protocols/gossipsub: Implement std::error::Error for error types (#2254)

Co-authored-by: Thomas Eizinger <thomas@eizinger.io>

Author: McFranko

protocols/gossipsub/CHANGELOG.md

@@ -14,6 +14,9 @@
 - Allow `message_id_fn`s to accept closures that capture variables.
   [PR 2103](https://github.com/libp2p/rust-libp2p/pull/2103)
 
+- Implement std::error::Error for error types.
+  [PR 2254](https://github.com/libp2p/rust-libp2p/pull/2254)
+
 # 0.32.0 [2021-07-12]
 
 - Update dependencies.

protocols/gossipsub/src/error.rs

@@ -40,6 +40,22 @@ pub enum PublishError {
     TransformFailed(std::io::Error),
 }
 
+impl std::fmt::Display for PublishError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl std::error::Error for PublishError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::SigningError(err) => Some(err),
+            Self::TransformFailed(err) => Some(err),
+            _ => None,
+        }
+    }
+}
+
 /// Error associated with subscribing to a topic.
 #[derive(Debug)]
 pub enum SubscriptionError {
@@ -49,6 +65,21 @@ pub enum SubscriptionError {
     NotAllowed,
 }
 
+impl std::fmt::Display for SubscriptionError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl std::error::Error for SubscriptionError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::PublishError(err) => Some(err),
+            _ => None,
+        }
+    }
+}
+
 impl From<SigningError> for PublishError {
     fn from(error: SigningError) -> Self {
         PublishError::SigningError(error)
@@ -95,6 +126,14 @@ pub enum ValidationError {
     TransformFailed,
 }
 
+impl std::fmt::Display for ValidationError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl std::error::Error for ValidationError {}
+
 impl From<std::io::Error> for GossipsubHandlerError {
     fn from(error: std::io::Error) -> GossipsubHandlerError {
         GossipsubHandlerError::Io(error)