feat: add support for custom measurments

README.md

@@ -50,7 +50,14 @@ server.listen(0, () => {
   - __`histogram`__ `<object>` prom-client [histogram options](https://github.com/siimon/prom-client?tab=readme-ov-file#histogram). Use it if you want to customize the histogram.
   - __`summary`__ `<object>` prom-client [summary options](https://github.com/siimon/prom-client?tab=readme-ov-file#summary). Use it if you want to customize the summary.
 
+Returns:
+
+- __`histogram`__ `<Histogram>` The histogram metric for measuring request duration.
+- __`summary`__ `<Summary>` The summary metric for measuring request duration.
+- __`startTimer({ request, [server] })`__ `<function>` A function that starts a timer for measuring request duration.
+The function can be used to add custom measurements that are not collected by diagnostic channel.
+- __`endTimer({ request, response, [server] })` `<function>` A function that ends a timer for custom request duration measurement.
+
 ## License
 
 Apache-2.0
-

index.js

@@ -64,19 +64,19 @@ module.exports = (registry, config = {}) => {
 
   const timers = new WeakMap()
 
-  diagnosticChannel.subscribe('http.server.request.start', (event) => {
-    const { request, server } = event
+  function startTimer (options) {
+    const { request, server } = options
 
     if (ignoreRoute(request, server)) return
 
     const summaryTimer = summary.startTimer()
     const histogramTimer = histogram.startTimer()
 
     timers.set(request, { summaryTimer, histogramTimer })
-  })
+  }
 
-  diagnosticChannel.subscribe('http.server.response.finish', (event) => {
-    const { request, response, server } = event
+  function endTimer (options) {
+    const { request, response, server } = options
 
     if (ignoreRoute(request, server)) return
 
@@ -93,5 +93,10 @@ module.exports = (registry, config = {}) => {
 
     if (summaryTimer) summaryTimer(labels)
     if (histogramTimer) histogramTimer(labels)
-  })
+  }
+
+  diagnosticChannel.subscribe('http.server.request.start', event => startTimer(event))
+  diagnosticChannel.subscribe('http.server.response.finish', event => endTimer(event))
+
+  return { summary, histogram, startTimer, endTimer }
 }

test/inject.test.js

@@ -0,0 +1,140 @@
+'use strict'
+
+const assert = require('node:assert/strict')
+const { test } = require('node:test')
+const { setTimeout: sleep } = require('node:timers/promises')
+const { Registry } = require('prom-client')
+const httpMetrics = require('../index.js')
+const { calculateEpsilon } = require('./helper.js')
+
+test('should calculate the http inject request duration histogram', async (t) => {
+  const registry = new Registry()
+  const { startTimer, endTimer } = httpMetrics(registry)
+
+  async function inject (url, ms) {
+    const request = { method: 'GET', url }
+    const response = { statusCode: 200 }
+
+    startTimer({ request })
+    await sleep(ms)
+    endTimer({ request, response })
+  }
+
+  await Promise.all([
+    inject('/500ms', 500),
+    inject('/1s', 1000),
+    inject('/2s', 2000),
+  ])
+
+  const expectedMeasurements = [0.501, 1.001, 2.001]
+  const expectedEpsilon = 0.05
+
+  const metrics = await registry.getMetricsAsJSON()
+  assert.strictEqual(metrics.length, 2)
+
+  const histogramMetric = metrics.find(
+    (metric) => metric.name === 'http_request_duration_seconds'
+  )
+  assert.strictEqual(histogramMetric.name, 'http_request_duration_seconds')
+  assert.strictEqual(histogramMetric.type, 'histogram')
+  assert.strictEqual(histogramMetric.help, 'request duration in seconds histogram for all requests')
+  assert.strictEqual(histogramMetric.aggregator, 'sum')
+
+  const histogramValues = histogramMetric.values
+
+  {
+    const histogramCount = histogramValues.find(
+      ({ metricName }) => metricName === 'http_request_duration_seconds_count'
+    )
+    assert.strictEqual(histogramCount.value, expectedMeasurements.length)
+  }
+
+  {
+    const histogramSum = histogramValues.find(
+      ({ metricName }) => metricName === 'http_request_duration_seconds_sum'
+    )
+    const value = histogramSum.value
+    const expectedValue = expectedMeasurements.reduce((a, b) => a + b, 0)
+    const epsilon = calculateEpsilon(value, expectedValue)
+    assert.ok(
+      epsilon < expectedEpsilon,
+      `expected ${expectedValue}, got ${value}, epsilon ${epsilon}`
+    )
+  }
+
+  for (const { metricName, labels, value } of histogramValues) {
+    assert.strictEqual(labels.method, 'GET')
+    assert.strictEqual(labels.status_code, 200)
+
+    if (metricName !== 'http_request_duration_seconds_bucket') continue
+
+    const expectedBucketMeasurements = expectedMeasurements.filter((m) => {
+      let le = labels.le
+      if (le === '+Inf') le = Infinity
+      if (le === '-Inf') le = -Infinity
+      return m < le
+    })
+
+    const expectedValue = expectedBucketMeasurements.length
+    assert.strictEqual(
+      value, expectedValue,
+      `le ${labels.le}: expected ${JSON.stringify(expectedBucketMeasurements)}`
+    )
+  }
+
+  const summaryMetric = metrics.find(
+    (metric) => metric.name === 'http_request_summary_seconds'
+  )
+  assert.strictEqual(summaryMetric.name, 'http_request_summary_seconds')
+  assert.strictEqual(summaryMetric.type, 'summary')
+  assert.strictEqual(summaryMetric.help, 'request duration in seconds summary for all requests')
+  assert.strictEqual(summaryMetric.aggregator, 'sum')
+
+  const summaryValues = summaryMetric.values
+
+  {
+    const summaryCount = summaryValues.find(
+      ({ metricName }) => metricName === 'http_request_summary_seconds_count'
+    )
+    assert.strictEqual(summaryCount.value, expectedMeasurements.length)
+  }
+
+  {
+    const summarySum = summaryValues.find(
+      ({ metricName }) => metricName === 'http_request_summary_seconds_sum'
+    )
+    const value = summarySum.value
+    const expectedValue = expectedMeasurements.reduce((a, b) => a + b, 0)
+    const epsilon = calculateEpsilon(value, expectedValue)
+    assert.ok(
+      epsilon < expectedEpsilon,
+      `expected ${expectedValue}, got ${value}, epsilon ${epsilon}`
+    )
+  }
+
+  const expectedSummaryValues = {
+    0.01: expectedMeasurements[0],
+    0.05: expectedMeasurements[0],
+    0.5: expectedMeasurements[1],
+    0.9: expectedMeasurements[2],
+    0.95: expectedMeasurements[2],
+    0.99: expectedMeasurements[2],
+    0.999: expectedMeasurements[2],
+  }
+
+  for (const { labels, value } of summaryValues) {
+    assert.strictEqual(labels.method, 'GET')
+    assert.strictEqual(labels.status_code, 200)
+
+    const quantile = labels.quantile
+    if (quantile === undefined) continue
+
+    const expectedValue = expectedSummaryValues[quantile]
+    const epsilon = calculateEpsilon(value, expectedValue)
+
+    assert.ok(
+      epsilon < expectedEpsilon,
+      `expected ${expectedValue}, got ${value}, epsilon ${epsilon}`
+    )
+  }
+})