Gin [Question] add X-Response-Time to response header

I want use middleware to output the every request Latency ,to reponse header ,like

package main

import (
    "time"

    "github.com/gin-gonic/gin"
)

func main() {
    r := gin.Default()
    r.Use(Latency)
    r.GET("/", func(c *gin.Context) {
        c.JSON(200, gin.H{
            "message": "pong",
        })
    })
    r.Run() // listen and serve on 0.0.0.0:8080
}

func Latency(c *gin.Context) {
    // Start timer
    start := time.Now()
    // Process request
    c.Next()
    // output the http request Latency to response header ,but not working ,how can log the cost time to response header
    c.Writer.Header().Set("Latency", time.Now().Sub(start).String())
}

but ,the reponse header not show `Latency',how can i log the Latency to reponse header? thks

Comment From: dtest11

solution

package main

import (
    "github.com/gin-gonic/gin"
    "time"
)

type XResponseTimer struct {
    gin.ResponseWriter
    start time.Time
}

func (w *XResponseTimer) WriteHeader(statusCode int) {
    duration := time.Now().Sub(w.start)
    w.Header().Set("X-Response-Time", duration.String())
    w.ResponseWriter.WriteHeader(statusCode)
}

func (w *XResponseTimer) Write(b []byte) (int, error) {
    return w.ResponseWriter.Write(b)
}

func NewXResponseTimer(c *gin.Context) {
    blw := &XResponseTimer{ResponseWriter: c.Writer, start: time.Now()}
    c.Writer = blw
    c.Next()
}

func main() {
    r := gin.Default()
    r.Use(NewXResponseTimer)
    r.Use(func(context *gin.Context) {
        //time.Sleep(1 * time.Second)
        context.Next()
    })
    r.GET("/", func(c *gin.Context) {
        time.Sleep(10 * time.Millisecond)
        c.JSON(200, gin.H{
            "message": "pong",
        })
    })
    //go browser.OpenURL("http://localhost:8080/")
    err := r.Run()
    if err != nil {
        panic(err)
    } // listen and serve on 0.0.0.0:8080
}

reponse

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
X-Response-Time: 10.314678ms
Date: Tue, 26 Jul 2022 15:25:55 GMT
Content-Length: 18

{"message":"pong"}

Comment From: dtest11

https://github.com/dtest11/reponse/blob/1f462b27a8930673eb85868e1bdc402a488693db/reponse_time_test.go#L8