Add option to exception handler middleware to suppress logging

[JamesNK]

Fixes #54554

Background

Exception handler middleware handles exceptions thrown in the app. There are various mechanisms for handling an exception:

• Registered IExceptionHandler instances. Return true to indicate exception is handled.
• Registered IProblemDetailsService instance. Return true to indicate exception is handled.
• Configured ExceptionHandlerOptions.ExceptionHandler delegate.
• Configured ExceptionHandlerOptions.StatusCodeSelector delegate.

If the exception is handled then the middleware invoke returns without rethrowing the exception. Unhandled exceptions are rethrown back into the middleware pipeline.

Problem

Today the exception handle middleware always writes the UnhandledException log message (skipped if the exception is related to the request being aborted). I think the idea here is the exception handler received an unhandled error. The problem is it is logged at an Error level, and customers who automatically log all Error level logs could get a potentially unwanted error the message.

The request from users is to only write the UnhandledException log message if the exception handler didn't handle the exception. That stops the error level UnhandledException log message from being logged.

Fix

The PR adds a callback to the exception handler options, ExceptionHandlerOptions.SuppressLoggingCallback (final name TBD). It keeps the current behavior but gives an option to opt-in to only logging the unhandled exception log message if the middleware didn't handle the exception.

[JamesNK]

Product changes ready to review. Tests coming.

[JamesNK]

API review: #59075

[Copilot]

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Files not reviewed (1)

• src/Middleware/Diagnostics/src/PublicAPI.Unshipped.txt: Language not supported

Comments suppressed due to low confidence (3)

src/Middleware/Diagnostics/test/UnitTests/ExceptionHandlerMiddlewareTest.cs:127

• [nitpick] The class name 'TestHttpResponseFeature' is ambiguous. It should be renamed to indicate its purpose more clearly or documented.

private sealed class TestHttpResponseFeature : HttpResponseFeature

src/Middleware/Diagnostics/src/ExceptionHandler/ExceptionHandlerOptions.cs:54

• [nitpick] The name SuppressLoggingIExceptionHandler is unclear. It should be renamed to SuppressLoggingForHandledExceptions.

public bool SuppressLoggingIExceptionHandler { get; set; }

src/Middleware/Diagnostics/src/ExceptionHandler/ExceptionHandlerOptions.cs:43

• There is a spelling error in the comment. It should be 'HTTP' instead of 'http'.

/// Gets or sets a delegate used to map an exception to a http status code.

[dotnet-policy-service]

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