A JS Foundation Project

Avoid HTTP redirects in requests

Avoid HTTP redirects in requests (@sonarwhal/rule-no-http-redirects)

no-http-redirects checks if there are any HTTP redirects in the page sonarwhal is analyzing.

Why is this important?

The following is a simplify version of what happens when the user requests a URL in a browser:

  1. DNS Lookup: Translate the domain to an IP. If the browser doesn’t know it, it has to ask a DNS server which in some cases involves multiple queries until the final IP is obtained.
  2. Open a [TCP connection][wikipedia-tcp-establishement] to the IP address requesting the URL.
  3. The server responds to that request by sending some content over the TCP connection. If the resource uses SSL, then TLS negotation(s) happen as well.

When a redirect happens, 3. contains the new URL the browser needs to request, so the whole sequence is repeated. DNS Lookup isn’t cheap, neither is creating a TCP connection. The impact of redirects is even more on mobile users, where the network latency is usually higher. As a rule of thumb, the more you can avoid redirects the better.

What does the rule check?

This rule checks:

  • If the target URL passed to sonarwhal has any redirect. E.g.: http://www.example.com --> http://example.com
  • If any resource in the page has any redirect. E.g.: http://example.com/script.js --> https://example.com/script.js

and alerts if at least one is found.

Examples that trigger the rule

  • Any URL passed to sonarwhal that redirects to another one
  • Any page with a resource (script, css, image) behind a redirect

Examples that pass the rule

  • No redirect for resources nor the target URL.

Can the rule be configured?

By default no redirects are allowed but you can change this behavior.

The following rule configuration used in the .sonarwhalrc file will allow 3 redirects for resources and 1 for the main URL:

"connector": {...},
"formatters": [...],
"rules": {
"no-http-redirects": ["error", {
"max-resource-redirects": 3,
"max-html-redirects": 1

Further Reading