how to make client send a disconnect packet?

[jedwards1211]

In some tests I'm writing I need to make clients voluntarily disconnect, and reconnect later when I tell them to, with same clientId and session resending any QoS 1/2 messages.

Oddly it seems like there's no way to do this....end() seems rather permanent and calling .reconnect() afterwards doesn't seem to do anything.

[dfeprado]

I have a app that have to publish to everyone that it are disconnecting. This is the way I do it:

cli.publish('topic', 'disconnected', 0, {}, () => {cli.end()})

I put this snippet in an disconnect function. Is this what you need?

[redboltz]

@jedwards1211
See the following test case:

MQTT.js/test/abstract_client.js

Lines 2825 to 2869 in 4bd3f3c

	it('should resend in-flight QoS 1 publish messages from the client if clean is false', function (done) {
	var reconnect = false
	var client = {}
	var incomingStore = new mqtt.Store({ clean: false })
	var outgoingStore = new mqtt.Store({ clean: false })
	var server2 = serverBuilder(config.protocol, function (serverClient) {
	serverClient.on('connect', function (packet) {
	var connack = version === 5 ? { reasonCode: 0 } : { returnCode: 0 }
	serverClient.connack(connack)
	})
	serverClient.on('publish', function (packet) {
	if (reconnect) {
	server2.close()
	client.end(true, done)
	} else {
	client.end(true, () => {
	client.reconnect({
	incomingStore: incomingStore,
	outgoingStore: outgoingStore
	})
	reconnect = true
	})
	}
	})
	})
	server2.listen(ports.PORTAND50, function () {
	client = connect({
	port: ports.PORTAND50,
	host: 'localhost',
	clean: false,
	clientId: 'cid1',
	reconnectPeriod: 0,
	incomingStore: incomingStore,
	outgoingStore: outgoingStore
	})
	client.on('connect', function () {
	if (!reconnect) {
	client.publish('topic', 'payload', {qos: 1})
	}
	})
	client.on('error', function () {})
	})
	})

incomingStore and outgoingStore can be passed from the outside of the client. And they have clean flag. If it set false, then the Store doesn't clean if the client calls the end(). So the QoS 1/2 messages are preserved after end() is called.

MQTT.js/test/abstract_client.js

Lines 2828 to 2829 in 4bd3f3c

	var incomingStore = new mqtt.Store({ clean: false })
	var outgoingStore = new mqtt.Store({ clean: false })

When the first client connection, set clean: false and incomingStore and outgoingStore.

MQTT.js/test/abstract_client.js

Lines 2852 to 2860 in 4bd3f3c

	client = connect({
	port: ports.PORTAND50,
	host: 'localhost',
	clean: false,
	clientId: 'cid1',
	reconnectPeriod: 0,
	incomingStore: incomingStore,
	outgoingStore: outgoingStore
	})

When you want to disconnect from the client side using DISCONNECT packet, you can call end() as follows:

MQTT.js/test/abstract_client.js

Lines 2840 to 2846 in 4bd3f3c

	client.end(true, () => {
	client.reconnect({
	incomingStore: incomingStore,
	outgoingStore: outgoingStore
	})
	reconnect = true
	})

In this case, client.reconnect() is called just after end() process is finished. But you can call reconnect anywhere.

The important point is passing incomingStore and outgoingStore as the reconnect argument.

Alternative approach:
You can create the new client instead of calling reconnect().
The key is managing incomingStore and outgoingStore by yourself at the outside of the client.

[redboltz]

The test case code set force option true when end() calling.

MQTT.js/test/abstract_client.js

Line 2840 in 4bd3f3c

client.end(true, () => {

In order to send DISCONNECT packet, you need to set force flag to false.

MQTT.js/lib/client.js

Line 861 in d8be59e

MqttClient.prototype.end = function (force, opts, cb) {

MQTT.js/lib/client.js

Line 911 in d8be59e

that._cleanUp(force, () => {

MQTT.js/lib/client.js

Lines 1050 to 1074 in d8be59e

	MqttClient.prototype._cleanUp = function (forced, done) {
	var opts = arguments[2]
	if (done) {
	debug('_cleanUp :: done callback provided for on stream close')
	this.stream.on('close', done)
	}
	debug('_cleanUp :: forced? %s', forced)
	if (forced) {
	if ((this.options.reconnectPeriod === 0) && this.options.clean) {
	flush(this.outgoing)
	}
	debug('_cleanUp :: (%s) :: destroying stream', this.options.clientId)
	this.stream.destroy()
	} else {
	var packet = xtend({ cmd: 'disconnect' }, opts)
	debug('_cleanUp :: (%s) :: call _sendPacket with disconnect packet', this.options.clientId)
	this._sendPacket(
	packet,
	setImmediate.bind(
	null,
	this.stream.end.bind(this.stream)
	)
	)
	}

See also #706 and #707.

[jedwards1211]

@redboltz Thanks for your examples.

As I mentioned in #1286 (comment), I think it would be better not to store a clean flag on the stores and instead have the client tell the stores whether to discard state when the client is shutting down. It's counterintuitive that passing clean: false in the connect options isn't enough.

[redboltz]

Ah, I just realized that you are the person who create the issue #1286.
I understand.
I think that the current status is we have a way to send disconnect and reconnect with preserving stores but it is not intuitive.
So there is no defect in the behavior but there is a room to improve.
Is that right?

[jedwards1211]

Right, I wasn't saying there's any incorrect behavior

[YoDaMa]

@redboltz do you think you could summarize this under the vNext discussion? #1324

The policy seems clunky right now, and I agree there's room for improvement.

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