Fix duplicate external addresses inserted (#927)

core/Cargo.toml

@@ -2,7 +2,7 @@
 name = "libp2p-core"
 edition = "2018"
 description = "Core traits and structs of libp2p"
-version = "0.3.3"
+version = "0.3.4"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"

core/src/swarm.rs

@@ -315,8 +315,10 @@ where TBehaviour: NetworkBehaviour,
                 },
                 Async::Ready(NetworkBehaviourAction::ReportObservedAddr { address }) => {
                     for addr in self.raw_swarm.nat_traversal(&address) {
+                        if self.external_addrs.iter().all(|a| *a != addr) {
                             self.external_addrs.push(addr);
                         }
+                    }
                 },
             }
         }