pwrite.py

# -*- coding: utf-8 -*-
import os

if os.name == "nt":
    import ctypes
    from ctypes import wintypes
    import msvcrt

    INVALID_HANDLE_VALUE = -1

    class _dummy_s(ctypes.Structure):
        _fields_ = [("Offset", wintypes.DWORD), ("OffsetHigh", wintypes.DWORD)]

    class _dummy_u(ctypes.Union):
        _fields_ = [("DUMMYSTRUCTNAME", _dummy_s), ("Pointer", ctypes.c_void_p)]

    class OVERLAPPED(ctypes.Structure):
        _fields_ = [
            ("Internal", ctypes.POINTER(wintypes.ULONG)),
            ("InternalHigh", ctypes.POINTER(wintypes.ULONG)),
            ("DUMMYUNIONNAME", _dummy_u),
            ("hEvent", wintypes.HANDLE),
        ]
        _anonymous_ = ("DUMMYUNIONNAME",)

    WriteFile = ctypes.windll.kernel32.WriteFile
    WriteFile.argtypes = [
        wintypes.HANDLE,
        wintypes.LPCVOID,
        wintypes.DWORD,
        wintypes.LPDWORD,
        ctypes.POINTER(OVERLAPPED),
    ]
    WriteFile.restype = wintypes.BOOL

    def check1(result, func, arg):
        if result == 0:
            raise ctypes.WinError()
        return result

    WriteFile.errcheck = check1

    _get_osfhandle = ctypes.windll.msvcrt._get_osfhandle
    _get_osfhandle.argtypes = [ctypes.c_int]
    _get_osfhandle.restype = ctypes.c_int

    def check2(result, func, arg):
        if result == INVALID_HANDLE_VALUE:
            raise ctypes.WinError()
        return result

    _get_osfhandle.errcheck = check2

    def pwrite(fd: int, data: bytes, offset: int) -> int:
        handle = _get_osfhandle(fd)
        # handle = msvcrt.get_osfhandle(fd)  # fuck, fuck, fuck, what's the difference between these two?
        written = wintypes.DWORD(0)
        overlapped = OVERLAPPED()
        overlapped.DUMMYSTRUCTNAME.OffsetHigh = wintypes.DWORD(offset >> 32)
        overlapped.DUMMYSTRUCTNAME.Offset = wintypes.DWORD(offset)
        WriteFile(
            wintypes.HANDLE(handle),
            ctypes.cast(ctypes.c_char_p(data), wintypes.LPCVOID),
            len(data),
            ctypes.byref(written),
            ctypes.byref(overlapped),
        )
        return written.value

else:
    from os import pwrite  # type: ignore