chore: Record subscriber usage metric

Author: jsumners-nr

.gitignore

@@ -22,3 +22,6 @@ nr-security-home
 # benchmark results
 benchmark_results
 bin/.env
+
+# Local developer resources:
+local/

lib/metrics/names.js

@@ -353,7 +353,8 @@ const FEATURES = {
   SOURCE_MAPS: `${SUPPORTABILITY.FEATURES}/EnableSourceMaps`,
   CERTIFICATES: SUPPORTABILITY.FEATURES + '/Certificates',
   INSTRUMENTATION: {
-    ON_REQUIRE: SUPPORTABILITY.FEATURES + '/Instrumentation/OnRequire'
+    ON_REQUIRE: SUPPORTABILITY.FEATURES + '/Instrumentation/OnRequire',
+    SUBSCRIBER_USED: SUPPORTABILITY.FEATURES + '/Instrumentation/SubscriberUsed'
   }
 }
 

lib/shimmer.js

@@ -306,7 +306,7 @@ const shimmer = (module.exports = {
   registerHooks(agent) {
     // add the packages from the subscriber based instrumentation
     // this is only added to add tracking metrics
-    pkgsToHook.push(...Object.keys(subscriptions), ...trackingPkgs)
+    Array.prototype.push.apply(pkgsToHook, trackingPkgs)
     this._ritm = new Hook(pkgsToHook, function onHook(exports, name, basedir) {
       return _postLoad(agent, exports, name, basedir)
     })

lib/subscribers/base.js

@@ -7,6 +7,8 @@
 // eslint-disable-next-line n/no-unsupported-features/node-builtins
 const { tracingChannel } = require('node:diagnostics_channel')
 const cat = require('#agentlib/util/cat.js')
+const recordSupportabilityMetric = require('./record-supportability-metric.js')
+
 // Used for the `traceCallback` work.
 // This can be removed when we add true support into orchestrion
 const makeCall = (fn) => (...args) => fn.call(...args)
@@ -28,38 +30,45 @@ const ArrayPrototypeSplice = makeCall(Array.prototype.splice)
 
 /**
  * @property {object} agent A New Relic Node.js agent instance.
- * @property {object} logger An agent logger instance.
+ * @property {TracingChannel} channel The tracing channel instance this subscriber will be monitoring.
+ * @property {string} channelName A unique name for the diagnostics channel
+ * that will be registered.
  * @property {object} config The agent configuration object.
+ * @property {string} id A unique identifier for the subscriber, combining the prefix, package
+ * name, and channel name.
+ * @property {object} logger An agent logger instance.
  * @property {string} packageName The name of the module being instrumented.
  * This is the same string one would pass to the `require` function.
- * @property {string} channelName A unique name for the diagnostics channel
- * that will be registered.
+ * @property {AsyncLocalStorage} store The async local storage instance used for context management.
+ * @property {number} [callback=null] Position of callback if it needs to be wrapped for instrumentation.
+ * -1 means last argument.
  * @property {string[]} [events=[]] Set of tracing channel event names to
  * register handlers for. For any name in the set, a corresponding method
  * must exist on the subscriber instance. The method will be passed the
  * event object. Possible event names are `start`, `end`, `asyncStart`,
  * `asyncEnd`, and `error`.
- *
- *  See {@link https://nodejs.org/api/diagnostics_channel.html#class-tracingchannel}
- * @property {boolean} [opaque=false] If true, any children segments will not be created.
+ * See {@link https://nodejs.org/api/diagnostics_channel.html#class-tracingchannel}
  * @property {boolean} [internal=false] If true, any children segments from the same library
  * will not be created.
+ * @property {boolean} [opaque=false] If true, any children segments will not be created.
  * @property {string} [prefix='orchestrion:'] String to prepend to diagnostics
  * channel event names. This provides a namespace for the events we are
  * injecting into a module.
- * @property {boolean} [requireActiveTx=true] If true, the subscriber will only handle events
- * when there is an active transaction.
  * @property {boolean} [propagateContext=false] If true, it will bind `asyncStart` to the store
  * and re-propagate the active context. It will also attach the `transaction` to the event in
  * `start.bindStore`. This is used for functions that queue async code and context is lost.
- * @property {string} id A unique identifier for the subscriber, combining the prefix, package
- * name, and channel name.
- * @property {TracingChannel} channel The tracing channel instance this subscriber will be monitoring.
- * @property {AsyncLocalStorage} store The async local storage instance used for context management.
- * @property {number} [callback=null] Position of callback if it needs to be wrapped for instrumentation.
- * -1 means last argument.
+ * @property {boolean} [requireActiveTx=true] If true, the subscriber will only handle events
+ * when there is an active transaction.
+ * @property {object} [targetModuleMeta] Defines the target module's name and
+ * version string, i.e. is an object `{ name, version }`. This is only necessary
+ * when target instrumentation can surface an unexpected name for the
+ * `packageName` property. For example, `express` uses multiple modules to
+ * compose its core functionality. We want to track things under the `express`
+ * name, but `packageName` will be set to `router` is most cases.
  */
 class Subscriber {
+  #usageMetricRecorded = false
+
   /**
    * @param {SubscriberParams} params the subscriber constructor params
    */
@@ -234,6 +243,15 @@ class Subscriber {
      * @returns {Context} The context after processing the event
      */
     const handler = (data) => {
+      if (this.#usageMetricRecorded === false) {
+        recordSupportabilityMetric({
+          agent: this.agent,
+          moduleName: this.packageName,
+          moduleVersion: data.moduleVersion
+        })
+        this.#usageMetricRecorded = true
+      }
+
       // only wrap the callback if a subscriber has a callback property defined
       if (this.callback !== null) {
         this.traceCallback(this.callback, data)

lib/subscribers/dc-base.js

@@ -4,8 +4,11 @@
  */
 
 'use strict'
+
 // eslint-disable-next-line n/no-unsupported-features/node-builtins
 const dc = require('node:diagnostics_channel')
+const recordSupportabilityMetric = require('./record-supportability-metric.js')
+const resolvePackageVersion = require('./resolve-package-version.js')
 
 /**
  * The baseline parameters available to all subscribers.
@@ -34,6 +37,8 @@ const dc = require('node:diagnostics_channel')
  * This is the same string one would pass to the `require` function.
  */
 class Subscriber {
+  #usageMetricRecorded = false
+
   /**
    * @param {SubscriberParams} params to function
    */
@@ -46,7 +51,7 @@ class Subscriber {
 
   set channels(channels) {
     if (!Array.isArray(channels)) {
-      throw new Error('channels must be a collection of with propertiesof channel and hook')
+      throw new Error('channels must be a collection of objects with properties channel and hook')
     }
     this._channels = channels
   }
@@ -73,18 +78,43 @@ class Subscriber {
 
   subscribe() {
     for (let index = 0; index < this.channels.length; index++) {
+      const chan = this.channels[index]
       const { hook, channel } = this.channels[index]
       const boundHook = hook.bind(this)
-      dc.subscribe(channel, boundHook)
-      this.channels[index].boundHook = boundHook
+      chan.boundHook = boundHook
+      chan.eventHandler = (message, name) => {
+        this.#supportability()
+        boundHook(message, name)
+      }
+      dc.subscribe(channel, chan.eventHandler)
     }
   }
 
   unsubscribe() {
     for (let index = 0; index < this.channels.length; index++) {
-      const { channel, boundHook } = this.channels[index]
-      dc.unsubscribe(channel, boundHook)
+      const { channel, eventHandler } = this.channels[index]
+      dc.unsubscribe(channel, eventHandler)
+    }
+  }
+
+  /**
+   * Since this class subscribes to diagnostics channels natively published by
+   * target modules, we do not get the package metadata that Orchestrion
+   * provides in its channel events. So we have to try and find the package
+   * manifest and get the version out of it in order to record our
+   * supportability metric.
+   */
+  #supportability() {
+    if (this.#usageMetricRecorded === true) {
+      return
     }
+    const version = resolvePackageVersion(this.id)
+    recordSupportabilityMetric({
+      agent: this.agent,
+      moduleName: this.id,
+      moduleVersion: version
+    })
+    this.#usageMetricRecorded = true
   }
 }
 

lib/subscribers/record-supportability-metric.js

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2025 New Relic Corporation. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+'use strict'
+
+module.exports = recordSupportabilityMetric
+
+const semver = require('semver')
+const {
+  FEATURES: {
+    INSTRUMENTATION: { SUBSCRIBER_USED }
+  }
+} = require('#agentlib/metrics/names.js')
+
+function recordSupportabilityMetric({
+  agent,
+  moduleName,
+  moduleVersion = 'unknown'
+} = {}) {
+  const major = moduleVersion === 'unknown'
+    ? semver.major(process.version)
+    : semver.major(moduleVersion)
+
+  let metric = agent.metrics.getOrCreateMetric(
+    `${SUBSCRIBER_USED}/${moduleName}/${major}`
+  )
+  metric.incrementCallCount()
+
+  metric = agent.metrics.getOrCreateMetric(
+    `${SUBSCRIBER_USED}/${moduleName}`
+  )
+  metric.incrementCallCount()
+}

lib/subscribers/resolve-package-version.js

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2025 New Relic Corporation. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+'use strict'
+
+const path = require('node:path')
+const defaultLogger = require('#agentlib/logger.js').child({
+  component: 'resolve-module-version'
+})
+
+module.exports = resolveModuleVersion
+
+/**
+ * Given a module name, attempt to read the version string from its
+ * associated package manifest. If the module is a built-in, or one that has
+ * been bundled with Node.js (e.g. `undici`), a package manifest will not be
+ * available. In this case, the string "unknown" will be returned.
+ *
+ * @param {string} moduleSpecifier What would be passed to `resolve()`.
+ * @param {object} [deps] Optional dependencies.
+ * @param {object} [deps.logger] Agent logger instance.
+ * @param {Function} [deps.req] Node.js require function.
+ *
+ * @returns {string} The version string from the package manifest or "unknown".
+ */
+function resolveModuleVersion(moduleSpecifier, {
+  logger = defaultLogger,
+  req = require
+} = {}) {
+  let pkgPath
+  try {
+    pkgPath = req.resolve(moduleSpecifier)
+  } catch {
+    logger.warn(
+      { moduleSpecifier },
+      'Could not resolve module path. Possibly a built-in or Node.js bundled module.'
+    )
+    return 'unknown'
+  }
+
+  const cwd = process.cwd()
+  let reachedCwd = false
+  let pkg
+  let base = path.dirname(pkgPath)
+  do {
+    try {
+      pkgPath = path.join(base, 'package.json')
+      pkg = req(pkgPath)
+    } catch {
+      base = path.resolve(path.join(base, '..'))
+      if (base === cwd) {
+        reachedCwd = true
+      } else if (reachedCwd === true) {
+        // We reached the supposed app root, attempted to load a manifest
+        // file in that location, and still couldn't find one. So we give up.
+        pkg = {}
+      }
+    }
+  } while (!pkg)
+
+  const version = pkg.version ?? 'unknown'
+  logger.trace({ moduleSpecifier, version }, 'Resolved package version.')
+  return version
+}

test/lib/custom-assertions/assert-pkg-tracking-metrics.js

@@ -4,9 +4,18 @@
  */
 
 'use strict'
-const NAMES = require('#agentlib/metrics/names.js')
-const assertMetrics = require('./assert-metrics')
+
 const semver = require('semver')
+const assertMetrics = require('./assert-metrics')
+
+const {
+  FEATURES: {
+    INSTRUMENTATION: {
+      SUBSCRIBER_USED,
+      ON_REQUIRE
+    }
+  }
+} = require('#agentlib/metrics/names.js')
 
 /**
  * assertion to verify tracking metrics for a given
@@ -16,19 +25,29 @@ const semver = require('semver')
  * @param {string} params.pkg name of package
  * @param {string} params.version version of package
  * @param {Agent} params.agent agent instance
+ * @param {boolean} params.subscriberType When true, the metrics are expected
+ * to have been generated from a subscriber based instrumentation. Otherwise,
+ * the metrics are expected to be generated from a shimmer based
+ * instrumentation.
  * @param {object} [deps] Injected dependencies.
  * @param {object} [deps.assert] Assertion library to use.
  */
 module.exports = function assertPackageMetrics(
-  { pkg, version, agent },
+  { pkg, version, agent, subscriberType = false },
   { assert = require('node:assert') } = {}
 ) {
-  const metrics = [
-    [{ name: `${NAMES.FEATURES.INSTRUMENTATION.ON_REQUIRE}/${pkg}` }]
-  ]
+  const metrics = []
+  const prefix = subscriberType === true
+    ? `${SUBSCRIBER_USED}/${pkg}`
+    : `${ON_REQUIRE}/${pkg}`
 
+  metrics.push([{ name: prefix }])
   if (version) {
-    metrics.push([{ name: `${NAMES.FEATURES.INSTRUMENTATION.ON_REQUIRE}/${pkg}/Version/${semver.major(version)}` }])
+    const major = semver.major(version)
+    const suffix = subscriberType === true
+      ? `/${major}`
+      : `/Version/${major}`
+    metrics.push([{ name: `${prefix}${suffix}` }])
   }
 
   assertMetrics(agent.metrics, metrics, false, false, { assert })

test/unit/lib/subscribers/base.test.js

@@ -182,6 +182,38 @@ test('should subscribe/unsubscribe to specific events on channel', (t) => {
   assert.equal(subscriber.subscriptions, null)
 })
 
+test('handler should record supportability metrics on first invocation', async (t) => {
+  const plan = tspl(t, { plan: 5 })
+  const { agent, subscriber } = t.nr
+  const name = 'test-segment'
+  const metricNameBase = 'Supportability/Features/Instrumentation/SubscriberUsed/test-package'
+  subscriber.enable()
+
+  const handler = subscriber.handler
+  let invocations = 0
+  subscriber.handler = (data, ctx) => {
+    invocations += 1
+    return handler.call(subscriber, data, ctx)
+  }
+
+  helper.runInTransaction(agent, () => {
+    const event = { name, moduleVersion: '1.0.0' }
+    subscriber.channel.start.runStores(event, () => {
+      const metrics = agent.metrics._metrics.unscoped
+      plan.equal(metrics[metricNameBase].callCount, 1)
+      plan.equal(metrics[`${metricNameBase}/1`].callCount, 1)
+
+      subscriber.channel.start.runStores(event, () => {
+        plan.equal(metrics[metricNameBase].callCount, 1)
+        plan.equal(metrics[`${metricNameBase}/1`].callCount, 1)
+        plan.equal(invocations, 2)
+      })
+    })
+  })
+
+  await plan.completed
+})
+
 test('should call handler in start if transaction is active and create a new segment', async (t) => {
   const plan = tspl(t, { plan: 4 })
   const { agent, subscriber } = t.nr