--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/libpam/message.rs	Fri Jun 06 22:35:08 2025 -0400
@@ -0,0 +1,334 @@
+//! Data and types dealing with PAM messages.
+
+use crate::constants::InvalidEnum;
+use crate::conv::Message;
+use crate::libpam::memory;
+use crate::libpam::memory::{CBinaryData, Immovable, NulError, TooBigError};
+use num_derive::FromPrimitive;
+use num_traits::FromPrimitive;
+use std::ffi::{c_int, c_void, CStr};
+use std::result::Result as StdResult;
+use std::str::Utf8Error;
+use std::{ptr, slice};
+
+#[derive(Debug, thiserror::Error)]
+#[error("error creating PAM message: {0}")]
+pub enum ConversionError {
+    InvalidEnum(#[from] InvalidEnum<Style>),
+    Utf8Error(#[from] Utf8Error),
+    NulError(#[from] NulError),
+    TooBigError(#[from] TooBigError),
+}
+
+/// The C enum values for messages shown to the user.
+#[derive(Debug, PartialEq, FromPrimitive)]
+pub enum Style {
+    /// Requests information from the user; will be masked when typing.
+    PromptEchoOff = 1,
+    /// Requests information from the user; will not be masked.
+    PromptEchoOn = 2,
+    /// An error message.
+    ErrorMsg = 3,
+    /// An informational message.
+    TextInfo = 4,
+    /// Yes/No/Maybe conditionals. A Linux-PAM extension.
+    RadioType = 5,
+    /// For server–client non-human interaction.
+    ///
+    /// NOT part of the X/Open PAM specification.
+    /// A Linux-PAM extension.
+    BinaryPrompt = 7,
+}
+
+impl TryFrom<c_int> for Style {
+    type Error = InvalidEnum<Self>;
+    fn try_from(value: c_int) -> StdResult<Self, Self::Error> {
+        Self::from_i32(value).ok_or(value.into())
+    }
+}
+
+impl From<Style> for c_int {
+    fn from(val: Style) -> Self {
+        val as Self
+    }
+}
+
+/// A message sent by PAM or a module to an application.
+/// This message, and its internal data, is owned by the creator
+/// (either the module or PAM itself).
+#[repr(C)]
+pub struct RawMessage {
+    /// The style of message to request.
+    style: c_int,
+    /// A description of the data requested.
+    ///
+    /// For most requests, this will be an owned [`CStr`], but for requests
+    /// with [`Style::BinaryPrompt`], this will be [`CBinaryData`]
+    /// (a Linux-PAM extension).
+    data: *mut c_void,
+    _marker: Immovable,
+}
+
+impl RawMessage {
+    pub fn set(&mut self, msg: Message) -> StdResult<(), ConversionError> {
+        let (style, data) = copy_to_heap(msg)?;
+        self.clear();
+        // SAFETY: We allocated this ourselves or were given it by PAM.
+        // Otherwise, it's null, but free(null) is fine.
+        unsafe { libc::free(self.data) };
+        self.style = style as c_int;
+        self.data = data;
+        Ok(())
+    }
+
+    /// Gets this message's data pointer as a string.
+    ///
+    /// # Safety
+    ///
+    /// It's up to you to pass this only on types with a string value.
+    unsafe fn string_data(&self) -> StdResult<&str, Utf8Error> {
+        if self.data.is_null() {
+            Ok("")
+        } else {
+            CStr::from_ptr(self.data.cast()).to_str()
+        }
+    }
+
+    /// Zeroes out the data stored here.
+    fn clear(&mut self) {
+        // SAFETY: We either created this data or we got it from PAM.
+        // After this function is done, it will be zeroed out.
+        unsafe {
+            if let Ok(style) = Style::try_from(self.style) {
+                match style {
+                    Style::BinaryPrompt => {
+                        if let Some(d) = self.data.cast::<CBinaryData>().as_mut() {
+                            d.zero_contents()
+                        }
+                    }
+                    Style::TextInfo
+                    | Style::RadioType
+                    | Style::ErrorMsg
+                    | Style::PromptEchoOff
+                    | Style::PromptEchoOn => memory::zero_c_string(self.data),
+                }
+            };
+            libc::free(self.data);
+            self.data = ptr::null_mut();
+        }
+    }
+}
+
+/// Copies the contents of this message to the C heap.
+fn copy_to_heap(msg: Message) -> StdResult<(Style, *mut c_void), ConversionError> {
+    let alloc = |style, text| Ok((style, memory::malloc_str(text)?.cast()));
+    match msg {
+        Message::MaskedPrompt(text) => alloc(Style::PromptEchoOff, text),
+        Message::Prompt(text) => alloc(Style::PromptEchoOn, text),
+        Message::RadioPrompt(text) => alloc(Style::RadioType, text),
+        Message::ErrorMsg(text) => alloc(Style::ErrorMsg, text),
+        Message::InfoMsg(text) => alloc(Style::TextInfo, text),
+        Message::BinaryPrompt { data, data_type } => Ok((
+            Style::BinaryPrompt,
+            (CBinaryData::alloc(data, data_type)?).cast(),
+        )),
+    }
+}
+
+/// Abstraction of a list-of-messages to be sent in a PAM conversation.
+///
+/// On Linux-PAM and other compatible implementations, `messages`
+/// is treated as a pointer-to-pointers, like `int argc, char **argv`.
+/// (In this situation, the value of `OwnedMessages.indirect` is
+/// the pointer passed to `pam_conv`.)
+///
+/// ```text
+/// ╔═ OwnedMsgs ═╗  points to  ┌─ Indirect ─┐       ╔═ Message ═╗
+/// ║ indirect ┄┄┄╫┄┄┄┄┄┄┄┄┄┄┄> │ base[0] ┄┄┄┼┄┄┄┄┄> ║ style     ║
+/// ║ count       ║             │ base[1] ┄┄┄┼┄┄┄╮   ║ data      ║
+/// ╚═════════════╝             │ ...        │   ┆   ╚═══════════╝
+///                                              ┆
+///                                              ┆    ╔═ Message ═╗
+///                                              ╰┄┄> ║ style     ║
+///                                                   ║ data      ║
+///                                                   ╚═══════════╝
+/// ```
+///
+/// On OpenPAM and other compatible implementations (like Solaris),
+/// `messages` is a pointer-to-pointer-to-array.  This appears to be
+/// the correct implementation as required by the XSSO specification.
+///
+/// ```text
+/// ╔═ OwnedMsgs ═╗  points to  ┌─ Indirect ─┐       ╔═ Message[] ═╗
+/// ║ indirect ┄┄┄╫┄┄┄┄┄┄┄┄┄┄┄> │ base ┄┄┄┄┄┄┼┄┄┄┄┄> ║ style       ║
+/// ║ count       ║             └────────────┘       ║ data        ║
+/// ╚═════════════╝                                  ╟─────────────╢
+///                                                  ║ style       ║
+///                                                  ║ data        ║
+///                                                  ╟─────────────╢
+///                                                  ║ ...         ║
+/// ```
+///
+/// ***THIS LIBRARY CURRENTLY SUPPORTS ONLY LINUX-PAM.***
+pub struct OwnedMessages {
+    /// An indirection to the messages themselves, stored on the C heap.
+    indirect: *mut MessageIndirector,
+    /// The number of messages in the list.
+    count: usize,
+}
+
+impl OwnedMessages {
+    /// Allocates data to store messages on the C heap.
+    pub fn alloc(count: usize) -> Self {
+        Self {
+            indirect: MessageIndirector::alloc(count),
+            count,
+        }
+    }
+
+    /// The pointer to the thing with the actual list.
+    pub fn indirector(&self) -> *const MessageIndirector {
+        self.indirect
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = &RawMessage> {
+        // SAFETY: we're iterating over an amount we know.
+        unsafe { (*self.indirect).iter(self.count) }
+    }
+
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut RawMessage> {
+        // SAFETY: we're iterating over an amount we know.
+        unsafe { (*self.indirect).iter_mut(self.count) }
+    }
+}
+
+impl Drop for OwnedMessages {
+    fn drop(&mut self) {
+        // SAFETY: We are valid and have a valid pointer.
+        // Once we're done, everything will be safe.
+        unsafe {
+            if let Some(indirect) = self.indirect.as_mut() {
+                indirect.free(self.count)
+            }
+            libc::free(self.indirect.cast());
+            self.indirect = ptr::null_mut();
+        }
+    }
+}
+
+/// An indirect reference to messages.
+///
+/// This is kept separate to provide a place where we can separate
+/// the pointer-to-pointer-to-list from pointer-to-list-of-pointers.
+#[repr(transparent)]
+pub struct MessageIndirector {
+    base: [*mut RawMessage; 0],
+    _marker: Immovable,
+}
+
+impl MessageIndirector {
+    /// Allocates memory for this indirector and all its members.
+    fn alloc(count: usize) -> *mut Self {
+        // SAFETY: We're only allocating, and when we're done,
+        // everything will be in a known-good state.
+        unsafe {
+            let me_ptr: *mut MessageIndirector =
+                libc::calloc(count, size_of::<*mut RawMessage>()).cast();
+            let me = &mut *me_ptr;
+            let ptr_list = slice::from_raw_parts_mut(me.base.as_mut_ptr(), count);
+            for entry in ptr_list {
+                *entry = libc::calloc(1, size_of::<RawMessage>()).cast();
+            }
+            me
+        }
+    }
+
+    /// Returns an iterator yielding the given number of messages.
+    ///
+    /// # Safety
+    ///
+    /// You have to provide the right count.
+    pub unsafe fn iter(&self, count: usize) -> impl Iterator<Item = &RawMessage> {
+        (0..count).map(|idx| &**self.base.as_ptr().add(idx))
+    }
+
+    /// Returns a mutable iterator yielding the given number of messages.
+    ///
+    /// # Safety
+    ///
+    /// You have to provide the right count.
+    pub unsafe fn iter_mut(&mut self, count: usize) -> impl Iterator<Item = &mut RawMessage> {
+        (0..count).map(|idx| &mut **self.base.as_mut_ptr().add(idx))
+    }
+
+    /// Frees this and everything it points to.
+    ///
+    /// # Safety
+    ///
+    /// You have to pass the right size.
+    unsafe fn free(&mut self, count: usize) {
+        let msgs = slice::from_raw_parts_mut(self.base.as_mut_ptr(), count);
+        for msg in msgs {
+            if let Some(msg) = msg.as_mut() {
+                msg.clear();
+            }
+            libc::free(msg.cast());
+            *msg = ptr::null_mut();
+        }
+    }
+}
+
+impl<'a> TryFrom<&'a RawMessage> for Message<'a> {
+    type Error = ConversionError;
+
+    /// Retrieves the data stored in this message.
+    fn try_from(input: &RawMessage) -> StdResult<Message, ConversionError> {
+        let style: Style = input.style.try_into()?;
+        // SAFETY: We either allocated this message ourselves or were provided it by PAM.
+        let result = unsafe {
+            match style {
+                Style::PromptEchoOff => Message::MaskedPrompt(input.string_data()?),
+                Style::PromptEchoOn => Message::Prompt(input.string_data()?),
+                Style::TextInfo => Message::InfoMsg(input.string_data()?),
+                Style::ErrorMsg => Message::ErrorMsg(input.string_data()?),
+                Style::RadioType => Message::ErrorMsg(input.string_data()?),
+                Style::BinaryPrompt => input.data.cast::<CBinaryData>().as_ref().map_or_else(
+                    || Message::BinaryPrompt {
+                        data_type: 0,
+                        data: &[],
+                    },
+                    |data| Message::BinaryPrompt {
+                        data_type: data.data_type(),
+                        data: data.contents(),
+                    },
+                ),
+            }
+        };
+        Ok(result)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::conv::Message;
+    use crate::libpam::message::OwnedMessages;
+
+    #[test]
+    fn test_owned_messages() {
+        let mut tons_of_messages = OwnedMessages::alloc(10);
+        let mut msgs: Vec<_> = tons_of_messages.iter_mut().collect();
+        assert!(msgs.get(10).is_none());
+        let last_msg = &mut msgs[9];
+        last_msg.set(Message::MaskedPrompt("hocus pocus")).unwrap();
+        let another_msg = &mut msgs[0];
+        another_msg
+            .set(Message::BinaryPrompt {
+                data: &[5, 4, 3, 2, 1],
+                data_type: 99,
+            })
+            .unwrap();
+        let overwrite = &mut msgs[3];
+        overwrite.set(Message::Prompt("what")).unwrap();
+        overwrite.set(Message::Prompt("who")).unwrap();
+    }
+}