feat: add req-frequency

package.json

@@ -99,6 +99,7 @@
     "data-uri-regex": "~0.1.4",
     "data-uri-to-buffer": "~5.0.1",
     "debug-logfmt": "~1.2.0",
+    "frequency-counter": "~1.0.1",
     "got": "~11.8.6",
     "helmet": "~7.1.0",
     "html-get": "~2.14.0",

src/server.js

@@ -11,6 +11,8 @@ const { API_URL, NODE_ENV, PORT } = require('./constant')
 
 const server = createServer(require('.'))
 
+require('./util/req-frequency')(server)
+
 server.listen(PORT, () => {
   debug({
     status: 'listening',

src/util/req-frequency.js

@@ -0,0 +1,21 @@
+'use strict'
+
+const debug = require('debug-logfmt')('req-frequency')
+const FrequencyCounter = require('frequency-counter')
+const onFinished = require('on-finished')
+
+module.exports = server => {
+  const min = new FrequencyCounter(60)
+  let requests = 0
+  const info = () => {
+    const perMinute = min.freq()
+    return { requests, perMinute, perSecond: Number(perMinute / 60).toFixed(1) }
+  }
+  server.on('request', (_, res) => {
+    ++requests
+    min.inc()
+    debug(info())
+    onFinished(res, () => --requests)
+  })
+  return info
+}