How to return byte array from Rust function to FFI C?

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13

Finally I tried example code. It caused segmentation fault. But because explanation given by @alice was clear, I immediately realized the cause. as_mut_ptr() of slice returns *mut T, this should not give to Box::from_raw() in this case. Because if do such, unintentionally create Box<T>. What we want creat is Box<[T]>. Here is correct code.

extern "C" fn free_buf(buf: Buffer) {
    let s = unsafe { std::slice::from_raw_parts_mut(buf.data, buf.len) };
-   let s = s.as_mut_ptr();
-   unsafe { Box::from_raw(s); }
+   unsafe { Box::from_raw(s as *mut [u8]); }
}
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