如何在仆人中使用 Reqbody 接收 POST

问题描述

下面的代码应该能够发送一个json主体。但我总是收到以下请求的错误：

curl -X POST -i http://localhost:8080/comTrade --data 'name=nut&age=12'

错误信息是：

Status Code: 405 Method Not Allowed
content-type: text/plain
date: Fri,12 Mar 2021 18:49:04 GMT
server: Warp/3.3.14
transfer-encoding: chunked

data User = User {
    age :: Int,name :: String
} deriving Generic

instance FromJSON User where
  parseJSON = withObject "User" parseUser

parseUser :: Object -> Parser User
parseUser o = do
  n <- (o .: "name")
  a <- (o .: "age")
  return (User a n) 

instance ToJSON  User where
  toJSON user = object 
    [ "age" .= age user,"name" .= name user
    ]

type ComTradeAPI =
  "comTrade" :> ReqBody '[JSON] User :> Post '[JSON] Int
  :<|> "test" :> Get '[JSON] User
  :<|> Raw

myServer :: Server ComTradeAPI
myServer = getUser
           :<|> test
           :<|> serveDirectoryWebApp "site"
    where
      test :: Handler User
      test = return (User 12 "nut")
      getUser :: User -> Handler Int
      getUser usr = return 12

main :: IO ()
main = openbrowser "http://localhost:8080/index.html"
    >> run 8080 (serve (Proxy :: Proxy ComTradeAPI) myServer)

谁能告诉我如何让servant-server接收POST消息？

解决方法

正如 Fyodor Soikin 在评论中指出的那样，OP 中的 cURL 示例不发布 JSON，而是发布 URL 编码的数据。如果您对 cURL 使用 -v (verbose) 选项而不是 -i，您可以看到这一点：

$ curl -v http://localhost:8080/comtrade -d "{ \"name\": \"nut\",\"age\": 12 }"
*   Trying ::1:8080...
* TCP_NODELAY set
*   Trying 127.0.0.1:8080...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 8080 (#0)
> POST /comtrade HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.67.0
> Accept: */*
> Content-Length: 28
> Content-Type: application/x-www-form-urlencoded
>
* upload completely sent off: 28 out of 28 bytes
* Mark bundle as not supporting multiuse
< HTTP/1.1 405 Method Not Allowed
< Transfer-Encoding: chunked
< Date: Sat,13 Mar 2021 12:52:59 GMT
< Server: Warp/3.2.28
< Content-Type: text/plain
<
Only GET or HEAD is supported

请注意，Content-Type 是 application/x-www-form-urlencoded。

ReqBody '[JSON] User 类型声明 API 期望主体为 JSON。然后，您需要做的第一件事是发布 JSON 而不是 URL 编码的数据。

然而，这本身还不够：

$ curl -v http://localhost:8080/comtrade -d "{ \"name\": \"nut\",13 Mar 2021 12:56:42 GMT
< Server: Warp/3.2.28
< Content-Type: text/plain
<
Only GET or HEAD is supported

请注意，cURL 仍然默认 Content-Type 为 application/x-www-form-urlencoded。由于 API 被声明为接收 JSON，因此您必须明确告诉它这里是 JSON：

$ curl -i http://localhost:8080/comtrade -H "Content-Type: application/json" -d "{ \"name\": \"nut\",\"age\": 12 }"
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Date: Sat,13 Mar 2021 12:58:09 GMT
Server: Warp/3.2.28
Content-Type: application/json;charset=utf-8

12

据我所知，Haskell 代码没有任何问题。这是一个正确使用HTTP协议的问题。

haskell haskell servant