IIS URL Rewrite - anchor in input causing strange behaviour.

KevinRHawley 1

Hi.
We recently migrated some content on a legacy IIS platform to a SharePoint online instance.
However, there are some documents in the wild & not in our control which contain links to the old IIS site.
We have successfully handled 99% of these using the URL Rewrite module to redirect to the new SharePoint locations.
However, we are seeing some very strange results with some of the input URLs that end in "#_blank".
When these links are clicked on the first time, the target location loads fine. However, if the very same link is clicked on again in the same browser session, then the entire query string is omitted from the target URL.
This happens even when using an incognito browser which cache cleared, etc.
For security reasons I can't put the actual rule here, but it's along the lines of
<rule name="A Rule Name" stopProcessing="true">
<match url="MatchThisSimplePattern" />
<action type="Redirect" url="https://site.sharepoint.com/sites/blah-blah/this/that/AllItems.aspx?id=%2Fsites%2Fstuff%2Dmorestuff%2Fthing%2Fsome%2Fthing%2Epdf&parent=%2Fstuff%2Fmorestuff%2things" appendQueryString="false" />
</rule>
And the URL of the source link is similar to https://domain.com/text/stuff/MatchThisSimplePattern.pdf#_blank
Note, if the source is entered in the browser without the #_blank, the issue goes away. Unfortunately, we can't update the source links we're trying to redirect.
In the above case, the redirect would happen the first time to the full target URL. The second time, everything beyond AllItems.aspx is removed from the target URL.
I've used a test IIS instance to make sure there is only one redirect (or any other) rule in existence, to make sure no other rules are causing any issues.
I can find no help or references to similar problems either in the URL Rewrite documentation, or anywhere else online.
Note, I've also tried adding as a Rewrite map entry, minus the #_blank. This produced the same behaviour.
Thanks
Kevin

KevinRHawley 1 Reputation point

2022-12-02T05:34:59.803+00:00

Update: A test by redirecting to google with a query string seems to indicate this is something happening in SharePoint. It works fine with Google. The Network tab in browser debug tools seems to indicate the redirect is correct. So something weird is happening in SharePoint. Theoretically, SharePoint shouldn't know whether the original URL had #_blank in it, but this does make a difference, such that the correct SharePoint location is arrived at only on the first occasion in one session. Each new time, SharePoint seems to lose the query string.
Yurong Dai-MSFT 2,831 Reputation points Microsoft Vendor

2022-12-05T10:05:12.167+00:00

Hi @ KevinRHawley-8826,

Now I think I understand your problem description. You have created URL rewrite rules, when you access a URL with an anchor, similar to: https://domain.com/text/stuff/MatchThisSimplePattern.pdf#_blank, the first access can be correctly redirected to https:/ /site.sharepoint.com/sites/blah-blah/this/that/AllItems.aspx?id=%2Fsites%2Fstuff%2Dmorestuff%2Fthing%2Fsome%2Fthing%2Epdf&parent=%2Fstuff%2Fmorestuff %2things, but if you access again, it will be redirected to https://site.sharepoint.com/sites/blah-blah/this/that/AllItems.aspx. Please correct me if I understand it wrong.
KevinRHawley 1 Reputation point

2022-12-05T23:04:12.357+00:00

Yes, thanks, I know this.
However, this doesn't explain why this situation occurs when #_blank is part of the source URL, but does not when it's not. Whatever the HTTP specification says, this is definitely having an effect on the target.
I appreciate how weird this issue seems. That's why I'm kind of stuck as to what to do about it.
KevinRHawley 1 Reputation point

2022-12-05T23:05:12.163+00:00

Have also tested in at least 3 different browsers, and it occurs in all.
Yurong Dai-MSFT 2,831 Reputation points Microsoft Vendor

2022-12-06T07:08:42.307+00:00

Hi @KevinRHawley ,
I suggest you try using FRT to trace rewrite rules, this will generate detailed log files where you can see how the rules are used internally. Then check the log files generated by the first access and the second access respectively, and compare whether there are any differences. For how to use failed request tracing to trace rewrite rules, please see this link: https://learn.microsoft.com/en-us/iis/extensions/url-rewrite-module/using-failed-request-tracing-to-trace-rewrite-rules
KevinRHawley 1 Reputation point

2022-12-11T23:23:10.697+00:00

Thanks.
Appreciate the response. Sorry for the slow reply. We've gone back to the source & have managed to persuade the 3rd party with the #_blank in their links to just update them to the new document locations.
I'm still curious to know what the root cause of this is, though. As has been pointed out, according to the HTTP specification, the server shouldn't know the anchor is there.
Kevin

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IIS URL Rewrite - anchor in input causing strange behaviour.

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