How to log request json body in case of error in Ocelot?

[rajeshgithub001]

I am serilog to log error from ocelot in case of downstream giving any error.
Using serilog i am sending the exception details to Application Insight.

Serilog configuration:

"Serilog": {
    "Using": [ "Serilog.Sinks.ApplicationInsights" ],
    "MinimumLevel": {
      "Default": "Information",
      "Override": {
        "Microsoft": "Warning"
      }
    },
    "WriteTo": [
      {
        "Name": "ApplicationInsights",
        "Args": {
          "instrumentationKey": "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
          "telemetryConverter": "Serilog.Sinks.ApplicationInsights.Sinks.ApplicationInsights.TelemetryConverters.TraceTelemetryConverter, Serilog.Sinks.ApplicationInsights"
        }
      }
    ],
    "Enrich": [ "FromLogContext" ],
    "Properties": {
      "Application": "API GATEWAY"
    }
  }

Now i want to log request json body in case of error only , How will i do it ?

Middleware didn't work as it didn't catch any ocelot exception, so its out of question.

[MirzaMerdovic]

Maybe using DelegatingHandler can solve your problem?
For example:

public class FakeHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        //do stuff and optionally call the base handler..
        var response = await base.SendAsync(request, cancellationToken);

        if (!response.IsSuccessStatusCode)
        {
            // TODO: Log stuff ... 
        }

        return response;
    }
}

[raman-m]

Yes, but Not all errors will be caught by delegating handler ❗

My recommendation is using PreErrorResponderMiddleware injection. See Middleware Injection.
It requires analysis of Ocelot error codes, with limited access to exception messages.

More advanced approach is replacing IExceptionToErrorMapper object in DI container.

Just define new class inheriting the IExceptionToErrorMapper interface.
Aggregate HttpExceptionToErrorMapper class member as private one.
Decorate behavior of the class or totally replace by new behavior of Decorator pattern.
So, public Error Map(Exception exception) method can be decorated like this:

    public class MyExceptionToErrorMapperDecorator : IExceptionToErrorMapper
    {
        private readonly HttpExceptionToErrorMapper _decorated; // New aggregation

        public MyExceptionToErrorMapperDecorator(IServiceProvider serviceProvider)
        {
            _decorated = new HttpExceptionToErrorMapper(serviceProvider);
        }

        public Error Map(Exception exception)
        {
            // Yahoo! This is the place where you can log your lovely exception
            // ... any logging
            return _decorated.Map(exception);
        }
    }

Don't forget to replace old mapper in Di container via services collection:

.ConfigureServices(services => {
        services.RemoveAll<IExceptionToErrorMapper>();
        services.TryAddSingleton<IExceptionToErrorMapper, MyExceptionToErrorMapperDecorator>();
})

Hope it helps!