write after end --nodejs 之response

index.js

var server=require("./server");
var route=require("./route");
var requestHandlers=require("./requestHanders");

var handle={};
handle["/"]=requestHandlers.start;
handle['/start']=requestHandlers.start;
handle["/upload"]=requestHandlers.upload;

server.start(route.route,handle);

server.js

var http =require("http");
var url=require("url");


function start(route,handle){
    var onRequest=function(request,response){
        var postData="";
        var pathname=url.parse(request.url).pathname;
        console.log("request for "+pathname+" have received");
        request.setEncoding("utf-8");
        request.addListener("data",function(postDataChunk){
            postData += postDataChunk;
            console.log("receive POST data chunk '"+ postDataChunk + "'.");
        })
        request.addListener("end",function(){
            console.log(postData);
            route(handle,pathname,response,postData);
        })
        route(handle,pathname,response);

    }
    http.createServer(onRequest).listen(3000);
    console.log("Server has started");
}
module.exports.start=start;

route.js

function route(handle,pathname,response,postData){
    console.log("about to route a request for"+ pathname);
    if(typeof handle[pathname]=='function'){
        console.log("route--"+postData);
       handle[pathname](response,postData);
    }else{
        console.log("No request handler found for "+ pathname);
        response.writeHead(404,{"Content-Type":"text/plain"});
        response.write("404 not found");
        response.end();
    }
}

module.exports.route=route;

requestHandles.js

var exec = require("child_process").exec;
var querystring=require("querystring");
function start(response,postData) {
    console.log("request handler 'start' was called");
    var body=''+
        ''+
        '"Content-Type" content="text/html";'+
        'charset=UTF-8" />'+
        ''+
        ''+
        '
" method="post">'+
        '" rows="</span><span class="hljs-number">20</span><span class="hljs-string">" cols="</span><span class="hljs-number">60</span><span class="hljs-string">" >'+
        '" value="Submit text" />' + 
        ''
+
        ''+
        '';
    response.writeHead(200,{ "Content-Type": "text/html"});
    response.end(body);
}

function upload(response,postData){
    console.log("request handler 'upload' was called");
    console.log("handle-upload"+ postData);
    response.writeHead(200, {
        "Content-Type": "text/plain"
    });
    var message="you have sent text "+ querystring.parse(postData).text;
    console.log(message);
    response.write(message);
    response.end();

}

module.exports.start=start;
module.exports.upload=upload;

浏览器中首先访问http://127.0.0.1:3000/start；
出现textarea输入，输入12334534523，点击提交
到http://127.0.0.1:3000/upload
正常应该返回，you have sent text 12334534523，
但是却返回you have sent text undefined

并且控制台中出现如下错误

events.js:183
      throw er; // Unhandled 'error' event
      ^

Error: write after end
    at write_ (_http_outgoing.js:625:15)
    at ServerResponse.write (_http_outgoing.js:620:10)
    at Object.upload [as /upload] (D:\study\js\study01\requestHanders.js:30:14)
    at route (D:\study\js\study01\route.js:5:24)
    at IncomingMessage. (D:\study\js\study01\server.js:17:13)
    at emitNone (events.js:106:13)
    at IncomingMessage.emit (events.js:208:7)
    at endReadableNT (_stream_readable.js:1056:12)
    at _combinedTickCallback (internal/process/next_tick.js:138:11)
    at process._tickCallback (internal/process/next_tick.js:180:9)

D:\study\js\study01>

求解？Any help with this would be amazing. The few sparse answers I’ve found online don’t help at all.