redoubt-alloc 0.1.0-rc.4

// Copyright (c) 2025-2026 Federico Hoerth <memparanoid@gmail.com>
// SPDX-License-Identifier: GPL-3.0-only
// See LICENSE in the repository root for full license text.

use alloc::vec::Vec;

use crate::error::AllockedVecError;
use redoubt_zero::{
    FastZeroizable, RedoubtZero, ZeroizationProbe, ZeroizeMetadata, ZeroizeOnDropSentinel,
};

/// Test behaviour for injecting failures in `AllockedVec` operations.
///
/// This is only available with the `test-utils` feature and allows users
/// to test error handling paths in their code by injecting failures.
///
/// The behaviour is sticky - once set, it remains active until changed.
///
/// # Example
///
/// ```rust
/// // test-utils feature required in dev-dependencies
/// use redoubt_alloc::{AllockedVec, AllockedVecBehaviour, AllockedVecError};
///
/// #[cfg(test)]
/// mod tests {
///     use super::*;
///
///     #[test]
///     fn test_handles_capacity_exceeded() -> Result<(), AllockedVecError> {
///         let mut vec = AllockedVec::with_capacity(10);
///
///         // Inject failure
///         vec.change_behaviour(AllockedVecBehaviour::FailAtPush);
///
///         // This will fail even though capacity allows it
///         let result = vec.push(1u8);
///         assert!(result.is_err());
///
///         // Reset to normal behaviour
///         vec.change_behaviour(AllockedVecBehaviour::None);
///
///         // Now it works
///         vec.push(1u8)?;
///         Ok(())
///     }
/// }
/// ```
#[cfg(any(test, feature = "test-utils"))]
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum AllockedVecBehaviour {
    /// Normal behaviour - no injected failures.
    #[default]
    None,
    /// Next `push()` call will fail with `CapacityExceeded`.
    FailAtPush,
    /// Next `drain_from()` call will fail with `CapacityExceeded`.
    FailAtDrainFrom,
}

#[cfg(any(test, feature = "test-utils"))]
impl ZeroizationProbe for AllockedVecBehaviour {
    fn is_zeroized(&self) -> bool {
        matches!(self, Self::None)
    }
}

#[cfg(any(test, feature = "test-utils"))]
impl ZeroizeMetadata for AllockedVecBehaviour {
    const CAN_BE_BULK_ZEROIZED: bool = false;
}

#[cfg(any(test, feature = "test-utils"))]
impl FastZeroizable for AllockedVecBehaviour {
    fn fast_zeroize(&mut self) {
        *self = AllockedVecBehaviour::None;
    }
}

/// Allocation-locked Vec that prevents reallocation after sealing.
///
/// Once `reserve_exact()` is called, the vector is sealed and cannot grow beyond
/// that capacity. All operations that would cause reallocation fail and zeroize data.
///
/// # Type Parameters
///
/// - `T`: The element type. Must implement `FastZeroizable`, `ZeroizeMetadata`, and `ZeroizationProbe` for automatic cleanup.
///
/// # Example
///
/// ```rust
/// use redoubt_alloc::{AllockedVec, AllockedVecError};
///
/// fn example() -> Result<(), AllockedVecError> {
///     let mut vec = AllockedVec::new();
///     vec.reserve_exact(5)?;
///
///     vec.push(1u8)?;
///     vec.push(2u8)?;
///
///     assert_eq!(vec.len(), 2);
///     assert_eq!(vec.capacity(), 5);
///     Ok(())
/// }
/// # example().unwrap();
/// ```
#[derive(RedoubtZero)]
#[fast_zeroize(drop)]
#[cfg_attr(any(test, feature = "test-utils"), derive(Clone))]
pub struct AllockedVec<T>
where
    T: FastZeroizable + ZeroizeMetadata + ZeroizationProbe,
{
    inner: Vec<T>,
    has_been_sealed: bool,
    #[cfg(any(test, feature = "test-utils"))]
    behaviour: AllockedVecBehaviour,
    __sentinel: ZeroizeOnDropSentinel,
}

impl<T> core::fmt::Debug for AllockedVec<T>
where
    T: FastZeroizable + ZeroizeMetadata + ZeroizationProbe,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.debug_struct("AllockedVec")
            .field("data", &"REDACTED")
            .field("len", &self.len())
            .field("capacity", &self.capacity())
            .finish()
    }
}

#[cfg(any(test, feature = "test-utils"))]
impl<T: FastZeroizable + ZeroizeMetadata + ZeroizationProbe + PartialEq> PartialEq
    for AllockedVec<T>
{
    fn eq(&self, other: &Self) -> bool {
        // Skip __sentinel (metadata that changes during zeroization)
        // Use `&` instead of `&&` to avoid branches and easier testing.
        (self.inner == other.inner)
            & (self.has_been_sealed == other.has_been_sealed)
            & (self.behaviour == other.behaviour)
    }
}

#[cfg(any(test, feature = "test-utils"))]
impl<T: FastZeroizable + ZeroizeMetadata + Eq + ZeroizationProbe> Eq for AllockedVec<T> {}

impl<T> AllockedVec<T>
where
    T: FastZeroizable + ZeroizeMetadata + ZeroizationProbe,
{
    pub(crate) fn realloc_with<F>(&mut self, capacity: usize, #[allow(unused)] mut hook: F)
    where
        T: Default,
        F: FnMut(&mut Self),
    {
        // No-op if capacity is the same
        if capacity == self.capacity() {
            return;
        }

        // When shrinking, truncate to fit in new capacity
        if capacity < self.capacity() {
            self.truncate(capacity);
        }

        let new_allocked_vec = {
            let mut allocked_vec = AllockedVec::<T>::with_capacity(capacity);
            allocked_vec
                .drain_from(self.as_mut_slice())
                .expect("realloc_with: drain_from cannot fail - new vec has sufficient capacity");
            allocked_vec
        };

        #[cfg(test)]
        hook(self);

        self.fast_zeroize();

        #[cfg(test)]
        hook(self);

        *self = new_allocked_vec;
    }

    /// Creates a new empty `AllockedVec` with zero capacity.
    ///
    /// The vector is not sealed until `reserve_exact()` is called.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::AllockedVec;
    ///
    /// let vec: AllockedVec<u8> = AllockedVec::new();
    /// assert_eq!(vec.len(), 0);
    /// assert_eq!(vec.capacity(), 0);
    /// ```
    pub fn new() -> Self {
        Self {
            inner: Vec::new(),
            has_been_sealed: false,
            #[cfg(any(test, feature = "test-utils"))]
            behaviour: AllockedVecBehaviour::default(),
            __sentinel: ZeroizeOnDropSentinel::default(),
        }
    }

    /// Creates a new `AllockedVec` with the specified capacity and seals it immediately.
    ///
    /// This is equivalent to calling `new()` followed by `reserve_exact(capacity)`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::AllockedVec;
    ///
    /// let mut vec = AllockedVec::<u8>::with_capacity(10);
    /// assert_eq!(vec.len(), 0);
    /// assert_eq!(vec.capacity(), 10);
    /// // Already sealed - cannot reserve again
    /// assert!(vec.reserve_exact(20).is_err());
    /// ```
    pub fn with_capacity(capacity: usize) -> Self {
        let mut vec = Self::new();

        vec.reserve_exact(capacity)
            .expect("Infallible: Vec capacity is 0 (has_been_sealed is false)");

        vec
    }

    /// Reserves exact capacity and seals the vector.
    ///
    /// After calling this method, the vector is sealed and cannot be resized.
    /// Subsequent calls to `reserve_exact()` will fail.
    ///
    /// # Errors
    ///
    /// Returns [`AllockedVecError::AlreadySealed`] if the vector is already sealed.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec: AllockedVec<u8> = AllockedVec::new();
    ///     vec.reserve_exact(10)?;
    ///
    ///     // Second reserve fails
    ///     assert!(vec.reserve_exact(20).is_err());
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn reserve_exact(&mut self, capacity: usize) -> Result<(), AllockedVecError> {
        if self.has_been_sealed {
            return Err(AllockedVecError::AlreadySealed);
        }

        self.inner.reserve_exact(capacity);
        self.has_been_sealed = true;

        // When unsafe feature is enabled, zero the entire capacity to prevent
        // reading garbage via as_capacity_slice() / as_capacity_mut_slice()
        #[cfg(any(test, feature = "unsafe"))]
        if capacity > 0 {
            redoubt_util::fast_zeroize_slice(unsafe { self.as_capacity_mut_slice() });
        }

        Ok(())
    }

    /// Pushes a value onto the end of the vector.
    ///
    /// # Errors
    ///
    /// Returns [`AllockedVecError::CapacityExceeded`] if the vector is at capacity.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec = AllockedVec::with_capacity(2);
    ///     vec.push(1u8)?;
    ///     vec.push(2u8)?;
    ///
    ///     // Exceeds capacity
    ///     assert!(vec.push(3u8).is_err());
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn push(&mut self, value: T) -> Result<(), AllockedVecError> {
        #[cfg(any(test, feature = "test-utils"))]
        if matches!(self.behaviour, AllockedVecBehaviour::FailAtPush) {
            return Err(AllockedVecError::CapacityExceeded);
        }

        if self.len() >= self.capacity() {
            return Err(AllockedVecError::CapacityExceeded);
        }

        self.inner.push(value);
        Ok(())
    }

    /// Returns the number of elements in the vector.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec = AllockedVec::with_capacity(10);
    ///     vec.push(1u8)?;
    ///     assert_eq!(vec.len(), 1);
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn len(&self) -> usize {
        self.inner.len()
    }

    /// Returns the total capacity of the vector.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::AllockedVec;
    ///
    /// let vec: AllockedVec<u8> = AllockedVec::with_capacity(10);
    /// assert_eq!(vec.capacity(), 10);
    /// ```
    pub fn capacity(&self) -> usize {
        self.inner.capacity()
    }

    /// Returns `true` if the vector contains no elements.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::AllockedVec;
    ///
    /// let vec: AllockedVec<u8> = AllockedVec::new();
    /// assert!(vec.is_empty());
    /// ```
    pub fn is_empty(&self) -> bool {
        self.inner.is_empty()
    }

    /// Returns an immutable slice view of the vector.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec = AllockedVec::with_capacity(3);
    ///     vec.push(1u8)?;
    ///     vec.push(2u8)?;
    ///
    ///     assert_eq!(vec.as_slice(), &[1, 2]);
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn as_slice(&self) -> &[T] {
        &self.inner
    }

    /// Returns a mutable slice view of the vector.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec = AllockedVec::with_capacity(3);
    ///     vec.push(1u8)?;
    ///     vec.push(2u8)?;
    ///
    ///     vec.as_mut_slice()[0] = 42;
    ///     assert_eq!(vec.as_slice(), &[42, 2]);
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn as_mut_slice(&mut self) -> &mut [T] {
        &mut self.inner
    }

    /// Truncates the vector to the specified length, zeroizing removed elements.
    ///
    /// If `new_len` is greater than or equal to the current length, this is a no-op.
    /// Otherwise, the elements beyond `new_len` are zeroized before truncation.
    ///
    /// # Security
    ///
    /// This method zeroizes removed elements before truncating to prevent sensitive
    /// data from remaining in spare capacity. A debug assertion verifies zeroization.
    ///
    /// # Note
    ///
    /// This method guarantees no data remains in spare capacity after the operation.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec = AllockedVec::with_capacity(5);
    ///     vec.push(1u8)?;
    ///     vec.push(2u8)?;
    ///     vec.push(3u8)?;
    ///
    ///     vec.truncate(1);
    ///
    ///     assert_eq!(vec.len(), 1);
    ///     assert_eq!(vec.as_slice(), &[1]);
    ///     // Elements at indices 1 and 2 have been zeroized in spare capacity
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn truncate(&mut self, new_len: usize) {
        if new_len < self.len() {
            self.inner[new_len..].fast_zeroize();

            debug_assert!(
                self.inner[new_len..].iter().all(|v| v.is_zeroized()),
                "AllockedVec::truncate: zeroization failed"
            );

            self.inner.truncate(new_len);
        }
    }

    /// Drains values from a mutable slice into the vector.
    ///
    /// The source slice is zeroized after draining (each element replaced with `T::default()`).
    ///
    /// # Errors
    ///
    /// Returns [`AllockedVecError::CapacityExceeded`] if adding all elements would exceed capacity.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec = AllockedVec::with_capacity(5);
    ///     let mut data = vec![1u8, 2, 3, 4, 5];
    ///
    ///     vec.drain_from(&mut data)?;
    ///
    ///     assert_eq!(vec.len(), 5);
    ///     assert!(data.iter().all(|&x| x == 0)); // Source zeroized
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn drain_from(&mut self, slice: &mut [T]) -> Result<(), AllockedVecError>
    where
        T: Default,
    {
        #[cfg(any(test, feature = "test-utils"))]
        if matches!(self.behaviour, AllockedVecBehaviour::FailAtDrainFrom) {
            return Err(AllockedVecError::CapacityExceeded);
        }

        // Note: checked_add overflow is practically impossible (requires len > isize::MAX),
        // but we keep this defensive check for integer overflow safety.
        let new_len = self
            .len()
            .checked_add(slice.len())
            .ok_or(AllockedVecError::Overflow)?;

        if new_len > self.capacity() {
            return Err(AllockedVecError::CapacityExceeded);
        }

        for item in slice.iter_mut() {
            let value = core::mem::take(item);
            self.inner.push(value);
        }

        Ok(())
    }

    /// Re-seals the vector with a new capacity, safely zeroizing the old allocation.
    ///
    /// This method allows expanding a sealed `AllockedVec` by:
    /// 1. Creating a new vector with the requested capacity
    /// 2. Draining data from the old vector to the new one (zeroizes source via `mem::take`)
    /// 3. Zeroizing the old vector (including spare capacity)
    /// 4. Replacing self with the new vector
    ///
    /// If `new_capacity <= current capacity`, this is a no-op.
    ///
    /// # Safety Guarantees
    ///
    /// - Old allocation is fully zeroized before being dropped
    /// - No unzeroized copies of data remain in memory
    /// - New allocation is sealed with the specified capacity
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec = AllockedVec::with_capacity(5);
    ///     vec.push(1u8)?;
    ///     vec.push(2u8)?;
    ///
    ///     // Expand capacity safely
    ///     vec.realloc_with_capacity(10);
    ///
    ///     // Now can push more elements
    ///     vec.push(3u8)?;
    ///     assert_eq!(vec.capacity(), 10);
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn realloc_with_capacity(&mut self, capacity: usize)
    where
        T: Default,
    {
        self.realloc_with(capacity, |_| {});
    }

    /// Fills the remaining capacity with `T::default()` values.
    ///
    /// This method creates default values for the unused capacity and appends them
    /// to the vector, preserving any existing elements. After this call,
    /// `len() == capacity()`.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::{AllockedVec, AllockedVecError};
    ///
    /// fn example() -> Result<(), AllockedVecError> {
    ///     let mut vec = AllockedVec::<u8>::with_capacity(5);
    ///     vec.push(1)?;
    ///     vec.push(2)?;
    ///
    ///     vec.fill_with_default();
    ///
    ///     assert_eq!(vec.len(), 5);
    ///     assert_eq!(vec.as_slice(), &[1, 2, 0, 0, 0]);
    ///     Ok(())
    /// }
    /// # example().unwrap();
    /// ```
    pub fn fill_with_default(&mut self)
    where
        T: Default,
    {
        let remaining = self.capacity() - self.len();
        let mut source: Vec<T> = (0..remaining).map(|_| T::default()).collect();
        self.drain_from(&mut source)
            .expect("infallible: remaining = capacity - len");
    }

    /// Changes the test behaviour for this vector.
    ///
    /// This is only available with the `test-utils` feature and allows injecting
    /// failures for testing error handling paths.
    ///
    /// # Example
    ///
    /// ```rust
    /// // test-utils feature required in dev-dependencies
    /// #[cfg(test)]
    /// mod tests {
    ///     use redoubt_alloc::{AllockedVec, AllockedVecBehaviour};
    ///
    ///     #[test]
    ///     fn test_error_handling() {
    ///         let mut vec = AllockedVec::with_capacity(10);
    ///         vec.change_behaviour(AllockedVecBehaviour::FailAtPush);
    ///
    ///         // Next push will fail
    ///         assert!(vec.push(1u8).is_err());
    ///     }
    /// }
    /// ```
    #[cfg(any(test, feature = "test-utils"))]
    pub fn change_behaviour(&mut self, behaviour: AllockedVecBehaviour) {
        self.behaviour = behaviour;
    }

    #[cfg(test)]
    pub(crate) fn __unsafe_expose_inner_for_tests<F>(&mut self, f: F)
    where
        F: FnOnce(&mut Vec<T>),
    {
        f(&mut self.inner);
    }

    /// Returns a raw mutable pointer to the vector's buffer.
    ///
    /// # Safety
    ///
    /// This method is only available with the `unsafe` feature.
    #[cfg(any(test, feature = "unsafe"))]
    #[inline(always)]
    pub fn as_mut_ptr(&mut self) -> *mut T {
        self.inner.as_mut_ptr()
    }

    /// Returns a slice of the full capacity, regardless of len.
    ///
    /// # Safety
    ///
    /// This method is only available with the `unsafe` feature.
    /// Elements beyond `len()` may not be properly initialized.
    /// The caller must ensure that accessing elements beyond `len()` is valid for type `T`.
    #[cfg(any(test, feature = "unsafe"))]
    #[inline(always)]
    pub unsafe fn as_capacity_slice(&self) -> &[T] {
        unsafe { core::slice::from_raw_parts(self.inner.as_ptr(), self.inner.capacity()) }
    }

    /// Returns a mutable slice of the full capacity, regardless of len.
    ///
    /// # Safety
    ///
    /// This method is only available with the `unsafe` feature.
    /// Elements beyond `len()` may not be properly initialized.
    /// The caller must ensure that accessing elements beyond `len()` is valid for type `T`.
    #[cfg(any(test, feature = "unsafe"))]
    #[inline(always)]
    pub unsafe fn as_capacity_mut_slice(&mut self) -> &mut [T] {
        unsafe { core::slice::from_raw_parts_mut(self.inner.as_mut_ptr(), self.inner.capacity()) }
    }

    /// Sets the length of the vector without any checks.
    ///
    /// This is useful after operations like `zeroize()` that clear the vector's
    /// length but preserve the underlying data, allowing the length to be restored.
    ///
    /// # Safety
    ///
    /// - `new_len` must be less than or equal to `capacity()`.
    /// - Elements at indices `0..new_len` must be properly initialized.
    /// - This method is only available with the `unsafe` feature.
    ///
    /// # Example
    ///
    /// ```rust
    /// use redoubt_alloc::AllockedVec;
    /// use redoubt_zero::FastZeroizable;
    ///
    /// let mut vec = AllockedVec::with_capacity(5);
    /// vec.push(1u8).unwrap();
    /// vec.push(2u8).unwrap();
    /// assert_eq!(vec.len(), 2);
    ///
    /// let old_len = vec.len();
    /// vec.fast_zeroize();
    ///
    /// assert_eq!(vec.len(), 2);
    /// assert_eq!(vec.as_slice(), &[0, 0]);  // Data was zeroized
    /// ```
    #[cfg(any(test, feature = "unsafe"))]
    #[inline(always)]
    pub unsafe fn set_len(&mut self, new_len: usize) {
        debug_assert!(new_len <= self.capacity());
        unsafe { self.inner.set_len(new_len) };
    }
}

impl<T> Default for AllockedVec<T>
where
    T: FastZeroizable + ZeroizeMetadata + ZeroizationProbe,
{
    fn default() -> Self {
        Self::new()
    }
}

impl<T> core::ops::Deref for AllockedVec<T>
where
    T: FastZeroizable + ZeroizeMetadata + ZeroizationProbe,
{
    type Target = [T];

    fn deref(&self) -> &Self::Target {
        &self.inner
    }
}