introduce safety and a particular EncryptHelper

src/wrapmime.rs

@@ -78,8 +78,8 @@ pub fn append_ct_param(
     value: &str,
 ) -> Result<(), Error> {
     unsafe {
-        let name_c = CString::new(name).unwrap().as_ptr();
-        let value_c = CString::new(value).unwrap().as_ptr();
+        let name_c = name.strdup();
+        let value_c = value.strdup();
 
         clist_append!(
             (*content).ct_parameters,
@@ -88,6 +88,8 @@ pub fn append_ct_param(
                 value_c as *const u8 as *const libc::c_char as *mut libc::c_char
             )
         );
+        libc::free(name_c as *mut libc::c_void);
+        libc::free(value_c as *mut libc::c_void);
     }
     Ok(())
 }