Haskell语言学习笔记（80）req

req

req 是一个好用，类型安全，可扩展，上层的HTTP客户端的库。

$ cabal install req
Installed req-1.1.0
Prelude> :m +Network.HTTP.Req
Prelude Network.HTTP.Req> 

官方示例

{-# LANGUAGE OverloadedStrings, DeriveGeneric #-}

import Control.Monad
import Control.Monad.IO.Class
import Data.Aeson
import Data.Default.Class
import Data.Maybe (fromJust)
import Data.Monoid ((<>))
import Data.Text (Text)
import GHC.Generics
import Network.HTTP.Req
import qualified Data.ByteString.Char8 as B

main1 :: IO ()
main1 = runReq def $ do
  let n :: Int
      n = 5
  bs <- req GET (https "httpbin.org" /: "bytes" /~ n) NoReqBody bsResponse mempty
  liftIO $ B.putStrLn (responseBody bs)

main2 :: IO ()
main2 = runReq def $ do
  let n, seed :: Int
      n    = 5
      seed = 100
  bs <- req GET (https "httpbin.org" /: "bytes" /~ n) NoReqBody bsResponse $
    "seed" =: seed
  liftIO $ B.putStrLn (responseBody bs)
  
data MyData = MyData
  { size  :: Int
  , color :: Text
  } deriving (Show, Generic)

instance ToJSON MyData
instance FromJSON MyData

main3 :: IO ()
main3 = runReq def $ do
  let myData = MyData
        { size  = 6
        , color = "Green" }
  v <- req POST (https "httpbin.org" /: "post") (ReqBodyJson myData) jsonResponse mempty
  liftIO $ print (responseBody v :: Value)
  
main4 :: IO ()
main4 = runReq def $ do
  let params =
        "foo" =: ("bar" :: Text) <>
        queryFlag "baz"
  response <- req POST (https "httpbin.org" /: "post") (ReqBodyUrlEnc params) jsonResponse mempty
  liftIO $ print (responseBody response :: Value)

main5 :: IO ()
main5 = runReq def $ do
  -- This is an example of what to do when URL is given dynamically. Of
  -- course in a real application you may not want to use 'fromJust'.
  let (url, options) = fromJust (parseUrlHttps "https://httpbin.org/get?foo=bar")
  response <- req GET url NoReqBody jsonResponse $
    "from" =: (15 :: Int)           <>
    "to"   =: (67 :: Int)           <>
    basicAuth "username" "password" <>
    options                         <> -- contains the ?foo=bar part
    port 443 -- here you can put any port of course
  liftIO $ print (responseBody response :: Value)

*Main> main1
?+???
*Main> main2
J??Y?
*Main> main3
Object (fromList [("origin",String "xx.xxx.xxx.xx"),("args",Object (fromList [])),("json",Object (fromList [("color",String "Green"),("size",Number 6.0)])),("data",String "{"color":"Green","size":6}"),("url",String "https://httpbin.org/post"),("headers",Object (fromList [("Content-Type",String "application/json; charset=utf-8"),("Accept-Encoding",String "gzip"),("Connection",String "close"),("Host",String "httpbin.org"),("Content-Length",String "26")])),("files",Object (fromList [])),("form",Object (fromList []))])
*Main> main4
Object (fromList [("origin",String "xx.xxx.xxx.xx"),("args",Object (fromList [])),("json",Null),("data",String ""),("url",String "https://httpbin.org/post"),("headers",Object (fromList [("Content-Type",String "application/x-www-form-urlencoded"),("Accept-Encoding",String "gzip"),("Connection",String "close"),("Host",String "httpbin.org"),("Content-Length",String "11")])),("files",Object (fromList [])),("form",Object (fromList [("foo",String "bar"),("baz",String "")]))])
*Main> main5
Object (fromList [("origin",String "xx.xxx.xxx.xx"),("args",Object (fromList [("to",String "67"),("from",String "15"),("foo",String "bar")])),("url",String "https://httpbin.org/get?from=15&to=67&foo=bar"),("headers",Object (fromList [("Authorization",String "Basic dXNlcm5hbWU6cGFzc3dvcmQ="),("Accept-Encoding",String "gzip"),("Connection",String "close"),("Host",String "httpbin.org")]))])

API

req
  :: ( MonadHttp    m
     , HttpMethod   method
     , HttpBody     body
     , HttpResponse response
     , HttpBodyAllowed (AllowsBody method) (ProvidesBody body) )
  => method            -- ^ HTTP method
  -> Url scheme        -- ^ 'Url'—location of resource
  -> body              -- ^ Body of the request
  -> Proxy response    -- ^ A hint how to interpret response
  -> Option scheme     -- ^ Collection of optional parameters
  -> m response        -- ^ Response
req method url body Proxy options

req 函数实现 Http 请求。
req 函数共有5个参数

• method
  GET POST PUT DELETE 之类的 HTTP 方法

• Url scheme
  Url 地址，由以下3部分组合而成

  1. http 或 https
  2. 域名
  3. /: + 字符串 或者 /~ + 对象

  https "httpbin.org" /: "encoding" /: "utf8"
  -- https://httpbin.org/encoding/utf8
  https "httpbin.org" /: "bytes" /~ (10 :: Int)
  -- https://httpbin.org/bytes/10
  

• body
  NoReqBody 没有请求体。
  ReqBodyJson object 有JSON请求体。（自动将 object 转换成 JSON）

• Proxy response
  bsResponse 应答是 ByteString。
  jsonResponse 应答是 JSON。（自动将 object 转换成 JSON）

• Option scheme
  mempty 没有查询参数。
  a := 1 <> b := 2 有两个查询参数。

• m response
  最后返回应答类型处于 Monad m 之中。
  Monad m 是 MonadHttp 的实例。

• 在指定 ReqBodyJson 以及 jsonResponse 时，需要 Data.Aeson 来定义对象与 JSON 之间的转换。

runReq :: MonadIO m
  => HttpConfig        -- ^ 'HttpConfig' to use
  -> Req a             -- ^ Computation to run
  -> m a
runReq config (Req m) = liftIO (runReaderT m config)

runReq 函数将 req Monad 中的计算结果取出来。
runReq 函数共有2个参数

• config
  Http 配置选项，包括代理服务器，重试次数等。
  Data.Default.Class.def 提供了默认选项。
  缺省情况下代理服务器的设置从 HTTP_PROXY 和 HTTPS_PROXY 两个环境变量中读取。
• Req m
  req Monad，包括 req 函数的调用。
• m a
  返回值处在 Monad m 之中。

示例2

{-# LANGUAGE OverloadedStrings, DeriveGeneric #-}

import Control.Monad
import Control.Monad.IO.Class
import Data.Aeson
import Data.Default.Class
import Data.Text (Text)
import GHC.Generics
import Network.HTTP.Req
import qualified Data.ByteString.Char8 as B

showPostAsString :: Int -> IO ()
showPostAsString n = runReq def $ do
  bs <- req GET (https "jsonplaceholder.typicode.com" /: "posts" /~ n) NoReqBody bsResponse mempty
  liftIO $ B.putStrLn (responseBody bs)

data Post = Post
  { userId  :: Int
  , id :: Int
  , title :: Text
  , body :: Text
  } deriving (Show, Generic)

instance ToJSON Post
instance FromJSON Post

showPostAsJson :: Int -> IO ()
showPostAsJson n = runReq def $ do
  v <- req GET (https "jsonplaceholder.typicode.com" /: "posts" /~ n) NoReqBody jsonResponse mempty
  liftIO $ print (responseBody v :: Post)

showPosts :: Int -> IO ()
showPosts n = runReq def $ do
  v <- req GET (https "jsonplaceholder.typicode.com" /: "posts") NoReqBody jsonResponse mempty
  liftIO $ mapM_ print $ take n (responseBody v :: [Post])

createPost :: IO ()
createPost = runReq def $ do
  let myPost = Post {
    userId = 101,
    Main.id = 102,
    title = "test title",
    body = "test body"
    }
  v <- req POST (https "jsonplaceholder.typicode.com" /: "posts") (ReqBodyJson myPost) jsonResponse mempty
  liftIO $ print (responseBody v :: Post)

updatePost :: Int -> IO ()
updatePost n = runReq def $ do
  let myPost = Post {
    userId = 101,
    Main.id = 0, -- unused
    title = "test title",
    body = "test body"
    }
  v <- req PUT (https "jsonplaceholder.typicode.com" /: "posts" /~ n) (ReqBodyJson myPost) jsonResponse mempty
  liftIO $ print (responseBody v :: Post)

deletePost :: Int -> IO ()
deletePost n = runReq def $ do
  v <- req DELETE (https "jsonplaceholder.typicode.com" /: "posts" /~ n) NoReqBody jsonResponse mempty
  liftIO $ print (responseBody v :: Value)

*Main> showPostAsString 1
{
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
  "body": "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"
}
*Main> showPostAsJson 1
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
*Main> showPosts 2
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
Post {userId = 1, id = 2, title = "qui est esse", body = "est rerum tempore vitae
sequi sint nihil reprehenderit dolor beatae ea dolores neque
fugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis
qui aperiam non debitis possimus qui neque nisi nulla"}
*Main> createPost
Post {userId = 101, id = 102, title = "test title", body = "test body"}
*Main> updatePost 1
Post {userId = 101, id = 1, title = "test title", body = "test body"}
*Main> deletePost 1
Object (fromList [])