Merge pull request #4 from jipan25/master

新增：退款接口

README.md

@@ -53,6 +53,21 @@ wxpay.closeOrder({ out_trade_no:"xxxxxx"}, function(err, result){
 	console.log(result);
 });
 ```
+退款接口
+```js
+let  params = {
+	appid: 'xxxxxxxx',
+	mch_id: '1234567890',
+    op_user_id: '商户号即可',
+    out_refund_no: '20140703'+Math.random().toString().substr(2, 10),
+    total_fee: '1', //原支付金额
+    refund_fee: '1', //退款金额
+    transaction_id: '微信订单号' }
+
+wxpay.refund(params, function(err, result){
+    console.log('refund', arguments);
+});
+```
 
 ### 原生支付 (NATIVE)
 
@@ -107,7 +122,14 @@ WeixinJSBridge.invoke(
 商户服务端处理微信的回调（express为例）
 ```js
 var router = express.Router();
-var wxpay = require('weixin-pay');
+var WXPay = require('weixin-pay');
+
+var wxpay = WXPay({
+	appid: 'xxxxxxxx',
+	mch_id: '1234567890',
+	partner_key: 'xxxxxxxxxxxxxxxxx', //微信商户平台API密钥
+	pfx: fs.readFileSync('./wxpay_cert.p12'), //微信商户平台证书
+});
 
 // 原生支付回调
 router.use('/wxpay/native/callback', wxpay.useWXCallback(function(msg, req, res, next){

lib/wxpay.js

@@ -165,4 +165,28 @@ WXPay.mix('closeOrder', function(order, fn){
 	}, function(err, res, body){
 		util.parseXML(body, fn);
 	});
-});
+});
+
+
+WXPay.mix('refund',function(order, fn){
+	if (!(order.transaction_id || order.out_refund_no)) { 
+		fn(null, { return_code: 'FAIL', return_msg:'缺少参数' });
+	}
+
+	order.nonce_str = order.nonce_str || util.generateNonceString();
+	util.mix(order, this.wxpayID);
+	order.sign = this.sign(order);
+
+	request({
+		url: "https://api.mch.weixin.qq.com/secapi/pay/refund",
+		method: "POST",
+		body: util.buildXML({xml: order}),
+		agentOptions: {
+			pfx: this.options.pfx,
+			passphrase: this.options.mch_id
+		}
+	}, function(err, response, body){
+		util.parseXML(body, fn);
+	});
+});
+