POST 请求 addListener('data',function(postDataChunk){}); 不触发

function onRequest(req,res){
  var postData = "";
  var pathname = url.parse(req.url).pathname;
  console.log('Request ' + pathname + ' received.');

  req.setEncoding('utf8');

  req.addListener("data",function(postDataChunk){
    console.log("进入 data");
    postData += postDataChunk;
    console.log("Received POST data chunk '" + postData +"'.");
  });

  req.addListener("end",function(){
    console.log("进入 end");
    route(handle,pathname,res,postData);
  });
}

POST 提交进入都不会触发 data 事件，end 事件每次都触发了，求解