Transmuting u8 buffer to struct in Rust

Question

I have a byte buffer of unknown size, and I want to create a local struct variable pointing to the memory of the beginning of the buffer. Following what I\'d do in C, I trie

Answer 1

If you don't want to copy the data to the struct but instead leave it in place, you can use slice::align_to. This creates a &MyStruct instead:

#[repr(C, packed)]
#[derive(Debug, Copy, Clone)]
struct MyStruct {
    foo: u16,
    bar: u8,
}

fn main() {
    let v = vec![1u8, 2, 3];

    // I copied this code from Stack Overflow
    // without understanding why this case is safe.
    let (head, body, _tail) = unsafe { v.align_to::() };
    assert!(head.is_empty(), "Data was not aligned");
    let my_struct = &body[0];

    println!("{:?}", my_struct);
}

Here, it's safe to use align_to to transmute some bytes to MyStruct because we've used repr(C, packed) and all of the types in MyStruct can be any arbitrary bytes.

See also:

• How to read a struct from a file in Rust?
• Can I take a byte array and deserialize it into a struct?