Load FITS images from hips2fits server by URL. Using cfitsio fits_open_file, files can be opened over the network using FTP or HTTP protocols by supplying the appropriate URL as the filename.

New protobuf messages REMOTE_FILE_REQUEST and REMOTE_FILE_RESPONSE (containing OPEN_FILE_ACK) will be added to carta-protobuf to support this feature. The request fields will be used to form the proper URL.