Namespace datadog blackhole target metrics & default off (#1926)

* feat(datadog): namespace recorded series under target/ prefix

Datadog blackhole now prefixes recorded metric names with target/,
matching the prometheus and expvar target metrics collectors. The record
policy continues to match on the unprefixed series name.

Also changes the default record policy to Disabled, so no target metrics
are recorded unless explicitly configured.

Both are breaking changes for consumers relying on unprefixed metric
names or default-all recording behavior.

* update rand + silence unused

* bump CI

Author: GeorgeHahn

.cargo/audit.toml

@@ -1,7 +1,8 @@
 [advisories]
 ignore = [
     "RUSTSEC-2020-0159",
-    "RUSTSEC-2026-0001",  # rkyv 0.7.46 UB in Arc/Rc - transitive via rust_decimal <- byte-unit
+    "RUSTSEC-2026-0001",  # rkyv 0.7.46 UB in Arc/Rc - optional dep of rust_decimal <- byte-unit, never compiled
+    "RUSTSEC-2026-0235",  # rkyv 0.7.46 OOB read - optional dep of rust_decimal <- byte-unit, never compiled
     "RUSTSEC-2024-0436",  # paste unmaintained - transitive via parquet
 ]
 

CHANGELOG.md

@@ -5,6 +5,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
+
+## Changed
+- **Breaking Change**: Datadog blackhole now records received series under the
+  `target/` prefix, matching the prometheus and expvar target metrics
+  collectors. The `record` policy still matches on the unprefixed series name.
+- **Breaking Change**: Datadog blackhole does not record any target metrics by
+  default.
+
+## Added
 - Datadog blackhole now accepts a `record` policy (`all` / `disabled` /
   `series_to_keep: [...]`) controlling which received series are recorded as
   capture metrics.
@@ -24,7 +33,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   metric, or omits the field entirely if the pool is empty.
 - `dogstatsd` generator now supports DogStatsD protocol v1.3 `|T` timestamps
   for count and gauge metrics via `timestamp.range` and `timestamp.probability`.
-- Fixed: `dogstatsd` tag generation would silently fail with a misleading
+
+## Fixed
+- `dogstatsd` tag generation would silently fail with a misleading
   `StringGenerate` error for any `tag_length` whose range collapses after
   reserving one byte for the `:` separator -- every constant or single-value
   range (e.g. `Constant(3)`, `Constant(4)`, `Inclusive { min: 100, max: 100 }`)

Cargo.lock

@@ -49,6 +49,9 @@ use tracing::{debug, error, info, trace, warn};
 use super::General;
 use crate::proto::datadog::intake::metrics::MetricPayload;
 
+/// Namespace for incoming metrics; matches other target-originated metrics.
+const TARGET_PREFIX: &str = "target/";
+
 #[derive(thiserror::Error, Debug)]
 /// Errors produced by [`Datadog`].
 pub enum Error {
@@ -112,7 +115,7 @@ pub enum RecordPolicy {
 
 impl Default for RecordPolicy {
     fn default() -> Self {
-        Self::All
+        Self::Disabled
     }
 }
 
@@ -367,9 +370,16 @@ async fn handle_v2_protobuf(
             );
 
             if !matches!(record, RecordPolicy::Disabled) {
+                let mut scratch = String::new();
+
                 for series in payload.series.iter().filter(|series| {
                     !series.points.is_empty() && record.records_series(&series.metric)
                 }) {
+                    scratch.clear();
+                    scratch.reserve(TARGET_PREFIX.len() + series.metric.len());
+                    scratch.push_str(TARGET_PREFIX);
+                    scratch.push_str(&series.metric);
+
                     // Parse Datadog tags (format: "key:value" or "key") into label pairs.
                     // Key-only tags are represented with an empty value.
                     let tag_pairs: Vec<(&str, &str)> = series
@@ -395,7 +405,7 @@ async fn handle_v2_protobuf(
                                 // COUNT
                                 #[expect(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
                                 let value = point.value.round() as u64;
-                                counter_incr(&series.metric, &tag_pairs, value, timestamp).await
+                                counter_incr(&scratch, &tag_pairs, value, timestamp).await
                             }
                             2 => {
                                 // RATE
@@ -409,11 +419,11 @@ async fn handle_v2_protobuf(
                                 }
                                 #[expect(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
                                 let val = (point.value * interval as f64).round() as u64;
-                                counter_incr(&series.metric, &tag_pairs, val, timestamp).await
+                                counter_incr(&scratch, &tag_pairs, val, timestamp).await
                             }
                             3 => {
                                 // GAUGE
-                                gauge_set(&series.metric, &tag_pairs, point.value, timestamp).await
+                                gauge_set(&scratch, &tag_pairs, point.value, timestamp).await
                             }
                             i => {
                                 warn!("Unknown metric type, skipping: {i}");