deelevate 0.1.0

Drop privileges on Windows
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use crate::psuedocon::HPCON;
use crate::win32_error_with_context;
use std::io::{Error as IoError, Result as IoResult};
use std::mem;
use std::ptr;
use winapi::shared::minwindef::DWORD;
use winapi::um::processthreadsapi::*;

const PROC_THREAD_ATTRIBUTE_PSEUDOCONSOLE: usize = 0x00020016;

pub struct ProcThreadAttributeList {
    data: Vec<u8>,
}

impl ProcThreadAttributeList {
    pub fn with_capacity(num_attributes: DWORD) -> IoResult<Self> {
        let mut bytes_required: usize = 0;
        unsafe {
            InitializeProcThreadAttributeList(
                ptr::null_mut(),
                num_attributes,
                0,
                &mut bytes_required,
            )
        };
        let mut data = Vec::with_capacity(bytes_required);
        // We have the right capacity, so force the vec to consider itself
        // that length.  The contents of those bytes will be maintained
        // by the win32 apis used in this impl.
        unsafe { data.set_len(bytes_required) };

        let attr_ptr = data.as_mut_slice().as_mut_ptr() as *mut _;
        let res = unsafe {
            InitializeProcThreadAttributeList(attr_ptr, num_attributes, 0, &mut bytes_required)
        };
        if res == 0 {
            Err(win32_error_with_context(
                "InitializeProcThreadAttributeList failed",
                IoError::last_os_error(),
            ))
        } else {
            Ok(Self { data })
        }
    }

    pub fn as_mut_ptr(&mut self) -> LPPROC_THREAD_ATTRIBUTE_LIST {
        self.data.as_mut_slice().as_mut_ptr() as *mut _
    }

    pub fn set_pty(&mut self, con: HPCON) -> IoResult<()> {
        let res = unsafe {
            UpdateProcThreadAttribute(
                self.as_mut_ptr(),
                0,
                PROC_THREAD_ATTRIBUTE_PSEUDOCONSOLE,
                con,
                mem::size_of::<HPCON>(),
                ptr::null_mut(),
                ptr::null_mut(),
            )
        };
        if res == 0 {
            Err(win32_error_with_context(
                "UpdateProcThreadAttribute failed",
                IoError::last_os_error(),
            ))
        } else {
            Ok(())
        }
    }
}

impl Drop for ProcThreadAttributeList {
    fn drop(&mut self) {
        unsafe { DeleteProcThreadAttributeList(self.as_mut_ptr()) };
    }
}