Detailed explanation of PHP development to implement WeChat refund function

function Home_index() {
  date_default_timezone_set("Asia/Shanghai");
  $date = date("YmdHis");
  $appid = "";
  $mch_id = "";
  $out_trade_no = "14487658021497944120";
  $op_user_id = "";
  $out_refund_no = $date;
  $total_fee = "500";
  $refund_fee = "500";
//  $transaction_id = "4009542001201706206596667604";
  $key = "";
  $nonce_str = nonceStr();
  $ref = strtoupper(md5("appid=$appid&mch_id=$mch_id&nonce_str=$nonce_str&op_user_id=$op_user_id"
          . "&out_refund_no=$out_refund_no&out_trade_no=$out_trade_no&refund_fee=$refund_fee&total_fee=$total_fee"
          . "&key=$key")); //sign加密MD5
  $refund = array(
  'appid' =>$appid, //应用ID，固定
  'mch_id' => $mch_id, //商户号，固定
  'nonce_str' => $nonce_str, //随机字符串
  'op_user_id' => $op_user_id, //操作员
  'out_refund_no' => $out_refund_no, //商户内部唯一退款单号
  'out_trade_no' => $out_trade_no, //商户订单号,pay_sn码 1.1二选一,微信生成的订单号，在支付通知中有返回
  // 'transaction_id'=>'1',//微信订单号 1.2二选一,商户侧传给微信的订单号
  'refund_fee' => $refund_fee, //退款金额
  'total_fee' => $total_fee, //总金额
  'sign' => $ref//签名
  );
  $url = "https://api.mch.weixin.qq.com/secapi/pay/refund";
  ; //微信退款地址，post请求
  $xml = arrayToXml($refund);
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $url);
  curl_setopt($ch, CURLOPT_HEADER, 1);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1); //证书检查
  if ($useCert == true) {
    // 设置证书
    curl_setopt($ch, CURLOPT_SSLCERTTYPE, 'pem');
    curl_setopt($ch, CURLOPT_SSLCERT, dirname(__FILE__) . '/WxPay/cert/apiclient_cert.pem');
    curl_setopt($ch, CURLOPT_SSLCERTTYPE, 'pem');
    curl_setopt($ch, CURLOPT_SSLKEY, dirname(__FILE__) . '/WxPay/cert/apiclient_key.pem');
    curl_setopt($ch, CURLOPT_SSLCERTTYPE, 'pem');
    curl_setopt($ch, CURLOPT_CAINFO, dirname(__FILE__) . '/WxPay/cert/rootca.pem');
  }
  curl_setopt($ch, CURLOPT_POST, 1);
  curl_setopt($ch, CURLOPT_POSTFIELDS, $xml);
  $xml = curl_exec($ch);
  // 返回结果0的时候能只能表明程序是正常返回不一定说明退款成功而已
  if ($xml) {
    curl_close($ch);
    // 把xml转化成数组
    libxml_disable_entity_loader(true);
    $xmlstring = simplexml_load_string($xml, 'SimpleXMLElement', LIBXML_NOCDATA);
//    var_dump($xmlstring);
    $result['errNum'] = 0;
    $result['info'] = object_to_array($xmlstring);
//    var_dump($result);
    return $result;
  } else {
    $error = curl_errno($ch);
    curl_close($ch);
    // 错误的时候返回错误码。
    $result['errNum'] = $error;
    return $result;
  }
}
function arrayToXml($arr) {
  $xml = "<root>";
  foreach ($arr as $key => $val) {
    if (is_array($val)) {
      $xml .= "<" . $key . ">" . arrayToXml($val) . "</" . $key . ">";
    } else {
      $xml .= "<" . $key . ">" . $val . "</" . $key . ">";
    }
  }
  $xml .= "</root>";
  return $xml;
}
function object_to_array($obj) {
  $obj = (array) $obj;
  foreach ($obj as $k => $v) {
    if (gettype($v) == &#39;resource&#39;) {
      return;
    }
    if (gettype($v) == &#39;object&#39; || gettype($v) == &#39;array&#39;) {
      $obj[$k] = (array) object_to_array($v);
    }
  }
  return $obj;
}
function nonceStr() {
  $chars = "abcdefghijklmnopqrstuvwxyz0123456789";
  $str = "";
  $length = 32;
  for ($i = 0; $i < $length; $i++) {
    $str .= substr($chars, mt_rand(0, strlen($chars) - 1), 1);
  }
  // 随机字符串
  return $str;
}
Home_index();