Implement std::error::Error for InboundFailure and OutboundFailure (#2033)

Co-authored-by: Max Inden <mail@max-inden.de>

protocols/request-response/CHANGELOG.md

@@ -1,6 +1,8 @@
 # 0.11.0 [unreleased]
 
 - Update `libp2p-swarm`.
+- Implement `std::error::Error` for `InboundFailure` and `OutboundFailure` [PR
+  2033](https://github.com/libp2p/rust-libp2p/pull/2033).
 
 # 0.10.0 [2021-03-17]
 

protocols/request-response/src/lib.rs

@@ -181,6 +181,19 @@ pub enum OutboundFailure {
     UnsupportedProtocols,
 }
 
+impl fmt::Display for OutboundFailure {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            OutboundFailure::DialFailure => write!(f, "Failed to dial the requested peer"),
+            OutboundFailure::Timeout => write!(f, "Timeout while waiting for a response"),
+            OutboundFailure::ConnectionClosed => write!(f, "Connection was closed before a response was received"),
+            OutboundFailure::UnsupportedProtocols => write!(f, "The remote supports none of the requested protocols")
+        }
+    }
+}
+
+impl std::error::Error for OutboundFailure {}
+
 /// Possible failures occurring in the context of receiving an
 /// inbound request and sending a response.
 #[derive(Debug, Clone, PartialEq)]
@@ -201,6 +214,19 @@ pub enum InboundFailure {
     ResponseOmission,
 }
 
+impl fmt::Display for InboundFailure {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            InboundFailure::Timeout => write!(f, "Timeout while receiving request or sending response"),
+            InboundFailure::ConnectionClosed => write!(f, "Connection was closed before a response could be sent"),
+            InboundFailure::UnsupportedProtocols => write!(f, "The local peer supports none of the protocols requested by the remote"),
+            InboundFailure::ResponseOmission => write!(f, "The response channel was dropped without sending a response to the remote")
+        }
+    }
+}
+
+impl std::error::Error for InboundFailure {}
+
 /// A channel for sending a response to an inbound request.
 ///
 /// See [`RequestResponse::send_response`].