Fixed #5047: patch_cache_control now respects existing max-age settings. Thanks, permon.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@6434 bcc190cf-cafb-0310-a4f2-bffc1f526a37

AUTHORS

@@ -234,6 +234,7 @@ answer newbie questions, and generally made Django that much better:
     Jay Parlar <parlar@gmail.com>
     pavithran s <pavithran.s@gmail.com>
     Barry Pederson <bp@barryp.org>
+    permonik@mesias.brnonet.cz
     petr.marhoun@gmail.com
     pgross@thoughtworks.com
     phaedo <http://phaedo.cx/>

django/utils/cache.py

@@ -57,6 +57,13 @@ def patch_cache_control(response, **kwargs):
         cc = dict([dictitem(el) for el in cc])
     else:
         cc = {}
+
+    # If there's already a max-age header but we're being asked to set a new
+    # max-age, use the minumum of the two ages. In practice this happens when
+    # a decorator and a piece of middleware both operate on a given view.
+    if 'max-age' in cc and 'max_age' in kwargs:
+        kwargs['max_age'] = min(cc['max-age'], kwargs['max_age'])
+
     for (k,v) in kwargs.items():
         cc[k.replace('_', '-')] = v
     cc = ', '.join([dictvalue(el) for el in cc.items()])