You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: hosts.go
    path of file: ./repos/malice/vendor/github.com/docker/docker/opts
    
    the code of the file until where you have to start completion: package opts

import (
	"fmt"
	"net"
	"net/url"
	"strconv"
	"strings"
)

var (
	// DefaultHTTPPort Default HTTP Port used if only the protocol is provided to -H flag e.g. dockerd -H tcp://
	// These are the IANA registered port number
    
func ValidateHost(val string) (string, error) {
	host := strings.TrimSpace(val)
	// The empty string means default and is not handled by parseDockerDaemonHost
	if host != "" {
		_, err := parseDockerDaemonHost(host)
		if err != nil {
			return val, err
		}
	}
	// Note: unlike most flag validators, we don't return the mutated value here
	//       we need to know what the user entered later (using ParseHost) to adjust for TLS
	return val, nil
}