return 400 (instead of 404) on invalid captures

servant-server/src/Servant/Server/Internal.hs

@@ -127,7 +127,7 @@ instance (KnownSymbol capture, FromHttpApiData a, HasServer sublayout context)
         route (Proxy :: Proxy sublayout)
               context
               (addCapture d $ case parseUrlPieceMaybe first :: Maybe a of
-                 Nothing -> return $ Fail err404
+                 Nothing -> return $ Fail err400
                  Just v  -> return $ Route v
               )
 

servant-server/test/Servant/Server/ErrorSpec.hs

@@ -63,7 +63,7 @@ errorOrderSpec =
   let badContentType  = (hContentType, "text/plain")
       badAccept       = (hAccept, "text/plain")
       badMethod       = methodGet
-      badUrl          = "home/nonexistent"
+      badUrl          = "nonexistent"
       badBody         = "nonsense"
       badAuth         = (hAuthorization, "Basic foofoofoo")
       goodContentType = (hContentType, "application/json")

servant-server/test/Servant/ServerSpec.hs

@@ -202,8 +202,8 @@ captureSpec = do
         response <- get "/2"
         liftIO $ decode' (simpleBody response) `shouldBe` Just tweety
 
-      it "returns 404 if the decoding fails" $ do
-        get "/notAnInt" `shouldRespondWith` 404
+      it "returns 400 if the decoding fails" $ do
+        get "/notAnInt" `shouldRespondWith` 400
 
     with (return (serve
         (Proxy :: Proxy (Capture "captured" String :> Raw))