golang gin 中间件，返回结果

package main

import (
    "net/http"
    "github.com/gin-gonic/gin"
)

func response() gin.HandlerFunc {
    return func(c *gin.Context) {
        c.Next()
        if c.Writer.Written() {
            return
        }

        params := c.Keys
        if len(params) == 0 {
            return
        }
        c.JSON(http.StatusOK, params)
    }
}

func main() {
    r := gin.Default()
    r.Use(response())

    r.GET("/ping", func(c *gin.Context) {
        c.String(http.StatusOK, "PONG")
    })

    r.GET("/status", func(c *gin.Context) {
        c.Status(http.StatusOK)
    })

    r.GET("/hello", func(c *gin.Context) {
        c.Set("message", "hello, world")
    })

    r.Run()
}

?  src  go run main.go
[GIN-debug] [WARNING] Creating an Engine instance with the Logger and Recovery middleware already attached.

[GIN-debug] [WARNING] Running in "debug" mode. Switch to "release" mode in production.
 - using env:	export GIN_MODE=release
 - using code:	gin.SetMode(gin.ReleaseMode)

[GIN-debug] GET    /ping                     --> main.main.func1 (4 handlers)
[GIN-debug] GET    /status                   --> main.main.func2 (4 handlers)
[GIN-debug] GET    /hello                    --> main.main.func3 (4 handlers)
[GIN-debug] Environment variable PORT is undefined. Using port :8080 by default
[GIN-debug] Listening and serving HTTP on :8080
[GIN] 2018/11/15 - 23:23:23 | 200 |     128.732µs |       127.0.0.1 | GET      /ping
[GIN] 2018/11/15 - 23:23:26 | 200 |       1.764µs |       127.0.0.1 | GET      /status
[GIN] 2018/11/15 - 23:23:31 | 200 |      135.48µs |       127.0.0.1 | GET      /hello

?  ~  http http://127.0.0.1:8080/ping
HTTP/1.1 200 OK
Content-Length: 4
Content-Type: text/plain; charset=utf-8
Date: Thu, 15 Nov 2018 15:23:23 GMT

PONG

?  ~  http http://127.0.0.1:8080/status
HTTP/1.1 200 OK
Content-Length: 0
Date: Thu, 15 Nov 2018 15:23:26 GMT



?  ~  http http://127.0.0.1:8080/hello
HTTP/1.1 200 OK
Content-Length: 26
Content-Type: application/json; charset=utf-8
Date: Thu, 15 Nov 2018 15:23:31 GMT

{
    "message": "hello, world"
}