Ошибка swagger 500

The setup for Swagger is varying greatly from version to version. This answer is for Swashbuckle 6.0.0-beta9 and Asp.Net Core 1.0. Inside of the ConfigureServices method of Startup.cs, you need to add —

 services.AddSwaggerGen(c =>
    {
      c.SingleApiVersion(new Info
      {
        Version = "v1",
        Title = "My Awesome Api",
        Description = "A sample API for prototyping.",
        TermsOfService = "Some terms ..."
      });
    });

Then in the Configure method you must add —

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();

    app.UseMvc();
    app.UseSwaggerGen();
    app.UseSwaggerUi();
}

Be sure you are referencing in Startup.cs —

using Swashbuckle.SwaggerGen.Generator;

My project.json file looks like —

"dependencies": {
    "Microsoft.AspNetCore.Mvc": "1.0.0-rc2-final",
    "Microsoft.AspNetCore.Server.IISIntegration": "1.0.0-rc2-final",
    "Microsoft.AspNetCore.Server.Kestrel": "1.0.0-rc2-final",
    "Microsoft.EntityFrameworkCore.SqlServer": "1.0.0-rc2-final",
    "Microsoft.EntityFrameworkCore.SqlServer.Design": "1.0.0-rc2-final",
    "Microsoft.EntityFrameworkCore.Tools": "1.0.0-*",
    "Microsoft.Extensions.Configuration.EnvironmentVariables": "1.0.0-rc2-final",
    "Microsoft.Extensions.Configuration.FileExtensions": "1.0.0-rc2-final",
    "Microsoft.Extensions.Configuration.Json": "1.0.0-rc2-final",
    "Microsoft.Extensions.Logging": "1.0.0-rc2-final",
    "Microsoft.Extensions.Logging.Console": "1.0.0-rc2-final",
    "Microsoft.Extensions.Logging.Debug": "1.0.0-rc2-final",
    "Swashbuckle": "6.0.0-beta9"
  },

  "tools": {
    "Microsoft.AspNetCore.Server.IISIntegration.Tools": {
      "version": "1.0.0-preview1-final",
      "imports": "portable-net45+win8+dnxcore50"
    },
    "Microsoft.EntityFrameworkCore.Tools": {
      "version": "1.0.0-preview1-final",
      "imports": [
        "portable-net45+win8+dnxcore50",
        "portable-net45+win8"
      ]
    }
  },

  "frameworks": {
    "net452": { }
  },
  "buildOptions": {
    "emitEntryPoint": true,
    "preserveCompilationContext": true,
    "xmlDoc": false
  },

  "publishOptions": {
    "include": [
      "wwwroot",
      "Views",
      "appsettings.json",
      "web.config"
    ]
  },

  "scripts": {
    "postpublish": [ "dotnet publish-iis --publish-folder %publish:OutputPath% --framework %publish:FullTargetFramework%" ]
  }
}

I was working with some ASP.NET WebApi code and needed to test something using the Swagger UI. Usually, it’s just a matter of starting the project and going to your /swagger directory. Unfortunately, in this case, I went to my swagger URL and got an error saying “Failed to load API definition — Fetch error — Internal Server Error /swagger/v1/swagger.json.” How do you fix this error?

I knew that it used to work but I’d just updated about a half zillion things in my code including upgrading to .NET Core 5 so I wasn’t really sure what broke it. I assumed the worst.

The dev tools in Edge was showing me that it was trying to access swagger.json but it was getting an HTTP 500 error. My guess was that I had a configuration problem in Startup.cs and that the swagger.json file either wasn’t being generated or it was in the wrong place. I checked a bunch of stuff and didn’t find anything.

I eventually started to figure out what was going wrong when I opened that call to swagger.json in its own tab.

The actual error message says that there’s an “ambiguous HTTP method for action”. I wasn’t really sure what that meant by helpfully the error message pointed me at the WebApi endpoint action that was causing the problem. Rather than being a problem with some kind of swagger config, the error was coming from the code that I’d just been working on.

Swashbuckle.AspNetCore.SwaggerGen.SwaggerGeneratorException: Ambiguous HTTP method for action - SwaggerError.WebApi.Controllers.WeatherForecastController.Overview (SwaggerError.WebApi). Actions require an explicit HttpMethod binding for Swagger/OpenAPI 3.0
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperations(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePaths(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwagger(String documentName, String host, String basePath)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

Here’s the code that’s causing the problem:

[ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{
    [Route("/[controller]/[action]/{id}")]
    public ActionResult Overview(int? id)
    {
        return Ok(id);
    }
}

Looks pretty ordinary, right? Nothing to exciting here. So what’s broken? What’s “ambiguous” about this? It’s missing the HttpGet attribute.

[ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{
    [HttpGet]
    [Route("/[controller]/[action]/{id}")]
    public ActionResult Overview(int? id)
    {
        return Ok(id);
    }
}

As soon as I added that missing [HttpGet] attribute, the Swagger UI was working again.

Summary

In short, the problem was a problem in my code. I’d assumed that my WebApi controller action would default to HTTP GET but it seems that that doesn’t agree with Swagger. As soon as I added that missing attribute, everything was fine.

I hope this helps.

-Ben

— Looking for help on your .NET Core projects? Want some guidance on how to get going with Azure DevOps or GitHub Actions? Need a Scrum coach to help your teams get over a delivery slump? We can help. Drop us a line at info@benday.com.

Problem

I have an ASP.NET CORE Web API (3.1) project with Swashbuckle.AspNetCore (6.1.1). When I run the project, I got this error below.

Error Message

Here is the error message that I got in Visual Studio Debug output windows.

(Inner Exception #1) System.InvalidOperationException: Error while validating the service descriptor ‘ServiceType: Microsoft.Extensions.ApiDescriptions.IDocumentProvider Lifetime: Singleton ImplementationType: Microsoft.Extensions.ApiDescriptions.DocumentProvider’: Unable to resolve service for type ‘Microsoft.AspNetCore.Mvc.ApiExplorer.IApiDescriptionGroupCollectionProvider’ while attempting to activate ‘Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator’.
—> System.InvalidOperationException: Unable to resolve service for type ‘Microsoft.AspNetCore.Mvc.ApiExplorer.IApiDescriptionGroupCollectionProvider’ while attempting to activate ‘Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator’.
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type serviceType, Type implementationType, CallSiteChain callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateConstructorCallSite(ResultCache lifetime, Type serviceType, Type implementationType, CallSiteChain callSiteChain)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, Int32 slot)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(Type serviceType, CallSiteChain callSiteChain)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateCallSite(Type serviceType, CallSiteChain callSiteChain)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.<>c__DisplayClass7_0.b__0(Type type)
at System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.GetCallSite(Type serviceType, CallSiteChain callSiteChain)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type serviceType, Type implementationType, CallSiteChain callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateConstructorCallSite(ResultCache lifetime, Type serviceType, Type implementationType, CallSiteChain callSiteChain)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, Int32 slot)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.GetCallSite(ServiceDescriptor serviceDescriptor, CallSiteChain callSiteChain)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.ValidateService(ServiceDescriptor descriptor)
— End of inner exception stack trace —
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.ValidateService(ServiceDescriptor descriptor)
at Microsoft.Extensions.DependencyInjection.ServiceProvider..ctor(IEnumerable`1 serviceDescriptors, ServiceProviderOptions options)<—

Solution

The solution is that you make sure that you have services.AddControllers(); in ConfigureServices(IServiceCollection services) method. If you don’t have it, please add that line. Your problem will be solved and you should be able to see the swagger page.

Example:

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public void ConfigureServices(IServiceCollection services)
{
   services.AddControllers();
   services.AddSwaggerGen(c =>
   {
         c.SwaggerDoc("v1", new OpenApiInfo { Title = "WebApplication9", Version = "v1" });
   });

...

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
   app.UseSwagger();
   app.UseSwaggerUI(c => c.SwaggerEndpoint("v1/swagger.json", "WebApplication9 v1"));

One more tip ~

If you are getting this error below, you need to make sure that you have at least one controller that has a method with [Http{Verb}] e.g. [HttpGet].

Failed to load API definition.

Fetch errorundefined https://localhost:**/swagger/v1/swagger.json

Because you might be using the attribute-routed instead of conventional-routed. Please check this code endpoints.MapControllers() in Startup.cs.

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app.UseEndpoints(endpoints =>
{
      endpoints.MapControllers();
});

If you are using the attribute-routed, you need to have the followings in order to see the swagger image.

1. At least one ApiController
2. That ApiController should have [Route("[controller]")] attribute.
3. It should have at least one method that has [Http{Verb}] e.g. [HttpGet].

Please refer to the example code below.

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[ApiController]
    [Route("[controller]")]
    public class PurchaseOrderController : ControllerBase
    {
        /// <summary>
        /// Create the Purchase Order.
        /// </summary>
        /// <param name="po">The details of Purchase order.</param>
        /// <returns>Http Status 201 - If Succed.</returns>
        [HttpPost]
        public async Task<IActionResult> Post(PurchaseOrderRequestModel po)
        {
            Console.Write(po.Id);
            await Task.Delay(1);
            return StatusCode(201, 1);
        }
    }

Hope it helps.