82 lines
2.8 KiB
Python
82 lines
2.8 KiB
Python
"""Fixed-size regular-file transfer; callers retain durability and byte readback."""
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import errno
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import os
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import stat
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import time
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from typing import BinaryIO
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from .policy import MAX_FILE_BYTES, DeliveryError
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CHUNK = 1024 * 1024
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UNSUPPORTED = {errno.ENOSYS, errno.EINVAL, errno.EOPNOTSUPP, errno.EXDEV}
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def _identity(info: os.stat_result) -> tuple[int, ...]:
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return (
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info.st_dev,
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info.st_ino,
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info.st_mode,
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info.st_nlink,
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info.st_uid,
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info.st_gid,
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info.st_size,
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info.st_mtime_ns,
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info.st_ctime_ns,
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)
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def transfer(
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incoming: BinaryIO, outgoing: BinaryIO, expected_bytes: int, *, deadline: float | None = None
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) -> None:
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"""Use fresh streams; unsupported kernel transfer resumes at the same offsets."""
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source, target = incoming.fileno(), outgoing.fileno()
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before = os.fstat(source)
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destination = os.fstat(target)
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if (
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type(expected_bytes) is not int
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or not 0 <= expected_bytes <= MAX_FILE_BYTES
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or not stat.S_ISREG(before.st_mode)
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or before.st_nlink != 1
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or before.st_size != expected_bytes
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or not stat.S_ISREG(destination.st_mode)
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or destination.st_nlink != 1
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or destination.st_size != 0
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or incoming.tell() != 0
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or outgoing.tell() != 0
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or os.lseek(source, 0, os.SEEK_CUR) != 0
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or os.lseek(target, 0, os.SEEK_CUR) != 0
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):
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raise DeliveryError("fixed-size regular copy input or fresh destination differs")
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def remaining() -> None:
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if deadline is not None and time.monotonic() >= deadline:
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raise DeliveryError("copy deadline exceeded; private partial target retained")
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total = 0
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kernel = hasattr(os, "sendfile")
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while total < expected_bytes:
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remaining()
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maximum = min(CHUNK, expected_bytes - total)
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if kernel:
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try:
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# Linux None advances the source offset, including a copied prefix
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# before falling back. Each call stays within the verified size.
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count = os.sendfile(target, source, None, maximum)
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except OSError as error:
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if error.errno not in UNSUPPORTED:
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raise
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kernel = False
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continue
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else:
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data = incoming.read(maximum)
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count = len(data)
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if count and outgoing.write(data) != count:
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raise DeliveryError("short copy write; private partial target retained")
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if not 0 < count <= maximum:
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raise DeliveryError("copy input bytes differ; private partial target retained")
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total += count
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remaining()
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if incoming.read(1) or _identity(os.fstat(source)) != _identity(before):
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raise DeliveryError("copy input changed; private partial target retained")
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