add a header to all responses in snap framework

Question

The title sums it up. I want add a header to all my responses in snap. I can add a modifyRequest handler for each of my routes like :

apiRoutes :: [(ByteString, Handler b Api ())]
apiRoutes = [("status",  addHeader)]


addHeader :: Handler b Api ()
addHeader = do
   modifyResponse (setHeader "Content-Type" "application/json")
   otherHandler

otherHandler :: Handler b Api ()
otherHandler = metod Get doActualStuff <|> metod Get doMoreActualStuff

Now if I have 100 different routes and I want to add the header to them all. I have to write an intercepter function for all those routes. and if I want to change the header I must modify all 100 intercepter functions.

Is there a short simple way ?

Answer 1

With the hint that sjakobi provided I figured it out. This can be done like:

apiRoutes :: [(ByteString, Handler b Api ())]
apiRoutes = map (mapSecond (addHeaders >>))
[("status",  addHeader)]


addHeaders :: Handler b Api ()
addHeaders = do
   modifyResponse (setHeader "Content-Type" "application/json")
   modifyResponse (setHeader "more-header" "more-header")

mapSecond :: (b -> c) -> (a,b) -> (a,c)
mapSecond f (a,b) = (a,f b)