Javascript files are served up as HTML files when using static-files declaration in appengine-web.xml

Question

I enabled the caching of static image files in appengine using the following in my appengine-web.xml:

<static-files>
<include path="/css/images/**.gif" expiration="1d" />
    <include path="/css/images/**.png" expiration="1d" />
    <include path="/css/images/wind_pointers/*.png" expiration="7d" />
    <include path="/css/images/**.jpg" expiration="1d" />
    <include path="/errors/*" />
</static-files>

This worked very well until I discovered an odd side effect: Sometimes, appengine serves up a JavaScript file with the content of my HTML page, so the result is that I get loads of JavaScript errors because the JavaScript interpreter is being fed HTML instead of JS:

JavaScript errors caused by .js file served up with HTML content

Now, if I simply comment out that static-files section in appengine-web.xml that I mentioned above, everything works fine: .js files are served up with their own content and I have no problems:

Javascript files are served up correctly.

This seems odd to me. The .js files aren't even in the directories specified in that static-files section. Have I got the syntax wrong in my appengine-web.xml that is causing some wierd bug to manifest?

Luckily, I am able to reproduce this easily and reliably on both the deployed app and my local dev server, by simply commenting out the static-files section in appengine-web.xml. It happens in both Chrome and IE. I'm using the Java appengine.

Did you try adding <include> elements for your .js files to your <static-files> tag entry ? — rickz
Another idea: add entry to your web.xml <mime-mapping> <extension>js</extension> <mime-type>application/javascript</mime-type> </mime-mapping> — rickz

Mark Silberbauer Mark Silberbauer · Accepted Answer · 2013-02-01T17:00:56

I have managed to figure out what was happening:

I had a filter in my web.xml that was coded with the intention that a special HTML page would be returned if the user requested a page but wasn't logged in. However, I found that this filter was applying itself to requests that browsers would make for .js files too so my filter would return the HTML file instead of the .js file.

The odd thing is that I don't have the problem when the section is removed from appengine-web.xml. Without that section, AppEngine reverts to default behaviour which according to the docs is to consider all files as static in which case I'd expect the problem to always happen. Also, sometimes a .js would return and sometimes an HTML would return - it seemed to be a race condition somewhere. It's still a mystery to me.

Anyway, I now ensure that the filter is only applied to requests for the site's HTML pages and this solved the issue. Thanks for all your comments.

Javascript files are served up as HTML files when using static-files declaration in appengine-web.xml

1 Answers