"fetching resource list" issue

I have configured Swashbuckle the same way I have done for other Web API websites, but this time I’m getting a message that says “fetching resource list: http://localhost:52302/swagger/docs/v1; Please wait” when I browse to http://localhost:52302/swagger/ui/index.

VERSION:

5.6.0 (Target Framework is “net46”)

STEPS TO REPRODUCE:

NuGet Packages

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="Autofac" version="3.5.2" targetFramework="net46" />
  <package id="Autofac.Configuration" version="3.3.0" targetFramework="net46" />
  <package id="Autofac.Owin" version="3.1.0" targetFramework="net46" />
  <package id="Autofac.Wcf" version="3.0.2" targetFramework="net46" />
  <package id="Autofac.WebApi2" version="3.4.0" targetFramework="net46" />
  <package id="Autofac.WebApi2.Owin" version="3.3.0" targetFramework="net46" />
  <package id="EntityFramework" version="6.1.3" targetFramework="net46" />
  <package id="FluentValidation" version="7.0.2" targetFramework="net46" />
  <package id="FluentValidation.WebApi" version="7.0.1" targetFramework="net46" />
  <package id="Hangfire" version="1.6.15" targetFramework="net46" />
  <package id="Hangfire.Autofac" version="2.3.1" targetFramework="net46" />
  <package id="Hangfire.Core" version="1.6.15" targetFramework="net46" />
  <package id="Hangfire.SqlServer" version="1.6.15" targetFramework="net46" />
  <package id="Microsoft.AspNet.Identity.Core" version="2.2.1" targetFramework="net46" />
  <package id="Microsoft.AspNet.Identity.EntityFramework" version="2.2.1" targetFramework="net46" />
  <package id="Microsoft.AspNet.Identity.Owin" version="2.2.1" targetFramework="net46" />
  <package id="Microsoft.AspNet.WebApi" version="5.2.3" targetFramework="net46" />
  <package id="Microsoft.AspNet.WebApi.Client" version="5.2.3" targetFramework="net46" />
  <package id="Microsoft.AspNet.WebApi.Core" version="5.2.3" targetFramework="net46" />
  <package id="Microsoft.AspNet.WebApi.Owin" version="5.2.3" targetFramework="net46" />
  <package id="Microsoft.AspNet.WebApi.WebHost" version="5.2.3" targetFramework="net46" />
  <package id="Microsoft.CodeDom.Providers.DotNetCompilerPlatform" version="1.0.4" targetFramework="net46" />
  <package id="Microsoft.Net.Compilers" version="2.2.0" targetFramework="net46" developmentDependency="true" />
  <package id="Microsoft.Owin" version="3.1.0" targetFramework="net46" />
  <package id="Microsoft.Owin.Host.SystemWeb" version="3.1.0" targetFramework="net46" />
  <package id="Microsoft.Owin.Security" version="3.1.0" targetFramework="net46" />
  <package id="Microsoft.Owin.Security.Cookies" version="3.1.0" targetFramework="net46" />
  <package id="Microsoft.Owin.Security.OAuth" version="3.1.0" targetFramework="net46" />
  <package id="Microsoft.Web.Infrastructure" version="1.0.0.0" targetFramework="net46" />
  <package id="Newtonsoft.Json" version="10.0.2" targetFramework="net46" />
  <package id="NLog" version="4.4.10" targetFramework="net46" />
  <package id="NLog.Config" version="4.4.10" targetFramework="net46" />
  <package id="NLog.Schema" version="4.4.10" targetFramework="net46" />
  <package id="Owin" version="1.0" targetFramework="net46" />
  <package id="Swashbuckle" version="5.6.0" targetFramework="net46" />
  <package id="Swashbuckle.Core" version="5.6.0" targetFramework="net46" />
  <package id="WebActivatorEx" version="2.0" targetFramework="net46" />
</packages>

Startup Class

[assembly: OwinStartup(typeof(MyNamespace.Startup))]

namespace MyNamespace
{
    public partial class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            var container = GetContainer();

            GlobalConfiguration.Configuration.DependencyResolver = new AutofacWebApiDependencyResolver(container);
            GlobalConfiguration.Configure(WebApiConfig.Register);
            GlobalConfiguration.Configure(SwaggerConfig.Register);

            app.Use<ExceptionLoggingMiddleware>();
            app.UseAutofacMiddleware(container);
            app.UseAutofacWebApi(GlobalConfiguration.Configuration);

            ConfigureAuth(app);
            ConfigureHangfire(app, container);
        }
    }
}

Web API Config

    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            ConfigureRoutes(config);
            ConfigureToOnlyUseBearerTokenAuth(config);
            ConfigureMessageHandlers(config);
            ConfigureJsonFormatter(config);

            FluentValidationModelValidatorProvider.Configure(config);
        }

        private static void ConfigureRoutes(HttpConfiguration config)
        {
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                "DefaultApi",
                "{controller}/{id}",
                new { id = RouteParameter.Optional });
        }

        private static void ConfigureToOnlyUseBearerTokenAuth(HttpConfiguration config)
        {
            config.SuppressDefaultHostAuthentication();
            config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));
            config.Filters.Add(new ValidateModelStateFilter());
            config.Filters.Add(new SingleMemberSessionFilter());
        }

        private static void ConfigureMessageHandlers(HttpConfiguration config)
        {
            config.MessageHandlers.Add(new RequestResponseLoggingHandler());
            config.MessageHandlers.Add(new ResponseWrappingHandler());
            config.Services.Add(typeof(IExceptionLogger), new ExceptionLoggingHandler());
        }

        private static void ConfigureJsonFormatter(HttpConfiguration config)
        {
            config.Formatters.Add(new JsonMediaTypeFormatter());
            config.Formatters.JsonFormatter.Indent = true;

            // allow model with [serializable] attribute to work normally with web api
            ((DefaultContractResolver)config.Formatters.JsonFormatter.SerializerSettings.ContractResolver).IgnoreSerializableAttribute = true;

            FluentValidationModelValidatorProvider.Configure(config);
        }
    }

Swagger Config

    public static class SwaggerConfig
    {
        public static void Register(HttpConfiguration config)
        {
            if (config == null) throw new ArgumentNullException(nameof(config));

            config.EnableSwagger(i =>
            {
                i.SingleApiVersion("v1", "My API");
                i.IncludeXmlComments(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Docs.xml")); // XML file is outputed to the root directory of website (not bin) and included in csproj file as content
            })
            .EnableSwaggerUi();
        }
    }

All the controllers have all the appropriate attributes on the methods and their parameters e.g. route, HTTP Get/Post/Put, From URI/From Body.

All request and response classes simple and are not the same the database models used for Entity Framework.

EXPECTED RESULT:

The Swagger documentation is displayed

ACTUAL RESULT:

Documentation doesn’t load and the following message is displayed. fetching resource list: http://localhost:52302/swagger/docs/v1; Please wait.

ADDITIONAL INFO

The API works, it’s only the Swagger documentation that has an issue

[TheMagnificent11]

I found the issue.

It’s our response handler. We don’t different HTTP results, it’s always 200 OK and the service response object has a success property and errors collection.

Response Handler

    public class ResponseWrappingHandler : DelegatingHandler
    {
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            var response = await base.SendAsync(request, cancellationToken);

            object content;
            HttpResponseMessage newResponse = null;

            if (response.Content is StreamContent)
            {
                // File download so just return
                return response;
            }

            if (response.TryGetContentValue(out content) && !response.IsSuccessStatusCode)
            {
                var error = content as HttpError;
                if (error?.ModelState != null)
                {
                    //Read as string
                    var httpErrorObject = await response.Content.ReadAsStringAsync();

                    //Convert to anonymous object
                    var anonymousErrorObject = new { message = "", ModelState = new Dictionary<string, string[]>() };

                    // Deserialize anonymous object
                    var deserializedErrorObject = JsonConvert.DeserializeAnonymousType(httpErrorObject, anonymousErrorObject);

                    // Get error messages from ModelState object
                    var modelStateErrors = deserializedErrorObject.ModelState
                        .Select(kvp => string.Join(". ", kvp.Value))
                        .ToList();

                    newResponse = request.CreateResponse(response.StatusCode, new ServiceResponse(modelStateErrors));
                }
                else
                {
                    return response;
                }
            }
            else if (content is ServiceResponse)
            {
                // Already is wrapped so don't worry about it
                return response;
            }

            if (newResponse == null)
            {
                newResponse = request.CreateResponse(response.StatusCode, new ServiceResponse<object>(content));
            }

            // Add Back the Response Headers
            foreach (var header in response.Headers) //Add back the response headers
            {
                newResponse.Headers.Add(header.Key, header.Value);
            }

            return newResponse;
        }
    }

Startup Web API Config

    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            ConfigureRoutes(config);
            ConfigureToOnlyUseBearerTokenAuth(config);
            ConfigureMessageHandlers(config);
            ConfigureJsonFormatter(config);

            FluentValidationModelValidatorProvider.Configure(config);
        }

        private static void ConfigureRoutes(HttpConfiguration config)
        {
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                "DefaultApi",
                "{controller}/{id}",
                new { id = RouteParameter.Optional });
        }

        private static void ConfigureToOnlyUseBearerTokenAuth(HttpConfiguration config)
        {
            config.SuppressDefaultHostAuthentication();
            config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));
            config.Filters.Add(new ValidateModelStateFilter());
            config.Filters.Add(new SingleMemberSessionFilter());
        }

        private static void ConfigureMessageHandlers(HttpConfiguration config)
        {
            config.MessageHandlers.Add(new RequestResponseLoggingHandler());

            // This line is the issue
            config.MessageHandlers.Add(new ResponseWrappingHandler());

            config.Services.Add(typeof(IExceptionLogger), new ExceptionLoggingHandler());
        }

        private static void ConfigureJsonFormatter(HttpConfiguration config)
        {
            config.Formatters.Add(new JsonMediaTypeFormatter());
            config.Formatters.JsonFormatter.Indent = true;

            // allow model with [serializable] attribute to work normally with web api
            ((DefaultContractResolver)config.Formatters.JsonFormatter.SerializerSettings.ContractResolver).IgnoreSerializableAttribute = true;

            FluentValidationModelValidatorProvider.Configure(config);
        }
    }

Any ideas on how to fix, other than removing it?

[Goddiewayne]

I had this issue as well, I had to troubleshoot each of my controllers by excluding them from the project thereby running them independently until I found the culprit. Somehow the [ResponseType(typeof())] of a particular controller action was the cause of the problem.