protocols/dcutr/example: Wait for relay to accept reservation request (…

…#2642)

When in listening mode, wait for the relay to accept our reservation
request. Only then can a client in dialing mode establish a relayed
connection to us via the relay.

See also
#2621 (comment)

protocols/dcutr/examples/client.rs

@@ -197,25 +197,46 @@ fn main() -> Result<(), Box<dyn Error>> {
         }
     }
 
-    // Wait till connected to relay to learn external address.
+    // Wait till connected to relay to learn external address. In case we are in listening mode,
+    // wait for the relay to accept our reservation request.
     block_on(async {
+        let mut learned_observed_addr = false;
+        let mut relay_accepted_reservation = false;
+
         loop {
             match swarm.next().await.unwrap() {
                 SwarmEvent::NewListenAddr { .. } => {}
                 SwarmEvent::Dialing { .. } => {}
                 SwarmEvent::ConnectionEstablished { .. } => {}
                 SwarmEvent::Behaviour(Event::Ping(_)) => {}
-                SwarmEvent::Behaviour(Event::Relay(_)) => {}
+                SwarmEvent::Behaviour(Event::Relay(client::Event::ReservationReqAccepted {
+                    ..
+                })) => {
+                    info!("Relay accepted our reservation request.");
+                    relay_accepted_reservation = true
+                }
                 SwarmEvent::Behaviour(Event::Identify(IdentifyEvent::Sent { .. })) => {}
                 SwarmEvent::Behaviour(Event::Identify(IdentifyEvent::Received {
                     info: IdentifyInfo { observed_addr, .. },
                     ..
                 })) => {
-                    info!("Observed address: {:?}", observed_addr);
-                    break;
+                    info!("Relay observes us under the address: {:?}", observed_addr);
+                    learned_observed_addr = true;
                 }
                 event => panic!("{:?}", event),
             }
+
+            // Check whether we are done.
+
+            if !learned_observed_addr {
+                continue;
+            }
+
+            if opts.mode == Mode::Listen && !relay_accepted_reservation {
+                continue;
+            }
+
+            break;
         }
     });
 

src/tutorials/hole_punching.rs

@@ -132,14 +132,20 @@
 //!
 //! ``` bash
 //! RUST_LOG=info ./client --secret-key-seed 1 --mode listen --relay-address /ip4/$RELAY_SERVER_IP/tcp/4001/p2p/12D3KooWDpJ7As7BWAwRMfu1VU2WCqNjvq387JEYKDBj4kx6nXTN
+//!
+//! [2022-05-11T10:38:52Z INFO  client] Local peer id: PeerId("XXX")
+//! [2022-05-11T10:38:52Z INFO  client] Listening on "/ip4/127.0.0.1/tcp/44703"
+//! [2022-05-11T10:38:52Z INFO  client] Listening on "/ip4/XXX/tcp/44703"
+//! [2022-05-11T10:38:54Z INFO  client] Relay accepted our reservation request.
+//! [2022-05-11T10:38:54Z INFO  client] Relay observes us under the address: "/ip4/XXX/tcp/53160"
 //! ```
 //!
 //! Now let's make sure that the listening client is not public, in other words let's make sure one
 //! can not reach it directly through the Internet. From the dialing client test that you can not
 //! connect on Layer 4 (TCP):
 //!
 //! ``` bash
-//! telnet $RELAY_SERVER_IP 4001
+//! telnet $LISTENING_CLIENT_IP_OBSERVED_BY_RELAY 53160
 //! ```
 //!
 //! ## Connecting to the listening client from the dialing client