Archive snapshots of websites locally (#672)

* Add basic HTML snapshots

* Implement asset list

* Add snapshot creation tests

* Add deletion tests

* Show file size

* Remove snapshots

* Create new snapshots

* Switch to single-file

* CSS tweak

* Remove auto refresh

* Show delete link when there is no file yet

* Add current date to display name

* Add flag for snapshot support

* Add option for disabling automatic snapshots

* Make snapshots sharable

* Document image variants

* Update README.md

* Add migrations

* Fix tests

bookmarks/views/assets.py

@@ -0,0 +1,43 @@
+import gzip
+import os
+
+from django.conf import settings
+from django.http import (
+    HttpResponse,
+    Http404,
+)
+
+from bookmarks.models import BookmarkAsset
+
+
+def view(request, asset_id: int):
+    try:
+        asset = BookmarkAsset.objects.get(pk=asset_id)
+    except BookmarkAsset.DoesNotExist:
+        raise Http404("Asset does not exist")
+
+    bookmark = asset.bookmark
+    is_owner = bookmark.owner == request.user
+    is_shared = (
+        request.user.is_authenticated
+        and bookmark.shared
+        and bookmark.owner.profile.enable_sharing
+    )
+    is_public_shared = bookmark.shared and bookmark.owner.profile.enable_public_sharing
+
+    if not is_owner and not is_shared and not is_public_shared:
+        raise Http404("Bookmark does not exist")
+
+    filepath = os.path.join(settings.LD_ASSET_FOLDER, asset.file)
+
+    if not os.path.exists(filepath):
+        raise Http404("Asset file does not exist")
+
+    if asset.gzip:
+        with gzip.open(filepath, "rb") as f:
+            content = f.read()
+    else:
+        with open(filepath, "rb") as f:
+            content = f.read()
+
+    return HttpResponse(content, content_type=asset.content_type)