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

dnscms/images/migrations/0006_backfill_file_hash_and_size.py

@@ -0,0 +1,32 @@
+from django.db import migrations
+from wagtail.utils.file import hash_filelike
+
+
+def backfill_file_hash_and_size(apps, schema_editor):
+    """
+    Images from the 2024 bulk import were created without Wagtail's upload
+    form, which is what sets file_hash and file_size. The hash versions image
+    URLs (see CustomImage.versioned_url).
+    """
+    CustomImage = apps.get_model("images", "CustomImage")
+    images = CustomImage.objects.filter(file_hash="") | CustomImage.objects.filter(
+        file_size__isnull=True
+    )
+    for image in images.iterator():
+        try:
+            with image.file.open("rb") as f:
+                image.file_hash = hash_filelike(f)
+                image.file_size = image.file.size
+        except FileNotFoundError:
+            continue
+        image.save(update_fields=["file_hash", "file_size"])
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("images", "0005_customimage_description"),
+    ]
+
+    operations = [
+        migrations.RunPython(backfill_file_hash_and_size, migrations.RunPython.noop),
+    ]

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"),
     ]