Feature request: use DST to represent structures with flexible array members #2771
Description
Input C/C++ Header
struct msg {
unsigned int tag;
unsigned int len;
char payload[];
};Bindgen Invocation
$ bindgen input.h
Actual Results
This produces an output using __IncompleteArrayField as expected:
#[repr(C)]
#[derive(Debug)]
pub struct msg {
pub tag: ::std::os::raw::c_uint,
pub len: ::std::os::raw::c_uint,
pub payload: __IncompleteArrayField<::std::os::raw::c_char>,
}Expected Results
It would be nice to have an option to model this by using a structure with a dynamic tail:
#[repr(C)]
#[derive(Debug)]
pub struct msg {
pub tag: ::std::os::raw::c_uint,
pub len: ::std::os::raw::c_uint,
pub payload: [:std::os::raw::c_char],
}These types of structures are awkward to use on their own, so it would need some helper methods:
impl msg {
// Size and alignment so memory can be allocated
fn layout(len: usize) -> ::std::alloc::Layout {
unsafe {
let p: *const Self = ::std::ptr::from_raw_parts(ptr::null(), len);
::std::alloc::Layout::for_value_raw(p)
}
}
// Convert a raw pointer into an immutable view for a given number of payload elements.
// Danger: Return lifetime unconstrained
unsafe fn from_ptr<'a>(ptr: *const (), len: usize) -> &'a Self {
let ptr: *const Self = ::std::ptr::from_raw_parts(ptr, len);
&*ptr
}
// Same but mutable, and maybe uninitialized, to to allow Rust to initialize/mutate it.
// Danger: Return lifetime unconstrained
unsafe fn from_ptr_mut<'a>(
ptr: *mut (),
len: usize,
) -> ::std::mem::MaybeUninit<&'a mut Self> {
let ptr: *mut Self = ::std::ptr::from_raw_parts_mut(ptr, len);
::std::mem::MaybeUninit::new(&mut *ptr)
}
}These methods would currently depend on the unstable ptr_metadata and layout_for_ptr features.