Function alloc 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn alloc(len: usize) -> *mut u8

Allocate len bytes and return a raw pointer.

The allocation is managed by Rust’s allocator; the caller is responsible for calling dealloc with the same pointer and length.

Safety

The caller must write exactly len bytes before passing the pointer back to parse or serialize, and must call dealloc(ptr, len) exactly once when done.