How to use the persistence.read_string function in Persistence

if SAVEFILE_HUNK_LOADER != hunk_id:
            input_file.seek(hunk_header_offset, os.SEEK_SET)
            raw_hunk_length = (hunk_payload_offset - hunk_header_offset) + hunk_length
            output_file.write(input_file.read(raw_hunk_length))
            continue

        # Write the as yet to be updated header.
        persistence.write_uint16(output_file, hunk_id)
        output_file_length_offset = output_file.tell()
        persistence.write_uint32(output_file, 0)
        output_file_payload_offset = output_file.tell()
        persistence.write_uint16(output_file, SNAPSHOT_HUNK_VERSIONS[SAVEFILE_HUNK_LOADER] + 1)

        # Transform the hunk from input file to output file.
        persistence.write_string(output_file, persistence.read_string(input_file)) # loader_system_name
        data_size = persistence.read_uint32(input_file)
        persistence.write_uint32(output_file, data_size) # loader_segments
        output_file.write(input_file.read(data_size))
        set_value = persistence.read_set_of_uint32s(input_file)
        persistence.write_dict_uint32_to_list_of_uint32s(output_file, { k: [] for k in set_value }) # loader_relocated_addresses
        set_value = persistence.read_set_of_uint32s(input_file)
        persistence.write_set_of_uint32s(output_file, set_value) # loader_relocatable_addresses
        persistence.write_uint16(output_file, persistence.read_uint16(input_file)) # loader_entrypoint_segment_id
        persistence.write_int32(output_file, persistence.read_uint32(input_file)) # loader_entrypoint_offset

        # Update the header length field, then fast forward to the end of the hunk.
        new_hunk_length = output_file.tell() - output_file_payload_offset
        output_file.seek(output_file_length_offset, os.SEEK_SET)
        persistence.write_uint32(output_file, new_hunk_length)
        output_file.seek(new_hunk_length, os.SEEK_CUR)

bytes_to_read = struct.calcsize(SEGMENTBLOCK_PACK_FORMAT)
    block.segment_id, block.segment_offset, block.address, block.length, block.flags, block.line_count, line_data_count = struct.unpack(SEGMENTBLOCK_PACK_FORMAT, f.read(bytes_to_read))

    if line_data_count > 0:
        if get_block_data_type(block) == DATA_TYPE_CODE:
            block.line_data = [ None ] * line_data_count
            for i in range(line_data_count):
                type_id = persistence.read_uint8(f)
                if type_id == SLD_INSTRUCTION:
                    block_offset = persistence.read_uint16(f)
                    block.line_data[i] = (type_id, block_offset)
                elif type_id == SLD_EQU_LOCATION_RELATIVE:
                    block_offset = persistence.read_uint32(f)
                    block.line_data[i] = (type_id, block_offset)
                elif type_id in (SLD_COMMENT_TRAILING, SLD_COMMENT_FULL_LINE):
                    text = persistence.read_string(f)
                    block.line_data[i] = (type_id, text)
    return block

logger.debug("convert_project_format_3_to_4: file hunk %d", hunk_id)

        # Copy unaffected hunks verbatim.
        if hunk_id != SAVEFILE_HUNK_DISASSEMBLY:
            input_file.seek(hunk_header_offset, os.SEEK_SET)
            raw_hunk_length = (hunk_payload_offset - hunk_header_offset) + hunk_length
            output_file.write(input_file.read(raw_hunk_length))
            continue

        ## 1. Load the hunk payload.
        branch_addresses = persistence.read_dict_uint32_to_set_of_uint32s(input_file)
        reference_addresses = persistence.read_dict_uint32_to_set_of_uint32s(input_file)
        symbols_by_address = persistence.read_dict_uint32_to_string(input_file)
        post_segment_addresses = persistence.read_dict_uint32_to_list_of_uint32s(input_file)
        flags = persistence.read_uint32(input_file)
        processor_name = persistence.read_string(input_file)

        # Reconstitute the segment block list.
        num_blocks = persistence.read_uint32(input_file)
        input_file_offset = input_file.tell()
        block_data_length = hunk_length - (input_file_offset - hunk_payload_offset)
        block_data_string = input_file.read(block_data_length)
        #blocks = [ None ] * num_blocks
        #for i in range(num_blocks):
        #    blocks[i] = read_SegmentBlock(input_file)
        ## 2. Write the generic hunk header, then the payload, then fill in the header.

        # Only these two are likely to have been in use.
        if processor_name == "m68k":
            processor_id = loaderlib.constants.PROCESSOR_M680x0
        elif processor_name == "mips":
            processor_id = loaderlib.constants.PROCESSOR_MIPS

def load_loader_hunk(f, program_data):
    program_data.loader_system_name = persistence.read_string(f)
    program_data.loader_segments = read_segment_list(f)
    program_data.loader_relocated_addresses = persistence.read_dict_uint32_to_set_of_uint32s(f)
    program_data.loader_relocatable_addresses = persistence.read_set_of_uint32s(f)
    program_data.loader_entrypoint_segment_id = persistence.read_uint16(f)
    program_data.loader_entrypoint_offset = persistence.read_uint32(f)

    ## POST PROCESSING
    program_data.loader_data_types = loaderlib.get_system_data_types(program_data.loader_system_name)