Troubleshoot WDC WebEngine Issues in Tableau 2019.4 and later


Prior to Tableau 2019.4, Web Data Connectors used an internal browser in Tableau called Qt WebKit. In Tableau 2019.4 and later, Web Data Connectors use Qt WebEngine, a Chromium-based browser. The Qt WebEngine is a significant upgrade over the previous internal browser and WDC developers will benefit from being able to use modern JavaScript tools and practices that improve the user interface and user interactions. The new browser provides better support for HTML5 and allows developers to use modern debugging tools and the Chrome DevTools for debugging WDC code.

However, because of the internal browser change, some customers might experience problems using their existing connectors in Tableau 2019.4 and later. This topic describes some of these issues and provides possible solutions.



Before you begin

Before diagnosing problems, be sure to launch Tableau Desktop with debugging enabled (--remote-debugging-port=9000 option) and check for console messages. For more information, see Debugging in the Simulator and the Debugger.

The console messages will also be written to the Tableau log file (regular log file on Tableau Desktop; the tabprotosrv logs on Tableau Server). To open the WDC in the debugger, open a new Chrome browser instance and set the URL to localhost:9000. Select the WDC in the browser and begin debugging. For more information, see Debugging a WDC in Tableau Desktop 2019.4 (and later).


Although the extract is created successfully, no data is inserted into it

Details: In Tableau 2019.4 and later, Web Data Connectors use Qt WebEngine as the internal browser. The version of the Qt WebEngine we currently use has a limitation in its data communication channel of approximately 128MB. This limitation restricts the amount of data that you can append to the extract at a time. In addition, the actual amount of data you can append could appear to be much smaller than 128MB, as there is often some additional information or metadata associated with the data. If your WDC appends more data than can be transmitted, the WDC is created and initialized but no data is added. For information on the Qt limitation, see QTBUG-47629

Resolution: Depending upon the size of your data, it’s a best practice to insert data into the table in amounts smaller than 128MB (accounting for the additional metadata). For more information and for example code showing one way of breaking up the data into smaller chunks, see Get Data - Best Practices.


Starting Tableau using tableau.exe -DebugWDC doesn’t work

Resolution: Starting with Tableau 2019.4, you can use the Chrome DevTools to debug WDCs. You no longer use the built-in debugger that was available in earlier versions of Tableau (before Tableau 2019.4). See Debugging a WDC in Tableau Desktop 2019.4 (and later).


Debugging connection was closed (when refreshing the extract)

Resolution: When performing data refreshes, you might find it challenging to stay connected to a remote debugging session using the Chrome Developer Tools. This is because Tableau disconnects the debugging connection before performing a refresh of an extract, causing the debugging session to be reset, which requires that you open a new instance of the Chrome Developer Tools to make the new connection. The recommended way to debug the getSchema and getData methods is to use the Tableau Data pane and then set breakpoints in the Developer Tools.

  1. Start Tableau (with remote debugging enabled and connect to your WDC (see Debugging a WDC in Tableau Desktop 2019.4 (and later)).

  2. In the Data pane, drag out a table to the join area (if it is not there already).

  3. Connect the Chrome Developer Tools to your WDC. Set your breakpoints on the getSchema and getData methods, and then click Update Now.


The WDC library (wdclib) version not supported

Details: Starting with Tableau 2019.4, Tableau no longer supports older versions of wdclib (the WDC library). This includes WDC versions 1.0, 1.1, 2.0.0, and 2.0.1. For more information, see WDC Versions.

Resolution: WDCs that use an old version of wdclib need to upgrade to the latest version. If you are a developer of a Web Data Connector, refer to the migration guide for the steps to upgrade from version 1.x, see Upgrading from WDC Version 1.x. If you are already using a 2.x library, you should be able to just upgrade to a newer version of the library (for example, wdclib-2.3.latest.js). For more information, see WDC Versions.


JavaScript console errors, such as not a valid WDC or tableau.XXX not a valid object

Details: In Tableau 2019.3 and earlier, Web Data Connectors use QT WebKit as the internal browser and are initialized in a synchronous manner, which prevents the WDC code from executing until all bootstrapping code is complete. With QT WebEngine, the Chromium-based internal browser used in Tableau 2019.4 and later, it is not possible to make this guarantee. If your WDC attempts to use the window.tableau object before the init method is called, problems might occur as the API is not fully initialized.

Resolution: For many WDCs, simply upgrading to the latest wdclib library will help. We have released patched versions of 2.1.x, 2.2.x, and 2.3.x to accommodate this. Make sure your WDC is using the latest version of one of those libraries: wdclib-2.1.latest.js, wdclib-2.2.latest.js, or wdclib-2.3.latest.js. You should also be aware that the WDC can’t reliably use the window.tableau object until after the WDC has been initialized. For example, it is illegal to use window.tableau.log before the WDC has been initialized. There is no resolution to this latter issue; WDCs should simply not do this.


Mixed-mode HTTP(S) errors

Details: In Tableau 2019.3 and earlier, which use the QT WebKit internal browser, mixed-mode HTTP and HTTPS calls are legal. For example, in earlier versions of Tableau, a WDC is able to make an AJAX request from an HTTPS host to an HTTP host, or can make HTTP requests for images, scripts, or other HTML elements from an HTTPS web page. In Tableau 2019.4 and later, the Chromium-based QT WebEngine browser reports errors when the WDC attempts mixed-mode calls.

Resolution: Always use HTTPS endpoints. Do not use mixed-mode.


Cookies are not preserved between instances of the WDC connection dialog

Details: In Tableau 2019.3 and earlier, cookies might have been preserved under Qt WebKit WDC connection dialog instances. This was never intentionally supported and does not work in Tableau 2019.4 and later, which use the Chromium-based Qt WebEngine browser.

Resolution: Don’t rely on cookies. Use tableau.connectionData to pass data and expect users may need to re-authenticate if you don’t preserve session data.