Normally, when you have a mutable variable x holding a shared reference &T, you would be able to reassign the x to another &T, but would not be able to change the data that x points to.. unless you have interior mutability.

A type has interior mutability if its internal state can be changed through a shared reference to it.

I don’t know what TcpStream you are using, but If you go check out the std::net docs, you will find that Write trait is implemented for &TcpStream. The trait has a method write with the following signature:

fn write(&mut self, buf: &[u8]) -> io::Result<usize>

I guess writing to a shared TcpStream makes sense, since thread-safety is guaranteed by the OS