Prevent OnQueryCanceled on file download

[MartinM]

Hi,

for my app I implemented CefMessageRouterBrowserSide::Handler and the following functions for the render process.

• OnContextCreated
• OnContextReleased
• OnProcessMessageReceived

The handler is used to inform my app, when the browser window has been maximized or restored. Therefore I'm using a persistent handler:

Code: Select all

// Create and send a new query.
if (window.cefQuery) {
  requestId = window.cefQuery({
    request: 'maximizedListener',
    persistent: true,
    onSuccess: function (response) {
      var value = true;
      if (response === 'maximized') {
        value = true;
      } else {
        value = false;
      }
      $scope.$apply(function () {
        $scope.maximized = value;
      });
    },
    onFailure: function () {
      $scope.$apply(function () {
        requestId = null;
      });
    }
  });
}


It is used to either show a maximize button or a restore button (like the typical Windows controls in the upper right corner of a window).

It works quite well, until I start a file download. For example a pdf download: <a href="pdf/file.pdf">file download</a>. In OnBeforeDownload I open a file save dialog via callback->Continue.

After that, I'm returning to my app, but the query in my MaximizeHandler has been canceled and the callback is now invalid. Does someone have a clue, how to reinstantiate the query or to make it outlive the pdf download in the first place? Because the JavaScript context is not really released here ...

This calling order might be helpful:

• OnBeforeBrowse
• --> OnQueryCanceled
• OnBeforeResourceLoad
• GetResourceHandler
• OnBeforeDownload

This is the code for my handler.

Code: Select all

const char kMaximizedListener[] = "maximizedListener";

// Handle messages in the browser process.
class MaximizeHandler : public CefMessageRouterBrowserSide::Handler {
public:
  MaximizeHandler() : callback_(NULL) {}

  CefRefPtr<Callback> GetCallback() {
    return callback_;
  }

  virtual bool OnQuery(CefRefPtr<CefBrowser> browser,
    CefRefPtr<CefFrame> frame,
    int64 query_id,
    const CefString& request,
    bool persistent,
    CefRefPtr<Callback> callback) OVERRIDE{

    const std::string& message_name = request;
    if (message_name.compare(kMaximizedListener) == 0) {
      callback_ = callback;
      return true;
    }

    return false;
  }

  virtual void OnQueryCanceled(CefRefPtr<CefBrowser> browser,
    CefRefPtr<CefFrame> frame,
    int64 query_id) OVERRIDE{
    callback_ = NULL;
  }

private:
  CefRefPtr<Callback> callback_;
};


P.S. I have an idea for a workaround. It is to start the download inside of a hidden iframe. Is this really necessary?

[amaitland]

Would be helpful if you could include, version, operating system, x86/x64, basic background info.

[MartinM]

Sure.

Win 8.1, 32-Bit Build 2357.

Flags: --no-proxy-server --disable-d3d11

[magreenblatt]

Probably the JavaScript is being executed again when the PDF file loads, and since you're not checking the |query_id| in MaximizeHandler it's removing the callback reference added the first time the JavaScript was executed.

[MartinM]

Hi Marshall, sorry I don't understand what you mean.

The handler is persistent and actually fires multiple times. Actually everytime I'm maximizing (SIZE_MAXIMIZED) or restoring (SIZE_RESTORED) my window. In the OnQuery function I'm saving the callback object for later. Then I retrieve it in my Windows message loop via my custom GetCallback() member function. I don't need the query_id here I think.

The problem (I think) is that CEF thinks I'm browsing away to another page and calls OnQueryCanceled, when all I do is start a file download.

[magreenblatt]

The problem (I think) is that CEF thinks I'm browsing away to another page and calls OnQueryCanceled, when all I do is start a file download.

You're probably correct because <a href="pdf/file.pdf"> will trigger OnBeforeBrowse. I'm not sure how to fix this in a generic way, but you could likely fix it in your application by not calling CefMessageRouterBrowserSide::OnBeforeBrowse if you know the file will be downloaded (by looking at the file extension, for example).

[MartinM]

Thanks a lot!

This works:

Code: Select all

bool SimpleHandler::OnBeforeBrowse(CefRefPtr<CefBrowser> browser, CefRefPtr<CefFrame> frame, CefRefPtr<CefRequest> request, bool is_redirect)
{
  CEF_REQUIRE_UI_THREAD();
  std::string url = request->GetURL();

  if (url.length() < 4 ||
    url.compare(url.length() - 4, 4, ".pdf") != 0) {
    message_router_->OnBeforeBrowse(browser, frame);
  }

  // Allow the navigation to proceed.
  return false;
}