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: message.go
    path of file: ./repos/plumber/vendor/github.com/eclipse/paho.mqtt.golang
    
    the code of the file until where you have to start completion: /*
 * Copyright (c) 2013 IBM Corp.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Seth Hoenig
 *    Allan Stockdill-Mander
 *    Mike Robertson
 */

package mqtt

import (
	"net/url"

	"github.com/eclipse/paho.mqtt.golang/packets"
	"sync"
)

// Message defines the externals that a message implementation must support
// these are received messages that are passed to the callbacks, not internal
// messages
type Message interface {
	Duplicate() bool
	Qos(
    
func newConnectMsgFromOptions(options *ClientOptions, broker *url.URL) *packets.ConnectPacket {
	m := packets.NewControlPacket(packets.Connect).(*packets.ConnectPacket)

	m.CleanSession = options.CleanSession
	m.WillFlag = options.WillEnabled
	m.WillRetain = options.WillRetained
	m.ClientIdentifier = options.ClientID

	if options.WillEnabled {
		m.WillQos = options.WillQos
		m.WillTopic = options.WillTopic
		m.WillMessage = options.WillPayload
	}

	username := options.Username
	password := options.Password
	if broker.User != nil {
		username = broker.User.Username()
		if pwd, ok := broker.User.Password(); ok {
			password = pwd
		}
	}
	if options.CredentialsProvider != nil {
		username, password = options.CredentialsProvider()
	}

	if username != "" {
		m.UsernameFlag = true
		m.Username = username
		//mustn't have password without user as well
		if password != "" {
			m.PasswordFlag = true
			m.Password = []byte(password)
		}
	}

	m.Keepalive = uint16(options.KeepAlive)

	return m
}