musli_zerocopy/buf/

mod.rs

//! Types associated within reading and binding to a [`Buf`].
//!
//! Buffers are slices of bytes without any inherent alignment. They allow use
//! to safely convert offset-like types to references for types which implements
//! [`ZeroCopy`].
//!
//! # Extension traits
//!
//! This module provides a couple of extension traits which can be used to alter
//! how types interact with buffers.
//!
//! The following is a more compact [`Ref<[u8]>`] which only occupies 4 bytes,
//! but restricts the offset and length.
//!
//! [`Ref<u8>`]: crate::pointer::Ref
//!
//! ```
//! use musli_zerocopy::{Error, Ref, ZeroCopy};
//! use musli_zerocopy::buf::{OwnedBuf, Buf, Load, LoadMut, Visit};
//!
//! #[derive(Clone, Copy, ZeroCopy)]
//! #[repr(C, packed)]
//! struct CompactSlice {
//!     // 3 bytes of offset.
//!     offset: [u8; 3],
//!     // one byte of length.
//!     len: u8,
//! }
//!
//! impl CompactSlice {
//!     /// Construct a new compact slice, panic if offset and length
//!     /// overflow 3 and 1 byte integers respectively.
//!     pub fn new(offset: usize, len: usize) -> Self {
//!         assert!(offset <= 0xffffffusize && len <= 0xff);
//!         let [a, b, c, ..] = offset.to_le_bytes();
//!
//!         Self {
//!             offset: [a, b, c],
//!             len: len as u8,
//!         }
//!     }
//!
//!     /// Get the length of the compact slice.
//!     pub fn len(&self) -> usize {
//!         self.len as usize
//!     }
//!
//!     fn to_slice(&self) -> Ref<[u8]> {
//!         let [a, b, c] = self.offset;
//!         let offset = u32::from_le_bytes([a, b, c, 0]);
//!         Ref::with_metadata(offset as usize, self.len as usize)
//!     }
//! }
//!
//! impl Load for CompactSlice {
//!     type Target = [u8];
//!
//!     fn load<'buf>(&self, buf: &'buf Buf) -> Result<&'buf Self::Target, Error> {
//!         buf.load(self.to_slice())
//!     }
//! }
//!
//! impl LoadMut for CompactSlice {
//!     fn load_mut<'buf>(&self, buf: &'buf mut Buf) -> Result<&'buf mut Self::Target, Error> {
//!         buf.load_mut(self.to_slice())
//!     }
//! }
//!
//! let mut buf1 = OwnedBuf::new();
//! let slice = buf1.store_slice(&[1u8, 2, 3, 4])?;
//! let slice_ref: Ref<Ref<[u8]>> = buf1.store(&slice)?;
//! assert_eq!(buf1.len(), 12);
//!
//! let slice = buf1.load(slice_ref)?;
//! assert_eq!(slice.len(), 4);
//! assert_eq!(buf1.load(*slice)?, &[1, 2, 3, 4]);
//!
//! let mut buf2 = OwnedBuf::new();
//! let slice = buf2.store_slice(&[1u8, 2, 3, 4])?;
//! let slice = CompactSlice::new(slice.offset(), slice.len());
//! let slice_ref: Ref<CompactSlice> = buf2.store(&slice)?;
//! assert_eq!(buf2.len(), 8);
//!
//! let slice = buf2.load(slice_ref)?;
//! assert_eq!(slice.len(), 4);
//! assert_eq!(buf2.load(*slice)?, &[1, 2, 3, 4]);
//! # Ok::<_, musli_zerocopy::Error>(())
//! ```

#[cfg(test)]
mod tests;

pub use self::buf::Buf;
mod buf;

pub use self::bind::Bindable;
mod bind;

pub use self::load::{Load, LoadMut};
mod load;

pub use self::visit::Visit;
pub(crate) mod visit;

pub use self::validator::Validator;
mod validator;

pub use self::padder::Padder;
mod padder;

pub use self::store_buf::StoreBuf;
mod store_buf;

#[cfg(feature = "alloc")]
pub use self::owned_buf::OwnedBuf;
#[cfg(feature = "alloc")]
mod owned_buf;

pub use self::slice_mut::SliceMut;
mod slice_mut;

#[cfg(feature = "alloc")]
use core::alloc::Layout;
use core::fmt;
use core::mem::{MaybeUninit, size_of};
use core::ptr::NonNull;

#[cfg(feature = "alloc")]
use alloc::borrow::Cow;

use crate::traits::ZeroCopy;

/// The type used to calculate default alignment for [`OwnedBuf`].
#[repr(transparent)]
pub struct DefaultAlignment(usize);

/// Error raised when allocation or space requirements in a fixed buffer fails.
#[derive(Debug)]
#[cfg_attr(test, derive(PartialEq))]
pub struct AllocError {
    kind: AllocErrorKind,
}

impl AllocError {
    /// Construct a new allocation error due to insufficient capacity.
    #[inline]
    pub(crate) fn capacity(current: usize, needed: usize) -> Self {
        Self {
            kind: AllocErrorKind::Capacity { current, needed },
        }
    }

    /// Construct a new allocation error due to an alignment requirement
    /// not being met.
    #[inline]
    pub(crate) fn misaligned<T>(addr: *const T, align: usize) -> Self {
        Self {
            kind: AllocErrorKind::Alignment {
                offset: addr.addr() % align,
                align,
            },
        }
    }

    /// Construct a new allocation error due to an underlying allocation
    /// failure.
    #[cfg(feature = "alloc")]
    #[inline]
    #[allow(clippy::self_named_constructors)]
    pub(crate) fn alloc_error(layout: Layout) -> Self {
        Self {
            kind: AllocErrorKind::AllocError { layout },
        }
    }
}

#[derive(Debug)]
#[cfg_attr(test, derive(PartialEq))]
enum AllocErrorKind {
    Capacity {
        current: usize,
        needed: usize,
    },
    Alignment {
        offset: usize,
        align: usize,
    },
    #[cfg(feature = "alloc")]
    AllocError {
        layout: Layout,
    },
}

impl fmt::Display for AllocError {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.kind {
            AllocErrorKind::Capacity { current, needed } => write!(
                f,
                "Container has the capacity {current}, but {needed} bytes are needed",
            ),
            AllocErrorKind::Alignment { offset, align } => {
                write!(f, "Container is not aligned to {align} by {offset} bytes",)
            }
            #[cfg(feature = "alloc")]
            AllocErrorKind::AllocError { layout } => {
                write!(
                    f,
                    "Failed to allocate {} bytes with alignment {}",
                    layout.size(),
                    layout.align()
                )
            }
        }
    }
}

impl core::error::Error for AllocError {}

/// Return the max capacity of this vector. This depends on the requested
/// alignment.
///
/// This follows how it's defined by `max_size_for_align` in [`Layout`].
///
/// [`Layout`]: core::alloc::Layout
#[inline]
pub fn max_capacity_for_align(align: usize) -> usize {
    isize::MAX as usize - (align - 1)
}

/// Construct a buffer with an alignment matching that of `T` which is either
/// wrapped in a [`Buf`] if it is already correctly aligned, or inside of an
/// allocated [`OwnedBuf`].
///
/// # Examples
///
/// ```no_run
/// use std::fs::read;
///
/// use musli_zerocopy::{Ref, ZeroCopy};
/// use musli_zerocopy::buf;
///
/// #[derive(ZeroCopy)]
/// #[repr(C)]
/// struct Person {
///     name: Ref<str>,
///     age: u32,
/// }
///
/// let bytes = read("person.bin")?;
/// let buf = buf::aligned_buf::<u128>(&bytes)?;
///
/// let s = buf.load(Ref::<Person>::zero())?;
/// # Ok::<_, anyhow::Error>(())
/// ```
#[cfg(feature = "alloc")]
pub fn aligned_buf<T>(bytes: &[u8]) -> Result<Cow<'_, Buf>, AllocError> {
    Buf::new(bytes).to_aligned::<T>()
}

/// Construct a buffer with a specific alignment which is either wrapped in a
/// [`Buf`] if it is already correctly aligned, or inside of an allocated
/// [`OwnedBuf`].
///
/// # Panics
///
/// Panics if `align` is not a power of two.
///
/// # Examples
///
/// ```no_run
/// use std::fs::read;
///
/// use musli_zerocopy::{Ref, ZeroCopy};
/// use musli_zerocopy::buf;
///
/// #[derive(ZeroCopy)]
/// #[repr(C)]
/// struct Person {
///     name: Ref<str>,
///     age: u32,
/// }
///
/// let bytes = read("person.bin")?;
/// let buf = buf::aligned_buf_with(&bytes, 16)?;
///
/// let s = buf.load(Ref::<Person>::zero())?;
/// # Ok::<_, anyhow::Error>(())
/// ```
#[cfg(feature = "alloc")]
pub fn aligned_buf_with(bytes: &[u8], align: usize) -> Result<Cow<'_, Buf>, AllocError> {
    Buf::new(bytes).to_aligned_with(align)
}

/// # Safety
///
/// Must be called with an alignment that is a power of two.
#[inline]
pub(crate) fn is_aligned_with<T>(ptr: *const T, align: usize) -> bool {
    ptr.addr() & (align - 1) == 0
}

/// Calculate padding with the assumption that alignment is a power of two.
#[inline(always)]
pub(crate) fn padding_to(len: usize, align: usize) -> usize {
    let mask = align - 1;
    (align - (len & mask)) & mask
}

/// Store the raw bytes associated with `*const T` into the buffer and advance
/// its position by `size_of::<T>()`.
///
/// This does not require `T` to be aligned.
///
/// # Safety
///
/// The caller must ensure that any store call only includes data up-to the size
/// of `Self`.
///
/// Also see the [type level safety documentation][#safety]
#[inline]
pub(crate) unsafe fn store_unaligned<T>(data: NonNull<MaybeUninit<u8>>, value: *const T)
where
    T: ZeroCopy,
{
    unsafe {
        data.as_ptr()
            .copy_from_nonoverlapping(value.cast(), size_of::<T>());

        if T::PADDED {
            let mut padder = Padder::new(data);
            T::pad(&mut padder);
            padder.remaining();
        }
    }
}