protocols/gossipsub: Add mesh metrics (#2316)

Enable instrumenting mesh through metrics and add gossipsub to
misc/metrics.

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

misc/metrics/src/gossipsub.rs

@@ -0,0 +1,52 @@
+// Copyright 2021 Protocol Labs.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use open_metrics_client::metrics::counter::Counter;
+use open_metrics_client::registry::Registry;
+
+pub struct Metrics {
+    messages: Counter,
+}
+
+impl Metrics {
+    pub fn new(registry: &mut Registry) -> Self {
+        let sub_registry = registry.sub_registry_with_prefix("gossipsub");
+
+        let messages = Counter::default();
+        sub_registry.register(
+            "messages",
+            "Number of messages received",
+            Box::new(messages.clone()),
+        );
+
+        Self { messages }
+    }
+}
+
+impl super::Recorder<libp2p_gossipsub::GossipsubEvent> for super::Metrics {
+    fn record(&self, event: &libp2p_gossipsub::GossipsubEvent) {
+        match event {
+            libp2p_gossipsub::GossipsubEvent::Message { .. } => {
+                self.gossipsub.messages.inc();
+            }
+            _ => {}
+        }
+    }
+}