Hiding Chrome’s intranet redirect detector requests (aka weird requests) in Fiddler

September 15, 2015

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This morning I saw this Tweet by Eric Lawrence, the creator of Fiddler:

#lol “Fiddler periodically receives alien communications” http://t.co/IZh0UrkbEP

This is a well known trick of Chrome, which you can read about here, and see its source code here.

Question is, now that we know what those “alien” requests are, how do we get rid of them in Fiddler’s session list?

1. Open Fiddler’s script (either through the FiddlerScript tab, or in the menu Rules->Customize Rules…)

2. Locate the OnReturningError method, and uncomment it

3. Place the following code in the method:

if (oSession.LocalProcess.StartsWith("chrome") && oSession.responseCode == 502 && oSession.HTTPMethodIs("HEAD") && oSession.hostname.IndexOf('.') < 0 && oSession.PathAndQuery.Equals("/")) {
    oSession["ui-hide"] = "Ignore ChromeDNSChecker";
    FiddlerApplication.Log.LogString("Hiding Chrome's intranet redirect detector request: " + oSession.url);

4. Restart Fiddler, and that should do the trick.

If you suspect the script is hiding valid requests, check the Log tab, and correct the script to ignore your host names.



Update (September 15th, 2015):

Altered the ui-hide reason from “true” to “Ignore ChromeDNSChecker” following Eric’s recommendation. This prints better when using Help->Troubleshoot to diagnose filtered session (filtered sessions appear with strikethrough, and the reason for hiding is shown in the comments column)

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