Unobserved exceptions on broken @import declarations #194
Description
Prerequisites
- Can you reproduce the problem in a MWE?
- Are you running the latest version of AngleSharp.Css?
- Did you check the FAQs to see if that helps you?
- Are you reporting to the correct repository? (there are multiple AngleSharp libraries, e.g.,
AngleSharp.Xmlfor Xml support) - Did you perform a search in the issues?
Description
I am able to reproduce unobserved task exceptions with empty @import declarations.
Steps to Reproduce
The main test looks like this:
[Fact]
public void Test()
{
var cssParsingOptions = new CssParserOptions
{
IsIncludingUnknownDeclarations = true,
IsIncludingUnknownRules = true,
IsToleratingInvalidSelectors = true
};
var config = Configuration.Default.WithCss(cssParsingOptions);
var browsingContext = BrowsingContext.New(config);
var htmlParser = new HtmlParser(new HtmlParserOptions(), browsingContext);
var input =
"""
<!DOCTYPE HTML>
<html>
<head>
</head>
<body>
<style type="text/css">
@import ;
</style>
</body>
</html>
""";
// Act
var (r, ex) = AssertExtensions.ThrowsUnobservedTaskException(() => htmlParser.ParseDocument(input));
// Assert
ex!.InnerException.Should().NotBeNull();
ex.InnerException!.Message.Should().StartWith("Object reference not set to an instance of an object.");
}
With additional helper to catch unobserved exceptions:
public static class AssertExtensions
{
public static (T result, Exception? unobservedException) ThrowsUnobservedTaskException<T>(Func<T> action)
{
Exception? unobservedException = null;
var unobservedExceptionHandler = new EventHandler<UnobservedTaskExceptionEventArgs>((sender, e) =>
{
unobservedException = e.Exception;
e.SetObserved();
});
TaskScheduler.UnobservedTaskException += unobservedExceptionHandler;
try
{
var result = action();
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();
Task.Delay(1000).Wait();
return (result, unobservedException);
}
finally
{
TaskScheduler.UnobservedTaskException -= unobservedExceptionHandler;
}
}
}
Expected Behavior
Expect not to throw unobserved exceptions.
Actual Behavior
Throws null-ref on this line:
https://github.com/AngleSharp/AngleSharp.Css/blob/devel/src/AngleSharp.Css/Parser/CssParser.cs#L243
Possible Solution / Known Workarounds
Add more proper null-checks in place where null-ref is thrown?