Add basic prometheus endpoint

beacon_node/http_server/src/prometheus_handler.rs

@@ -0,0 +1,43 @@
+use beacon_chain::BeaconChain;
+use iron::{status::Status, Handler, IronResult, Request, Response};
+use prometheus::{IntCounter, Encoder, Opts, Registry, TextEncoder};
+use std::sync::Arc;
+use types::EthSpec;
+
+pub struct PrometheusHandler<T, U, F, E: EthSpec> {
+    pub beacon_chain: Arc<BeaconChain<T, U, F, E>>,
+}
+
+impl<T, U, F, E> PrometheusHandler<T, U, F, E> where E: EthSpec {}
+
+impl<T, U, F, E> Handler for PrometheusHandler<T, U, F, E>
+where
+    E: EthSpec + 'static,
+    U: slot_clock::SlotClock + Send + Sync + 'static,
+    T: Send + Sync + 'static,
+    F: Send + Sync + 'static,
+{
+    fn handle(&self, _: &mut Request) -> IronResult<Response> {
+        // Create a Counter.
+        let counter_opts = Opts::new("present_slot", "direct_slot_clock_reading");
+        let counter = IntCounter::with_opts(counter_opts).unwrap();
+
+        // Create a Registry and register Counter.
+        let r = Registry::new();
+        r.register(Box::new(counter.clone())).unwrap();
+
+        if let Ok(Some(slot)) = self.beacon_chain.slot_clock.present_slot() {
+            counter.inc_by(slot.as_u64() as i64);
+        }
+
+        // Gather the metrics.
+        let mut buffer = vec![];
+        let encoder = TextEncoder::new();
+        let metric_families = r.gather();
+        encoder.encode(&metric_families, &mut buffer).unwrap();
+
+        let prom_string = String::from_utf8(buffer).unwrap();
+
+        Ok(Response::with((Status::Ok, prom_string)))
+    }
+}