退款接口文档:https://pay.weixin.qq.com/wiki/doc/api/wxa/wxa_api.php?chapter=9_4

条件:laravel框架

1.根据订单号或者支付号,即可进行退款
2.退款金额可以少于支付金额(扣除手续费什么的)
3.退款需要证书(两种方式:windows将apiclient_cert.p12执行一遍即可导入系统;其他系统需要在代码中引入另外2个.pem文件;建议都使用引入文件,比较方便);证书获取说明https://pay.weixin.qq.com/wiki/doc/api/wxa/wxa_api.php?chapter=4_3

注:linux遇上一个bug,正反斜杠写法导致的错误;
原来的引入路径为"app_path().'\Libs\common\wx_cert\apiclient_key.pem';//证书路径",这个写法在linux上会导致postXmlSSLCurl()函数返回400错误;
改为正确写法:"app_path().'/Libs/common/wx_cert/apiclient_cert.pem";//证书路径

以下为退款类

<?php
namespace App\Libs\common;
class WeixinRefund {


    function __construct($openid,$appid,$mch_id,$key,$outTradeNo,$totalFee,$outRefundNo,$refundFee){
        //初始化退款类需要的变量
        $this->openid = $openid;//openid
        $this->APPID = $appid;
        $this->MCHID = $mch_id;
        $this->key = $key;
        $this->outTradeNo = $outTradeNo;//订单号order_sn
        $this->totalFee = $totalFee;//订单总金额
        $this->outRefundNo = $outRefundNo;//退款单号
        $this->refundFee = $refundFee;//需要退款的金额
        $this->SSLCERT_PATH = app_path().'/Libs/common/wx_cert/apiclient_cert.pem';//证书路径
        $this->SSLKEY_PATH = app_path().'/Libs/common/wx_cert/apiclient_key.pem';//证书路径
        
        
    }
    public function refund(){
    
        //对外暴露的退款接口
        $result = $this->wxrefundapi();
        return $result;
    }
    private function wxrefundapi(){
        //通过微信api进行退款流程
        $parma = array(
            'appid'=> $this->APPID,
            'mch_id'=> $this->MCHID,
            'nonce_str'=> $this->createNoncestr(),
            'out_refund_no'=> $this->outRefundNo,
            'out_trade_no'=> $this->outTradeNo,
            'total_fee'=> floatval(($this->totalFee) * 100),
            'refund_fee'=> floatval(($this->refundFee) * 100),
      
        );

        $parma['sign'] = $this->getSign($parma);
        $xmldata = $this->arrayToXml($parma);
        
        $xmlresult = $this->postXmlSSLCurl($xmldata,'https://api.mch.weixin.qq.com/secapi/pay/refund');

        //echo '<prE>';var_dump($xmlresult);die;
        $result = $this->xmlToArray($xmlresult);
        return $result;
    }
//需要使用证书的请求
    function postXmlSSLCurl($xml,$url,$second=30)
    {
        $ch = curl_init();
        //超时时间
        curl_setopt($ch, CURLOPT_TIMEOUT, $second);
        //这里设置代理，如果有的话
        //curl_setopt($ch,CURLOPT_PROXY, '8.8.8.8');
        //curl_setopt($ch,CURLOPT_PROXYPORT, 8080);
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
        //设置header
        curl_setopt($ch, CURLOPT_HEADER, FALSE);
        //要求结果为字符串且输出到屏幕上
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
        //设置证书
        //使用证书：cert 与 key 分别属于两个.pem文件
        //默认格式为PEM，可以注释
        curl_setopt($ch, CURLOPT_SSLCERTTYPE, 'PEM');
        curl_setopt($ch, CURLOPT_SSLCERT, $this->SSLCERT_PATH);
        //默认格式为PEM，可以注释
        curl_setopt($ch, CURLOPT_SSLKEYTYPE, 'PEM');
        curl_setopt($ch, CURLOPT_SSLKEY, $this->SSLKEY_PATH);
        //post提交方式
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $xml);
        $data = curl_exec($ch);
        //返回结果
        if ($data) {
            curl_close($ch);
            return $data;
        } else {
            $error = curl_errno($ch);
            echo "curl出错，错误码:$error" . "<br>";
            curl_close($ch);
            return false;
        }
    }
    
    
    

    //作用：生成签名
    private function getSign($Obj) {
        foreach ($Obj as $k => $v) {
            $Parameters[$k] = $v;
        }
        //签名步骤一：按字典序排序参数
        ksort($Parameters);
        $String = $this->formatBizQueryParaMap($Parameters, false);
        //签名步骤二：在 string 后加入 KEY
        $String = $String . "&key=" . $this->key;
        //签名步骤三：MD5 加密
        $String = md5($String);
        //签名步骤四：所有字符转为大写
        $result_ = strtoupper($String);
        return $result_;
    }
    
    
    ///作用：格式化参数，签名过程需要使用
    private function formatBizQueryParaMap($paraMap, $urlencode) {
        $buff = "";
        ksort($paraMap);
        foreach ($paraMap as $k => $v) {
            if ($urlencode) {
                $v = urlencode($v);
            }
            $buff .= $k . "=" . $v . "&";
        }
        $reqPar = '';
        if (strlen($buff) > 0) {
            $reqPar = substr($buff, 0, strlen($buff) - 1);
        }
        return $reqPar;
    }



    //作用：产生随机字符串，不长于 32 位
    private function createNoncestr($length = 32) {
        $chars = "abcdefghijklmnopqrstuvwxyz0123456789";
        $str = "";
        for ($i = 0; $i < $length; $i++) {
            $str .= substr($chars, mt_rand(0, strlen($chars) - 1), 1);
        }
        return $str;
    }


    //数组转换成 xml
    private function arrayToXml($arr) {
    
        $xml = "<xml>
                   <appid>".$arr['appid']."</appid>
                   <mch_id>".$arr['mch_id']."</mch_id>
                   <nonce_str>".$arr['nonce_str']."</nonce_str> 
                   <out_refund_no>".$arr['out_refund_no']."</out_refund_no>
                   <out_trade_no>".$arr['out_trade_no']."</out_trade_no>
                   <refund_fee>".$arr['refund_fee']."</refund_fee>
                   <total_fee>".$arr['total_fee']."</total_fee>
                   <transaction_id></transaction_id>
                   <sign>".$arr['sign']."</sign>
                </xml>";
        
   /*     $xml = "";
        foreach ($arr as $key => $val) {
            if (is_array($val)) {
                $xml .= "<" . $key . ">" . arrayToXml($val) . "</" . $key . ">";
            } else {
                $xml .= "<" . $key . ">" . $val . "</" . $key . ">";
            }
        }
        $xml .= "</xml>";
        */
        //echo($xml);die;
        return $xml;
    }


    //xml 转换成数组
    private function xmlToArray($xml) {
        //禁止引用外部 xml 实体
        libxml_disable_entity_loader(true);
        $xmlstring = simplexml_load_string($xml, 'SimpleXMLElement', LIBXML_NOCDATA);
        $val = json_decode(json_encode($xmlstring), true);
        return $val;
    }
}

调用该类:

public function wx_refund($order_id,$price){

      ////此处省略了获取参数的相关代码

        //调用退款接口(openid/订单号/订单金额/退款号/退款金额 注:这里订单号=退款号,订单实付金额=退款金额
        $wx_refund = new WeixinRefund($openid,$config['c_appid'],$mch['c_appid'],$mch['c_key'], $order['t_order_number'], $totalFee, $order['t_order_number'], $refundFee);
        $return = $wx_refund->refund();//返回值为数组格式

        $return['order_id'] = $order_id;

        $this->log_add('退款返回值',$return);//写入本地日志,使用的是laravel自带的Logger日志记录函数

        if ($return['result_code'] == 'SUCCESS') {//支付成功处理订单信息(更新订单支付状态
            return true;
        }else{
            return false;
        }
    }

以下为退款成功时的返回值,作参考使用

{
    ["return_code"] => string(7)"SUCCESS"
    ["return_msg"] => string(2)"OK" 
    ["appid"] => string(18)"wxafe501b449dcae9a" 
    ["mch_id"] => string(10)"1568688591" 
    ["nonce_str"] => string(16)"QrTSO1nsbUm85lav" 
    ["sign"] => string(32)"0475BBBECB3E0EA44CE2BF0DC87948F3" 
    ["result_code"] => string(7)"SUCCESS" 
    ["transaction_id"] => string(28)"4200000455202001013871227500"
    ["out_trade_no"] => string(32)"20200101175340157787242047007765" 
    ["out_refund_no"] => string(32)"20200101175340157787242047007765"
    ["refund_id"] => string(29)"50000403182020010113932540592" 
    ["refund_channel"] => array(0) {}
   ["refund_fee"] => string(1)"1" 
    ["coupon_refund_fee"] => string(1)"0" 
    ["total_fee"] => string(1)"1" 
    ["cash_fee"] => string(1)"1"
    ["coupon_refund_count"] => string(1)"0" 
    ["cash_refund_fee"] => string(1)"1"
}