Cherry pick ef445e2 Option to transform primary field target to provide information about the target rather than just it's URL plone#1903

Author: JeffersonBledsoe

src/plone/restapi/serializer/dxfields.py

@@ -23,6 +23,7 @@
 from zope.schema.interfaces import IVocabularyTokenized
 
 import logging
+import os
 
 
 log = logging.getLogger(__name__)
@@ -203,6 +204,19 @@ def __call__(self):
         if namedfile is None:
             return
 
+        enable_transform = os.environ.get("enable_link_target_transform", False)
+
+        if enable_transform:
+            download_url = "/".join((self.context.absolute_url(), "@@download", self.field.__name__))
+            result = {
+                "url": self.context.absolute_url(),
+                "download": download_url,
+                "filename": namedfile.filename,
+                "content-type": namedfile.contentType,
+                "size": namedfile.getSize(),
+            }
+            return json_compatible(result)
+
         return "/".join(
             (self.context.absolute_url(), "@@download", self.field.__name__)
         )