GCP Structured Logger

Outputs structured logs that are formatted in GCP logging.

Basic Usage

Most basic usage it to create a Logging object and use the logger property.

const { Logging, LogSeverity } = require('gcp-structured-logger')

const logging = new Logging({
   projectId: '<project-id>',
   logName: '<label for logName>', // Useful for filtering in Log viewer
   serviceContext: {
      service: '<service name>', // Name that appears in Error Reporter
      version: '<version>', // Optional version
   },
   extraLabels: { // Optional extra labels useful for more filtering
   },
   requestUserExtractor: () => {} // See below
})

logging.logger.info('Some log message', {
   extra: 'data'
}, ['Array'])

Error reporting

To report errors to GCP Error Reporting the reportError method on a logger can be used. An optional severity can also be passed in, or it is picked up from the provided error. If no severity is passed in ERROR is used.

const err = new Error('An error occurred')

logging.logger.reportError(err)

// With severity
logging.logger.reportError(err, LogSeverity.ALERT)

Monitoring Node Process

These get logged out to GCP Error reporting.

// Listen out for uncaughtException (uses uncaughtExceptionMonitor in v12.17+) and unhandled Promise rejections
logging.attachToProcess(logging.logger)

// To remove from the process
const detachLogger = logging.attachToProcess(logging.logger)
detachLogger()

With Express

Can be use with express as a logging middleware and error handler.

If the err has a statusCode or status property that is greater or equal to 500, then the severity of the err is set to WARNING.

const express = require('express')

const app = express()

// App setup - set port, trust proxy, etc

// Add ability to use req.log in later middleware
app.use(logger.makeLoggingMiddleware())

app.use((req, res, next) => {
   req.log.debug('Incoming request')
   next()
})

// Add routes
// And a final error handler if needed
app.use((req, res, next) => next({ status: 404, message: 'Not found' }))

// Report next(err)
app.use(logger.makeErrorMiddleware())

With NextJS

Can be use Next.js in the middleware file, it should be added as the first middleware (to allow you to use req.log in future middlewares). This then adds the .log property onto all requests.

import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'
 
export function middleware(request: NextRequest) {
   logger.nextJSMiddleware(request);

   // Continue or do usual middleware handling
   return NextResponse.next();
}

You can also pass in a requestUserExtractor function when creating a Logging instance for setting the user of the error.

This is useful if you've attached the logged in user, etc. to the request or the headers contains some user info.

If requestUserExtractor returns no value (or is not provided), no user will be set on the reported error.

const logging = new Logging({
   projectId: '<project-id>',
   logName: '<label for logName>',
   serviceContext: {
      service: '<service name>',
   },
   requestUserExtractor: req => {
      // Parameter is the request that log.reportError was called on
      return req.get('user-id')
   },
})