fix(swarm): display cause of denied listen error

The display of `ListenError` could be more helpful. The inner `cause` already implements `Error` which in turn requires `Display`. This is then just a matter of using said impl requirement to get an useful display

Pull-Request: #4232.

Cargo.lock

@@ -3150,7 +3150,7 @@ dependencies = [
 
 [[package]]
 name = "libp2p-swarm"
-version = "0.43.1"
+version = "0.43.2"
 dependencies = [
  "async-std",
  "either",

Cargo.toml

@@ -87,7 +87,7 @@ libp2p-quic = { version = "0.8.0-alpha", path = "transports/quic" }
 libp2p-relay = { version = "0.16.1", path = "protocols/relay" }
 libp2p-rendezvous = { version = "0.13.0", path = "protocols/rendezvous" }
 libp2p-request-response = { version = "0.25.1", path = "protocols/request-response" }
-libp2p-swarm = { version = "0.43.1", path = "swarm" }
+libp2p-swarm = { version = "0.43.2", path = "swarm" }
 libp2p-swarm-derive = { version = "0.33.0", path = "swarm-derive" }
 libp2p-swarm-test = { version = "0.2.0", path = "swarm-test" }
 libp2p-tcp = { version = "0.40.0", path = "transports/tcp" }

swarm/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 0.43.2 - unreleased
+- Display the cause of a `ListenError::Denied`.
+  See [PR 4232]
+
+[PR 4232]: https://github.com/libp2p/rust-libp2p/pull/4158
+
 ## 0.43.1
 
 - Do not announce external address candidate before address translation, unless translation does not apply.

swarm/Cargo.toml

@@ -3,7 +3,7 @@ name = "libp2p-swarm"
 edition = "2021"
 rust-version = { workspace = true }
 description = "The libp2p swarm"
-version = "0.43.1"
+version = "0.43.2"
 authors = ["Parity Technologies <admin@parity.io>"]
 license = "MIT"
 repository = "https://github.com/libp2p/rust-libp2p"

swarm/src/lib.rs

@@ -1684,8 +1684,8 @@ impl fmt::Display for ListenError {
             ListenError::Transport(_) => {
                 write!(f, "Listen error: Failed to negotiate transport protocol(s)")
             }
-            ListenError::Denied { .. } => {
-                write!(f, "Listen error")
+            ListenError::Denied { cause } => {
+                write!(f, "Listen error: Denied: {cause}")
             }
             ListenError::LocalPeerId { endpoint } => {
                 write!(f, "Listen error: Local peer ID at {endpoint:?}.")