Happstack, Yesod

[Corentin Dupont]

Hi guys,

can I use servant with Happstack?

My app is currently built with Happstack, so it would be nice to handle the REST API also with it.

It seems there is only an alpha release now, right?

And what about Yesod? Is it supported?

Thanks,

Corentin

[Julian Arni]

With Yesod it's fairly easy - you can just use the `Raw` combinator

type MyAPI = ServantAPI :<|> "yesod" :> Raw

myServer :: Server MyAPI

myServer = servantServer :<|> toWaiApp ...

With Happstack, servant-happstack is an option (though then you would not be able to use the above method for Yesod, I believe).

Alternatively, you can just proxy the requests to the other frameworks, either by (a) having a proxy server that dispatches to either servant or the other framework based on route or headers or whatever it is, or (b) having one of the servant routes use a proxy (e.g., http-proxy [0]), and again use Raw. (a) is a pretty common technique generally.

[0] https://hackage.haskell.org/package/http-proxy

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[Corentin Dupont]

Thanks.

I saw servant-happstack here:
https://github.com/haskell-servant/servant/tree/servercommon/servant-happstack

Do you know when it will be released?

[Julian Arni]

Nope... the initial work was done by Jeremy Shaw, but someone would have to take over the task of merging it (which involves refactoring some of the common logic, and which relates to work that Greg Hale did with servant-snap). I don't know if anyone is working on that though.

[Corentin Dupont]

OK... I also use happstack-authenticate for authentication of my website. Can it be used with servant?

I'm not sure if happstack-authenticate can use the auth token in the HTTP header.

In general, how and where do you retrieve an auth token? Should I retrieve from happstack-authenticate?

I found this:
https://hackage.haskell.org/package/happstack-authenticate-2.3.4/docs/src/Happstack-Authenticate-Core.html#getToken

is this the token I should put in the header when making an API request?

[Corentin Dupont]

Hi again guys,

is there some resource for using authentication with Yesod and Servant?

Thanks

[Julian Arni]

On Thu, May 12, 2016 at 8:18 PM, Corentin Dupont <corenti...@gmail.com> wrote:

Hi again guys,

is there some resource for using authentication with Yesod and Servant?

I don't think anyone has blogged about it. But how are those two connected? If in the same Application, you can use authentication/session Middleware, and it'll just work for both.
 

[Yann Esposito]

Actually I'm using a Yesod application which use their plugin system for authentication.

Here is some working code:

~~~~

import Data.CaseInsensitive (CI)

identityHeaderName :: CI ByteString

identityHeaderName = "Yesod-Identity"

addQueryId :: Maybe ByteString -> W.Request -> W.Request

addQueryId identity req =

  let f = maybe id (\x hs -> (identityHeaderName,x):hs) identity

  in req {W.requestHeaders = f (W.requestHeaders req)}

removeIdentityQuery :: W.Request -> W.Request

removeIdentityQuery req = req {

  W.requestHeaders = filter ((/= identityHeaderName) . fst)

                            (W.requestHeaders req)

  }

addIdentity :: Maybe ByteString -> Middleware

addIdentity identity app req sendResp =

  let req' = removeIdentityQuery req

      req'' = addQueryId identity req'

  in

    app req'' sendResp

addIdentity :: Maybe ByteString -> Middleware

addIdentity identity app req sendResp =

  let req' = removeIdentityQuery req

      req'' = addQueryId identity req'

  in

    app req'' sendResp

followToApp :: Handler TypedContent

followToApp = do

  app <- getYesod

  auth <- maybeAuth

  let identity = case auth of

                      Just (Entity _ u) -> Just (encodeUtf8 (userIdent u))

                      Nothing -> Nothing

  print identity

  sendWaiApplication (addIdentity identity (appREST app))

getHomeR :: Texts -> Handler TypedContent

getHomeR _ = followToApp

postHomeR :: Texts -> Handler TypedContent

postHomeR _ = followToApp

~~~~

and I had to put this in config/routes:

~~~

!/*Texts HomeR GET POST

~~~

The `appREST` is the WAI application returned by Servant that I initialise in Foundation.hs.

I added `appREST` field of type Application in the App record.