json - 如何在 Yesod 中编写一个接收文件/图像上传的 JSON 端点？

Question

我看到很多帖子涉及编写表单小部件来处理图像上传，但我的 Yesod 服务器只是一个 JSON API。我将通过 Angular 文件上传接收 Post 请求。

Answer 1

一个简单的方法是将文件编码为 base64 数据，然后 然后将其作为 JSON 的一部分发送。但是这种方法的缺点是 它增加了数据大小。

例子:

#!/usr/bin/env stack
{- stack
     --resolver lts-6.24
     --install-ghc
     runghc
     --package yesod
     --package yesod-core
     --package persistent
     --package text
     --package aeson
     --package bytestring
     --package base64-bytestring
-}

{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE FlexibleInstances#-}
{-# LANGUAGE OverloadedStrings#-}
{-# LANGUAGE ScopedTypeVariables #-}

import Control.Monad (join)
import Control.Applicative
import Data.Text (Text, unpack)
import qualified Data.Text.Lazy.Encoding
import Data.Typeable (Typeable)
import Text.Blaze.Html.Renderer.Utf8 (renderHtml)
import Yesod
import Data.Aeson
import Data.Aeson.Types
import qualified Data.ByteString as BS
import Data.ByteString (ByteString)
import qualified Data.ByteString.Base64 as BS
import qualified Data.Text.Encoding as T

data App = App

mkYesod
  "App"
  [parseRoutes|
/json/test TestR POST
|]

instance Yesod App where
  approot = ApprootStatic "http://localhost:3006"

instance RenderMessage App FormMessage where
  renderMessage _ _ = defaultFormMessage

data Test = Test {
      fileData :: Text,
      name :: String
} deriving (Show, Eq, Ord)

instance FromJSON Test where
    parseJSON (Object v) = Test <$>
                           v .: "fileData" <*>
                           v .: "name"
    parseJSON _ = empty

postTestR :: Handler TypedContent
postTestR = do
  testData :: Test <- requireJsonBody
  let fileData' = BS.decode (T.encodeUtf8 $ fileData testData)
  case fileData' of
    Left err -> error err
    Right dat -> liftIO $ BS.writeFile "/home/sibi/myfile" dat
  selectRep $ provideRep $ return emptyObject

main :: IO ()
main = warp 3006 App

执行时:

$ curl -H "Content-Type: application/json" -H "Accept: application/json" -X POST -d '{"fileData":"aGVsbG8gd29ybGQ=","name":"Filename"}' http://127.0.0.1:3006/json/test
$ cat /home/sibi/myfile
hello world