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|
WAI: Web Application Interface
==============================
Getting started
---------------
You want a minimal example? Here it is!
~~~ {.haskell}
{-# LANGUAGE OverloadedStrings #-}
import Network.Wai
import Network.HTTP.Types
import Network.Wai.Handler.Warp (run)
app :: Application
app _ respond = do
putStrLn "I've done some IO here"
respond $ responseLBS
status200
[("Content-Type", "text/plain")]
"Hello, Web!"
main :: IO ()
main = do
putStrLn $ "http://localhost:8080/"
run 8080 app
~~~
Put that code into a file named _hello.hs_ and install [wai] and [warp] from Hackage:
cabal install wai warp
Run it:
runhaskell hello.hs
Point your browser to:
http://localhost:8080/
Serving static content
----------------------
We can modify our previous example to serve static content. For this create a file named _index.html_:
<p>Hello, Web!</p>
Now we redefine `responseBody` to refer to that file:
~~~ {.haskell}
app2 :: Application
app2 _ respond = respond index
index :: Response
index = responseFile
status200
[("Content-Type", "text/html")]
"index.html"
Nothing
~~~
Basic dispatching
-----------------
An `Application` maps `Request`s to `Response`s:
ghci> :info Application
type Application = Request -> (Response -> IO ResponseReceived) -> IO ResponseReceived
Depending on the path info provided with each `Request` we can serve different `Response`s:
~~~ {.haskell}
app3 :: Application
app3 request respond = respond $ case rawPathInfo request of
"/" -> index
"/raw/" -> plainIndex
_ -> notFound
plainIndex :: Response
plainIndex = responseFile
status200
[("Content-Type", "text/plain")]
"index.html"
Nothing
notFound :: Response
notFound = responseLBS
status404
[("Content-Type", "text/plain")]
"404 - Not Found"
~~~
Doing without overloaded strings
--------------------------------
For the sake of efficiency, WAI uses the [bytestring] package. We used GHCs [overloaded strings] to almost hide this fact. But we can easily do without. What follows is a more verbose definition of `notFound`, that works without GHC extensions:
~~~ {.haskell .ignore}
import qualified Data.ByteString.Char8 as B8
import qualified Data.ByteString.Lazy.Char8 as LB8
import Data.CaseInsensitive (mk)
notFound = responseLBS
status404
[(mk $ B8.pack "Content-Type", B8.pack "text/plain")]
(LB8.pack "404 - Not Found")
~~~
[wai]: http://hackage.haskell.org/package/wai
[warp]: http://hackage.haskell.org/package/warp
[overloaded strings]: http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#overloaded-strings
[bytestring]: http://hackage.haskell.org/package/bytestring
|
