Add new connection setting for delay between reconnect attempts

README.md

@@ -164,6 +164,10 @@ $connectionSettings = (new \PhpMqtt\Client\ConnectionSettings)
     // This setting is only relevant if setReconnectAutomatically() is set to true.
     ->setMaxReconnectAttempts(3)
 
+    // Defines the delay between reconnect attempts in milliseconds.
+    // This setting is only relevant if setReconnectAutomatically() is set to true.
+    ->setDelayBetweenReconnectAttempts(0)
+
     // The keep alive interval is the number of seconds the client will wait without sending a message
     // until it sends a keep alive signal (ping) to the broker. The value cannot be less than 1 second
     // and may not be higher than 65535 seconds. A reasonable value is 10 seconds (the default).

src/Concerns/ValidatesConfiguration.php

@@ -47,6 +47,10 @@ protected function ensureConnectionSettingsAreValid(ConnectionSettings $settings
             throw new ConfigurationInvalidException('The maximum reconnect attempts cannot be fewer than 1.');
         }
 
+        if ($settings->getDelayBetweenReconnectAttempts() < 0) {
+            throw new ConfigurationInvalidException('The delay between reconnect attempts cannot be lower than 0.');
+        }
+
         if ($settings->getUsername() !== null && trim($settings->getUsername()) === '') {
             throw new ConfigurationInvalidException('The username may not consist of white space only.');
         }

src/ConnectionSettings.php

@@ -19,6 +19,7 @@ class ConnectionSettings
     private int $keepAliveInterval                     = 10;
     private bool $reconnectAutomatically               = false;
     private int $maxReconnectAttempts                  = 3;
+    private int $delayBetweenReconnectAttempts         = 0;
     private ?string $lastWillTopic                     = null;
     private ?string $lastWillMessage                   = null;
     private int $lastWillQualityOfService              = 0;
@@ -226,6 +227,30 @@ public function getMaxReconnectAttempts(): int
         return $this->maxReconnectAttempts;
     }
 
+    /**
+     * Defines the delay between reconnect attempts in milliseconds.
+     * This setting is only relevant if {@see setReconnectAutomatically()} is set to true.
+     *
+     * @param int $delayBetweenReconnectAttempts
+     * @return ConnectionSettings
+     */
+    public function setDelayBetweenReconnectAttempts(int $delayBetweenReconnectAttempts): ConnectionSettings
+    {
+        $copy = clone $this;
+
+        $copy->delayBetweenReconnectAttempts = $delayBetweenReconnectAttempts;
+
+        return $copy;
+    }
+
+    /**
+     * @return int
+     */
+    public function getDelayBetweenReconnectAttempts(): int
+    {
+        return $this->delayBetweenReconnectAttempts;
+    }
+
     /**
      * If the broker should publish a last will message in the name of the client when the client
      * disconnects abruptly, this setting defines the topic on which the message will be published.

src/MqttClient.php

@@ -409,7 +409,8 @@ protected function performConnectionHandshake(bool $useCleanSession = false): vo
      */
     protected function reconnect(): void
     {
-        $maxReconnectAttempts = $this->settings->getMaxReconnectAttempts();
+        $maxReconnectAttempts          = $this->settings->getMaxReconnectAttempts();
+        $delayBetweenReconnectAttempts = $this->settings->getDelayBetweenReconnectAttempts();
 
         for ($i = 1; $i <= $maxReconnectAttempts; $i++) {
             try {
@@ -420,6 +421,10 @@ protected function reconnect(): void
                 if ($i === $maxReconnectAttempts) {
                     throw $e;
                 }
+
+                if ($delayBetweenReconnectAttempts > 0) {
+                    usleep($delayBetweenReconnectAttempts * 1000);
+                }
             }
         }
     }