直接直接定义一个空串data接收数据的
function(chunk){

data += chunk

}
可现在是json数据了，昨天试了没法这样做。
然后想用可写流对象，结果总是错，下面两种方式说
events.js:160

  throw er; // Unhandled 'error' event
  ^

Error: not implemented

at Writable._write (_stream_writable.js:459:6)
at doWrite (_stream_writable.js:331:12)
at writeOrBuffer (_stream_writable.js:317:5)
at Writable.write (_stream_writable.js:243:11)
at IncomingMessage.ondata (_stream_readable.js:555:20)
at emitOne (events.js:96:13)
at IncomingMessage.emit (events.js:188:7)
at readableAddChunk (_stream_readable.js:176:18)
at IncomingMessage.Readable.push (_stream_readable.js:134:10)
at HTTPParser.parserOnBody (_http_common.js:123:22)

  var writer = new Write()

    req.pipe( writer )
    req.on("end",function () {
        console.log('数据'+ writer)
        res.writeHead(
            200,{'Content-Type':'text/plain'}
        )
        res.end( "响应数据: " + writer  )
    })

var callback = function (  ) {
  var callback = function (  ) {
        console.log('数据'+ writer)
        res.writeHead(
            200,{'Content-Type':'text/plain'}
        )
        res.end( "响应数据: " + writer  )
    }


    var writer = new Write()
    req.on('data',function (chunk) {
        writer.write(chunk , callback   )
    })

后端获取json数据应该怎么写？