如何使用Warp和Aeson在HTTP上传送JSON

问题描述

我想使用创建在Haskell上运行的基于HTTP的高性能API，如下所示：一个HTTP后端。

服务器应根据请求返回JSON数据。这些数据应使用进行序列化

但是， 需要一个响应对象，而Aeson会返回懒惰的 ByteString s。 p>

如何将两个库绑定在一起？对于这个问题的范围，我对查询解析或路由不感兴趣，但是以一个如何将两个库绑定在一起以提供带有正确头的正确JSON为例。

：这个问题故意没有显示任何研究成果，因为它被回答为Q& A-style-ish。如果您需要研究工作，请参阅我的答案。 /www.haskell.org/haskellwiki/Web/Serversrel =nofollow> HaskellWiki最小变形示例。

为简单起见，我删除了任何代码如路由，通过存根和注释替换最相关的部分放置什么。

我们将在此示例中序列化的JSON数据是 [ 一， b， C] 。

连接两个库的问题是，虽然 warp 需要Blaze 来正确构建它的响应，而 Aeson 返回（如你所说）一个懒惰 ByteString 。
将两者连接在一起的适当函数称为。

  { - ＃LANGUAGE OverloadedStrings＃ - } 
导入Data.Aeson 
导入Data.Text（文本）
导入Network.Wai 
导入Network.Wai.Handler.Warp 
 import Network.HTTP.Types（status200）
 import Network.HTTP.Types.Header（hContentType）
 import Blaze.ByteString.Builder.ByteString（fromLazyByteString） 
将合格的Data.ByteString.UTF8导入为BU 
 
 main = do 
 let port = 3000 
 putStrLn $侦听端口++ show port 
运行端口应用程序
 
应用程序::应用程序
应用程序请求f = f $ 
案例pathInfo请求
  - 在此处放置自定义路由
 _  - > anyRoute 
 
  - 将被转换为JSON的数据
 jsonData = [a，b，c] :: [Text] 
 
 anyRoute = responseLBS 
 status200 
 [（hContentType，application / json）] 
（encode jsonData）
  

2015年1月1日更新：修正Warp / WAI 3.x的示例

I want to create a high-performance HTTP-based API running on Haskell using warp as a HTTP backend.

The server shall return JSON data upon request. This data shall be serialized by using Aeson

However, warp requires a response object whereas Aeson returns lazy ByteStrings.

How can I tie both libraries together? For this question's scope I'm not interested in query parsing or routing, but in an example of how to tie both libraries together to deliver a correct JSON with correct headers.

Note: This question intentionally does not show any research effort, as it was answered Q&A-style-ish. See my answer if you require research effort.

解决方案

I'll build my example on the HaskellWiki minimal warp example.

For the sake of simplicity I removed any code like routing, replacing the most relevant parts by stubs and comments where to place what.

The JSON data we will serialize in this example is the list ["a","b","c"]. The same response (= the JSON) will be returned for any URL.

The issue in connecting both libraries is that while warp requires a Blaze Builder to build its response properly, while Aeson returns (as you said) a lazy ByteString.The appropriate function to connect both together is called fromLazyByteString.

{-# LANGUAGE OverloadedStrings #-}
import Data.Aeson
import Data.Text (Text)
import Network.Wai
import Network.Wai.Handler.Warp
import Network.HTTP.Types (status200)
import Network.HTTP.Types.Header (hContentType)
import Blaze.ByteString.Builder.ByteString (fromLazyByteString)
import qualified Data.ByteString.UTF8 as BU

main = do
    let port = 3000
    putStrLn $ "Listening on port " ++ show port
    run port app

app :: Application
app req f = f $
    case pathInfo req of
        -- Place custom routes here
        _ -> anyRoute

-- The data that will be converted to JSON
jsonData = ["a","b","c"] :: [Text]

anyRoute = responseLBS
            status200
            [(hContentType, "application/json")]
            (encode jsonData)

Update 05/01/2015: Fix example for Warp/WAI 3.x

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