Automatically close useless connections (#816)

* Automatically close useless connections

* Add a timeout before dropping the connection

* Rework the timeout

* Use OR to combine the outcome

protocols/ping/src/dial_handler.rs

@@ -193,6 +193,11 @@ where
         }
     }
 
+    #[inline]
+    fn connection_keep_alive(&self) -> bool {
+        false
+    }
+
     fn shutdown(&mut self) {
         // Put `Shutdown` in `self.out_state` if we don't have any substream open.
         // Otherwise, keep the state as it is but call `shutdown()` on the substream. This

protocols/ping/src/listen_handler.rs

@@ -105,6 +105,11 @@ where
     #[inline]
     fn inject_dial_upgrade_error(&mut self, _: Self::OutboundOpenInfo, _: ProtocolsHandlerUpgrErr<<Self::OutboundProtocol as OutboundUpgrade<Self::Substream>>::Error>) {}
 
+    #[inline]
+    fn connection_keep_alive(&self) -> bool {
+        false
+    }
+
     #[inline]
     fn shutdown(&mut self) {
         for ping in self.ping_in_substreams.iter_mut() {