upload.py

    # Is dataset an image?
    image = check_image( dataset.path )
    if image:
        if not PIL:
            image = None
        # get_image_ext() returns None if nor a supported Image type
        ext = get_image_ext( dataset.path, image )
        data_type = ext
    # Is dataset content multi-byte?
    elif dataset.is_multi_byte:
        data_type = 'multi-byte char'
        ext = sniff.guess_ext( dataset.path, is_multi_byte=True )
    # Is dataset content supported sniffable binary?
    else:
        type_info = Binary.is_sniffable_binary( dataset.path )
        if type_info:
            data_type = type_info[0]
            ext = type_info[1]
    if not data_type:
        # See if we have a gzipped file, which, if it passes our restrictions, we'll uncompress
        is_gzipped, is_valid = check_gzip( dataset.path )
        if is_gzipped and not is_valid:
            file_err( 'The gzipped uploaded file contains inappropriate content', dataset, json_file )
            return