Validate uploaded album archives with libmagic

requirements.txt

@@ -12,3 +12,4 @@ djangorestframework>=3.5.3,<3.6
 django-ical>=1.4,<2
 django-libsass>=0.7,<1
 django-cors-headers>=2.0.0,<2.1
+python-magic>=0.4.13,<0.5

website/photos/admin.py

+import magic
 import os
 import tarfile
 from zipfile import ZipFile, is_zipfile, ZipInfo
@@ -14,7 +15,7 @@ from .models import Album, Photo
 
 def validate_uploaded_archive(uploaded_file):
     types = ['application/gzip', 'application/zip']
-    if uploaded_file.content_type not in types:
+    if magic.from_buffer(uploaded_file.read(), mime=True) not in types:
         raise ValidationError("Only zip and tar files are allowed.")