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Custom Spans

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Custom Spans

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This is an example of how to use custom spans. For general information about the Elastic APM Node.js Span API, see the Span API documentation.

If you want to track and time a custom event that happens in your application during a transaction, you can add a new span to an existing transaction.

In the example below, we create an Express app that times how long it takes to:

  1. Receive the body of an HTTP POST or PUT request
  2. Parse JSON sent by the client 
var apm = require('elastic-apm-node').start()
var app = require('express')()

// body reader middleware
app.use(function (req, res, next) {
  if (req.method !== 'POST' && req.method !== 'PUT') {
    return next()
  }

  // `startSpan` will only return a span if there's an
  // active transaction
  var span = apm.startSpan('receiving body')

  var buffers = []
  req.on('data', function (chunk) {
    buffers.push(chunk)
  })
  req.on('end', function () {
    req.body = Buffer.concat(buffers).toString()

    // end the span after we're done loading data from the
    // client
    if (span) span.end()

    next()
  })
})

// JSON parser middleware
app.use(function (req, res, next) {
  if (req.headers['content-type'] !== 'application/json') {
    return next()
  }

  // start a span to measure the time it takes to parse
  // the JSON
  var span = apm.startSpan('parse json')

  try {
    req.json = JSON.parse(req.body)
  } catch (e) {}

  // when we've processed the json, stop the custom span
  if (span) span.end()

  next()
})

// ...your route handler goes here...

app.listen(3000)
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