fix: resubscribe when no session present (#895) (#1650)

src/lib/client.ts

@@ -2105,8 +2105,11 @@ export default class MqttClient extends TypedEventEmitter<MqttClientEventCallbac
 		const _resubscribeTopicsKeys = Object.keys(this._resubscribeTopics)
 		if (
 			!this._firstConnection &&
+			// Only resubscribe in case of clean connection or if the server does not have a stored session.
+			// The Session Present flag is available since v3.1.1
+			// https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc385349254
 			(this.options.clean ||
-				(this.options.protocolVersion === 5 &&
+				(this.options.protocolVersion >= 4 &&
 					!this.connackPacket.sessionPresent)) &&
 			_resubscribeTopicsKeys.length > 0
 		) {

test/abstract_client.ts

@@ -3165,6 +3165,39 @@ export default function abstractTest(server, config) {
 			})
 		})
 
+		it('should resubscribe when clean=false and sessionPresent=false', function _test(done) {
+			const client = connect({
+				clientId: 'test',
+				reconnectPeriod: 100,
+				clean: false,
+				protocolVersion: 4,
+			})
+			let tryReconnect = true
+			let reconnectEvent = false
+
+			client.on('reconnect', () => {
+				reconnectEvent = true
+			})
+
+			client.on('connect', () => {
+				if (tryReconnect) {
+					client.subscribe('hello', () => {
+						client.stream.end()
+
+						server.once('client', (serverClient) => {
+							serverClient.on('subscribe', () => {
+								client.end(done)
+							})
+						})
+					})
+
+					tryReconnect = false
+				} else {
+					assert.isTrue(reconnectEvent)
+				}
+			})
+		})
+
 		it('should not resubscribe when reconnecting if resubscribe is disabled', function _test(done) {
 			const client = connect({ reconnectPeriod: 100, resubscribe: false })
 			let tryReconnect = true

test/server_helpers_for_client_tests.ts

@@ -36,6 +36,9 @@ export default function serverBuilder(
 			if (!serverClient.writable) return false
 			let rc = 'returnCode'
 			const connack = {}
+			if (serverClient.options.protocolVersion >= 4) {
+				connack['sessionPresent'] = false
+			}
 			if (
 				serverClient.options &&
 				serverClient.options.protocolVersion === 5