define("TOKEN", "weixin");
$wechatObj = new wechatCallbackapiTest();
if (isset($_GET['echostr'])) {
  $wechatObj->valid();
}else{
  $wechatObj->responseMsg();
}

class wechatCallbackapiTest
{
  public function valid()
  {
    $echoStr = $_GET["echostr"];
    if($this->checkSignature()){
      echo $echoStr;
      exit;
    }
  }
  private function checkSignature()
  {
    $signature = $_GET["signature"];
    $timestamp = $_GET["timestamp"];
    $nonce = $_GET["nonce"];
    $token = TOKEN;
    $tmpArr = array($token, $timestamp, $nonce);
    sort($tmpArr);
    $tmpStr = implode( $tmpArr );
    $tmpStr = sha1( $tmpStr );
    if( $tmpStr == $signature ){
      return true;
    }else{
      return false;
    }
  }
  public function responseMsg()
  {
    $postStr = $GLOBALS["HTTP_RAW_POST_DATA"];
    if (!emptyempty($postStr)){
      $postObj = simplexml_load_string($postStr, 'SimpleXMLElement', LIBXML_NOCDATA);
      $fromUsername = $postObj->FromUserName;
      $toUsername = $postObj->ToUserName;
      $keyword = trim($postObj->Content);
      $time = time();
      $textTpl = "<xml>
            <ToUserName><![CDATA[%s]]></ToUserName>
            <FromUserName><![CDATA[%s]]></FromUserName>
            <CreateTime>%s</CreateTime>
            <MsgType><![CDATA[%s]]></MsgType>
            <Content><![CDATA[%s]]></Content>
            <FuncFlag>0</FuncFlag>
            </xml>";
      if($keyword != " " || !emptyempty( $keyword ) )
      {
  msgType = "text";
  //$contentStr .= date("Y-m-d H:i:s",time());
  $resultStr = sprintf($textTpl, $fromUsername, $toUsername, $time, $msgType, $contentStr);
  echo $resultStr;
      }
    }else{
      echo "";
      exit;
    }
  }
}