realip.go

// From return client's real public IP address from http request headers.
func From(r *http.Request) string {
	// Fetch header value
	xRealIP := r.Header.Get("X-Real-IP")
	xForwardedFor := r.Header.Get("X-Forwarded-For")

	// If both empty, return IP from remote address
	if xRealIP == "" && xForwardedFor == "" {
		var remoteIP string

		// If there are colon in remote address, remove the port number
		// otherwise, return remote address as is
		if strings.ContainsRune(r.RemoteAddr, ':') {
			remoteIP, _, _ = net.SplitHostPort(r.RemoteAddr)
		} else {
			remoteIP = r.RemoteAddr
		}

		return remoteIP
	}

	// Check list of IP in X-Forwarded-For and return the first global address
	for _, address := range strings.Split(xForwardedFor, ",") {
		address = strings.TrimSpace(address)
		isPrivate, err := isPrivateAddress(address)
		if !isPrivate && err == nil {
			return address
		}
	}

	// If nothing succeed, return X-Real-IP
	return xRealIP
}