Only accept a certain file type in FileField, server-side

Question

How can I restrict FileField to only accept a certain type of file (video, audio, pdf, etc.) in an elegant way, server-side?

Answer 1

A few people have suggested using python-magic to validate that the file actually is of the type you are expecting to receive. This can be incorporated into the validator suggested in the accepted answer:

import os
import magic
from django.core.exceptions import ValidationError

def validate_is_pdf(file):
    valid_mime_types = ['application/pdf']
    file_mime_type = magic.from_buffer(file.read(1024), mime=True)
    if file_mime_type not in valid_mime_types:
        raise ValidationError('Unsupported file type.')
    valid_file_extensions = ['.pdf']
    ext = os.path.splitext(file.name)[1]
    if ext.lower() not in valid_file_extensions:
        raise ValidationError('Unacceptable file extension.')

This example only validates a pdf, but any number of mime-types and file extensions can be added to the arrays.

Assuming you saved the above in validators.py you can incorporate this into your model like so:

from myapp.validators import validate_is_pdf

class PdfFile(models.Model):
    file = models.FileField(upload_to='pdfs/', validators=(validate_is_pdf,))