It return unexpected remote IP when nginx proxy pass to "localhost" address.

[beanbest]

I create my app and serve it on a nginx proxy config.

my gin app:

package main

import (
	"net/http"

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

func main() {
	r := gin.Default()
	r.GET("/ip", func(c *gin.Context) {
		c.String(http.StatusOK, c.ClientIP())
	})
	r.Run(":9000")
}

my nginx config:

location / {
        proxy_pass  http://localhost:9000;
        proxy_set_header Host $http_host;
        proxy_set_header X-Forward-For $remote_addr;
        proxy_set_header  X-Real-IP $remote_addr;
        proxy_set_header  X-Appengine-Remote-Addr $remote_addr;
        add_header Access-Control-Allow-Origin *;
        proxy_set_header   Upgrade          $http_upgrade;
        proxy_set_header   Connection       upgrade;
        proxy_set_header   Accept-Encoding  gzip;
    }

my /etc/hosts config

::1	 localhost	localhost.localdomain	localhost6	localhost6.localdomain6
127.0.0.1	localhost	localhost.localdomain	localhost4	localhost4.localdomain4

request result:

curl -s http://test.beanbest.net/ip
10.10.10.123
curl -s http://test.beanbest.net/ip
::1
curl -s http://test.beanbest.net/ip
10.10.10.123
curl -s http://test.beanbest.net/ip
::1
curl -s http://test.beanbest.net/ip
10.10.10.123
curl -s http://test.beanbest.net/ip
::1

I expect that it return 10.10.10.123 everytime，But it return ::1 and 10.10.10.123 alternately.

Environment

• go version: go1.17.3 linux/amd64

[Bisstocuz]

There is a temporary solution below, I will create a new PR to fix this.

You should set the bind address to a IPv4 value:

func main() {
	r := gin.Default()
	r.GET("/ip", func(c *gin.Context) {
		c.String(http.StatusOK, c.ClientIP())
	})
	r.Run("127.0.0.1:9000")
}

Or give a IPv4 upstream address in nginx:

location / {
        proxy_pass  http://127.0.0.1:9000;
        proxy_set_header Host $http_host;
        proxy_set_header X-Forward-For $remote_addr;
        proxy_set_header  X-Real-IP $remote_addr;
        proxy_set_header  X-Appengine-Remote-Addr $remote_addr;
        add_header Access-Control-Allow-Origin *;
        proxy_set_header   Upgrade          $http_upgrade;
        proxy_set_header   Connection       upgrade;
        proxy_set_header   Accept-Encoding  gzip;
    }

[beanbest]

Yes, the above method can be used to temporarily circumvent this problem.

And looking forward, Gin will solve this problem completely.

[Bisstocuz]

Hi, #2967 has been merged, you can close this issue.