Crate bytecheck

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bytecheck

bytecheck is a type validation framework for Rust.

For some types, creating an invalid value immediately results in undefined behavior. This can cause some issues when trying to validate potentially invalid bytes, as just casting the bytes to your type can technically cause errors. This makes it difficult to write validation routines, because until you’re certain that the bytes represent valid values you cannot cast them.

bytecheck provides a framework for performing these byte-level validations and implements checks for basic types along with a derive macro to implement validation for custom structs and enums.

Design

CheckBytes is at the heart of bytecheck, and does the heavy lifting of verifying that some bytes represent a valid type. Implementing it can be done manually or automatically with the derive macro.

Examples

use bytecheck::CheckBytes;

#[derive(CheckBytes, Debug)]
struct Test {
    a: u32,
    b: bool,
    c: char,
}
#[repr(C, align(16))]
struct Aligned<const N: usize>([u8; N]);

macro_rules! bytes {
    ($($byte:literal,)*) => {
        (&Aligned([$($byte,)*]).0 as &[u8]).as_ptr()
    };
    ($($byte:literal),*) => {
        bytes!($($byte,)*)
    };
}

// This type is laid out as (u32, char, bool)
// In this example, the architecture is assumed to be little-endian
unsafe {
    // These are valid bytes for (0, 'x', true)
    Test::check_bytes(
        bytes![
            0u8, 0u8, 0u8, 0u8, 0x78u8, 0u8, 0u8, 0u8,
            1u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8
        ].cast(),
        &mut ()
    ).unwrap();

    // Changing the bytes for the u32 is OK, any bytes are a valid u32
    Test::check_bytes(
        bytes![
            42u8, 16u8, 20u8, 3u8, 0x78u8, 0u8, 0u8, 0u8,
            1u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8
        ].cast(),
        &mut ()
    ).unwrap();

    // Characters outside the valid ranges are invalid
    Test::check_bytes(
        bytes![
            0u8, 0u8, 0u8, 0u8, 0x00u8, 0xd8u8, 0u8, 0u8,
            1u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8
        ].cast(),
        &mut ()
    ).unwrap_err();
    Test::check_bytes(
        bytes![
            0u8, 0u8, 0u8, 0u8, 0x00u8, 0x00u8, 0x11u8, 0u8,
            1u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8
        ].cast(),
        &mut ()
    ).unwrap_err();

    // 0 is a valid boolean value (false) but 2 is not
    Test::check_bytes(
        bytes![
            0u8, 0u8, 0u8, 0u8, 0x78u8, 0u8, 0u8, 0u8,
            0u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8
        ].cast(),
        &mut ()
    ).unwrap();
    Test::check_bytes(
        bytes![
            0u8, 0u8, 0u8, 0u8, 0x78u8, 0u8, 0u8, 0u8,
            2u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8, 255u8
        ].cast(),
        &mut ()
    ).unwrap_err();
}

Features

  • verbose: Some validation algorithms are optimized for speed and do not report full error details by default. This feature provides full error information.
  • std: Enables standard library support (enabled by default). If the std feature is not enabled, the alloc crate is required.

Crate support

Some common crates need to be supported by bytecheck before an official integration has been made. Support is provided by bytecheck for these crates, but in the future crates should depend on bytecheck and provide their own implementations. The crates that already have support provided by bytecheck should work toward integrating the implementations into themselves.

Crates supported by bytecheck:

Structs

Enums

Traits

  • CheckBytes
    A type that can check whether a pointer points to a valid value.
  • Error
    An error that can be debugged and displayed.

Type Definitions

  • ErrorBox
    The type used for boxing errors.

Derive Macros

  • CheckBytes
    Derives CheckBytes for the labeled type.