[Haskell-cafe] Using wreq Session handling in a monad transformer stack

[Chris Wong]

Hi Cody,

I don't use wreq myself, but withSession [1] is probably what you want.

Here's an example:

withInitialState :: (ScraperState -> IO a) -> IO a
withInitialState callback = withSession $ \session ->
    let initialState = PS {
            -- ... other options here ...
            currentSession = session
            }
    in callback initialState

[1] http://hackage.haskell.org/package/wreq-0.2.0.0/docs/Network-Wreq-Session.html

On Mon, Nov 17, 2014 at 10:08 AM, Cody Goodman
<codygman.consulting at gmail.com> wrote:
> Could I somehow add a Wreq.Session.Session to my monad transformer
> stack? Should I use something other than Wreq? How would I create a
> default Session, Wreq doesn't seem to export the constructor.
> Basically I want to achieve Sessions/cookie handling.
>
> lpaste of my code:
> http://lpaste.net/114405
>
>
> my full code (for those who want to view in email):
>
> {-# LANGUAGE OverloadedStrings #-}
> module Network.Scraper.State where
>
> import           Control.Lens                     ((^.))
> import           Control.Monad
> import           Control.Monad.IO.Class           (liftIO)
> import qualified Control.Monad.Trans.State.Strict as ST
> import qualified Data.ByteString.Lazy             as LBS
> import           Data.Maybe                       (fromJust, fromMaybe)
> import           Data.Monoid
> import qualified Data.Text                        as T
> import qualified Data.Text.IO                     as TIO
> import           Network.Wreq                     (FormParam (..))
> import qualified Network.Wreq                     as Wreq
> import           Network.Wreq.Session             (Session (..), withSession)
> import qualified Network.Wreq.Session             as Sesh
> import           Network.Wreq.Types
> import           Safe
> import           Text.HTML.DOM                    (parseLBS)
> import           Text.XML.Cursor
> import qualified Text.XML.Cursor.Generic          as CG
>
>
> data ScraperState =
>   PS { currentOptions :: Wreq.Options
>      , currentHtml    :: LBS.ByteString
>      , currentCursor  :: Maybe Cursor
>      , currentSession :: Session
>      } deriving (Show)
>
> type Scraper = ST.StateT ScraperState IO
>
> toCursor = fromDocument . parseLBS
>
> initialSt =
>   PS { currentOptions = Wreq.defaults
>      , currentHtml = ("" :: LBS.ByteString)
>      , currentCursor = Nothing
>      -- , currentSession = ... how do I get a Session? Wreq doesn't
> seem to export this type
>      }
>
> setCurrentOptions :: Wreq.Options -> Scraper ()
> setCurrentOptions o = do
>    scraper <- ST.get
>    ST.put $ scraper { currentOptions = o }
>
> -- getCurrentPage :: Shpider Page
> getCurrentCursor :: Scraper (Maybe Cursor)
> getCurrentCursor = do
>    scraper <- ST.get
>    return $ currentCursor scraper
>
> getCurrentSession :: Scraper (Session)
> getCurrentSession = do
>    scraper <- ST.get
>    return $ currentSession scraper
>
> setCurrentSession :: Session -> Scraper ()
> setCurrentSession s = do
>    scraper <- ST.get
>    ST.put $ scraper { currentSession = s}
>
> setCurrentCursor :: Cursor -> Scraper ( )
> setCurrentCursor c = do
>    scraper <- ST.get
>    ST.put $ scraper { currentCursor = Just c }
>
> setCurrentHtml :: LBS.ByteString -> Scraper ()
> setCurrentHtml html = do
>    scraper <- ST.get
>    ST.put $ scraper { currentHtml = html }
>
> runScraper :: Scraper a -> IO a
> runScraper k = evalScraperWith k initialSt
>
> evalScraperWith :: Scraper a -> ScraperState -> IO a
> evalScraperWith k s = withSession $ \sesh -> do
>   -- set the current session to the mutable session variable
>   return $ setCurrentSession sesh
>   ST.evalStateT k s
>
> formShortInfo' f = formInfo'
>   where
>     go Nothing = "N/A"
>     go (Just x) = x
>     formInfo = (headMay . attribute "name" $ f, headMay . attribute
> "action" $ f)
>     formInfo' = (\(x,y) -> (go x, go y)) formInfo
>
> ppTuple :: (T.Text, T.Text) -> T.Text
> ppTuple = \(x,y) -> "[" <> x <> "]" <> ": " <> y
>
> -- move to ../Spider.hs
> printFormNames :: Scraper ()
> printFormNames = do
>   c <- getCurrentCursor
>   let c' = fromMaybe (error "No cursor set") c
>       forms = c' $// element "form"
>       formInfo = map (ppTuple . formShortInfo') forms
>   liftIO $ mapM_ (TIO.putStrLn) formInfo
>
> getFormByName :: T.Text -> Scraper [Cursor]
> getFormByName name = do
>   c <- getCurrentCursor
>   let c' = fromMaybe (error "No cursor set") c
>   return $ c' $// element "form" >=> attributeIs "name" name
>
> get :: String -> Scraper (LBS.ByteString)
> get url = do
>   r <- liftIO $ Wreq.get url
>   let html = r ^. Wreq.responseBody
>   setCurrentHtml html
>   setCurrentCursor (toCursor html)
>   return html
>
> post :: Postable a => String -> a -> Scraper (LBS.ByteString)
> post url params = do
>   r <- liftIO $ Wreq.post url params
>   let html = r ^. Wreq.responseBody
>   setCurrentHtml html
>   setCurrentCursor (toCursor html)
>   return html
>
> test :: Scraper ()
> test = do
>   get "https://www.google.com" >> printFormNames
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