Fix broken beacon chain metrics, add slot clock metrics

eth2/utils/slot_clock/src/lib.rs

@@ -1,9 +1,15 @@
+#[macro_use]
+extern crate lazy_static;
+
+mod metrics;
 mod system_time_slot_clock;
 mod testing_slot_clock;
 
+use std::time::Duration;
+
 pub use crate::system_time_slot_clock::{Error as SystemTimeSlotClockError, SystemTimeSlotClock};
 pub use crate::testing_slot_clock::{Error as TestingSlotClockError, TestingSlotClock};
-use std::time::Duration;
+pub use metrics::scrape_for_metrics;
 pub use types::Slot;
 
 pub trait SlotClock: Send + Sync + Sized {
@@ -17,4 +23,6 @@ pub trait SlotClock: Send + Sync + Sized {
     fn present_slot(&self) -> Result<Option<Slot>, Self::Error>;
 
     fn duration_to_next_slot(&self) -> Result<Option<Duration>, Self::Error>;
+
+    fn slot_duration_millis(&self) -> u64;
 }

eth2/utils/slot_clock/src/metrics.rs

@@ -0,0 +1,29 @@
+use crate::SlotClock;
+pub use lighthouse_metrics::*;
+use types::{EthSpec, Slot};
+
+lazy_static! {
+    pub static ref PRESENT_SLOT: Result<IntGauge> =
+        try_create_int_gauge("slotclock_present_slot", "The present wall-clock slot");
+    pub static ref PRESENT_EPOCH: Result<IntGauge> =
+        try_create_int_gauge("slotclock_present_epoch", "The present wall-clock epoch");
+    pub static ref MILLISECONDS_PER_SLOT: Result<IntGauge> = try_create_int_gauge(
+        "slotclock_slot_time_milliseconds",
+        "The duration in milliseconds between each slot"
+    );
+}
+
+/// Update the global metrics `DEFAULT_REGISTRY` with info from the slot clock.
+pub fn scrape_for_metrics<T: EthSpec, U: SlotClock>(clock: &U) {
+    let present_slot = match clock.present_slot() {
+        Ok(Some(slot)) => slot,
+        _ => Slot::new(0),
+    };
+
+    set_gauge(&PRESENT_SLOT, present_slot.as_u64() as i64);
+    set_gauge(
+        &PRESENT_EPOCH,
+        present_slot.epoch(T::slots_per_epoch()).as_u64() as i64,
+    );
+    set_gauge(&MILLISECONDS_PER_SLOT, clock.slot_duration_millis() as i64);
+}

eth2/utils/slot_clock/src/system_time_slot_clock.rs

@@ -52,6 +52,10 @@ impl SlotClock for SystemTimeSlotClock {
     fn duration_to_next_slot(&self) -> Result<Option<Duration>, Error> {
         duration_to_next_slot(self.genesis_seconds, self.slot_duration_seconds)
     }
+
+    fn slot_duration_millis(&self) -> u64 {
+        self.slot_duration_seconds * 1000
+    }
 }
 
 impl From<SystemTimeError> for Error {

eth2/utils/slot_clock/src/testing_slot_clock.rs

@@ -40,6 +40,10 @@ impl SlotClock for TestingSlotClock {
     fn duration_to_next_slot(&self) -> Result<Option<Duration>, Error> {
         Ok(Some(Duration::from_secs(1)))
     }
+
+    fn slot_duration_millis(&self) -> u64 {
+        0
+    }
 }
 
 #[cfg(test)]