of the connection object.
+	virtual ~IClientConnection() = default;
 
 	// Pre-allocated (in ctor) connection list and descriptor sets, which
 	// only contain `this`.

lib/netplay/open_connection_result.h

@@ -43,16 +43,25 @@ struct OpenConnectionResult
 		: open_socket(open_socket)
 	{ }
 
-public:
 	bool hasError() const { return errorCode.has_value(); }
-public:
+
 	OpenConnectionResult(const OpenConnectionResult& other) = delete; // non construction-copyable
 	OpenConnectionResult& operator=(const OpenConnectionResult&) = delete; // non copyable
 	OpenConnectionResult(OpenConnectionResult&&) = default;
 	OpenConnectionResult& operator=(OpenConnectionResult&&) = default;
-public:
 
-	std::unique_ptr<IClientConnection> open_socket;
+	struct ConnectionCloser
+	{
+		void operator() (IClientConnection* conn)
+		{
+			if (conn)
+			{
+				conn->close();
+			}
+		}
+	};
+
+	std::unique_ptr<IClientConnection, ConnectionCloser> open_socket;
 	optional<std::error_code> errorCode = nullopt;
 	std::string errorString;
 };