Fix for duplicate webhook deliveries

includes/class-wc-webhook.php

@@ -20,6 +20,14 @@ require_once 'legacy/class-wc-legacy-webhook.php';
  */
 class WC_Webhook extends WC_Legacy_Webhook {
 
+	/**
+	 * Store which object IDs this webhook has processed (ie scheduled to be delivered)
+	 * within the current page request.
+	 *
+	 * @var array
+	 */
+	protected $processed = array();
+
 	/**
 	 * Stores webhook data.
 	 *
@@ -103,6 +111,9 @@ class WC_Webhook extends WC_Legacy_Webhook {
 			return;
 		}
 
+		// Mark this $arg as processed to ensure it doesn't get processed again within the current request.
+		$this->processed[] = $arg;
+
 		/**
 		 * Process webhook delivery.
 		 *
@@ -123,7 +134,7 @@ class WC_Webhook extends WC_Legacy_Webhook {
 	 * @return bool       True if webhook should be delivered, false otherwise.
 	 */
 	private function should_deliver( $arg ) {
-		$should_deliver = $this->is_active() && $this->is_valid_topic() && $this->is_valid_action( $arg ) && $this->is_valid_resource( $arg );
+		$should_deliver = $this->is_active() && $this->is_valid_topic() && $this->is_valid_action( $arg ) && $this->is_valid_resource( $arg ) && ! $this->is_already_processed( $arg );
 
 		/**
 		 * Let other plugins intercept deliver for some messages queue like rabbit/zeromq.
@@ -280,6 +291,19 @@ class WC_Webhook extends WC_Legacy_Webhook {
 		return true;
 	}
 
+	/**
+	 * Checks if the specified resource has already been queued for delivery within the current request.
+	 *
+	 * Helps avoid duplication of data being sent for topics that have more than one hook defined.
+	 *
+	 * @param mixed $arg First hook argument.
+	 *
+	 * @return bool
+	 */
+	protected function is_already_processed( $arg ) {
+		return false !== array_search( $arg, $this->processed, true );
+	}
+
 	/**
 	 * Deliver the webhook payload using wp_safe_remote_request().
 	 *