Network-error-logging NPM

Network Error Logging

This is Express middleware to set the NEL HTTP response header. You can read more about it here.

To use:

const NEL = require('network-error-logging')

// ...

app.use(NEL({
	report_to: 'endpoint-1', // REQUIRED to register. OPTIONAL if intention is to remove a previous registration. defined in the Report-To header
	max_age: 31536000, // REQUIRED. seconds
	include_subdomains: true, // OPTIONAL
	success_fraction: 0.5, // OPTIONAL. sampling rate
	failure_fraction: 0.5, // OPTIONAL. sampling rate
	request_headers: ["If-None-Match"], // OPTIONAL. request headers whose names and values are included in the network error reports
	response_headers: ["ETag"] // OPTIONAL. response headers whose names and values are included in the network error reports
}))

For further documentation on each field, see https://w3c.github.io/network-error-logging/#nel-response-header.

This header is best set with a previously defined Report-To group. This module is a great way to do that.

https://report-uri.com/ is a great reporting platform for monitoring CSP, NEL, etc. error logs.