From e4452ed79819e230a3a89b687ade106cc760ec9b Mon Sep 17 00:00:00 2001
From: Martin Gotink <m.gotink@gmail.com>
Date: Sun, 10 Feb 2013 15:42:12 +0100
Subject: [PATCH] Send 304 if If-Modified-Since header is set

---
 .../HashAndCacheResourceMapper.groovy         | 24 ++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/grails-app/resourceMappers/org/grails/plugin/cachedresources/HashAndCacheResourceMapper.groovy b/grails-app/resourceMappers/org/grails/plugin/cachedresources/HashAndCacheResourceMapper.groovy
index c576604..b62606b 100644
--- a/grails-app/resourceMappers/org/grails/plugin/cachedresources/HashAndCacheResourceMapper.groovy
+++ b/grails-app/resourceMappers/org/grails/plugin/cachedresources/HashAndCacheResourceMapper.groovy
@@ -28,7 +28,12 @@ class HashAndCacheResourceMapper {
             if (log.debugEnabled) {
                 log.debug "Setting caching headers on ${req.requestURI}"
             }
-            cacheHeadersService.cache resp, [neverExpires: true, shared: true]
+
+            if (isCachedOnClient(req)) {
+                resp.sendError(304) // Not modified
+            } else {
+                cacheHeadersService.cache resp, [neverExpires: true, shared: true]
+            }
         }
     }
     
@@ -51,6 +56,23 @@ class HashAndCacheResourceMapper {
             param
         }
     }
+
+    boolean isCachedOnClient(request) {
+        def modifiedDate = -1
+
+        try {
+            modifiedDate = request.getDateHeader('If-Modified-Since')
+        } catch (IllegalArgumentException iae) {
+            log.error ("Couldn't parse If-Modified-Since header", iae)
+        }
+
+        if (modifiedDate != -1) {
+            // Resource is static, if the If-Modified-Since header is set the resource is cached
+            return true
+        }
+
+        false
+    }
     
     boolean getShortenLinks() {
         resourceService.getConfigParamOrDefault('shorten', true)