feat: add expected_network_height metric

CHANGELOG.md

@@ -83,6 +83,9 @@
 - [#4315](https://github.com/ChainSafe/forest/pull/4315) Add support for the
   `Filecoin.StateGetNetworkParams` RPC method.
 
+- [#4326](https://github.com/ChainSafe/forest/pull/4326) Added
+  `expected_network_height` metric to the Prometheus metrics.
+
 ### Changed
 
 - [#4170](https://github.com/ChainSafe/forest/pull/4170) Change the default

src/daemon/mod.rs

@@ -196,6 +196,16 @@ pub(super) async fn start(
         });
     }
 
+    // Read Genesis file
+    // * When snapshot command implemented, this genesis does not need to be
+    //   initialized
+    let genesis_header = read_genesis_header(
+        config.client.genesis_file.as_ref(),
+        chain_config.genesis_bytes(&db).await?.as_deref(),
+        &db,
+    )
+    .await?;
+
     if config.client.enable_metrics_endpoint {
         // Start Prometheus server port
         let prometheus_listener = TcpListener::bind(config.client.metrics_address)
@@ -212,17 +222,15 @@ pub(super) async fn start(
                 .await
                 .context("Failed to initiate prometheus server")
         });
-    }
 
-    // Read Genesis file
-    // * When snapshot command implemented, this genesis does not need to be
-    //   initialized
-    let genesis_header = read_genesis_header(
-        config.client.genesis_file.as_ref(),
-        chain_config.genesis_bytes(&db).await?.as_deref(),
-        &db,
-    )
-    .await?;
+        let chain_config_clone = chain_config.clone();
+        let genesis_timestamp = genesis_header.timestamp;
+        services.spawn(async move {
+            crate::networks::metrics::network_metrics_loop(chain_config_clone, genesis_timestamp)
+                .await;
+            Ok(())
+        });
+    }
 
     // Initialize ChainStore
     let chain_store = Arc::new(ChainStore::new(

src/networks/metrics.rs

@@ -0,0 +1,37 @@
+// Copyright 2019-2024 ChainSafe Systems
+// SPDX-License-Identifier: Apache-2.0, MIT
+
+use std::sync::Arc;
+
+use once_cell::sync::Lazy;
+use prometheus_client::metrics::gauge::Gauge;
+
+use super::ChainConfig;
+
+pub static EXPECTED_NETWORK_HEIGHT: Lazy<Gauge> = Lazy::new(|| {
+    let metric = Gauge::default();
+    crate::metrics::default_registry().register(
+        "expected_network_height",
+        "The expected network height based on the current time and the genesis block time.",
+        metric.clone(),
+    );
+    metric
+});
+
+/// Task to periodically update network-related metrics.
+pub async fn network_metrics_loop(config: Arc<ChainConfig>, genesis_timestamp: u64) {
+    loop {
+        // For this particular metric, we theoretically could have initiated the value once and
+        // increased it by one every `block_delay_secs`, but this would have made the metric less
+        // responsive and more fragile, e.g., on system clock changes. Given that the operation is cheap, we just
+        // recalculate it every second.
+        let now_epoch = chrono::Utc::now()
+            .timestamp()
+            .saturating_add(config.block_delay_secs as i64)
+            .saturating_sub(genesis_timestamp as i64)
+            / config.block_delay_secs as i64;
+
+        EXPECTED_NETWORK_HEIGHT.set(now_epoch);
+        tokio::time::sleep(tokio::time::Duration::from_secs(1)).await;
+    }
+}

src/networks/mod.rs

@@ -30,6 +30,8 @@ pub mod calibnet;
 pub mod devnet;
 pub mod mainnet;
 
+pub mod metrics;
+
 /// Newest network version for all networks
 pub const NEWEST_NETWORK_VERSION: NetworkVersion = NetworkVersion::V17;