/usr/include/nanohttp-1.0/ is in libnanohttp-dev 1.1.0-17.1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/nanohttp-1.0/nanohttp/
/usr/include/nanohttp-1.0/nanohttp/nanohttp-base64.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-client.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-common.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-logging.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-mime.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-request.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-response.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-server.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-socket.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-ssl.h
/usr/include/nanohttp-1.0/nanohttp/nanohttp-stream.h