Add RSA::private_key_from_pem_cb

use ssl::error::{SslError, StreamError};

use std::ptr;

use std::io::{self, Read, Write};

use libc::c_int;

use libc::{c_int, c_void};

use bn::BigNum;

use bio::MemBio;

use crypto::HashTypeInternals;

use crypto::hash;

use crypto::util::{CallbackState, invoke_passwd_cb};

pub struct RSA(*mut ffi::RSA);

        }

    }

    /// Reads an RSA private key from PEM formatted data and supplies a password callback.

    pub fn private_key_from_pem_cb<R, F>(reader: &mut R, pass_cb: F) -> Result<RSA, SslError>

        where R: Read, F: FnMut(&mut [i8]) -> usize

    {

        let mut cb = CallbackState::new(pass_cb);

        let mut mem_bio = try!(MemBio::new());

        try!(io::copy(reader, &mut mem_bio).map_err(StreamError));

        unsafe {

            let cb_ptr = &mut cb as *mut _ as *mut c_void;

            let rsa = try_ssl_null!(ffi::PEM_read_bio_RSAPrivateKey(mem_bio.get_handle(),

                                                                    ptr::null_mut(),

                                                                    Some(invoke_passwd_cb::<F>),

                                                                    cb_ptr));

            Ok(RSA(rsa))

        }

    }

    /// Writes an RSA private key as unencrypted PEM formatted data

    pub fn private_key_to_pem<W>(&self, writer: &mut W) -> Result<(), SslError>

        where W: Write