If enable the gzip middleware, the gin server returns an incorrect response for 404 status by default

[mstmdev]

Enable the gzip middleware, that 404 response like this:

HTTP/1.1 404 Not Found
Vary: Accept-Encoding
Date: Wed, 29 Dec 2021 09:44:42 GMT
Content-Length: 0

Disable the gzip middleware, that 404 response like this:

HTTP/1.1 404 Not Found
Content-Type: text/plain
Date: Wed, 29 Dec 2021 09:47:08 GMT
Content-Length: 18

404 page not found

Because of the gz.Close() will writing the GZIP footer to c.Writer.

gzip/handler.go

Lines 55 to 60 in c784c8e

	c.Writer = &gzipWriter{c.Writer, gz}
	defer func() {
	gz.Close()
	c.Header("Content-Length", fmt.Sprint(c.Writer.Size()))
	}()
	c.Next()

So gin will not write default404Body in serveError func.
We need to customize the gin.Engine.NoRoute that responds to the correct 404 content now.

https://github.com/gin-gonic/gin/blob/d062a6a6155236883f4c3292379ab94b1eac8b05/gin.go#L632-L637

[runephilosof-karnovgroup]

I see almost the same results.

runephilosof@fedora:~/code/go-test$ curl -i -H 'Accept-Encoding: gzip' localhost:9000/
HTTP/1.1 404 Not Found
Content-Encoding: gzip
Vary: Accept-Encoding
Date: Wed, 20 Sep 2023 12:18:32 GMT
Content-Length: 23

But the 23 bytes is just the gzip overhead for an empty string

~/code/go-test$ curl -H 'Accept-Encoding: gzip' localhost:9000/ --output foo.gz
~/code/go-test$ gunzip foo.gz
~/code/go-test$ ls -l foo
-rw-r--r--. 1 runephilosof runephilosof 0 Sep 20 14:22 foo

Using

package main

import (
	"fmt"
	"github.com/gin-contrib/gzip"
	"github.com/gin-gonic/gin"
	"log"
	"net/http"
	"time"
)

func main() {

	r := gin.Default()
	r.Use(func(c *gin.Context) {
		c.Writer.Header().Add("Vary", "Origin")
	}, gzip.Gzip(gzip.DefaultCompression))
	r.GET("/ping", func(c *gin.Context) {
		c.String(http.StatusOK, "pong "+fmt.Sprint(time.Now().Unix()))
	})

	// Listen and Server in 0.0.0.0:8080
	if err := r.Run(":9000"); err != nil {
		log.Fatal(err)
	}

}