ResourceHandler - Reset Stream.Position when CanSeek

[jpespartero]

• What version of the product are you using?
  Nuget 75.1.142

• What architecture x86 or x64?
  x64

• On what operating system?
  Win10

• Are you using WinForms, WPF or OffScreen?
  WinForms

• What steps will reproduce the problem?
  A custom ResourceHandler implementation that provides local memory images to the browser has stopped working correctly from the version 75.1.141.

The image is not displayed in the browser, but the ResourceHandler is providing the image stream.

The same code works fine up to version 73.1.30. Note that the interface has been updated to return a CefReturnValue instead of a bool.

` public override CefReturnValue ProcessRequestAsync(IRequest request, ICallback callback){

        var uri = new Uri(request.Url);
        string url = System.Net.WebUtility.UrlDecode(request.Url);
        Bitmap image = ...// Some code to get the image from memory
       
        if (image != null)
        {
            Stream = new MemoryStream();
            image.Save(Stream, ImageFormat.Png);
            MimeType = ResourceHandler.GetMimeType(".png");
        }

        callback.Continue();
        //return true;   // Up to version v73.1.30
        return CefReturnValue.Continue;   // From v75.1.141
    }`

• What is the expected output? What do you see instead?
  Image displayed in the browser

• Please provide any additional information below.

  • A stack trace if available, any Exception information.
    No exception is shown

  • Does the cef log provide any relevant information?
    No

[amaitland]

Testing with 58c9585 and loading https://cefsharp.example/logo.png in either the WinForms and WPF example and the PNG file loads correctly. If you look at https://github.com/cefsharp/CefSharp/releases/tag/v75.1.142 you will see there is exactly one commit to the cefsharp/75 branch (the one referenced above).

I suspect what you are seeing is a subtle change in behaviour as part of the new Network Service changes, see #2743

Please no binary (zip, etc) links, fork the MinimalExample and push your changes to GitHub. (Alternatively use a code sharing service list Gist or Pastebin).

As per https://github.com/cefsharp/CefSharp/blob/master/.github/ISSUE_TEMPLATE/bug_report.md#bug-report please provide an example that reproduces the problem, and incomplete code snippet is not sufficient.

[amaitland]

Where exactly in your code are you using a ResourceHandler to load an image?

@TKGNET I asked this because I'm after an example that reproduces this issue. Your code doesn't actually do that. You are using a IResponseFilter which is actually unrelated to this issue specifically. You need to make changes to adapt to the new NetworkService implementation, see #2743 (comment)

[no-response]

This issue has been automatically closed because there has been no response to our request for more information from the original author. With only the information that is currently in the issue, we don't have enough information to take action. Please reach out if you have or find the answers we need so that we can investigate further.

[jpespartero]

sorry for the delay in the answer @amaitland. I have prepared an example project based on the WinForms minimal example.

https://github.com/jpespartero/CefSharp.MinimalExample

The ImageMemorySchemeHandler implemented contains a Dictionary with in-memory images and handles an url image request to provide the Stream and MimeType in the custom implementation of the ProcessRequestAsync method.

Maybe, I'm doing something wrong, but if load the image from a file in the Stream the image is displayed properly.

{
byte[] bytes = File.ReadAllBytes(file);
Stream = new MemoryStream(bytes);
var fileExtension = Path.GetExtension(file);
MimeType = GetMimeType(fileExtension);
}
callback.Continue();
return CefReturnValue.Continue;

[amaitland]

Thanks for the example 👍

You need to reset the Stream.Position = 0; after you've saved the image to the MemoryStream.

This is a regression in CefSharp and a PR would to reset the Position would be welcome.

Generally speaking it's best to reset Stream.Position after you've written to it, specially before you hand the stream over to a 3rd party library.

[jpespartero]

Thanks a lot for the quick response and the solution provided!
Yes, reseting the stream position solves the issue and the image is loaded properly. It is not a problem to do it once the image is saved, so from our side it is solved.