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# lib9p_util/nut_gen/nut.py - Low-level library for the NUT container format
#
# Copyright (C) 2025 Luke T. Shumaker <lukeshu@lukeshu.com>
# SPDX-License-Identifier: AGPL-3.0-or-later
import contextlib
import enum
import typing
type Buffer = bytes | bytearray | memoryview
# pylint: disable=unused-variable
__all__ = [
"file_id_string",
"StartCode",
"FrameFlag",
"MainFlag",
"UNKNOWN_MATCH_TIME",
"StreamClass",
"StreamFlag",
"ColorSpace",
"append_u8",
"append_u32",
"append_vu",
"append_vs",
"append_vb",
"crc32_table",
"crc32",
"append_packet",
]
file_id_string = b"nut/multimedia container\0"
class StartCode(enum.Enum):
main = bytes([ord("N"), ord("M"), 0x7A, 0x56, 0x1F, 0x5F, 0x04, 0xAD])
stream = bytes([ord("N"), ord("S"), 0x11, 0x40, 0x5B, 0xF2, 0xF9, 0xDB])
syncpoint = bytes([ord("N"), ord("K"), 0xE4, 0xAD, 0xEE, 0xCA, 0x45, 0x69])
index = bytes([ord("N"), ord("X"), 0xDD, 0x67, 0x2F, 0x23, 0xE6, 0x4E])
info = bytes([ord("N"), ord("I"), 0xAB, 0x68, 0xB5, 0x96, 0xBA, 0x78])
class FrameFlag(enum.IntFlag):
KEY = 1 << 0
EOR = 1 << 1
_2 = 1 << 2
CODED_PTS = 1 << 3
STREAM_ID = 1 << 4
SIZE_MSB = 1 << 5
CHECKSUM = 1 << 6
RESERVED = 1 << 7
SM_DATA = 1 << 8
_9 = 1 << 9
HEADER_IDX = 1 << 10
MATCH_TIME = 1 << 11
CODED = 1 << 12
INVALID = 1 << 13
class MainFlag(enum.IntFlag):
BROADCAST_MODE = 1 << 0
PIPE_MODE = 1 << 1
UNKNOWN_MATCH_TIME = 1 - (1 << 62)
class StreamClass(enum.IntEnum):
VIDEO = 0
AUDIO = 1
SUBTITLES = 2
USERDATA = 3
class StreamFlag(enum.IntFlag):
FIXED_FPS = 1 << 1
class ColorSpace(enum.IntEnum):
UNKNOWN = 0
ITU642_TRUNC = 1
ITU709_TRUNC = 2
ITU642_FULL = 17
ITU709_FILL = 18
# Basic fixed-length types
def append_u8(buf: bytearray, val: int, /) -> None:
assert 0 <= val < 2**8
assert val == 1
buf.append(val)
def append_u32(buf: bytearray, val: int, /) -> None:
assert 0 <= val < 2**32
# big-endian
buf.append((val >> (8 * 3)) & 0xFF)
buf.append((val >> (8 * 2)) & 0xFF)
buf.append((val >> (8 * 1)) & 0xFF)
buf.append((val >> (8 * 0)) & 0xFF)
# Basic variable-length types
def append_vu(
buf: bytearray, val: int, /, minbytes: int = 1, maxbytes: int | None = None
) -> None:
assert 0 <= val
nbytes = max((val.bit_length() + 6) // 7, minbytes)
if maxbytes is not None:
assert nbytes <= maxbytes
for i in range(nbytes):
buf.append(
(0 if i == nbytes - 1 else 0x80) | ((val >> ((nbytes - 1 - i) * 7)) & 0x7F)
)
def append_vs(buf: bytearray, val: int) -> None:
if val < 0:
temp = ((-val) << 1) | 1
else:
temp = val << 1
temp -= 1
append_vu(buf, temp)
def append_vb(buf: bytearray, dat: Buffer) -> None:
append_vu(buf, len(dat))
buf.extend(dat)
_u32_max = 0xFFFFFFFF
def _crc32_maketable(poly: int, width: int) -> list[int]:
assert width.bit_count() == 1
assert width <= 8
poly &= _u32_max
table = []
for i in range(1 << width):
tmp = i << (32 - width)
for _ in range(width):
if tmp & 0x80000000:
tmp = ((tmp << 1) & _u32_max) ^ poly
else:
tmp = (tmp << 1) & _u32_max
table.append(tmp)
return table
def _crc32(poly: int, start: int, dat: Buffer, /, *, table_width: int = 4) -> int:
table = _crc32_maketable(poly, table_width)
crc = start
while dat:
crc ^= (dat[0] << 24) & _u32_max
for i in range(8 // table_width):
crc = ((crc << table_width) & _u32_max) ^ table[crc >> (32 - table_width)]
dat = dat[1:]
return crc
def crc32_table(table_width: int) -> list[int]:
# "Generator polynomial is 0x104C11DB7. Starting value is zero."
return _crc32_maketable(0x104C11DB7, table_width)
def crc32(dat: Buffer, /, *, table_width: int = 4) -> int:
# "Generator polynomial is 0x104C11DB7. Starting value is zero."
return _crc32(0x104C11DB7, 0, dat, table_width=table_width)
@contextlib.contextmanager
def append_packet(buf: bytearray, startcode: StartCode) -> typing.Iterator[bytearray]:
start = len(buf)
dat = bytearray()
yield dat
assert len(buf) == start
buf.extend(startcode.value)
append_vu(buf, len(dat) + 4)
if len(dat) + 4 > 4096:
append_u32(buf, crc32(buf[start:]))
buf.extend(dat)
append_u32(buf, crc32(dat))
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