371 lines
11 KiB
Python
371 lines
11 KiB
Python
import math
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import os
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from struct import pack, unpack, calcsize
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from typing import BinaryIO, Dict, Iterable, List, Optional, Tuple, Union, cast
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# segment structure base
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SEG_STRUCT = [
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(">L", "number"),
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(">B", "flags"),
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(">B", "retention_flags"),
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(">B", "page_assoc"),
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(">L", "data_length"),
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]
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# segment header literals
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HEADER_FLAG_DEFERRED = 0b10000000
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HEADER_FLAG_PAGE_ASSOC_LONG = 0b01000000
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SEG_TYPE_MASK = 0b00111111
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REF_COUNT_SHORT_MASK = 0b11100000
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REF_COUNT_LONG_MASK = 0x1fffffff
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REF_COUNT_LONG = 7
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DATA_LEN_UNKNOWN = 0xffffffff
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# segment types
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SEG_TYPE_IMMEDIATE_GEN_REGION = 38
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SEG_TYPE_END_OF_PAGE = 49
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SEG_TYPE_END_OF_FILE = 50
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# file literals
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FILE_HEADER_ID = b'\x97\x4A\x42\x32\x0D\x0A\x1A\x0A'
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FILE_HEAD_FLAG_SEQUENTIAL = 0b00000001
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FILE_HEAD_FLAG_PAGES_UNKNOWN = 0b00000010
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def bit_set(bit_pos: int, value: int) -> bool:
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return bool((value >> bit_pos) & 1)
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def check_flag(flag: int, value: int) -> bool:
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return bool(flag & value)
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def masked_value(mask: int, value: int) -> int:
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for bit_pos in range(0, 31):
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if bit_set(bit_pos, mask):
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return (value & mask) >> bit_pos
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raise Exception("Invalid mask or value")
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def mask_value(mask: int, value: int) -> int:
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for bit_pos in range(0, 31):
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if bit_set(bit_pos, mask):
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return (value & (mask >> bit_pos)) << bit_pos
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raise Exception("Invalid mask or value")
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def unpack_int(format: str, buffer: bytes) -> int:
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assert format in {">B", ">I", ">L"}
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[result] = cast(Tuple[int], unpack(format, buffer))
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return result
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JBIG2SegmentFlags = Dict[str, Union[int, bool]]
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JBIG2RetentionFlags = Dict[str, Union[int, List[int], List[bool]]]
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JBIG2Segment = Dict[str, Union[bool, int, bytes, JBIG2SegmentFlags,
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JBIG2RetentionFlags]]
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class JBIG2StreamReader:
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"""Read segments from a JBIG2 byte stream"""
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def __init__(self, stream: BinaryIO) -> None:
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self.stream = stream
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def get_segments(self) -> List[JBIG2Segment]:
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segments: List[JBIG2Segment] = []
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while not self.is_eof():
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segment: JBIG2Segment = {}
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for field_format, name in SEG_STRUCT:
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field_len = calcsize(field_format)
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field = self.stream.read(field_len)
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if len(field) < field_len:
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segment["_error"] = True
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break
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value = unpack_int(field_format, field)
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parser = getattr(self, "parse_%s" % name, None)
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if callable(parser):
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value = parser(segment, value, field)
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segment[name] = value
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if not segment.get("_error"):
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segments.append(segment)
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return segments
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def is_eof(self) -> bool:
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if self.stream.read(1) == b'':
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return True
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else:
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self.stream.seek(-1, os.SEEK_CUR)
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return False
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def parse_flags(
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self,
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segment: JBIG2Segment,
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flags: int,
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field: bytes
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) -> JBIG2SegmentFlags:
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return {
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"deferred": check_flag(HEADER_FLAG_DEFERRED, flags),
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"page_assoc_long": check_flag(HEADER_FLAG_PAGE_ASSOC_LONG, flags),
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"type": masked_value(SEG_TYPE_MASK, flags)
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}
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def parse_retention_flags(
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self,
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segment: JBIG2Segment,
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flags: int,
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field: bytes
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) -> JBIG2RetentionFlags:
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ref_count = masked_value(REF_COUNT_SHORT_MASK, flags)
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retain_segments = []
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ref_segments = []
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if ref_count < REF_COUNT_LONG:
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for bit_pos in range(5):
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retain_segments.append(bit_set(bit_pos, flags))
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else:
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field += self.stream.read(3)
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ref_count = unpack_int(">L", field)
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ref_count = masked_value(REF_COUNT_LONG_MASK, ref_count)
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ret_bytes_count = int(math.ceil((ref_count + 1) / 8))
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for ret_byte_index in range(ret_bytes_count):
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ret_byte = unpack_int(">B", self.stream.read(1))
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for bit_pos in range(7):
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retain_segments.append(bit_set(bit_pos, ret_byte))
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seg_num = segment["number"]
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assert isinstance(seg_num, int)
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if seg_num <= 256:
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ref_format = ">B"
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elif seg_num <= 65536:
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ref_format = ">I"
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else:
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ref_format = ">L"
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ref_size = calcsize(ref_format)
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for ref_index in range(ref_count):
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ref_data = self.stream.read(ref_size)
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ref = unpack_int(ref_format, ref_data)
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ref_segments.append(ref)
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return {
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"ref_count": ref_count,
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"retain_segments": retain_segments,
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"ref_segments": ref_segments,
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}
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def parse_page_assoc(
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self,
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segment: JBIG2Segment,
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page: int,
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field: bytes
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) -> int:
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if cast(JBIG2SegmentFlags, segment["flags"])["page_assoc_long"]:
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field += self.stream.read(3)
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page = unpack_int(">L", field)
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return page
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def parse_data_length(
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self,
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segment: JBIG2Segment,
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length: int,
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field: bytes
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) -> int:
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if length:
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if (cast(JBIG2SegmentFlags, segment["flags"])["type"] ==
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SEG_TYPE_IMMEDIATE_GEN_REGION) \
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and (length == DATA_LEN_UNKNOWN):
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raise NotImplementedError(
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"Working with unknown segment length "
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"is not implemented yet"
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)
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else:
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segment["raw_data"] = self.stream.read(length)
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return length
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class JBIG2StreamWriter:
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"""Write JBIG2 segments to a file in JBIG2 format"""
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EMPTY_RETENTION_FLAGS: JBIG2RetentionFlags = {
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'ref_count': 0,
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'ref_segments': cast(List[int], []),
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'retain_segments': cast(List[bool], [])
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}
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def __init__(self, stream: BinaryIO) -> None:
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self.stream = stream
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def write_segments(
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self,
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segments: Iterable[JBIG2Segment],
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fix_last_page: bool = True
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) -> int:
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data_len = 0
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current_page: Optional[int] = None
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seg_num: Optional[int] = None
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for segment in segments:
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data = self.encode_segment(segment)
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self.stream.write(data)
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data_len += len(data)
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seg_num = cast(Optional[int], segment["number"])
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if fix_last_page:
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seg_page = cast(int, segment.get("page_assoc"))
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if cast(JBIG2SegmentFlags, segment["flags"])["type"] == \
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SEG_TYPE_END_OF_PAGE:
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current_page = None
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elif seg_page:
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current_page = seg_page
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if fix_last_page and current_page and (seg_num is not None):
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segment = self.get_eop_segment(seg_num + 1, current_page)
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data = self.encode_segment(segment)
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self.stream.write(data)
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data_len += len(data)
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return data_len
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def write_file(
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self,
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segments: Iterable[JBIG2Segment],
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fix_last_page: bool = True
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) -> int:
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header = FILE_HEADER_ID
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header_flags = FILE_HEAD_FLAG_SEQUENTIAL | FILE_HEAD_FLAG_PAGES_UNKNOWN
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header += pack(">B", header_flags)
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self.stream.write(header)
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data_len = len(header)
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data_len += self.write_segments(segments, fix_last_page)
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seg_num = 0
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for segment in segments:
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seg_num = cast(int, segment["number"])
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eof_segment = self.get_eof_segment(seg_num + 1)
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data = self.encode_segment(eof_segment)
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self.stream.write(data)
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data_len += len(data)
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return data_len
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def encode_segment(self, segment: JBIG2Segment) -> bytes:
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data = b''
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for field_format, name in SEG_STRUCT:
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value = segment.get(name)
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encoder = getattr(self, "encode_%s" % name, None)
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if callable(encoder):
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field = encoder(value, segment)
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else:
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field = pack(field_format, value)
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data += field
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return data
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def encode_flags(self, value: JBIG2SegmentFlags, segment: JBIG2Segment
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) -> bytes:
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flags = 0
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if value.get("deferred"):
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flags |= HEADER_FLAG_DEFERRED
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if "page_assoc_long" in value:
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flags |= HEADER_FLAG_PAGE_ASSOC_LONG \
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if value["page_assoc_long"] else flags
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else:
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flags |= HEADER_FLAG_PAGE_ASSOC_LONG \
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if cast(int, segment.get("page", 0)) > 255 else flags
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flags |= mask_value(SEG_TYPE_MASK, value["type"])
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return pack(">B", flags)
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def encode_retention_flags(
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self,
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value: JBIG2RetentionFlags,
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segment: JBIG2Segment
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) -> bytes:
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flags = []
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flags_format = ">B"
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ref_count = value["ref_count"]
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assert isinstance(ref_count, int)
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retain_segments = cast(List[bool], value.get("retain_segments", []))
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if ref_count <= 4:
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flags_byte = mask_value(REF_COUNT_SHORT_MASK, ref_count)
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for ref_index, ref_retain in enumerate(retain_segments):
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flags_byte |= 1 << ref_index
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flags.append(flags_byte)
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else:
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bytes_count = math.ceil((ref_count + 1) / 8)
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flags_format = ">L" + ("B" * bytes_count)
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flags_dword = mask_value(
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REF_COUNT_SHORT_MASK,
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REF_COUNT_LONG
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) << 24
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flags.append(flags_dword)
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for byte_index in range(bytes_count):
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ret_byte = 0
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ret_part = retain_segments[byte_index * 8:byte_index * 8 + 8]
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for bit_pos, ret_seg in enumerate(ret_part):
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ret_byte |= 1 << bit_pos if ret_seg else ret_byte
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flags.append(ret_byte)
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ref_segments = cast(List[int], value.get("ref_segments", []))
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seg_num = cast(int, segment["number"])
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if seg_num <= 256:
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ref_format = "B"
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elif seg_num <= 65536:
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ref_format = "I"
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else:
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ref_format = "L"
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for ref in ref_segments:
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flags_format += ref_format
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flags.append(ref)
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return pack(flags_format, *flags)
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def encode_data_length(self, value: int, segment: JBIG2Segment) -> bytes:
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data = pack(">L", value)
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data += cast(bytes, segment["raw_data"])
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return data
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def get_eop_segment(
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self,
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seg_number: int,
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page_number: int
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) -> JBIG2Segment:
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return {
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'data_length': 0,
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'flags': {'deferred': False, 'type': SEG_TYPE_END_OF_PAGE},
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'number': seg_number,
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'page_assoc': page_number,
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'raw_data': b'',
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'retention_flags': JBIG2StreamWriter.EMPTY_RETENTION_FLAGS
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}
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def get_eof_segment(self, seg_number: int) -> JBIG2Segment:
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return {
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'data_length': 0,
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'flags': {'deferred': False, 'type': SEG_TYPE_END_OF_FILE},
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'number': seg_number,
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'page_assoc': 0,
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'raw_data': b'',
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'retention_flags': JBIG2StreamWriter.EMPTY_RETENTION_FLAGS
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}
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