feat: build info in metrics

CHANGELOG.md

@@ -50,6 +50,9 @@
   snapshots instead of moving or copying them. This can be invoked with
   `--import-snapshot <path> --import-mode=symlink`.
 
+- [#4533](https://github.com/ChainSafe/forest/pull/4641) Added `build_info`
+  metric to Prometheus metrics, which include the current build's version.
+
 - [#4628](https://github.com/ChainSafe/forest/issues/4628) Added support for
   devnets (2k networks) in the offline Forest.
 

src/metrics/mod.rs

@@ -80,7 +80,9 @@ where
         warn!("Failed to register process metrics: {err}");
     }
 
-    // Add the DBCollector to the registry
+    DEFAULT_REGISTRY.write().register_collector(Box::new(
+        crate::utils::version::ForestVersionCollector::new(),
+    ));
     DEFAULT_REGISTRY
         .write()
         .register_collector(Box::new(crate::metrics::db::DBCollector::new(db_directory)));

src/utils/version/mod.rs

@@ -3,6 +3,11 @@
 
 use git_version::git_version;
 use once_cell::sync::Lazy;
+use prometheus_client::{
+    collector::Collector,
+    encoding::{DescriptorEncoder, EncodeLabelSet, EncodeMetric},
+    metrics::{family::Family, gauge::Gauge},
+};
 
 /// Current git commit hash of the Forest repository.
 pub const GIT_HASH: &str =
@@ -15,3 +20,43 @@ pub static FOREST_VERSION_STRING: Lazy<String> =
 
 pub static FOREST_VERSION: Lazy<semver::Version> =
     Lazy::new(|| semver::Version::parse(env!("CARGO_PKG_VERSION")).expect("Invalid version"));
+
+#[derive(Clone, Debug, Hash, PartialEq, Eq, EncodeLabelSet)]
+pub struct VersionLabel {
+    version: &'static str,
+}
+
+impl VersionLabel {
+    pub const fn new(version: &'static str) -> Self {
+        Self { version }
+    }
+}
+
+#[derive(Debug)]
+pub struct ForestVersionCollector {
+    version: Family<VersionLabel, Gauge>,
+}
+
+impl ForestVersionCollector {
+    pub fn new() -> Self {
+        Self {
+            version: Family::default(),
+        }
+    }
+}
+
+impl Collector for ForestVersionCollector {
+    fn encode(&self, mut encoder: DescriptorEncoder) -> Result<(), std::fmt::Error> {
+        let metric_encoder = encoder.encode_descriptor(
+            "build_info",
+            "semantic version of the forest binary",
+            None,
+            self.version.metric_type(),
+        )?;
+        self.version
+            .get_or_create(&VersionLabel::new(FOREST_VERSION_STRING.as_str()))
+            .set(1);
+        self.version.encode(metric_encoder)?;
+        Ok(())
+    }
+}