如何在 servant 中使用 Reqbody 接收 POST

Question

下面的代码应该能够发送 json 正文。但是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？

Answer 1

正如 Fyodor Soikin 在评论中指出的那样，OP 中的 cURL 示例没有 post JSON，但是URL-编码数据。如果您使用 -v (verbose) 选项代替 cURL 而不是 -i:

$ 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

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

ReqBody '[JSON] User 类型声明 API 期望正文为 JSON。那么，您需要做的第一件事就是 post JSON 而不是 URL 编码数据。

然而，这本身是不够的：

$ 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 12:56:42 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 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。是正确使用HTTP协议的问题

如何在 servant 中使用 Reqbody 接收 POST

How to receive POST with Reqbody in servant

haskell

servant