define("TOKEN", "wechat");
$wechatObj = new wechatCallbackapiTest();
$wechatObj->valid();

class wechatCallbackapiTest
{
    public function valid()
    {
        $echoStr = $_GET["echostr"];
        //valid signature , option
        if($this->checkSignature()){
            echo $echoStr;
            exit;
        }
    }

    public function responseMsg()
    {
        //get post data, May be due to the different environments
        $postStr = $GLOBALS["HTTP_RAW_POST_DATA"];
        //extract post data
        if (!empty($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 == "?" || $keyword == "? ")
                {
                    $msgType = "text";
                    $content = date("Y-m-d H:i:s", time());
                    $resultStr = sprintf($textTpl, $fromUsername, $toUsername, $time, $msgType, $content);
                    echo $resultStr;
                }
        }else {
            echo "";
            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;
        }
    }
}