Description

When a user accesses a Gin-based web application through a reverse proxy server, and the application uses c.GetClientIP() to obtain the client IP address, it currently only recognizes the following formats:

IPv4 addresses

IPv6 addresses without square brackets

For example, the following addresses can be correctly recognized:

192.168.8.39
240e:318:2f4a:de56::240

However, in real production environments, some reverse proxy servers do not provide IP addresses in this “plain” format. For example, IIS automatically adds square brackets around IPv6 addresses, which may result in the following X-Forwarded-For header:

X-Forwarded-For: [240e:318:2f4a:de56::240]

This format with square brackets cannot currently be recognized.

In addition, some scenarios include the client port in the X-Forwarded-For header. For example:

When IIS uses Application Request Routing (ARR) + URL Rewrite as a reverse proxy and the “Include TCP port from clientIP” option is enabled.

Some cloud load balancers also provide similar settings, such as
routing.http.xff_client_port.enabled.

In these cases, the X-Forwarded-For header may look like this:

X-Forwarded-For: 192.168.8.39:38792
X-Forwarded-For: [240e:318:2f4a:de56::240]:38792

These formats that include a port number are also not recognized.

Gin Version

v1.12.0

Can you reproduce the bug?

Yes

Source Code

// main.go
package main
import (
	"github.com/gin-gonic/gin"
)
func main() {
	r := gin.Default()
	r.SetTrustedProxies([]string{"0.0.0.0/0", "::/0"})
	r.GET("/ip", func(c *gin.Context) {
		c.String(200, c.ClientIP())
	})
	r.Run(":8081")
}

Execute the test in Windows CMD, Test results：

curl -H "X-Forwarded-For: 192.168.8.39" http://127.0.0.1:8080/ip
Response content: 192.168.8.39

curl -H "X-Forwarded-For: 240e:318:2f4a:de56::240" http://127.0.0.1:8080/ip
Response content: 240e:318:2f4a:de56::240

curl -H "X-Forwarded-For: [240e:318:2f4a:de56::240]" http://127.0.0.1:8080/ip
Response content: 127.0.0.1

curl -H "X-Forwarded-For: 192.168.8.39:38792" http://127.0.0.1:8080/ip
Response content: 127.0.0.1

curl -H "X-Forwarded-For: [240e:318:2f4a:de56::240]:38792" http://127.0.0.1:8080/ip
Response content: 127.0.0.1

Go Version

1.25.7

Operating System

Windows 11 Build 26200