Add Zipkin trace capturing with output to JSON. (#22106)

@timneutkens this adds a trace capturing script alongside the other tracing sundry.  This will be utilized by the performance automation.  Additionally, its nice to have an option other than running the ZipKin JAR to get at the raw data.

bench/capture-trace.js

@@ -0,0 +1,66 @@
+const http = require('http')
+const fs = require('fs')
+
+const PORT = 9411
+const HOST = '0.0.0.0'
+
+const traces = []
+
+const onReady = () => console.log(`Listening on http://${HOST}:${PORT}`)
+const onRequest = async (req, res) => {
+  if (
+    req.method !== 'POST' ||
+    req.url !== '/api/v2/spans' ||
+    (req.headers && req.headers['content-type']) !== 'application/json'
+  ) {
+    res.writeHead(200)
+    return res.end()
+  }
+
+  try {
+    const body = JSON.parse(await getBody(req))
+    for (const traceEvent of body) {
+      traces.push(traceEvent)
+    }
+    res.writeHead(200)
+  } catch (err) {
+    console.warn(err)
+    res.writeHead(500)
+  }
+
+  res.end()
+}
+
+const getBody = (req) =>
+  new Promise((resolve, reject) => {
+    let data = ''
+    req.on('data', (chunk) => {
+      data += chunk
+    })
+    req.on('end', () => {
+      if (!req.complete) {
+        return reject('Connection terminated before body was received.')
+      }
+      resolve(data)
+    })
+    req.on('aborted', () => reject('Connection aborted.'))
+    req.on('error', () => reject('Connection error.'))
+  })
+
+const main = () => {
+  const args = process.argv.slice(2)
+  const outFile = args[0] || `./trace-${Date.now()}.json`
+
+  process.on('SIGINT', () => {
+    console.log(`\nSaving to ${outFile}...`)
+    fs.writeFileSync(outFile, JSON.stringify(traces, null, 2))
+    process.exit()
+  })
+
+  const server = http.createServer(onRequest)
+  server.listen(PORT, HOST, onReady)
+}
+
+if (require.main === module) {
+  main()
+}