如何使用Wreq设置HTTP请求体？customMethod请求体设置咨询

我来帮你梳理下Wreq里关于请求体的这两个常见问题，都是实际开发中很容易碰到的场景：

1. 如何使用Wreq库设置HTTP请求体？ #

Wreq的常用HTTP方法（比如post、put）本身就内置了请求体参数，你可以根据要发送的内容类型选择对应的方式：

• 发送JSON格式请求体：如果你的数据类型实现了ToJSON类型类，直接用json函数把数据转换成请求体即可：

  import Network.Wreq
  import Data.Aeson (ToJSON)
  
  data User = User { name :: String, email :: String } deriving (ToJSON)
  
  main = do
    let user = User "Alice" "alice@example.com"
    response <- post "https://api.example.com/users" (json user)
    print response
  

• 发送原始字节数据：用Raw构造器指定Content-Type和字节流，适合上传二进制文件或自定义格式内容：

  import Network.Wreq
  import qualified Data.ByteString.Lazy as BL
  
  main = do
    let rawContent = BL.pack [0x48, 0x65, 0x6C, 0x6C, 0x6F] -- "Hello"的字节
        body = Raw "application/octet-stream" rawContent
    response <- post "https://api.example.com/upload" body
    print response
  

• 发送表单数据：用form函数构造application/x-www-form-urlencoded格式的请求体：

  import Network.Wreq
  
  main = do
    let formData = form [("username", "alice"), ("password", "secure123")]
    response <- post "https://api.example.com/login" formData
    print response
  

2. 使用customMethod时如何设置请求体？ #

确实，customMethod不像post/put那样直接带请求体参数——它的设计是通过Options来配置请求的所有细节，包括请求体。你需要用setRequestBody函数（来自Network.Wreq.Types）把请求体注入到默认选项里，再传给customMethod。

举个实际例子，比如发送一个PATCH请求并携带JSON体：

import Network.Wreq
import Network.Wreq.Types (setRequestBody)
import Data.Aeson (ToJSON)

data UserUpdate = UserUpdate { email :: String } deriving (ToJSON)

main = do
  let updateData = UserUpdate "alice_new@example.com"
      -- 构造带请求体的Options
      opts = defaults & setRequestBody (json updateData)
  -- 发送PATCH请求
  response <- customMethod "PATCH" "https://api.example.com/users/1" opts
  print response

如果要发送原始文本或二进制内容，同样用Raw构造器注入到Options中：

import Network.Wreq
import Network.Wreq.Types (setRequestBody)
import qualified Data.ByteString.Lazy as BL

main = do
  let textBody = Raw "text/plain" (BL.pack "This is a custom method request")
      opts = defaults & setRequestBody textBody
  response <- customMethod "PUT" "https://api.example.com/custom" opts
  print response

简单来说，customMethod把请求配置的灵活性交给了Options，只要用setRequestBody把请求体绑定到选项上，就能实现和post/put一样的请求体效果。

内容的提问来源于stack exchange，提问作者Chris Stryczynski