ImageField not validating due to missing libraries

[fabian@…]

IMHO, it is worth to be mentioned in the documentation that libjpeg must be available on the system PRIOR to PIL being installed.
Else, validating a form with an ImageField will fail with corrupt image error, due to django/forms/fields.py plays down the Exception in line 592, which most probably is IOError: "decoder jpeg not available"

On a Mac, it can be easily downloaded on
​http://ethan.tira-thompson.com/Mac_OS_X_Ports.html

On most Linux distributions, libjpeg-dev is available in the repositories.

Afterwards, PIL must be re-compiled and -installed in order to let it know about it.

[Simon Charette]

When installing PIL using setup.py install or via pip you get clear warnings that support for a specific format is not available.

    --------------------------------------------------------------------
    *** TKINTER support not available (Tcl/Tk 8.5 libraries needed)
    *** JPEG support not available
    *** ZLIB (PNG/ZIP) support not available
    *** FREETYPE2 support not available
    *** LITTLECMS support not available
    --------------------------------------------------------------------
    To add a missing option, make sure you have the required
    library, and set the corresponding ROOT variable in the
    setup.py script.

IMHO the warning raised by PIL's setup nails it but I'd like to hear someone else about that.

[Aymeric Augustin]

I also don't believe that our installation documentation has to go into this level of detail, especially since PIL's installer does the right thing.

The ticket also says that Django is masking an exception. Maybe we could improve that part?

[Simon Charette]

I can't see how we can be more explicit without confusing the user. The actual exception message is "Upload a valid image. The file you uploaded was either not an image or a corrupted image.".

The only think I can think of is raising a different error message if DEBUG=True by telling the developer this might be due to an unavailable decoder?

[fabian@…]

django/forms/fields.py, lines 592 - 596:

        except Exception: # Python Imaging Library doesn't recognize it as an image
            raise ValidationError(self.error_messages['invalid_image'])
        if hasattr(f, 'seek') and callable(f.seek):
            f.seek(0)
        return f

I suggest to put the Exception message into the error if DEBUG=True.
Otherwise, the developer always has to check the django code to get those details.

So, for instance:

        except Exception: # Python Imaging Library doesn't recognize it as an image
            if settings.DEBUG: raise ValidationError(self.error_messages['invalid_image'], e)
            raise ValidationError(self.error_messages['invalid_image'])
        if hasattr(f, 'seek') and callable(f.seek):
            f.seek(0)
        return f

[anonymous]

Of course it'll be

        except Exception, e: # Python Imaging Library doesn't recognize it as an image
            if settings.DEBUG: raise ValidationError(self.error_messages['invalid_image'], e)
            raise ValidationError(self.error_messages['invalid_image'])
        if hasattr(f, 'seek') and callable(f.seek):
            f.seek(0)
        return f

...

[Aymeric Augustin]

Well, this won't help debug the issue when it happens in production. I'm going to improve the docs a bit.

[Aymeric Augustin]

I just attached a proposal. What do you think?

[Simon Charette]

Looks good to me.

[anonymous]

Agreed, I think this should do it. Thanks.

[Aymeric Augustin <aymeric.augustin@…>]

In [5e94ef293cb1cfe4dc43cbd5509653c0e0bf66cf]:

Fixed #18374 -- Explained "corrupt image" error

Thanks fabian and charettes.