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chromiumembedded / cef

Chromium Embedded Framework (CEF). A simple framework for embedding Chromium-based browsers in other applications.
https://bitbucket.org/chromiumembedded/cef/
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Call `DownloadHandler::CanDownload` when downloading a PDF file from the PDF viewer #3783

Open lucamuscat opened 4 weeks ago

lucamuscat commented 4 weeks ago

Describe the bug Typically, DownloadHandler::CanDownload is called before any download, giving the developer the opportunity to decide whether a file should be downloaded. DownloadHandler::CanDownload is not executed when a PDF file is downloaded through the PDF viewer plugin, circumventing the logic found in DownloadHandler::CanDownload.

Although one may argue that the PDF is technically already downloaded, thereby making this method call redundant, it subverts the exceptation that DownloadHandler::CanDownload method is called on all downloads.

My current workaround is to move my DownloadHandler::CanDownload logic into DownloadHandler::OnBeforeDownload, and returning false in DownloadHandler::OnBeforeDownload, allowing the alloy runtime to cancel the download by default. This is a hacky/dirty workaround which I wish to avoid.

To Reproduce Steps to reproduce the behavior:

  1. Clone my fork of cef-project containing the MVP of the bug
  2. Build the project, and run the minimal executable. DownloadHandler::CanDownload will log a message starting with CanDownload when triggered, allowing you to grep for the log.
  3. Download a normal file as a sanity check, and observe the CanDownload log
  4. Open a PDF file, and press the download button, observe that the log is not emitted.

Expected behavior DownloadHandler::CanDownload is called when downloading a PDF file through the PDF viewer.

Versions (please complete the following information):

Additional context So far, I have only tried reproducing the bug in the minimal project in cef-project, but I also observe this behaviour in another project.

Let me know if I can provide more information. If you know where I can look to start fixing this bug, kindly let me know.

Regards, Luca

magreenblatt commented 1 week ago

As background, the "Download" button in the PDF viewer should trigger a call to PdfViewWebPlugin::HandleSaveMessage (via onDownloadClick_ in the JS code). There is a different code path for original vs edited PDF files (SaveToFile vs SaveToBuffer). SaveToFile calls PDFDocumentHelper::SaveUrlAs and SaveToBuffer calls saveData_ (JS code). The SaveToFile case should call DownloadManagerImpl::DownloadUrl. However, the SaveToBuffer case would not trigger a download because it operates using local (in memory) PDF modifications.