Add gauge metric to export latest block height

src/index.rs

@@ -6,7 +6,7 @@ use crate::{
     chain::Chain,
     daemon::Daemon,
     db::{DBStore, Row, WriteBatch},
-    metrics::{Histogram, Metrics},
+    metrics::{Gauge, Histogram, Metrics},
     signals::ExitFlag,
     types::{HeaderRow, ScriptHash, ScriptHashRow, SpendingPrefixRow, TxidRow},
 };
@@ -15,6 +15,7 @@ use crate::{
 struct Stats {
     update_duration: Histogram,
     update_size: Histogram,
+    height: Gauge,
 }
 
 impl Stats {
@@ -30,6 +31,7 @@ impl Stats {
                 "Index update size (in bytes)",
                 "step",
             ),
+            height: metrics.gauge("index_height", "Latest indexed block height"),
         }
     }
 }
@@ -187,6 +189,7 @@ impl Index {
                     self.observe_duration("block", || {
                         index_single_block(block, height).extend(&mut batch)
                     });
+                    self.stats.height.set(height);
                 })?;
                 let heights: Vec<_> = heights.collect();
                 assert!(

src/metrics.rs

@@ -52,6 +52,25 @@ mod metrics_impl {
                 .expect("failed to register Histogram");
             Histogram { hist }
         }
+
+        pub fn gauge(&self, name: &str, desc: &str) -> Gauge {
+            let gauge = prometheus::Gauge::new(name, desc).unwrap();
+            self.reg
+                .register(Box::new(gauge.clone()))
+                .expect("failed to register Gauge");
+            Gauge { gauge }
+        }
+    }
+
+    #[derive(Clone)]
+    pub struct Gauge {
+        gauge: prometheus::Gauge,
+    }
+
+    impl Gauge {
+        pub fn set(&self, value: usize) {
+            self.gauge.set(value as f64)
+        }
     }
 
     #[derive(Clone)]
@@ -76,7 +95,7 @@ mod metrics_impl {
 }
 
 #[cfg(feature = "metrics")]
-pub use metrics_impl::{Histogram, Metrics};
+pub use metrics_impl::{Gauge, Histogram, Metrics};
 
 #[cfg(not(feature = "metrics"))]
 mod metrics_fake {
@@ -95,6 +114,17 @@ mod metrics_fake {
         pub fn histogram_vec(&self, _name: &str, _desc: &str, _label: &str) -> Histogram {
             Histogram {}
         }
+
+        pub fn gauge(&self, _name: &str, _desc: &str) -> Gauge {
+            Gauge {}
+        }
+    }
+
+    #[derive(Clone)]
+    pub struct Gauge {}
+
+    impl Gauge {
+        pub fn set(&self, _value: usize) {}
     }
 
     #[derive(Clone)]
@@ -113,4 +143,4 @@ mod metrics_fake {
 }
 
 #[cfg(not(feature = "metrics"))]
-pub use metrics_fake::{Histogram, Metrics};
+pub use metrics_fake::{Gauge, Histogram, Metrics};