[Preliminary support for ETag / If-Not-Modified in feeds.
prb@mult.ifario.us**20080303202256] {
hunk ./servletsrc/perpubplat.hs 22
-import Data.ByteString.Lazy.Char8 ( unpack )
+import Data.ByteString.Lazy.Char8 ( unpack, pack )
+import Data.Digest.MD5 ( md5 )
hunk ./servletsrc/perpubplat.hs 39
-
hunk ./servletsrc/perpubplat.hs 64
-serve_feed :: (F.Feedable f) => Controllers -> f -> CGI CGIResult
-serve_feed con f = do { m <- liftIO $ DataC.get_model (data_c con)
-                      ; setStatus 200 "OK"
-                      ; let items = F.items f m
-                      ; setHeader "Content-type" "application/atom+xml"
-                      ; setHeader "Last-Modified" $ Utils.iso8601toRfc1123 $ S.last_updated items
-                      ; output $ S.assemble_feed f m items }
+serve_feed :: (F.Feedable f, Show f) => Controllers -> f -> CGI CGIResult
+serve_feed con f =
+    do { m <- liftIO $ DataC.get_model (data_c con)
+       ; let items = F.items f m
+       ; let last_updated = S.last_updated items
+       ; let etag = show . md5 . pack $ (show f) ++ (last_updated)
+       ; ifNoneMatch <- requestHeader "If-None-Match"
+       ; let etag_didnt_match = 
+                 case ifNoneMatch of
+                   Nothing -> True
+                   Just e ->
+                       e /= etag                                     
+       ; ifModifiedSince <- requestHeader "If-Modified-Since"
+       {- From the HTTP 1.1 spec:
+
+          "If none of the entity tags match, then the server MAY
+          perform the requested method as if the If-None-Match header
+          field did not exist, but MUST also ignore any
+          If-Modified-Since header field(s) in the request. That is,
+          if no entity tags match, then the server MUST NOT return a
+          304 (Not Modified) response. "
+
+        -}
+       ; let modified =
+                 etag_didnt_match && 
+                 case ifModifiedSince of
+                   Nothing -> True
+                   Just d -> 
+                       (Utils.httpDateToIso8601 d) < last_updated
+       ; if modified then
+             do { setStatus 200 "OK"
+                ; setHeader "Content-type" "application/atom+xml"
+                ; setHeader "Last-Modified" $ Utils.iso8601toRfc1123 last_updated
+                ; setHeader "ETag" $ etag
+                ; output $ S.assemble_feed f m items }
+         else
+             do { setStatus 304 "Not Modified"
+                ; output $ ""}
+       }
hunk ./src/Utilities.hs 189
-
-rfc1123toIso8601 :: String -> String
-rfc1123toIso8601 d = case P.parse rfc1123DateParser d d of
-                       Left _ -> ""
-                       Right d' -> d'
}