How to implement efficient IP whitelist in gin-gonic/gin middleware

Question

I have an application which I need to restrict to a handful of IPs. I can write a middleware and return if request IP is not from allowed list, however I would like this process to be as efficient as possible. I.e. I would like to drop the connection as early as possible. What is the earliest stage I can drop connection, preferably with an HTTP response. I do not have control on host firewall or border firewall to filter traffic, and again, I won't be able to provide an HTTP response, even if I had control of firewall.

Also I would prefer if I could get a description of a life cycle of an HTTP request in gin.

Answer 1

Add a middleware as Lansana described.

It's important that you declare it as early in the chain as possible.

r := gin.New()

whitelist := make(map[string]bool)
whitelist["127.0.0.1"] = true

r.Use(middleware.IPWhiteList(whitelist))

I'd write the middleware like this, if you're not in the whitelist, return an error that is appropriate, in the following snippet i'm returning a JSON error.

package middleware

import (
    "log"
    "net/http"

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

func IPWhiteList(whitelist map[string]bool) gin.HandlerFunc {
    return func(c *gin.Context) {
        if !whitelist[c.ClientIP()] {
            c.AbortWithStatusJSON(http.StatusForbidden, gin.H{
                "status":  http.StatusForbidden,
                "message": "Permission denied",
            })
            return
        }
    }
}