From 6b8f63c4d525d6407eb4fef8c454cc96a3970f96 Mon Sep 17 00:00:00 2001
From: Damian Mooyman <damian@silverstripe.com>
Date: Thu, 14 Jun 2018 14:11:31 +1200
Subject: [PATCH] Refactor redirect cache busting into middleware

---
 docs/en/04_Changelogs/4.2.0.md                        | 4 ++++
 src/Control/Middleware/HTTPCacheControlMiddleware.php | 5 +++++
 src/Control/RequestHandler.php                        | 3 ---
 src/Forms/Form.php                                    | 6 +-----
 4 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/docs/en/04_Changelogs/4.2.0.md b/docs/en/04_Changelogs/4.2.0.md
index d94fbc699..f942dea09 100644
--- a/docs/en/04_Changelogs/4.2.0.md
+++ b/docs/en/04_Changelogs/4.2.0.md
@@ -357,3 +357,7 @@ class PageController extends ContentController
    Note this is different from `Vary: Accept-Encoding`,
    which is important for compression (e.g. gzip), and usually added by
    other layers such as Apache's mod_gzip.
+ * DataObject no longer automatically invokes `HTTP::register_modification_date`
+   with LastModified on construction. User code should instead invoke
+   `HTTPCacheControlMiddleware::singleton()->registerModificationDate()` explicitly.
+   
diff --git a/src/Control/Middleware/HTTPCacheControlMiddleware.php b/src/Control/Middleware/HTTPCacheControlMiddleware.php
index 5038493a7..ea331a48a 100644
--- a/src/Control/Middleware/HTTPCacheControlMiddleware.php
+++ b/src/Control/Middleware/HTTPCacheControlMiddleware.php
@@ -769,5 +769,10 @@ class HTTPCacheControlMiddleware implements HTTPMiddleware, Resettable
             // Even if publicCache(true) is specified, errors will be uncacheable
             $this->disableCache(true);
         }
+
+        // Don't cache redirects
+        if ($response->isRedirect()) {
+            $this->disableCache(true);
+        }
     }
 }
diff --git a/src/Control/RequestHandler.php b/src/Control/RequestHandler.php
index 5ab831c2f..369799f4c 100644
--- a/src/Control/RequestHandler.php
+++ b/src/Control/RequestHandler.php
@@ -657,9 +657,6 @@ class RequestHandler extends ViewableData
      */
     public function redirectBack()
     {
-        // Don't cache the redirect back ever
-        HTTPCacheControlMiddleware::singleton()->disableCache(true);
-
         // Prefer to redirect to ?BackURL, but fall back to Referer header
         // As a last resort redirect to base url
         $url = $this->getBackURL()
diff --git a/src/Forms/Form.php b/src/Forms/Form.php
index 186ebf659..0619f78f5 100644
--- a/src/Forms/Form.php
+++ b/src/Forms/Form.php
@@ -1812,13 +1812,9 @@ class Form extends ViewableData implements HasRequestHandler
     /**
      * Can the body of this form be cached?
      *
-     * Figure out if we can cache this form
-     * - forms with validation shouldn't be cached, because their error messages won't be shown
-     * - forms with security tokens shouldn't be cached because security tokens expire
-     *
      * @return bool
      */
-    public function canBeCached()
+    protected function canBeCached()
     {
         if ($this->getSecurityToken()->isEnabled()) {
             return false;