For the scenarios you tested, can you compare how this would behave in a regular AspNetCore app? I think we should align with that behavior as best we can. If client disconnects, is an exception thrown? Is the request considered failed or successful?

For the scenarios you tested, can you compare how this would behave in a regular AspNetCore app? I think we should align with that behavior as best we can. If client disconnects, is an exception thrown? Is the request considered failed or successful?

Here's what I found using a plain aspnet app:

RequestAborted

• Not utilizing the CT: work gets to complete without interuption, no errors or exceptions; no response sent as client does not exist
• Utilizes CT, but not catching exception: work stops, no exception is seen (handled by the framework maybe?); no response sent as client does not exist
• Utilizes CT & catches exceptions: OperationCanceledException is thrown and is handled by user code, no errors or exceptions; no response sent as client does not exist

CancellationTokenSource cancelled

• Not utilizing the CT: work gets to complete without interuption, no errors or exceptions; successful completion with user defined status code
• Utilizes CT, but not catching exception: TaskCancelled exception is thrown; fails with 500 internal server error
• Utilizes CT & catches exceptions: OperationCanceledException is thrown and handled by user code, no errors or exceptions; successful completion with user defined status code

Here's the app I used, or do you think I need to try and replicate what we're doing with the YARP as well?

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/process", async (HttpContext context) =>
{
    var cancellationToken = context.RequestAborted; // Client disconnect
    // var cancellationToken = new CancellationTokenSource(TimeSpan.FromSeconds(5)).Token; // Cancel after 5 seconds

    try
    {
        // Simulate some work that can be cancelled
        Console.WriteLine("Starting work...");
        for (int i = 0; i < 10; i++)
        {
            // Simulate work
            await Task.Delay(1000, cancellationToken);
            Console.WriteLine($"Work iteration {i + 1} completed.");
        }
        Console.WriteLine("Work completed.");

        context.Response.StatusCode = StatusCodes.Status200OK;
        await context.Response.WriteAsync("Processing completed successfully.");
    }
    catch (OperationCanceledException)
    {
        Console.WriteLine("Request was cancelled.");
        context.Response.StatusCode = StatusCodes.Status499ClientClosedRequest; // Status code for client closed request
        await context.Response.WriteAsync("Request was cancelled.");
    }
});

app.Run();

Don't need to test with YARP directly, but I would like us to compare with your found results for AspNetCore with what happens in the functions YARP scenario today.

Also: StatusCodes.Status499ClientClosedRequest - good to know there is a specific HTTP code for that! Do you know if we set this status code in functions host for client disconnect scenarios?

Don't need to test with YARP directly, but I would like us to compare with your found results for AspNetCore with what happens in the functions YARP scenario today.

Also: StatusCodes.Status499ClientClosedRequest - good to know there is a specific HTTP code for that! Do you know if we set this status code in functions host for client disconnect scenarios?

@jviau Status499ClientClosedRequest is technically an unofficial status code, and no, we don't use it anywhere in the host/

In comparison, here is the result to the exact same code as above but in a function app with what we have today in dev:

RequestAborted

• Not utilizing the CT: work gets to complete without interuption, DefaultHttpProxyService retry handler throws exception, function invocation fails with forwarder error from host, status code 500, no response to client
  • Exception the moment we cancel: Unsupported exception type in RetryProxyHandler. Request will not be retried. Exception: System.Threading.Tasks.TaskCanceledException: The operation was canceled.
  • Exception after the function completes: Microsoft.Azure.WebJobs.Host.FunctionInvocationException: Exception while executing function: Functions.MyHttpTriggerNoCT - Failed to proxy request with ForwarderError: RequestCanceled
• Utilizes CT, but not catching exception: work stops, DefaultHttpProxyService retry handler throws exception, function invocation fails with exception, status code 500, no response to client
  • Exception the moment we cancel: Unsupported exception type in RetryProxyHandler. Request will not be retried. Exception: System.Threading.Tasks.TaskCanceledException: The operation was canceled.
  • User code gets unhandled exception: Microsoft.Azure.WebJobs.Script.Workers.Rpc.RpcException: Result: Function 'MyHttpTriggerCTNoCatch', Invocation id 'e33ab37a-069f-4a89-b64c-2e7152946142': An exception was thrown by the invocation.
  • Exception after the function completes: Microsoft.Azure.WebJobs.Host.FunctionInvocationException: Exception while executing function: Functions.MyHttpTriggerNoCT - Failed to proxy request with ForwarderError: RequestCanceled
• Utilizes CT & catches exceptions: OperationCanceledException is thrown and is handled by user code, DefaultHttpProxyService retry handler throws exception, function invocation fails with forwarder error from host, status code 500, no response to client
  • Exception the moment we cancel: Unsupported exception type in RetryProxyHandler. Request will not be retried. Exception: System.Threading.Tasks.TaskCanceledException: The operation was canceled.
  • Exception after the function completes: Microsoft.Azure.WebJobs.Host.FunctionInvocationException: Exception while executing function: Functions.MyHttpTriggerNoCT - Failed to proxy request with ForwarderError: RequestCanceled

CancellationTokenSource cancelled

• Not utilizing the CT: work gets to complete without interuption, no errors or exceptions, function invocation successful with user defined status code
• Utilizes CT, but not catching exception: work stops, TaskCancelled exception is thrown, function invocation fails with unhandled cancellation exception, status code 500 returned to client
• Utilizes CT & catches exceptions: OperationCanceledException is thrown and handled by user code, no errors or exceptions; function invocation successful with user defined status code

And with my changes in this PR:

RequestAborted

• Not utilizing the CT: work gets to complete without interruption, function invocation successful, status code 499 (our http logs/trace), no response to client
  • New Log: The client disconnected while the function was processing the request.
• Utilizes CT, but not catching exception: work stops, TaskCancelled exception is thrown, function invocation fails with unhandled exception, status code 499, no response to client
  • User code gets unhandled exception: Microsoft.Azure.WebJobs.Script.Workers.Rpc.RpcException: Result: Function 'MyHttpTriggerCTNoCatch', Invocation id 'e33ab37a-069f-4a89-b64c-2e7152946142': An exception was thrown by the invocation.
  • New Log: The client disconnected while the function was processing the request.
• Utilizes CT & catches exceptions: OperationCanceledException is thrown and is handled by user code, function invocation successful, status code 499, no response to client
  • New Log: The client disconnected while the function was processing the request.

CancellationTokenSource cancelled

• Not utilizing the CT: work gets to complete without interruption, no errors or exceptions, function invocation successful with user defined status code
• Utilizes CT, but not catching exception: work stops, TaskCancelled exception is thrown, function invocation fails with unhandled exception, status code 500 returned to client
• Utilizes CT & catches exceptions: OperationCanceledException is thrown and handled by user code, no errors or exceptions; function invocation successful with user defined status code