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"""For internal use only. It provides a slice-like file reader."""
import os
from typing import Union
try:
# pylint: disable=no-name-in-module
from multiprocessing import Lock
except ImportError:
from threading import Lock # type: ignore
class FileBuffer:
"""A slice-able file reader"""
def __init__(self, database: str) -> None:
# pylint: disable=consider-using-with
self._handle = open(database, "rb")
self._size = os.fstat(self._handle.fileno()).st_size
if not hasattr(os, "pread"):
self._lock = Lock()
def __getitem__(self, key: Union[slice, int]):
if isinstance(key, slice):
return self._read(key.stop - key.start, key.start)
if isinstance(key, int):
return self._read(1, key)[0]
raise TypeError("Invalid argument type.")
def rfind(self, needle: bytes, start: int) -> int:
"""Reverse find needle from start"""
pos = self._read(self._size - start - 1, start).rfind(needle)
if pos == -1:
return pos
return start + pos
def size(self) -> int:
"""Size of file"""
return self._size
def close(self) -> None:
"""Close file"""
self._handle.close()
if hasattr(os, "pread"):
def _read(self, buffersize: int, offset: int) -> bytes:
"""read that uses pread"""
# pylint: disable=no-member
return os.pread(self._handle.fileno(), buffersize, offset)
else:
def _read(self, buffersize: int, offset: int) -> bytes:
"""read with a lock
This lock is necessary as after a fork, the different processes
will share the same file table entry, even if we dup the fd, and
as such the same offsets. There does not appear to be a way to
duplicate the file table entry and we cannot re-open based on the
original path as that file may have replaced with another or
unlinked.
"""
with self._lock:
self._handle.seek(offset)
return self._handle.read(buffersize)