Add OpenMetrics HTTP blackhole body

examples/lading-openmetrics.yaml

@@ -0,0 +1,29 @@
+blackhole:
+  - http:
+      binding_addr: "127.0.0.1:9100"
+      concurrent_requests_max: 1000
+      response_delay_millis: 100
+      headers:
+        content-type: "text/plain; version=0.0.4"
+      body_variant:
+        openmetrics:
+          metric_name_prefix: "om_scale"
+          include_help: true
+          include_type: true
+          counters:
+            count: 240
+          gauges:
+            count: 180
+          histograms:
+            count: 20
+            buckets: ["0.005", "0.01", "0.025", "0.05", "0.1", "0.25", "0.5", "1", "2.5", "5"]
+          summaries:
+            count: 40
+            quantiles: ["0.5", "0.75", "0.9", "0.95", "0.99"]
+          labels:
+            services: ["checkout", "catalog", "payments", "fulfillment", "search"]
+            regions: ["us-east-1", "us-west-2", "eu-central-1", "ap-southeast-1"]
+            methods: ["GET", "POST", "PUT", "DELETE"]
+            status_classes: ["2xx", "3xx", "4xx", "5xx"]
+            consumers: ["consumer-00", "consumer-01", "consumer-02", "consumer-03"]
+            route_count: 60

lading/src/blackhole/http.rs

@@ -12,6 +12,7 @@ use bytes::Bytes;
 use http::{HeaderMap, header::InvalidHeaderValue, status::InvalidStatusCode};
 use http_body_util::{BodyExt, combinators::BoxBody};
 use hyper::{Request, Response, StatusCode, header};
+use lading_payload::openmetrics;
 use metrics::counter;
 use serde::{Deserialize, Serialize};
 use std::{net::SocketAddr, time::Duration};
@@ -39,6 +40,9 @@ pub enum Error {
     /// Failed to deserialize the configuration.
     #[error("Failed to deserialize the configuration: {0}")]
     Serde(#[from] serde_json::Error),
+    /// `OpenMetrics` payload generation failed.
+    #[error("OpenMetrics payload error: {0}")]
+    OpenMetrics(#[from] lading_payload::openmetrics::Error),
     /// Wrapper for [`crate::blackhole::common::Error`].
     #[error(transparent)]
     Common(#[from] crate::blackhole::common::Error),
@@ -75,6 +79,9 @@ pub enum BodyVariant {
     RawBytes,
     /// Respond with a hardcoded string value
     Static(String),
+    /// Respond with a generated `OpenMetrics` text exposition body.
+    #[serde(rename = "openmetrics")]
+    OpenMetrics(Box<openmetrics::Config>),
 }
 
 fn default_body_variant() -> BodyVariant {
@@ -111,6 +118,7 @@ pub struct Config {
     pub binding_addr: SocketAddr,
     /// the body variant to respond with, default nothing
     #[serde(default = "default_body_variant")]
+    #[serde(with = "serde_yaml::with::singleton_map_recursive")]
     pub body_variant: BodyVariant,
     /// Headers to include in the response; default is `Content-Type: application/json`
     #[serde(with = "http_serde::header_map", default = "default_headers")]
@@ -233,6 +241,7 @@ impl Http {
             BodyVariant::Nothing => vec![],
             BodyVariant::RawBytes => config.raw_bytes.clone(),
             BodyVariant::Static(val) => val.as_bytes().to_vec(),
+            BodyVariant::OpenMetrics(conf) => openmetrics::OpenMetrics::new(conf)?.into_bytes(),
         };
 
         Ok(Self {
@@ -339,4 +348,36 @@ raw_bytes: [0x01, 0x02, 0x10]
             },
         );
     }
+
+    #[test]
+    fn config_deserializes_openmetrics() {
+        let contents = r#"
+binding_addr: "127.0.0.1:1000"
+body_variant:
+  openmetrics:
+    metric_name_prefix: "om_test"
+    counters:
+      count: 2
+    gauges:
+      count: 3
+    histograms:
+      count: 1
+      buckets: ["0.5", "1"]
+    summaries:
+      count: 1
+      quantiles: ["0.5", "0.99"]
+"#;
+        let config: Config =
+            serde_yaml::from_str(contents).expect("Contents do not match the structure expected");
+        match config.body_variant {
+            BodyVariant::OpenMetrics(openmetrics) => {
+                assert_eq!(openmetrics.metric_name_prefix, "om_test");
+                assert_eq!(openmetrics.counters.count, 2);
+                assert_eq!(openmetrics.gauges.count, 3);
+                assert_eq!(openmetrics.histograms.count, 1);
+                assert_eq!(openmetrics.summaries.count, 1);
+            }
+            other => panic!("expected openmetrics body variant, got {other:?}"),
+        }
+    }
 }

lading_payload/src/lib.rs

@@ -22,6 +22,7 @@ pub use datadog_logs::DatadogLog;
 pub use dogstatsd::DogStatsD;
 pub use fluent::Fluent;
 pub use json::Json;
+pub use openmetrics::OpenMetrics;
 pub use opentelemetry::log::OpentelemetryLogs;
 pub use opentelemetry::metric::OpentelemetryMetrics;
 pub use opentelemetry::trace::OpentelemetryTraces;
@@ -39,6 +40,7 @@ pub mod datadog_logs;
 pub mod dogstatsd;
 pub mod fluent;
 pub mod json;
+pub mod openmetrics;
 pub mod opentelemetry;
 pub mod procfs;
 pub mod splunk_hec;