track open/close state in connection, disconnect on read error, clarify error codes a little

src/connection.h

@@ -11,6 +11,7 @@ int GetProcessId();
 struct BaseConnection {
     static BaseConnection* Create();
     static void Destroy(BaseConnection*&);
+    bool isOpen{false};
     bool Open();
     bool Close();
     bool Write(const void* data, size_t length);