Unify common metric fns into a crate

eth2/utils/lighthouse_metrics/src/lib.rs

@@ -0,0 +1,49 @@
+use prometheus::{HistogramOpts, HistogramTimer, Opts};
+
+pub use prometheus::{Histogram, IntCounter, Result};
+
+pub fn try_create_int_counter(name: &str, help: &str) -> Result<IntCounter> {
+    let opts = Opts::new(name, help);
+    let counter = IntCounter::with_opts(opts)?;
+    prometheus::register(Box::new(counter.clone()))?;
+    Ok(counter)
+}
+
+pub fn try_create_histogram(name: &str, help: &str) -> Result<Histogram> {
+    let opts = HistogramOpts::new(name, help);
+    let histogram = Histogram::with_opts(opts)?;
+    prometheus::register(Box::new(histogram.clone()))?;
+    Ok(histogram)
+}
+
+pub fn start_timer(histogram: &Result<Histogram>) -> Option<HistogramTimer> {
+    if let Ok(histogram) = histogram {
+        Some(histogram.start_timer())
+    } else {
+        None
+    }
+}
+
+pub fn stop_timer(timer: Option<HistogramTimer>) {
+    timer.map(|t| t.observe_duration());
+}
+
+pub fn inc_counter(counter: &Result<IntCounter>) {
+    if let Ok(counter) = counter {
+        counter.inc();
+    }
+}
+
+pub fn observe(histogram: &Result<Histogram>, value: f64) {
+    if let Ok(histogram) = histogram {
+        histogram.observe(value);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}