func main() {
    openhttplisten()
}
func openhttplisten() {
    http.handlefunc("/", receiveclientrequest)
    fmt.println("go server start running...")
    err := http.listenandserve(":9090", nil)
    if err != nil {
        log.fatal("listenandserve: ", err)
    }
}
func receiveclientrequest(w http.responsewriter, r *http.request) {
    w.header().set("access-control-allow-origin", "*")             //允许访问所有域
    w.header().add("access-control-allow-headers", "content-type") //header的类型
    w.header().set("content-type", "application/json")             //返回数据格式是json
    r.parseform()
    fmt.println("收到客户端请求: ", r.form)

func ldns(w http.responsewriter, req *http.request) {
    if origin := req.header.get("origin"); origin != "" {
        w.header().set("access-control-allow-origin", origin)
        w.header().set("access-control-allow-methods", "post, get, options, put, delete")
        w.header().set("access-control-allow-headers",
            "accept, content-type, content-length, accept-encoding, x-csrf-token, authorization")
    }
    if req.method == "options" {
        return
    }
    // 响应http code
    w.writeheader(200)
    query := strings.split(req.host, ".")
    value, err := ldns.ramdbmgr.get(query[0])
    fmt.println("access-control-allow-origin", "*")
    if err != nil {
        io.writestring(w, `{"message": ""}`)
        return
    }
    io.writestring(w, value)
}

import (
 "github.com/gin-gonic/gin"
 "net/http"
)
// 跨域中间件
func cors() gin.handlerfunc {
 return func(c *gin.context) {
  method := c.request.method
  origin := c.request.header.get("origin")
  if origin != "" {
   c.header("access-control-allow-origin", origin)
   c.header("access-control-allow-methods", "post, get, options, put, delete, update")
   c.header("access-control-allow-headers", "origin, x-requested-with, content-type, accept, authorization")
   c.header("access-control-expose-headers", "content-length, access-control-allow-origin, access-control-allow-headers, cache-control, content-language, content-type")
   c.header("access-control-allow-credentials", "false")
   c.set("content-type", "application/json")
  }
  if method == "options" {
   c.abortwithstatus(http.statusnocontent)
  }
  c.next()
 }
}

router := gin.default()
// 要在路由组之前全局使用「跨域中间件」, 否则options会返回404
router.use(cors())