misc/metrics: Add auxiliary crate to record events as OpenMetrics (#2063)

This commit adds an auxiliary crate recording protocol and Swarm events
and exposing them as metrics in the OpenMetrics format.

misc/metrics/src/lib.rs

@@ -0,0 +1,76 @@
+// 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.
+
+//! Auxiliary crate recording protocol and Swarm events and exposing them as
+//! metrics in the [OpenMetrics] format.
+//!
+//! [OpenMetrics]: https://github.com/OpenObservability/OpenMetrics/
+//!
+//! See `examples` directory for more.
+
+#[cfg(feature = "identify")]
+mod identify;
+#[cfg(feature = "kad")]
+mod kad;
+#[cfg(feature = "ping")]
+mod ping;
+mod swarm;
+
+use open_metrics_client::registry::Registry;
+
+/// Set of Swarm and protocol metrics derived from emitted events.
+pub struct Metrics {
+    #[cfg(feature = "identify")]
+    identify: identify::Metrics,
+    #[cfg(feature = "kad")]
+    kad: kad::Metrics,
+    #[cfg(feature = "ping")]
+    ping: ping::Metrics,
+    swarm: swarm::Metrics,
+}
+
+impl Metrics {
+    /// Create a new set of Swarm and protocol [`Metrics`].
+    ///
+    /// ```
+    /// use open_metrics_client::registry::Registry;
+    /// use libp2p_metrics::Metrics;
+    /// let mut registry = Registry::default();
+    /// let metrics = Metrics::new(&mut registry);
+    /// ```
+    pub fn new(registry: &mut Registry) -> Self {
+        let sub_registry = registry.sub_registry_with_prefix("libp2p");
+        Self {
+            #[cfg(feature = "identify")]
+            identify: identify::Metrics::new(sub_registry),
+            #[cfg(feature = "kad")]
+            kad: kad::Metrics::new(sub_registry),
+            #[cfg(feature = "ping")]
+            ping: ping::Metrics::new(sub_registry),
+            swarm: swarm::Metrics::new(sub_registry),
+        }
+    }
+}
+
+/// Recorder that can record Swarm and protocol events.
+pub trait Recorder<Event> {
+    /// Record the given event.
+    fn record(&self, event: &Event);
+}