undermythumb now fingerprints images before storage.

exampleproject/blog/models.py

@@ -8,21 +8,25 @@ class BlogPost(models.Model):
     title = models.CharField(max_length=100)
 
     # an image with thumbnails
-    artwork = ImageWithThumbnailsField(max_length=255,
-                                       upload_to='artwork/',
-                                       thumbnails=(('homepage_image', CropRenderer(300, 150)),
-                                                   ('pagination_image', CropRenderer(150, 75))),
-                                       help_text='Source artwork. Thumbnails automatically generated from this field.')
+    artwork = ImageWithThumbnailsField(
+        max_length=255,
+        upload_to='artwork/',
+        blank=True,
+        thumbnails=(('homepage_image', CropRenderer(300, 150)),
+                    ('pagination_image', CropRenderer(150, 75))),
+        help_text='Source artwork. Thumbnails automatically generated '
+                  'from this field.')
 
     # an override field, capable of rolling up a path
-    # when it has no value. useful for overriding 
+    # when it has no value. useful for overriding
     # auto-generated thumbnails. the fallback path
     # should point to an ImageFieldFile of some sort.
     #
     # under the hood, this is just an ImageField
-    homepage_image = ImageFallbackField(fallback_path='artwork.thumbnails.homepage_image',
-                                        upload_to='artwork/',
-                                        help_text='Optional override for "homepage_image" thumbnail.')
+    homepage_image = ImageFallbackField(
+        fallback_path='artwork.thumbnails.homepage_image',
+        upload_to='artwork/',
+        help_text='Optional override for "homepage_image" thumbnail.')
 
     def __unicode__(self):
         return self.title

undermythumb/fields.py

@@ -3,7 +3,6 @@
 from django.db.models.fields.files import (ImageField,
                                            ImageFieldFile,
                                            ImageFileDescriptor)
-from django.utils.encoding import force_unicode
 
 from undermythumb.files import (ThumbnailFieldFile,
                                 ImageWithThumbnailsFieldFile)
@@ -98,10 +97,33 @@ def __init__(self, thumbnails=None, fallback_path=None, *args, **kwargs):
         self.thumbnails = thumbnails or []
         self.fallback_path = fallback_path
 
-    def get_thumbnail_filename(self, instance, original, key, ext):
-        # return filename
-        base, _ext = os.path.splitext(force_unicode(original))
-        return '%s-%s%s' % (base, key, ext)
+    def get_thumbnail_filename(self, instance, original_file,
+                               thumbnail_name, ext):
+        """Generates a predictable thumbnail filename.
+
+        Thumbnail generation follows this template: ::
+
+            {thumbnail_name}.{source file hash}.{ext}
+
+        Place no expensive calculations here -- this runs any
+        time a thumbnail field is accessed.
+
+        :param instance: Model instance containing the field
+        :param original_file: Uploaded image file
+        :param thumbnail_name: Model instance field name
+        :param ext: File extension *with* '.' separator.
+        """
+
+        path = os.path.dirname(original_file.name)
+        hash_value, _ = os.path.splitext(os.path.basename(original_file.name))
+
+        filename = '%(thumbnail)s.%(hash)s%(ext)s' % {
+            'path': path,
+            'thumbnail': thumbnail_name,
+            'hash': hash_value,
+            'ext': ext}
+
+        return os.path.join(path, filename)
 
     def south_field_triple(self):
         """Return a description of this field for South.

undermythumb/files.py

@@ -1,3 +1,6 @@
+from hashlib import sha1
+import os
+
 from django.db.models.fields.files import ImageFieldFile
 
 
@@ -24,20 +27,20 @@ def _populate(self):
                     key = attname
                     ext = '.%s' % renderer.format
 
-                    name = self.field.get_thumbnail_filename(
-                        instance=self.instance,
-                        original=self.file,
-                        key=key,
-                        ext=ext)
+                name = self.field.get_thumbnail_filename(
+                    instance=self.instance,
+                    original_file=self.file,
+                    thumbnail_name=key,
+                    ext=ext)
 
-                    thumbnail = ThumbnailFieldFile(
-                        attname,
-                        renderer,
-                        self.instance,
-                        self.field,
-                        name)
+                thumbnail = ThumbnailFieldFile(
+                    attname,
+                    renderer,
+                    self.instance,
+                    self.field,
+                    name)
 
-                    self._cache[attname] = thumbnail
+                self._cache[attname] = thumbnail
 
     def clear_cache(self):
         self._cache = {}
@@ -74,13 +77,20 @@ def __init__(self, *args, **kwargs):
         self.thumbnails = ThumbnailSet(self)
 
     def save(self, name, content, save=True):
-        """Save the original image, and its thumbnails.
-        """
+        # set file name to first 8 chars of hash of contents
+        _, ext = os.path.splitext(name)
+        file_hash = sha1(content.read()).hexdigest()[:8]
+        name = file_hash + ext
+
+        # save source file
         super(ImageWithThumbnailsFieldFile, self).save(name, content, save)
 
         self.thumbnails.clear_cache()
 
-        # iterate over thumbnail
         for thumbnail in self.thumbnails:
             rendered = thumbnail.renderer.generate(content)
             self.field.storage.save(thumbnail.name, rendered)
+            setattr(self.instance, self.field.attname, thumbnail.name)
+
+        if save:
+            self.instance.save()