id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
18515	Problematic validation code in FileField	Michael Angeletti	nobody	"The following code in {{{django.db.models.fields.files}}} (line # 235 in master @ HEAD) is problematic.

{{{
    def validate(self, value, model_instance):
        """"""
        Validates that the generated file name still fits within max_length.
        """"""
        # The generated file name stored in the database is generally longer
        # than the uploaded file name. Using the length of generated name in
        # the error message would be confusing. However, in the common case
        # (ie. upload_to='path/to/upload/dir'), the length of the generated
        # name equals the length of the uploaded name plus a constant. Thus
        # we can tell the user how much shorter the name should be (roughly).
        length = len(self.generate_filename(model_instance, value.name))
        if self.max_length and length > self.max_length:
            error_values = {'extra': length - self.max_length}
            raise ValidationError(self.error_messages['max_length'] % error_values)
}}}

Given the following:

{{{
def oops_asset_path(instance, filename):
    """"""
    Returns the upload path for a ``Oops.asset``.
    """"""
    return 'oops/user_{upk}/{dt}/{fn}'.format(
        upk=instance.user_id,
        dt=timezone.now().strftime('%Y_%j_%H_%M_%S_%f'),
        fn=re.sub(r'[^\w\.]', '_', filename).lower())


class Oops(models.Model):
    asset = models.FileField(_(u'asset'), upload_to=oops_asset_path)

}}}

When an {{{Oops}}} instance is saved with the {{{asset}}} file name {{{the-best-file-name-ever.jpg}}}, it's converted to something like:

{{{
oops/user_3145/2012_178_00_16_02_738638/the_best_file_name_ever.jpg
}}}

which is expected. Then, when the {{{Oops}}} is saved again in a form (e.g., an inline model formset I use for multiple uploads) the above validation code runs the existing name through my {{{oops_asset_path}}}, which returns:

{{{
oops/user_3145/2012_178_00_16_03_457362/oops_user_3145_2012_178_00_16_02_738638_the_best_file_name_ever.jpg
}}}

This causes the {{{max_length}}} validation error, since the new name is clearly too long:

{{{
Filename is 7 characters too long.
}}}

The file name isn't changed permanently, but these erroneous validation errors are only avoided by increasing the field's {{{max_length}}}.

I can't think of any solution to this that doesn't include either a database query or else some sort of annotation on the {{{FileField}}} by forms... both of which scare me."	Bug	closed	File uploads/storage	1.4	Normal	fixed	max_length, FileField, fields	Michael Angeletti	Accepted	1	0	0	0	0	0