Unexpected growth of History file in CEF directory

[yulianovikova]

Is there an existing issue for this?

• I have searched both open/closed issues, no issue already exists.

CefSharp Version

127.3.50

Operating System

Windows 10

Architecture

x64

.Net Version

.net 8

Implementation

OffScreen

Reproduction Steps

1. Initialize Cef as following:

Cef.Initialize(
    new CefSettings
    {
        BrowserSubprocessPath = Path.ChangeExtension(typeof(Program).Assembly.Location, ".exe"),
        CefCommandLineArgs = { "disable-gpu-shader-disk-cache" },
        LogSeverity = LogSeverity.Disable
    },
    performDependencyCheck: true,
    browserProcessHandler: null);

2. Create a ChromiumWebBrowser to render a small html (without javascript or much data and styles) from string as following:

using var browser = new ChromiumWebBrowser(new HtmlString(html));

3. Take a screenshot of the rendered page

await browser.WaitForInitialLoadAsync();
await browser.WaitForRenderIdleAsync(100, cancellationToken: ct);
await browser.CaptureScreenshotAsync(CaptureScreenshotFormat.Png); // this step is not really important; it's just for the context

Expected behavior

According to the documentation for CachePath setting:
If the value is empty then browsers will be created in "incognito mode" where in-memory caches are used for storage and no data is persisted to disk.
So we do not expect any changes on disk after we render html string.

Actual behavior

1. A directory with the name CEF is created under %USERPROFILE%\AppData\Local.
2. The file History in this directory starts to grow after each render. We looked inside the CEF history (through cef sample app) and found out that all our HTML pages are actually stored there. As a result, the file History grows up very quickly, up to several GB
   
3. After the History file reaches this size, the application tries to read all this data in memory and experiences performance problems on startup. It consumes a lot of memory and disk IO
   

Regression?

We did not experience any similar problems in versions 124.3.80 and earlier. It started from v125.0.210.

Known Workarounds

We haven't found any workarounds. But I guess if history contains rendered HTML, we should not use shared cache at all. So we are planning to create a separate RequestContext for each render:

using var browser = new ChromiumWebBrowser(new HtmlString(html), requestContext: new RequestContext(new RequestContextSettings
        {
            CachePath = null,
            PersistSessionCookies = false,
            PersistUserPreferences = false
        }));

By the way, the file History in AppData/Local/CEF doesn't grow this way. I assume in this case the cache is actually stored in memory.

Does this problem also occur in the CEF Sample Application

Not Tested

Other information

I'm not really sure it is a bug, but the growth of the History file on disk was kind of unexpected. It caused problems for us only because we render pages from HTML strings, so the browser history contains a lot of data. Probably it would not affect other CefSharp users as much.

[amaitland]

If the value is empty then browsers will be created in "incognito mode" where in-memory caches are used for storage and no data is persisted to disk.
So we do not expect any changes on disk after we render html string.

The doc is out of date, I've created #4925 to update it. There's been upstream changes in behaviour.

Make sure to set a RootCachePath unique to your application also.

using var browser = new ChromiumWebBrowser(new HtmlString(html));

HtmlString creates a data uri, so you are loading the whole of your web page into the history.

Use one of the other methods to load html. Defer browser creation and then do your setup.

https://github.com/cefsharp/CefSharp/wiki/General-Usage#loading-htmlcssjavascriptetc-from-diskdatabaseembedded-resourcestream

I'm not really sure it is a bug, but the growth of the History

Your loading the html into the history, so no surprising.

[yulianovikova]

Thank you!