/usr/include/simgear/io/ is in libsimgear-dev 3.0.0-6+b2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/simgear/io/DAVMultiStatus.hxx
/usr/include/simgear/io/HTTPClient.hxx
/usr/include/simgear/io/HTTPContentDecode.hxx
/usr/include/simgear/io/HTTPFileRequest.hxx
/usr/include/simgear/io/HTTPMemoryRequest.hxx
/usr/include/simgear/io/HTTPRequest.hxx
/usr/include/simgear/io/SVNDirectory.hxx
/usr/include/simgear/io/SVNReportParser.hxx
/usr/include/simgear/io/SVNRepository.hxx
/usr/include/simgear/io/iochannel.hxx
/usr/include/simgear/io/lowlevel.hxx
/usr/include/simgear/io/raw_socket.hxx
/usr/include/simgear/io/sg_binobj.hxx
/usr/include/simgear/io/sg_file.hxx
/usr/include/simgear/io/sg_netBuffer.hxx
/usr/include/simgear/io/sg_netChannel.hxx
/usr/include/simgear/io/sg_netChat.hxx
/usr/include/simgear/io/sg_serial.hxx
/usr/include/simgear/io/sg_socket.hxx
/usr/include/simgear/io/sg_socket_udp.hxx