wai: Web Application Interface.

[ library, mit, web ] [ Propose Tags ]

Provides a common protocol for communication between web applications and web servers.

API docs and the README are available at http://www.stackage.org/package/wai.

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Versions [RSS] 0.0.0, 0.0.1, 0.1.0, 0.2.0, 0.2.1, 0.2.2,, 0.3.0, 0.3.1, 0.3.2, 0.4.0, 0.4.1, 0.4.2, 0.4.3, 1.0.0, 1.1.0,, 1.2.0,,,, 1.3.0,,,, 1.4.0,,, 1.4.1, 2.0.0, 2.1.0,,,, 3.0.0,,, 3.0.1,, 3.0.2,,,,,,, 3.2.0,, 3.2.1,,, 3.2.2,, 3.2.3, 3.2.4
Change log ChangeLog.md
Dependencies base (>=4.12 && <5), bytestring (>=0.10.4), http-types (>=0.7), network (>=, text (>=0.7), vault (>=0.3 && <0.4) [details]
License MIT
Author Michael Snoyman
Maintainer michael@snoyman.com
Category Web
Home page https://github.com/yesodweb/wai
Source repo head: git clone git://github.com/yesodweb/wai.git
head: git clone git://github.com/yesodweb/wai.git
Uploaded by KazuYamamoto at 2023-12-10T10:13:43Z
Distributions Arch:3.2.4, Debian:, Fedora:3.2.3, FreeBSD:, LTSHaskell:3.2.4, NixOS:3.2.4, Stackage:3.2.4, openSUSE:3.2.4
Reverse Dependencies 457 direct, 3278 indirect [details]
Downloads 171696 total (403 in the last 30 days)
Rating 2.5 (votes: 4) [estimated by Bayesian average]
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Status Docs available [build log]
Last success reported on 2023-12-10 [all 1 reports]

Readme for wai-3.2.4

[back to package description]

WAI: Web Application Interface

Getting started

You want a minimal example? Here it is!

{-# 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
        [("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:


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:

app2 :: Application
app2 _ respond = respond index

index :: Response
index = responseFile
    [("Content-Type", "text/html")]

Basic dispatching

An Application maps Requests to Responses:

ghci> :info  Application
type Application = Request -> (Response -> IO ResponseReceived) -> IO ResponseReceived

Depending on the path info provided with each Request we can serve different Responses:

app3 :: Application
app3 request respond = respond $ case rawPathInfo request of
    "/"     -> index
    "/raw/" -> plainIndex
    _       -> notFound

plainIndex :: Response
plainIndex = responseFile
    [("Content-Type", "text/plain")]

notFound :: Response
notFound = responseLBS
    [("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:

import qualified Data.ByteString.Char8 as B8
import qualified Data.ByteString.Lazy.Char8 as LB8
import           Data.CaseInsensitive (mk)

notFound = responseLBS
    [(mk $ B8.pack "Content-Type", B8.pack "text/plain")]
    (LB8.pack "404 - Not Found")