models: handle ENOENT from file-magic (fixes #22745)

magic.Magic.file() does not return None or raise an exception on a
missing file, it just return the string "cannot open ...".

fargo/fargo/models.py

@@ -5,11 +5,6 @@ import os
 import re
 import threading
 
-try:
-    import magic
-except ImportError:
-    magic = None
-
 from django.conf import settings
 from django.core.urlresolvers import reverse
 from django.db import models
@@ -181,11 +176,8 @@ class Document(models.Model):
         '''Create content_hash if new'''
         if not self.content_hash:
             self.content_hash = utils.sha256_of_file(self.content)
-        if magic is not None:
-            magic_object = magic.open(magic.MIME)
-            magic_object.load()
-            self.mime_type = magic_object.file(str(self.content.file.name)).split(';')[0]
-            magic_object.close()
+        if not self.mime_type:
+            self.mime_type = utils.get_mime_type(self.content.file.name) or ''
         super(Document, self).save(*args, **kwargs)
 
     @property

fargo/fargo/utils.py

@@ -1,5 +1,12 @@
 import hashlib
+
 from django.utils.timezone import utc
+from django.utils.encoding import smart_bytes
+
+try:
+    import magic
+except ImportError:
+    magic = None
 
 
 def to_isodate(dt):
@@ -18,3 +25,18 @@ def sha256_of_file(f):
     for chunk in f.chunks():
         hasher.update(chunk)
     return hasher.hexdigest()
+
+
+def get_mime_type(path):
+    if magic is None:
+        return None
+
+    magic_object = magic.open(magic.MIME)
+    magic_object.load()
+    mime_type = magic_object.file(smart_bytes(path))
+    magic_object.close()
+    if mime_type:
+        mime_type = mime_type.split(';')[0]
+        if mime_type.startswith('cannot open'):
+            mime_type = None
+    return mime_type