--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/conv.rs	Thu Mar 05 16:25:10 2015 -0800
@@ -0,0 +1,84 @@
+use libc::{c_char, c_int};
+use std::{ptr};
+use std::ffi::{CStr, CString};
+
+use constants;
+use constants::*;
+use module::{PamItem, PamResult};
+
+#[allow(missing_copy_implementations)]
+pub enum AppDataPtr {}
+
+#[repr(C)]
+struct PamMessage {
+    msg_style: PamMessageStyle,
+    msg:       *const c_char,
+}
+
+#[repr(C)]
+struct PamResponse {
+    resp: *const c_char,
+    resp_retcode: AlwaysZero,
+}
+
+/// `PamConv` acts as a channel for communicating with user.
+///
+/// Communication is mediated by the pam client (the application that invoked
+/// pam).  Messages sent will be relayed to the user by the client, and response
+/// will be relayed back.
+#[repr(C)]
+pub struct PamConv {
+    conv: extern fn(num_msg: c_int,
+                    pam_message: &&PamMessage,
+                    pam_response: &*mut PamResponse,
+                    appdata_ptr: *const AppDataPtr
+                   ) -> PamResultCode,
+    appdata_ptr: *const AppDataPtr,
+}
+
+impl PamConv {
+    /// Sends a message to the pam client.
+    ///
+    /// This will typically result in the user seeing a message or a prompt.
+    /// There are several message styles available:
+    ///
+    /// - PAM_PROMPT_ECHO_OFF
+    /// - PAM_PROMPT_ECHO_ON
+    /// - PAM_ERROR_MSG
+    /// - PAM_TEXT_INFO
+    /// - PAM_RADIO_TYPE
+    /// - PAM_BINARY_PROMPT
+    ///
+    /// Note that the user experience will depend on how the client implements
+    /// these message styles - and not all applications implement all message
+    /// styles.
+    pub fn send(&self, style: PamMessageStyle, msg: &str) -> PamResult<Option<String>> {
+        let resp_ptr: *mut PamResponse = ptr::null_mut();
+        let msg = PamMessage {
+            msg_style: style,
+            msg: CString::new(msg).unwrap().as_ptr(),
+        };
+
+        let ret = (self.conv)(1, &&msg, &resp_ptr, self.appdata_ptr);
+
+        if constants::PAM_SUCCESS == ret {
+            let s = unsafe { resp_ptr.as_ref() }
+            .and_then(|r| {
+                if r.resp.is_null() {
+                    None
+                }
+                else {
+                    let bytes = unsafe { CStr::from_ptr(r.resp).to_bytes() };
+                    String::from_utf8(bytes.to_vec()).ok()
+                }
+            });
+            Ok(s)
+        } else {
+            Err(ret)
+        }
+    }
+}
+
+impl PamItem for PamConv {
+    fn item_type(_: Option<Self>) -> PamItemType { PAM_CONV }
+}