Implemented fallback handler.

[Lucu.git] / Network / HTTP / Lucu / Resource / Tree.hs

diff --git a/Network/HTTP/Lucu/Resource/Tree.hs b/Network/HTTP/Lucu/Resource/Tree.hs
index bb12dd0ee5c49bb7c3fdce0d58c6e090626eaeb0..2cd498f7ade7c7f4e5435d2344e161a5717cf65e 100644 (file)
--- a/Network/HTTP/Lucu/Resource/Tree.hs
+++ b/Network/HTTP/Lucu/Resource/Tree.hs
@@ -4,6 +4,8 @@
 module Network.HTTP.Lucu.Resource.Tree
     ( ResourceDef(..)
     , ResTree
+    , FallbackHandler
+
     , mkResTree    -- [ ([String], ResourceDef) ] -> ResTree
 
     , findResource -- ResTree -> URI -> Maybe ([String], ResourceDef)
@@ -35,6 +37,15 @@ import           System.IO.Error hiding (catch)
 import           Prelude hiding (catch)
 
 
+-- |'FallbackHandler' is an extra resource handler for resources which
+-- can't be statically located somewhere in the resource tree. The
+-- Lucu httpd first search for a resource in the tree, and then call
+-- fallback handlers to ask them for a resource. If all of the
+-- handlers returned 'Prelude.Nothing', the httpd responds with 404
+-- Not Found.
+type FallbackHandler = [String] -> IO (Maybe ResourceDef)
+
+
 -- "/aaa/bbb/ccc" にアクセスされた時、もし "/aaa/bbb" に貪欲なリソース
 -- があれば、假に "/aaa/bbb/ccc" に何らかのリソースがあったとしても必ず
 -- "/aaa/bbb" が撰ばれる。"/aaa/bbb" のリソースが貪欲でなければ、それは
@@ -55,7 +66,7 @@ data ResourceDef = ResourceDef {
     -- greedy resource at \/aaa\/bbb, it is always chosen even if
     -- there is another resource at \/aaa\/bbb\/ccc. If the resource
     -- at \/aaa\/bbb is not greedy, it is just ignored. Greedy
-    -- resource is like a CGI script.
+    -- resources are like CGI scripts.
     , resIsGreedy         :: !Bool
     -- | A 'Network.HTTP.Lucu.Resource.Resource' to be run when a GET
     -- request comes for the resource path. If 'resGet' is Nothing,
@@ -89,13 +100,13 @@ data ResourceDef = ResourceDef {
     , resDelete           :: !(Maybe (Resource ()))
     }
 
--- | 'ResTree' is an opaque structure which is a map from resource
--- path to 'ResourceDef'.
-type ResTree    = ResNode -- root だから Map ではない
+-- |'ResTree' is an opaque structure which is a map from resource path
+-- to 'ResourceDef'.
+newtype ResTree = ResTree ResNode -- root だから Map ではない
 type ResSubtree = Map String ResNode
 data ResNode    = ResNode !(Maybe ResourceDef) !ResSubtree
 
--- | 'mkResTree' converts a list of @(path, def)@ to a 'ResTree' e.g.
+-- |'mkResTree' converts a list of @(path, def)@ to a 'ResTree' e.g.
 --
 -- @
 --   mkResTree [ ([]        , 'Network.HTTP.Lucu.StaticFile.staticFile' \"\/usr\/include\/stdio.h\" ) -- \/
@@ -112,12 +123,12 @@ mkResTree list = list `seq` processRoot list
             in
               if null roots then
                   -- "/" にリソースが定義されない。"/foo" とかにはあるかも。
-                  ResNode Nothing children
+                  ResTree (ResNode Nothing children)
               else
                   -- "/" がある。
                   let (_, def) = last roots
                   in 
-                    ResNode (Just def) children
+                    ResTree (ResNode (Just def) children)
 
       processNonRoot :: [ ([String], ResourceDef) ] -> ResSubtree
       processNonRoot list
@@ -139,16 +150,19 @@ mkResTree list = list `seq` processRoot list
               subtree
 
 
-findResource :: ResTree -> URI -> Maybe ([String], ResourceDef)
-findResource (ResNode rootDefM subtree) uri
-    = let pathStr = uriPath uri
-          path    = [x | x <- splitBy (== '/') pathStr, x /= ""]
-      in
-        if null path then
-            do def <- rootDefM
-               return (path, def)
-        else
-            walkTree subtree path []
+findResource :: ResTree -> [FallbackHandler] -> URI -> IO (Maybe ([String], ResourceDef))
+findResource (ResTree (ResNode rootDefM subtree)) fbs uri
+    = do let pathStr     = uriPath uri
+             path        = [x | x <- splitBy (== '/') pathStr, x /= ""]
+             foundInTree = if null path then
+                               do def <- rootDefM
+                                  return (path, def)
+                           else
+                               walkTree subtree path []
+         if isJust foundInTree then
+             return foundInTree
+           else
+             fallback path fbs
     where
       walkTree :: ResSubtree -> [String] -> [String] -> Maybe ([String], ResourceDef)
 
@@ -167,6 +181,13 @@ findResource (ResNode rootDefM subtree) uri
                                                           return (soFar ++ [x], def)
                                                 _   -> walkTree children xs (soFar ++ [x])
 
+      fallback :: [String] -> [FallbackHandler] -> IO (Maybe ([String], ResourceDef))
+      fallback _    []     = return Nothing
+      fallback path (x:xs) = do m <- x path
+                                case m of
+                                  Just def -> return $! Just ([], def)
+                                  Nothing  -> fallback path xs
+
 
 runResource :: ResourceDef -> Interaction -> IO ThreadId
 runResource def itr