Return TCP listener errors. (#1218)

* Add listener ID and error event.

Report listener errors to client code so they are aware that an error
occurred within a listener. By default we continue to poll listeners
which produced an error, but clients can remove listeners by ID.

* tcp: Report errors.

Instead of silently waiting after errors we return all errors, but pause
after each error, before continuing.

* Add a test.

To ease testing, `Listener` is made generic and we test that no values
and errors are lost. Elapsed time between item generation is not
measured.

* Support the new methods in core-derive.

* Address review concerns.

* Remove `Display` impl of `ListenerId`.

* Add 'static bound to `on_listener_error` error.

misc/core-derive/src/lib.rs

@@ -56,6 +56,7 @@ fn build_struct(ast: &DeriveInput, data_struct: &DataStruct) -> TokenStream {
     let into_proto_select_ident = quote!{::libp2p::swarm::IntoProtocolsHandlerSelect};
     let peer_id = quote!{::libp2p::core::PeerId};
     let connected_point = quote!{::libp2p::core::ConnectedPoint};
+    let listener_id = quote!{::libp2p::core::nodes::ListenerId};
 
     // Name of the type parameter that represents the substream.
     let substream_generic = {
@@ -284,6 +285,32 @@ fn build_struct(ast: &DeriveInput, data_struct: &DataStruct) -> TokenStream {
         })
     };
 
+    // Build the list of statements to put in the body of `inject_listener_error()`.
+    let inject_listener_error_stmts = {
+        data_struct.fields.iter().enumerate().filter_map(move |(field_n, field)| {
+            if is_ignored(&field) {
+                return None
+            }
+            Some(match field.ident {
+                Some(ref i) => quote!(self.#i.inject_listener_error(id, err);),
+                None => quote!(self.#field_n.inject_listener_error(id, err);)
+            })
+        })
+    };
+
+    // Build the list of statements to put in the body of `inject_listener_closed()`.
+    let inject_listener_closed_stmts = {
+        data_struct.fields.iter().enumerate().filter_map(move |(field_n, field)| {
+            if is_ignored(&field) {
+                return None
+            }
+            Some(match field.ident {
+                Some(ref i) => quote!(self.#i.inject_listener_closed(id);),
+                None => quote!(self.#field_n.inject_listener_closed(id);)
+            })
+        })
+    };
+
     // Build the list of variants to put in the body of `inject_node_event()`.
     //
     // The event type is a construction of nested `#either_ident`s of the events of the children.
@@ -467,6 +494,14 @@ fn build_struct(ast: &DeriveInput, data_struct: &DataStruct) -> TokenStream {
                 #(#inject_new_external_addr_stmts);*
             }
 
+            fn inject_listener_error(&mut self, id: #listener_id, err: &(dyn std::error::Error + 'static)) {
+                #(#inject_listener_error_stmts);*
+            }
+
+            fn inject_listener_closed(&mut self, id: #listener_id) {
+                #(#inject_listener_closed_stmts);*
+            }
+
             fn inject_node_event(
                 &mut self,
                 peer_id: #peer_id,