Question

My scenario is this:

1. A client application executes a HTTP POST against an endpoint exposed by OpenRasta.
2. The body of the request contains an error that causes a problem in the codec – which is a custom implementation of OpenRasta.Codecs.IMediaTypeReader. This converts a JSON payload to the POCO expected by the handler.
3. The codec throws an exception that describes the error in a useful way. For example: Newtonsoft.Json.JsonReaderException: After parsing a value an unexpected character was encountered: ". Line 4, position 5.
4. The client application receives a HTTP 405 – MethodNotAllowed. The client doesn’t see any of the exception details.

If the codec is modified to catch a JsonReaderException and return Missing.Value, similar to the Implementing a codec wiki, then the client receives a HTTP 500 – Internal Server Error. The body of the response also describes the following exception:

System.InvalidOperationException: The operation is not ready for invocation.
   at OpenRasta.OperationModel.MethodBased.MethodBasedOperation.Invoke()
   at OpenRasta.OperationModel.Interceptors.OperationWithInterceptors.<Invoke>b__0()
   at OpenRasta.OperationModel.Interceptors.OperationWithInterceptors.Invoke()
   at OpenRasta.OperationModel.OperationExecutor.Execute(IEnumerable`1 operations)
   at OpenRasta.Pipeline.Contributors.OperationInvokerContributor.ExecuteOperations(ICommunicationContext context)
   at OpenRasta.Pipeline.PipelineRunner.ExecuteContributor(ICommunicationContext context, ContributorCall call)

How should I modify my application so that:

• The client receives a HTTP 400 Bad Request.
• The client receives a string containing the details of the exception encountered in the codec.

Answer 1

Having found this thread on Google Groups which contains all the answers, my current implementation looks something like this.

Within my implementation of IConfigurationSource:

using (OpenRastaConfiguration.Manual)
{
    ResourceSpace.Uses.PipelineContributor<ErrorCheckingContributor>(); 

    // Other configuration here
}

Then ErrorCheckingContributor looks something like this:

public class ErrorCheckingContributor : IPipelineContributor
{
    public void Initialize(IPipeline pipelineRunner)
    {
        pipelineRunner
            .Notify(CheckRequestDecoding)
            .After<KnownStages.IOperationResultInvocation>()
            .And.Before<KnownStages.ICodecResponseSelection>(); 
    }

    private static PipelineContinuation CheckRequestDecoding(ICommunicationContext context)
    {
        if (context.ServerErrors.Count == 0)
        {
            return PipelineContinuation.Continue;
        }

        var first = context.ServerErrors[0];
        if (first.Exception is Newtonsoft.Json.JsonReaderException)
        {
            context.Response.Entity.ContentType = MediaType.TextPlain;
            context.Response.Entity.ContentLength = first.Exception.Message.Length;
            using (var sw = new StreamWriter(context.Response.Entity.Stream))
            {
                sw.Write(first.Exception.Message);
            }
        }

        return PipelineContinuation.Continue;
    } 
}

There’s some things to be aware of with the above:

• If a handler were to throw a JsonReaderException, it would also be processed here.
• It doesn’t check what media types the client accepts. This is different from exceptions thrown by Handlers that do go through codec selection.
• Tried setting context.OperationResult to context.ServerErrors – but it doesn’t go through the codec.