Add custom information to the Stackdriver error log in Firebase Functions.

index.js

const functions = require('firebase-functions')

const reportError = require('./reportError')
const raiseReferenceError = require('./raiseReferenceError')
const raiseSyntaxError = require('./raiseSyntaxError')
const raiseTypeError = require('./raiseTypeError')

exports.stackdriverErrorLogging = functions.https.onRequest((req, res) => {
  try {
    switch (Math.floor(Math.random() * 3)) {
      case 0:
        raiseReferenceError()
        break

      case 1:
        raiseSyntaxError()
        break

      default:
        raiseTypeError()
        break
    }

    // unreachable code
    res.send('Hello from Firebase!')
  } catch (error) {
    reportError(error, { query: req.query }, req).then(() => {
      res.send('an error occurred.')
    })
  }
})

raiseReferenceError.js

module.exports = () => {
  console.log(foo)
}

raiseSyntaxError.js

module.exports = () => {
  eval(',')
}

raiseTypeError.js

module.exports = () => {
  const foo = null
  foo()
}

reportError.js

// https://firebase.google.com/docs/functions/reporting-errors#manually_reporting_errors
const { Logging } = require('@google-cloud/logging')

// Instantiates a client
const logging = new Logging()

module.exports = function reportError (err, context = {}, req = undefined) {
  // Use Stackdriver only on production environment.
  if (process.env.NODE_ENV !== 'production') {
    return new Promise((resolve, reject) => {
      console.error(err, context)
      return resolve()
    })
  }

  const log = logging.log('cloudfunctions.googleapis.com%2Fcloud-functions')

  // https://cloud.google.com/logging/docs/api/ref_v2beta1/rest/v2beta1/MonitoredResource
  const metadata = {
    severity: 'ERROR',
    resource: {
      type: 'cloud_function',
      labels: {
        function_name: process.env.FUNCTION_NAME,
        project: process.env.GCLOUD_PROJECT,
        region: process.env.FUNCTION_REGION
      }
    }
  }

  // Extract execution_id, trace from http request
  // https://stackoverflow.com/a/55642248/7908771
  if (req) {
    const traceId = req.get('x-cloud-trace-context').split('/')[0]
    Object.assign(metadata, {
      trace: `projects/${process.env.GCLOUD_PROJECT}/traces/${traceId}`,
      labels: {
        execution_id: req.get('function-execution-id')
      }
    })
  }

  // https://cloud.google.com/error-reporting/reference/rest/v1beta1/ErrorEvent
  const errorEvent = {
    message: err.stack,
    serviceContext: {
      service: process.env.FUNCTION_NAME,
      resourceType: 'cloud_function'
    },
    context: context
  }

  // Write the error log entry
  return new Promise((resolve, reject) => {
    log.write(log.entry(metadata, errorEvent), (error) => {
      if (error) {
        return reject(error)
      }
      return resolve()
    })
  })
}