Define a 'before_serve_document' hook

docs/reference/hooks.rst

@@ -697,3 +697,14 @@ Page serving
     def block_googlebot(page, request, serve_args, serve_kwargs):
         if request.META.get('HTTP_USER_AGENT') == 'GoogleBot':
             return HttpResponse("<h1>bad googlebot no cookie</h1>")
+
+
+Document serving
+----------------
+
+.. _before_serve_document:
+
+``before_serve_document``
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+  Called when Wagtail is about to serve a document. The callable passed into the hook will receive the document object and the request object. If the callable returns an ``HttpResponse``, that response will be returned immediately to the user, instead of serving the document.

wagtail/wagtaildocs/views/serve.py

@@ -3,12 +3,13 @@ from __future__ import absolute_import, unicode_literals
 from wsgiref.util import FileWrapper
 
 from django.conf import settings
-from django.http import BadHeaderError, Http404, StreamingHttpResponse
+from django.http import BadHeaderError, Http404, HttpResponse, StreamingHttpResponse
 from django.shortcuts import get_object_or_404
 from unidecode import unidecode
 
 from wagtail.utils import sendfile_streaming_backend
 from wagtail.utils.sendfile import sendfile
+from wagtail.wagtailcore import hooks
 from wagtail.wagtaildocs.models import document_served, get_document_model
 
 
@@ -22,6 +23,11 @@ def serve(request, document_id, document_filename):
     if doc.filename != document_filename:
         raise Http404('This document does not match the given filename.')
 
+    for fn in hooks.get_hooks('before_serve_document'):
+        result = fn(doc, request)
+        if isinstance(result, HttpResponse):
+            return result
+
     # Send document_served signal
     document_served.send(sender=Document, instance=doc, request=request)