Network.Wai

Defines the interface implemented by all web applications.

Example application:

 module Main where

 import qualified Data.ByteString as S
 import qualified Data.ByteString.Char8 as C (pack, unpack)
 import Network.Wai (Application(..), Enumerator(..))
 import System.Directory (getCurrentDirectory)
 import System.FilePath ((</>), makeRelative)
 import System.IO

 sendFile :: FilePath -> IO Enumerator
 sendFile fname = do
   cwd <- getCurrentDirectory
   h <- openBinaryFile (cwd </> makeRelative "/" fname) ReadMode
   let yieldBlock f z = do
              block <- S.hGetNonBlocking h 1024
              if S.null block then hClose h >> return z
                else do
                  z' <- f z block
                  case z' of
                    Left z''  -> hClose h >> return z''
                    Right z'' -> yieldBlock f z''
   return yieldBlock

 fileServer :: Application
 fileServer environ = do
   -- Here you should add security checks, etc.
   let contentType = (C.pack "Content-Type",
                      C.pack "application/octet-stream")
   enumerator <- sendFile $ C.unpack $ pathInfo environ
   return (200, pack "OK", [contentType], enumerator)

The Application type

type Application = Environment -> IO (Int, ByteString, Headers, Enumerator)

An application takes an environment and returns a HTTP status code, a sequence of headers and an Enumerator containing the response body.

type Enumerator = forall a. (a -> ByteString -> IO (Either a a)) -> a -> IO a

A left-fold enumerator.

data Environment

An environment providing information regarding the request.

Constructors

Environment

Fields

requestMethod :: Method

The HTTP request method, such as "GET" or "POST".

scriptName :: ByteString

The initial portion of the request URL's "path" that corresponds to the application, so that the application knows its virtual "location". This may be an empty string, if the application corresponds to the "root" of the server.

pathInfo :: ByteString

The remainder of the request URL's "path", designating the virtual "location" of the request's target within the application. This may be an empty string, if the request URL targets the application root and does not have a trailing slash.

queryString :: Maybe ByteString

The portion of the request URL that follows the "?", if any. May be empty or absent.

requestProtocol :: (Int, Int)

The version of the protocol the client used to send the request. Typically this will be (1, 0) or (1, 1) and may be used by the application to determine how to treat any HTTP request headers.

headers :: Headers

The client-supplied HTTP request headers.

input :: Enumerator

An Enumerator from which the HTTP body can be read.

errors :: String -> IO ()

A function with which error output can be written, for the purpose of recording program or other errors in a standardized and possibly centralized location. This function will not add a trailing newline to the string.

type Headers = [(ByteString, ByteString)]

The HTTP request headers.

data Method

The HTTP request method.

Constructors

Options

Get

Head

Post

Put

Delete

Trace

Connect

Instances

Eq Method

Show Method

PrettyPrint Method

Converts from a Method enumeration to the corresponding HTTP string.