error[E0499]: cannot borrow `sock` as mutable more than once at a time
  --> src/main.rs:74:9
   |
38 |         let packet = sock.next().unwrap();
   |                      ---- first mutable borrow occurs here
...
74 |         sock.sendpacket(resp_packet);
   |         ^^^^ second mutable borrow occurs here
75 |     }
   |     - first borrow ends here

error: aborting due to previous error