readFilePositionalWindows

fn readFilePositionalWindows(file: File, buffer: []u8, offset: u64) File.ReadPositionalError!usize {
    var iosb: windows.IO_STATUS_BLOCK = undefined;
    const short_buffer_len = std.math.lossyCast(u32, buffer.len);
    const signed_offset: windows.LARGE_INTEGER = @intCast(offset);
    if (file.flags.nonblocking) {
        var done: bool = false;
        switch (windows.ntdll.NtReadFile(
            file.handle,
            null, // event
            flagApc,
            &done, // APC context
            &iosb,
            buffer.ptr,
            short_buffer_len,
            &signed_offset,
            null, // key
        )) {
            // We must wait for the APC routine.
            .PENDING, .SUCCESS => while (!done) {
                // Once we get here we must not return from the function until the
                // operation completes, thereby releasing reference to the iosb.
                const alertable_syscall = AlertableSyscall.start() catch |err| switch (err) {
                    error.Canceled => |e| {
                        var cancel_iosb: windows.IO_STATUS_BLOCK = undefined;
                        _ = windows.ntdll.NtCancelIoFileEx(file.handle, &iosb, &cancel_iosb);
                        while (!done) waitForApcOrAlert();
                        return e;
                    },
                };
                waitForApcOrAlert();
                alertable_syscall.finish();
            },
            else => |status| iosb.u.Status = status,
        }
    } else {
        const syscall: Syscall = try .start();
        while (true) switch (windows.ntdll.NtReadFile(
            file.handle,
            null, // event
            null, // APC routine
            null, // APC context
            &iosb,
            buffer.ptr,
            short_buffer_len,
            &signed_offset,
            null, // key
        )) {
            .PENDING => unreachable, // unrecoverable: wrong File nonblocking flag
            .CANCELLED => try syscall.checkCancel(),
            else => |status| {
                syscall.finish();
                iosb.u.Status = status;
                break;
            },
        };
    }
    return ntReadFileResult(&iosb) catch |err| switch (err) {
        error.EndOfStream => 0,
        else => |e| e,
    };
}