rust/cpp_kernel/cpp.rs

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// Rust Protobuf runtime using the C++ kernel.

use std::alloc::{dealloc, Layout};
use std::boxed::Box;
use std::ops::Deref;
use std::ptr::NonNull;
use std::slice;

/// TODO(b/272728844): Replace this placeholder code with a real implementation.
#[repr(C)]
pub struct Arena {
    _data: [u8; 0],
}

impl Arena {
    pub unsafe fn new() -> *mut Self {
        let arena = Box::new(Arena { _data: [] });
        Box::leak(arena) as *mut _
    }

    pub unsafe fn free(arena: *mut Self) {
        let arena = Box::from_raw(arena);
        std::mem::drop(arena);
    }
}

/// Represents serialized Protobuf wire format data. It's typically produced by
/// `<Message>.serialize()`.
///
/// This struct is ABI compatible with the equivalent struct on the C++ side. It
/// owns (and drops) its data.
// copybara:strip_begin
// LINT.IfChange
// copybara:strip_end
#[repr(C)]
#[derive(Debug)]
pub struct SerializedData {
    /// Owns the memory.
    data: NonNull<u8>,
    len: usize,
}
// copybara:strip_begin
// LINT.ThenChange(//depot/google3/third_party/protobuf/rust/cpp_kernel/cpp_api.
// h) copybara:strip_end

impl Deref for SerializedData {
    type Target = [u8];
    fn deref(&self) -> &Self::Target {
        unsafe { slice::from_raw_parts(self.data.as_ptr(), self.len) }
    }
}

impl Drop for SerializedData {
    fn drop(&mut self) {
        unsafe {
            dealloc(self.data.as_ptr(), Layout::array::<u8>(self.len).unwrap());
        };
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // We need to allocate the byte array so SerializedData can own it and
    // deallocate it in its drop. This function makes it easier to do so for our
    // tests.
    fn allocate_byte_array(content: &'static [u8]) -> (*mut u8, usize) {
        let content: &mut [u8] = Box::leak(content.into());
        (content.as_mut_ptr(), content.len())
    }

    #[test]
    fn test_serialized_data_roundtrip() {
        let (ptr, len) = allocate_byte_array(b"Hello world");
        let serialized_data = SerializedData { data: NonNull::new(ptr).unwrap(), len: len };
        assert_eq!(&*serialized_data, b"Hello world");
    }
}