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"thumb.php" should not throw fatal MWException when missing query parameters
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Description

[/w/thumb.php?f=Example.png](https://en.wikipedia.org/w/thumb.php?f=Example.png)

[/w/thumb.php?f=Example.png&h=100](https://en.wikipedia.org/w/thumb.php?f=Example.png&h=100)

[c012c80f] /w/thumb.php?f=Screenshot.png MWException from line 60 of .../mediawiki/includes/media/ImageHandler.php: No width specified to ImageHandler::makeParamString

Backtrace:

#0 includes/filerepo/file/File.php(929): ImageHandler->makeParamString(array)
#1 includes/filerepo/file/File.php(912): File->generateThumbName(string, array)
#2 thumb.php(253): File->thumbName(array)
#3 thumb.php(35): wfStreamThumb(array)
#4 {main}

Event Timeline

Krinkle raised the priority of this task from to Needs Triage.
Krinkle updated the task description. (Show Details)
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Presumably this should throw an HTTP 400 error with some sensible text instead?

The exception is not thrown in the strict sense, it is caught and rendered via wfThumbError( 500, $e->getHTML() ). Should we display a human-readable error message instead of the backtrace? Seems helpful for debugging.

ImageHandler::makeParamString() throws MWException when the width is missing; child classes return false instead, and that is handled nicely (compare https://commons.wikimedia.org/w/thumb.php?f=Example.svg ). So there are two ways to fix this:

  1. have ImageHandler::makeParamString() return false - violates the function signature (as documented at MediaHandler::makeParamString()) but child classes do that already so this at least makes it consistent
  2. create a new exception subclass
In T88508#1016745, @Tgr wrote:

have ImageHandler::makeParamString() return false

That does not seem to be handled correctly by the methods calling makeParamString, so better not mess with it.

gerritbot added a subscriber: gerritbot.

Change 188730 had a related patch set uploaded (by Gergő Tisza):
Handle missing width nicely in thumb.php

https://gerrit.wikimedia.org/r/188730

Patch-For-Review

Change 188730 merged by jenkins-bot:
Handle missing width nicely in thumb.php

https://gerrit.wikimedia.org/r/188730