protobuf/rust/shared.rs

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//! Kernel-agnostic logic for the Rust Protobuf Runtime.
//!
//! For kernel-specific logic this crate delegates to the respective __runtime
//! crate.

#[cfg(cpp_kernel)]
#[path = "cpp.rs"]
pub mod __runtime;
#[cfg(upb_kernel)]
#[path = "upb.rs"]
pub mod __runtime;

mod proxied;

pub use __runtime::SerializedData;

use std::fmt;
use std::slice;
use std::ptr::NonNull;

/// An error that happened during deserialization.
#[derive(Debug, Clone)]
pub struct ParseError;

impl fmt::Display for ParseError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Couldn't deserialize given bytes into a proto")
    }
}

/// An ABI-stable, FFI-safe borrowed slice of bytes.
///
/// Has semantics equivalent to `&[u8]` in Rust and `std::string_view` in C++,
/// but is not ABI-compatible with them.
///
/// TODO: Is `ptr` allowed to be null or dangling when `len` is 0?
#[repr(C)]
#[derive(Copy, Clone)]
pub struct PtrAndLen {
    /// Borrows the memory.
    pub ptr: *const u8,
    pub len: usize,
}

impl PtrAndLen {
    pub unsafe fn as_ref<'a>(self) -> &'a [u8] {
        assert!(self.len == 0 || !self.ptr.is_null());
        if self.len == 0 {
            slice::from_raw_parts(NonNull::dangling().as_ptr(), 0)
        } else {
            slice::from_raw_parts(self.ptr, self.len)
        }
    }
}