Snap interface - getting the OS and Browser information

Question

I am using the Snap information and I was wondering if there was some type of Request function ( such as ::Request -> IO Snap() or ::Request -> Handler App App()) that returns the OS or Browser information of the user visiting the webpage.

I would like to get the OS and Browser information of the person who is visiting the webpage.

Answer 1

You can get the User-Agent HTTP header via getHeader, because Request has a HasHeaders instance.

Example snippet:

import qualified Data.ByteString.Char8 as CS
import qualified Data.CaseInsensitive as CI
import Data.Maybe (listToMaybe)

uaName :: ByteString
uaName = CS.pack "User-Agent"
-- You can avoid CS.pack with OverloadedStrings extension.

uahName :: CI ByteString
uahName = CI.mk uaName
-- OverloadedStrings also gets rid of the CI.mk call.

getUserAgent :: Request -> Snap (Maybe ByteString)
getUserAgent rq = return . coerce $ getHeader uahName rq
 where 
    coerce :: Maybe [ByteString] -> Maybe ByteString
    coerce = (>>= listToMaybe)
    -- Some HTTP headers can appear multiple times, hence the list.
    -- `coerce` ignores all but the first occurrence.

For more detailed / less voluntary information, you could inject JS into an initial request and set cookies that can be extracted with rqCookies in a lter request.