feat: add Prometheus metrics

Cargo.toml

@@ -13,6 +13,7 @@ femme = "2.1.0"
 humantime = "2.0.1"
 hyper = { version = "0.14", features = ["tcp"] }
 log = "0.4.11"
+prometheus-client = "0.22.2"
 serde = { version = "1.0.114", features = ["derive"] }
 sled = "0.34.2"
 structopt = "0.3.15"

README.md

@@ -20,3 +20,11 @@ $ ./target/release/notifiers --certificate-file <file.p12> --password <password>
 ```sh
 $ curl -X POST -d '{ "token": "<device token>" }' http://localhost:9000/register
 ```
+
+### Enabling metrics
+
+To enable OpenMetrics (Prometheus) metrics endpoint,
+run with `--metrics` argument,
+e.g. `--metrics 127.0.0.1:9001`.
+Metrics can then be retrieved with
+`curl http://127.0.0.1:9001/metrics`.

src/lib.rs

@@ -1,3 +1,4 @@
+pub mod metrics;
 pub mod notifier;
 pub mod server;
 pub mod state;

src/main.rs

@@ -1,10 +1,11 @@
 use std::path::PathBuf;
+use std::sync::Arc;
 
 use anyhow::{Context, Result};
 use async_std::prelude::*;
 use structopt::StructOpt;
 
-use notifiers::{notifier, server, state};
+use notifiers::{metrics, notifier, server, state};
 
 #[derive(Debug, StructOpt)]
 struct Opt {
@@ -23,6 +24,10 @@ struct Opt {
     /// The port on which to start the server.
     #[structopt(long, default_value = "9000")]
     port: u16,
+    /// The host and port on which to start the metrics server.
+    /// For example, `127.0.0.1:9001`.
+    #[structopt(long)]
+    metrics: Option<String>,
     /// The path to the database file.
     #[structopt(long, default_value = "notifiers.db", parse(from_os_str))]
     db: PathBuf,
@@ -37,11 +42,23 @@ async fn main() -> Result<()> {
     let opt = Opt::from_args();
     let certificate = std::fs::File::open(&opt.certificate_file).context("invalid certificate")?;
 
-    let state = state::State::new(&opt.db, certificate, &opt.password, opt.topic.clone())?;
+    let metrics_state = Arc::new(metrics::Metrics::new());
+
+    let state = state::State::new(
+        &opt.db,
+        certificate,
+        &opt.password,
+        opt.topic.clone(),
+        metrics_state.clone(),
+    )?;
 
     let state2 = state.clone();
     let host = opt.host.clone();
     let port = opt.port;
+
+    if let Some(metrics_address) = opt.metrics.clone() {
+        async_std::task::spawn(async move { metrics::start(metrics_state, metrics_address).await });
+    }
     let server = async_std::task::spawn(async move { server::start(state2, host, port).await });
 
     let notif = async_std::task::spawn(async move { notifier::start(state, opt.interval).await });

src/metrics.rs

@@ -0,0 +1,60 @@
+//! Prometheus (OpenMetrics) metrics server.
+//!
+//! It is listening on its own address
+//! to allow exposting it on a private network only
+//! independently of the main service.
+
+use std::sync::Arc;
+
+use prometheus_client::encoding::text::encode;
+use prometheus_client::metrics::counter::Counter;
+use prometheus_client::registry::Registry;
+
+use anyhow::Result;
+
+#[derive(Debug, Default)]
+pub struct Metrics {
+    pub registry: Registry,
+
+    pub direct_notifications_total: Counter,
+}
+
+impl Metrics {
+    pub fn new() -> Self {
+        let mut registry = Registry::default();
+        let direct_notifications_total = Counter::default();
+        registry.register(
+            "direct_notifications_total",
+            "Number of direct notifications",
+            direct_notifications_total.clone(),
+        );
+        Self {
+            registry,
+            direct_notifications_total,
+        }
+    }
+
+    /// Counts direct notification.
+    pub fn inc_direct_notification(&self) {
+        self.direct_notifications_total.inc();
+    }
+}
+
+type State = Arc<Metrics>;
+
+pub async fn start(state: State, server: String) -> Result<()> {
+    let mut app = tide::with_state(state);
+    app.at("/metrics").get(metrics);
+    app.listen(server).await?;
+    Ok(())
+}
+
+async fn metrics(req: tide::Request<State>) -> tide::Result<tide::Response> {
+    let mut encoded = String::new();
+    encode(&mut encoded, &req.state().registry).unwrap();
+    let response = tide::Response::builder(tide::StatusCode::Ok)
+        .body(encoded)
+        .content_type("application/openmetrics-text; version=1.0.0; charset=utf-8")
+        .build();
+    Ok(response)
+}

src/server.rs

@@ -73,6 +73,7 @@ async fn notify_device(mut req: tide::Request<State>) -> tide::Result<tide::Resp
             match res.code {
                 200 => {
                     info!("delivered notification for {}", device_token);
+                    req.state().metrics().inc_direct_notification();
                 }
                 _ => {
                     warn!("unexpected status: {:?}", res);

src/state.rs

@@ -6,6 +6,8 @@ use async_std::sync::Arc;
 use log::*;
 use std::io::Seek;
 
+use crate::metrics::Metrics;
+
 #[derive(Debug, Clone)]
 pub struct State {
     inner: Arc<InnerState>,
@@ -20,6 +22,8 @@ pub struct InnerState {
     sandbox_client: Client,
 
     topic: Option<String>,
+
+    metrics: Arc<Metrics>,
 }
 
 impl State {
@@ -28,6 +32,7 @@ impl State {
         mut certificate: std::fs::File,
         password: &str,
         topic: Option<String>,
+        metrics: Arc<Metrics>,
     ) -> Result<Self> {
         let db = sled::open(db)?;
         let production_client =
@@ -45,6 +50,7 @@ impl State {
                 production_client,
                 sandbox_client,
                 topic,
+                metrics,
             }),
         })
     }
@@ -64,4 +70,8 @@ impl State {
     pub fn topic(&self) -> Option<&str> {
         self.inner.topic.as_deref()
     }
+
+    pub fn metrics(&self) -> &Metrics {
+        self.inner.metrics.as_ref()
+    }
 }