All Fanstatic resources being served with ‘text/html’ mimetype by WebOb/WSGI

If you’re finding that you’re using Fanstatic to serve static resources within your Python-based server process, you may be left scracthing your head if you suddenly find that resources aren’t being served correctly. For me, this was manifesting as an incorrect Content-Type header, always being set to text/html for any type of static file being served. As a side effect, because I’m using Diazo to theme my backend Pyramid application, this was automatically seeing this mimetype being returned to the browser and trying to “theme” the raw files. The global picture looked like a whole bunch of web fonts that weren’t loading on my end application.

Whoops. There goes a morning.

Solution

Good news - it’s easy; it’s just a difference between environments on two different types of hosts. Deep down under the hood, Fanstatic is serving files using webob.static.FileApp and once you know this key piece of information, it’s easy to see that WebOb is using the Python mimetypes module and its mimetypes.guess_type(filename) function to lookup what type a file is.

So, you just need to make sure that the mimetypes module is able to know about the extensions you’re serving. It uses mimetypes.knownfiles to look up locations for finding mime types (http://docs.python.org/2/library/mimetypes.html#mimetypes.knownfiles). You’ll notice that with the different file locations listed, a different host with different services installed will know about different mimetypes. For instance, if you’re got Apache or Nginx installed on your host, you’ll probably see their mime.types file paths in the list, causing your application to (inadvertently) know about a lot more file extensions.

In case your system is like mine and doesn’t know about web fonts, here’s what I’ve taken to putting into /usr/local/etc/mime.types:

image/svg+xml                         svg svgz
application/vnd.ms-fontobject         eot
application/x-font-ttf                tff
font/opentype                         ott
font/x-woff                           woff
... any other file types your system doesn't know about...

and restarting my Python process. You can confirm if the above worked by checking using:

python -c 'import mimetypes; print(mimetypes.knownfiles)'

and also:

>>> import mimetypes; print(mimetypes.guess_type('foo.woff'))
('font/x-woff', None)

to make sure something that isn’t (None, None) returned.

That’s all.

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