Allow gap between async requests (#937)

* Allow gap between async requests

* Include explanation of ASYNC_REQUEST_INTERVAL in config_extended.php

Author: bramley

public_html/lists/admin/init.php

@@ -786,10 +786,14 @@
 }
 if (!defined('HTTP_PROXY_HOST')) {
     define('HTTP_PROXY_HOST', false);
-} 
+}
 if (!defined('HTTP_PROXY_PORT')) {
     define('HTTP_PROXY_PORT', false);
 }
+// interval in milliseconds between asynchronous requests
+if (!defined('ASYNC_REQUEST_INTERVAL')) {
+    define('ASYNC_REQUEST_INTERVAL', 0);
+}
 
 if (!isset($GLOBALS['export_mimetype'])) {
     $GLOBALS['export_mimetype'] = 'application/csv';

public_html/lists/admin/js/phplistapp.js

@@ -77,8 +77,12 @@ function loadDivContent(index) {
         div = asyncLoadDiv[index];
         url = asyncLoadUrl[index];
         $("#"+div).html(busyImage + '<span class="loadingprogressbanner"></span>');
-        $("#"+div).load(url, function() {
-            loadDivContent(index + 1);
+        $("#"+div).load(url, function(response, status, xhr) {
+            if (status == "error") {
+                $("#"+div).html('');
+            } else {
+                setTimeout(() => loadDivContent(index + 1), asyncRequestInterval);
+            }
         });
     }
 }

public_html/lists/admin/lib.php

@@ -2385,6 +2385,7 @@ function asyncLoadContentDiv($url,$divname)
         if (typeof asyncLoadDiv == "undefined") {
             var asyncLoadDiv = new Array();
             var asyncLoadUrl = new Array();
+            var asyncRequestInterval = ' . ASYNC_REQUEST_INTERVAL . ';
         }
         asyncLoadDiv[asyncLoadDiv.length] = "'.$divname.'";
         asyncLoadUrl[asyncLoadUrl.length] = "'.$url.'";

public_html/lists/config/config_extended.php

@@ -893,18 +893,22 @@
 // adds constant to email headers
 define('GOOGLE_SENDERID', '');
 
-// For ajax based signup forms (https://discuss.phplist.org/t/solved-ajax-subscribe-api/974) the access-control-allow-origin header 
+// For ajax based signup forms (https://discuss.phplist.org/t/solved-ajax-subscribe-api/974) the access-control-allow-origin header
 // has to be set properly.
 // Add the addresses of the websites you want to allow to perform ajax requests to PHPList.
 define('ACCESS_CONTROL_ALLOW_ORIGINS', ['https://example.com','https://example.org']);
 
 // when using Mysql, what engine should we use
 // there is no need to set this, when you have a valid engine defined in your Mysql server settings
 // If you set this, the next time upgrade is run on commandline, the system will attempt to change all tables to this engine.
-// this is useful for old systems that have been created 
+// this is useful for old systems that have been created
 // for valid engines, check your server documentation (MariaDB or Mysql)
 // Warning, setting this value incorrectly will cause your database creation to break
 // the current value is a sensible one to use. It is advised not to change this.
-// if you are on a shared hosting environment, make sure you have the database permissions to update the 
+// if you are on a shared hosting environment, make sure you have the database permissions to update the
 // information.schema tables.
 $mysql_database_engine = 'InnoDB';
+
+// The subscriber totals for each list on the lists page are calculated by sending a sequence of asynchronous requests.
+// You can include a delay between requests using this setting. The value is in milliseconds.
+define('ASYNC_REQUEST_INTERVAL', 0);