helper: add metrics for agg job timings

crates/daphne-server/src/metrics.rs

@@ -10,6 +10,7 @@ pub trait DaphneServiceMetrics: DaphneMetrics {
     fn count_http_status_code(&self, status_code: u16);
     fn daphne(&self) -> &dyn DaphneMetrics;
     fn auth_method_inc(&self, method: AuthMethod);
+    fn aggregate_job_latency(&self, time: std::time::Duration);
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -27,6 +28,7 @@ mod prometheus {
         DapError,
     };
     use prometheus::{register_int_counter_vec_with_registry, IntCounterVec, Registry};
+    use std::time::Duration;
 
     impl DaphneMetrics for DaphnePromServiceMetrics {
         fn report_inc_by(&self, status: ReportStatus, val: u64) {
@@ -76,6 +78,10 @@ mod prometheus {
         fn daphne(&self) -> &dyn DaphneMetrics {
             self
         }
+
+        fn aggregate_job_latency(&self, _time: Duration) {
+            // unimplemented by default due to elevated cardinality
+        }
     }
 
     #[derive(Clone)]

crates/daphne-server/src/router/helper.rs

@@ -50,12 +50,19 @@ async fn agg_job(
         resource::AggregationJobId,
     >,
 ) -> AxumDapResponse {
+    let timer = std::time::Instant::now();
+
     let resp = helper::handle_agg_job_init_req(
         &*app,
         req,
         fetch_replay_protection_override(app.kv()).await,
     )
     .await;
+
+    let elapsed = timer.elapsed();
+
+    app.server_metrics().aggregate_job_latency(elapsed);
+
     AxumDapResponse::from_result_with_success_code(resp, app.server_metrics(), StatusCode::CREATED)
 }