接收客服发给用户的文件消息 

POST https://im.yourdomain.com/messages

请求参数：

{
	"action":"chat",
	"message":{
		"id":1636240,
		"appid":1000001,
		"type":"voice" | "file",
		"chat_id":354345,
		"from_user":242392,
		"to_user":"e4d8c2abfc783e0b8f0d7b4eb93812e5",
		"filename":"文件资料.zip",
		"url":"https://kchat-files-aliyun.kf5.com/d38456182bec44166adb7d9948b1e95a.zip",
		"create_time":1480594319
	}}

用户服务器响应：

状态码 200