Function alloc_perry_string

native/shared/src/string_header.rs:45–67

Allocate a Perry 0.5.x heap string suitable for returning across the FFI boundary (declared as `returns: "string"` in package.json). Layout matches `StringHeader` above: 5×u32 header (utf16_len, byte_len, capacity, refcount, flags) followed by UTF-8 data. Older engine code allocated 12 bytes (Perry 0.4.x layout) and Perry's 0.5.x runtime read 8 bytes into the payload — strings came back with a ga

(s: &str)

/// 0.5.x runtime read 8 bytes into the payload — strings came back with a
/// garbage prefix and read past the end. Always go through this helper.
pub fn alloc_perry_string(s: &str) -> *const u8 {
    let bytes = s.as_bytes();
    let byte_len = bytes.len();
    // ASCII fast path: utf16_len == byte_len when every byte is < 0x80.
    let utf16_len = if bytes.iter().all(|&b| b < 0x80) {
        byte_len
    } else {
        s.encode_utf16().count()
    };
    let total = std::mem::size_of::<StringHeader>() + byte_len;
    let layout = std::alloc::Layout::from_size_align(total, 4).unwrap();
    unsafe {
        let ptr = std::alloc::alloc(layout);
        if ptr.is_null() { return std::ptr::null(); }
        *(ptr as *mut u32)         = utf16_len as u32;
        *(ptr.add(4)  as *mut u32) = byte_len  as u32;
        *(ptr.add(8)  as *mut u32) = byte_len  as u32; // capacity
        *(ptr.add(12) as *mut u32) = 1;                // refcount=unique
        *(ptr.add(16) as *mut u32) = 0;                // flags
        std::ptr::copy_nonoverlapping(bytes.as_ptr(), ptr.add(20), byte_len);
        ptr
    }
}