dnscms: version image URLs by file hash so media can be cached as immutable

dnscms/images/models.py

@@ -4,6 +4,7 @@ from django.utils.translation import gettext_lazy as _
 from grapple.models import (
     GraphQLString,
 )
+from grapple.utils import get_media_item_url
 from wagtail.images.models import AbstractImage, AbstractRendition, Image
 from wagtail.search import index
 
@@ -44,7 +45,20 @@ class CustomImage(AbstractImage):
             ("choose_image", "Can choose image"),
         ]
 
+    @property
+    def versioned_url(self):
+        # Original files keep their upload name, so deleting an image and
+        # uploading another with the same name reuses the URL. The content hash
+        # makes the URL change with the file, which lets the media proxy and
+        # Next's image optimizer cache it as immutable.
+        url = get_media_item_url(self)
+        if not self.file_hash:
+            return url
+        return f"{url}?v={self.file_hash[:8]}"
+
     graphql_fields = [
+        # Replaces Grapple's own `url` field and resolver
+        GraphQLString("url", source="versioned_url", required=True),
         GraphQLString("alt"),
         GraphQLString("attribution"),
     ]