99 lines
2.9 KiB
Markdown
99 lines
2.9 KiB
Markdown
# servant-js
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This library lets you derive automatically Javascript functions that let you query each endpoint of a *servant* webservice.
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It contains a powerful system allowing you to generate functions for several frameworks (Angular, AXios, JQuery) as well as
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vanilla (framework-free) javascript code.
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## Example
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Read more about the following example [here](https://github.com/haskell-servant/servant/tree/master/servant-js/tree/master/examples#examples).
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``` haskell
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{-# LANGUAGE DataKinds #-}
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{-# LANGUAGE TypeOperators #-}
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{-# LANGUAGE DeriveGeneric #-}
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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
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import Control.Concurrent.STM
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import Control.Monad.IO.Class
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import Data.Aeson
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import Data.Proxy
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import GHC.Generics
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import Network.Wai.Handler.Warp (run)
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import Servant
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import Servant.JS
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import System.FilePath
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-- * A simple Counter data type
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newtype Counter = Counter { value :: Int }
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deriving (Generic, Show, Num)
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instance ToJSON Counter
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-- * Shared counter operations
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-- Creating a counter that starts from 0
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newCounter :: IO (TVar Counter)
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newCounter = newTVarIO 0
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-- Increasing the counter by 1
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counterPlusOne :: MonadIO m => TVar Counter -> m Counter
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counterPlusOne counter = liftIO . atomically $ do
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oldValue <- readTVar counter
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let newValue = oldValue + 1
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writeTVar counter newValue
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return newValue
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currentValue :: MonadIO m => TVar Counter -> m Counter
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currentValue counter = liftIO $ readTVarIO counter
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-- * Our API type
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type TestApi = "counter" :> Post '[JSON] Counter -- endpoint for increasing the counter
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:<|> "counter" :> Get '[JSON] Counter -- endpoint to get the current value
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type TestApi' = TestApi -- The API we want a JS handler for
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:<|> Raw -- used for serving static files
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-- this proxy only targets the proper endpoints of our API,
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-- not the static file serving bit
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testApi :: Proxy TestApi
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testApi = Proxy
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-- this proxy targets everything
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testApi' :: Proxy TestApi'
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testApi' = Proxy
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-- * Server-side handler
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-- where our static files reside
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www :: FilePath
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www = "examples/www"
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-- defining handlers
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server :: TVar Counter -> Server TestApi
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server counter = counterPlusOne counter -- (+1) on the TVar
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:<|> currentValue counter -- read the TVar
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server' :: TVar Counter -> Server TestApi'
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server counter = server counter
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:<|> serveDirectory www -- serve static files
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runServer :: TVar Counter -- ^ shared variable for the counter
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-> Int -- ^ port the server should listen on
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-> IO ()
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runServer var port = run port (serve testApi' $ server' var)
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main :: IO ()
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main = do
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-- write the JS code to www/api.js at startup
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writeJSForAPI testApi jquery (www </> "api.js")
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-- setup a shared counter
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cnt <- newCounter
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-- listen to requests on port 8080
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runServer cnt 8080
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```
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