关于php微信订阅号开发之token验证后自动发送消息给订阅号但是没有消息返回的问题

<?php
 /**
 * wechat php test
 */
 //define your token
 define("TOKEN", "codcodog");
 $wechatObj = new wechatCallbackapiTest();
 //$wechatObj->valid();
 $wechatObj->responseMsg();
 class wechatCallbackapiTest
 {
  public function valid()
  {
   $echoStr = $_GET["echostr"];
   //valid signature , option
   if($this->checkSignature()){
   header('content-type:text');
    echo $echoStr;
    exit;
   }
  }
  public function responseMsg()
  {
   //get post data, May be due to the different environments
   $postStr = $GLOBALS["HTTP_RAW_POST_DATA"];
   //$postStr = file_get_contents("php://input");
   file_put_contents("log.txt",$postStr,FILE_APPEND );
   //extract post data
   if (!empty($postStr)){
     /* libxml_disable_entity_loader is to prevent XML eXternal Entity Injection,
     the best way is to check the validity of xml by yourself */
     libxml_disable_entity_loader(true);
     $postObj = simplexml_load_string($postStr, 'SimpleXMLElement', LIBXML_NOCDATA);
     $fromUsername = $postObj->FromUserName; //用户
     $toUsername = $postObj->ToUserName;  //公众平台
     $keyword = trim($postObj->Content);
     $time = time();
     $textTpl = "<xml>
        <ToUserName><![CDATA[%s]]></ToUserName>
        <FromUserName><![CDATA[%s]]></FromUserName>
        <CreateTime>%s</CreateTime>
        <MsgType><![CDATA[%s]]></MsgType>
        <Content><![CDATA[%s]]></Content>
        <FuncFlag></FuncFlag>
        </xml>";    
     if(!empty( $keyword ))
     {
      $msgType = "text";
      $contentStr = "Welcome to wechat world!";
      $resultStr = sprintf($textTpl, $fromUsername, $toUsername, $time, $msgType, $contentStr);
      echo $resultStr;
     }else{
      echo "Input something...";
     }
   }else {
    echo "";
    exit;
   }
  }
  private function checkSignature()
  {
   // you must define TOKEN by yourself
   if (!defined("TOKEN")) {
    throw new Exception('TOKEN is not defined!');
   }
   $signature = $_GET["signature"];
   $timestamp = $_GET["timestamp"];
   $nonce = $_GET["nonce"];
   $token = TOKEN;
   $tmpArr = array($token, $timestamp, $nonce);
   // use SORT_STRING rule
   sort($tmpArr, SORT_STRING);
   $tmpStr = implode( $tmpArr );
   $tmpStr = sha( $tmpStr );
   if( $tmpStr == $signature ){
    return true;
   }else{
    return false;
   }
  }
 }
 ?>