esp-idf/components/fatfs/fatfs_utils/long_filename_utils.py

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# SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
# SPDX-License-Identifier: Apache-2.0
from typing import List
from .entry import Entry
from .utils import convert_to_utf16_and_pad
# File name with long filenames support can be as long as memory allows. It is split into entries
# holding 13 characters of the filename, thus the number of required entries is ceil(len(long_name) / 13).
# This is computed using `get_required_lfn_entries_count`.
# For creating long name entries we need to split the name by 13 characters using `split_name_to_lfn_entries`
# and in every entry into three blocks with sizes 5, 6 and 2 characters using `split_name_to_lfn_entry`.
def get_required_lfn_entries_count(lfn_full_name: str) -> int:
"""
Compute the number of entries required to store the long name.
One long filename entry can hold 13 characters with size 2 bytes.
E.g. "thisisverylongfilenama.txt" with length of 26 needs 2 lfn entries,
but "thisisverylongfilenamax.txt" with 27 characters needs 3 lfn entries.
"""
entries_count: int = (len(lfn_full_name) + Entry.CHARS_PER_ENTRY - 1) // Entry.CHARS_PER_ENTRY
return entries_count
def split_name_to_lfn_entries(name: str, entries: int) -> List[str]:
"""
If the filename is longer than 8 (name) + 3 (extension) characters,
generator uses long name structure and splits the name into suitable amount of blocks.
E.g. 'thisisverylongfilenama.txt' would be split to ['THISISVERYLON', 'GFILENAMA.TXT'],
in case of 'thisisverylongfilenamax.txt' - ['THISISVERYLON', 'GFILENAMAX.TX', 'T']
"""
return [name[i * Entry.CHARS_PER_ENTRY:(i + 1) * Entry.CHARS_PER_ENTRY] for i in range(entries)]
def split_name_to_lfn_entry_blocks(name: str) -> List[bytes]:
"""
Filename is divided into three blocks in every long file name entry. Sizes of the blocks are defined
by LDIR_Name1_SIZE, LDIR_Name2_SIZE and LDIR_Name3_SIZE, thus every block contains LDIR_Name{X}_SIZE * 2 bytes.
If the filename ends in one of the blocks, it is terminated by zero encoded to two bytes (0x0000). Other unused
characters are set to 0xFFFF.
E.g.:
'GFILENAMA.TXT' -> [b'G\x00F\x00I\x00L\x00E\x00', b'N\x00A\x00M\x00A\x00.\x00T\x00', b'X\x00T\x00'];
'T' -> [b'T\x00\x00\x00\xff\xff\xff\xff\xff\xff', b'\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff',
b'\xff\xff\xff\xff']
Notice that since every character is coded using 2 bytes be must add 0x00 to ASCII symbols ('G' -> 'G\x00', etc.),
since character 'T' ends in the first block, we must add '\x00\x00' after 'T\x00'.
"""
max_entry_size: int = Entry.LDIR_Name1_SIZE + Entry.LDIR_Name2_SIZE + Entry.LDIR_Name2_SIZE
assert len(name) <= max_entry_size
blocks_: List[bytes] = [
convert_to_utf16_and_pad(content=name[:Entry.LDIR_Name1_SIZE],
expected_size=Entry.LDIR_Name1_SIZE),
convert_to_utf16_and_pad(content=name[Entry.LDIR_Name1_SIZE:Entry.LDIR_Name1_SIZE + Entry.LDIR_Name2_SIZE],
expected_size=Entry.LDIR_Name2_SIZE),
convert_to_utf16_and_pad(content=name[Entry.LDIR_Name1_SIZE + Entry.LDIR_Name2_SIZE:],
expected_size=Entry.LDIR_Name3_SIZE)
]
return blocks_
def build_lfn_unique_entry_name_order(entities: list, lfn_entry_name: str) -> int:
"""
The short entry contains only the first 6 characters of the file name,
and we have to distinguish it from other names within the directory starting with the same 6 characters.
To make it unique, we add its order in relation to other names such that lfn_entry_name[:6] == other[:6].
The order is specified by the character, starting with '1'.
E.g. the file in directory 'thisisverylongfilenama.txt' will be named 'THISIS~1TXT' in its short entry.
If we add another file 'thisisverylongfilenamax.txt' its name in the short entry will be 'THISIS~2TXT'.
"""
preceding_entries: int = 0
for entity in entities:
if entity.name[:6] == lfn_entry_name[:6]:
preceding_entries += 1
return preceding_entries + ord('1')
def build_lfn_full_name(name: str, extension: str) -> str:
"""
The extension is optional, and the long filename entry explicitly specifies it,
on the opposite as for short file names.
"""
return f'{name}.{extension}' if len(extension) > 0 else name