Refit: How to handle Failure while connecting to API

[mdawood1991]

How to I handle can't connect to the API exception.

Currently my app crashes due to the following exception not been handled.

{System.Net.WebException: Error: ConnectFailure (Connection refused) ---> System.Net.Sockets.SocketException: Connection refused
  at System.Net.Sockets.Socket.Connect (System.Net.EndPoint remoteEP) [0x000cb] in /Users/builder/data/lanes/3415/7db2aac3/source/mono/mcs/class/System/System.Net.Sockets/Socket.cs:1313 
  at System.Net.WebConnection.Connect (System.Net.HttpWebRequest request) [0x0019b] in /Users/builder/data/lanes/3415/7db2aac3/source/mono/mcs/class/System/System.Net/WebConnection.cs:195 
  --- End of inner exception stack trace ---
  at System.Net.HttpWebRequest.EndGetRequestStream (IAsyncResult asyncResult) [0x00043] in /Users/builder/data/lanes/3415/7db2aac3/source/mono/mcs/class/System/System.Net/HttpWebRequest.cs:882 
  at System.Threading.Tasks.TaskFactory`1[TResult].FromAsyncCoreLogic (IAsyncResult iar, System.Func`2 endFunction, System.Action`1 endAction, System.Threading.Tasks.Task`1 promise, Boolean requiresSynchronization) [0x00014] in /Users/builder/data/lanes/3415/7db2aac3/source/mono/external/referencesource/mscorlib/system/threading/Tasks/FutureFactory.cs:550 
--- End of stack trace from previous location where exception was thrown ---

This is my API Interface

    public interface IUserService
    {
        [Post("/Account/Authenticate")]
        Task<User> Authenticate([Body] User user);
    }

Then this is how I initialize and call the service

            var _userService = RestService.For<IUserService>("http://192.168.0.100:44314/api");
            user = await _userService.Authenticate(user);

[geocine]

Implement a custom HttpClientHandler

[mdawood1991]

@geocine is there an example for this somewhere?

[ahmedalejo]

@mdawood1991 please take a look at the following issues:

• #198 Handle 500 internal server error
• #231 Disable Refit from hiding HTTP content in case response code wasn't 200 (ApiException)
• #240 QUESTION Exception Handling
• #253 How to handle the exceptions.
• #258 How to enable logging?

[ahmedalejo]

silly but why isn´t a try/catch block enough?

[mdawood1991]

@ahmedalejo I am already using a try catch on the part where I am calling the service:

            {
                user = await _userService.Authenticate(user);
                return user;
            }
            catch (ApiException apiException)
            {
                var apiValidation = apiException.GetContentAs<ValidationContainer>();
                validationContainer.AddMessage(MessageTypeEnum.Error, apiValidation.Message);
                return null;
            }

but when the API/server is down the exception is not caught.

[Cheesebaron]

GetContentAs, won't it call the service?

[mdawood1991]

This is what is happening below.

I have a try catch(ApiException ex) and catch(Exception ex) - The ApiException happens when the server is up and running and the server response HTTPStatusCode != 200, but when the sever is down the Exception ex happens.

I don't want to add two types of catch wherever I make a server/api call - There must be a way to assign a generic exception handler to the refit service.

[clairernovotny]

There are two different things going on though...semantically, they are different exceptions. The ApiException is for when the API itself is throwing and WebException is when the wire/server/network itself is the issue. I'm not sure it really makes sense to combine them as you'd typically want to take different actions based on those.

For WebException you may want to retry a few times. For an ApiException you'd likely simply fail.

[mdawood1991]

@onovotny yes - but there must be some sort of Exception handler I can do for the refit service - I don't want to add multiple catch statements whenever there is a API service call.

[geocine]

@mdawood1991 Actually I opened an issue a wihle ago that relates to your issue https://github.com/paulcbetts/refit/issues/272

[mdawood1991]

@geocine your issue is related to ApiException. ApiException gets called when there is a response other than 200 from the server. What I want to handle is API Access errors/exceptions e.g Http Timeout, Http server refused connection to socket, or website not available etc.

[bennor]

This has been on my radar for a while. We should probably split ApiException into ApiRequestException and ApiResponseException that derive from a common base. We're not handling request exceptions (e.g. dns errors, etc) at all at the moment, which is why you get the raw WebException.

A workaround in the meantime (if using C#6) is:

catch(Exception ex) when (ex is ApiException || ex is WebException)
{
    // do whatever you need to
}

I've actually used something similar to deal with retries for transient errors (this was before I knew about Polly):

public class TransientExceptionHelper
{
    private static readonly ISet<HttpStatusCode> TransientErrorStatusCodes = new HashSet<HttpStatusCode>(new[]
    {
        HttpStatusCode.BadGateway,
        HttpStatusCode.GatewayTimeout,
        HttpStatusCode.InternalServerError,
        HttpStatusCode.ServiceUnavailable,
        HttpStatusCode.RequestTimeout
    });
    public static bool IsTransient(Exception exception)
    {
        var apiException = exception as ApiException;
        if (apiException != null)
        {
            return TransientErrorStatusCodes.Contains(apiException.StatusCode);
        }
        return exception is HttpRequestException || exception is OperationCanceledException;
    }
}

// Usage
catch (Exception transientEx) when (TransientExceptionHelper.IsTransient(transientEx))
{
    // Handle retries
}

[mdawood1991]

@bennor I am using Polly like this:

            {
                var userAssets = await Policy
                                   .Handle<Exception>()
                                   //.RetryAsync(retryCount: 1)
                                   .WaitAndRetryAsync(new[]
                                   {
                                     TimeSpan.FromSeconds(1),
                                     TimeSpan.FromSeconds(2),
                                   })
                                   .ExecuteAsync(async () => await _assetService.GetAssetsSummaryList(filter));

                return userAssets;
            }
            catch (ApiException apiException)
            {
                //Some Server error e.g. 500, 401, 403 etc.

                apiException.HandleApiException(validationContainer);
            }
            catch (Exception exception)
            {
                // HTTP RequestTimeout, ServiceUnavailable
                exception.HandleWebException(validationContainer);
            }
            return null;

Is this the best way to do it using Polly?

[viralsavaniIM]

@mdawood1991 I am fairly new at using Polly but I have been using it like this:

.Handle<Exception>()
.WaitAndRetryAsync
(
  new TimeSpan[]{TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(3)},
  (exception, timespan) =>
      {
       // TODO: Replace Console with log
       if (exception.GetType() == typeof(ApiException))
       {
           // API is throwing
        }
        else
        {
         // any other exceptions
        }

        Console.WriteLine("Exception: " + exception.Message + exception.StackTrace);
      }
)
.ExecuteAsync(async () => await _ApiCache.GetAllPostsCached(userId));

[oooolivierrrr]

Is there a way to not throw an exception ? I mean, this will dramatically kill performances. Besides, it's not really an exception since we got a response. An exception would be the server not responding at all.

[rekosko]

I still don't get it why this library is throwing ApiException when status code is not successful. I agree with @oooolivierrrr - you got actual response so why treat it as exception? I'm returning e.g. BadRequest respones from the api that are already wrapped into custom WebApiResponse that contains some extras that I may use on the client and if I want to not deal with exceptions in my case I would need to define my api client as: Task<ApiResponse<WebApiResponse<User>>> Authenticate([Body] User user); which is hilarious and wrapping client calls with try catch is out of option because this is not a valid solution and just a hacky way to make it actually work.

[angelru]

Any solution ???

[rekosko]

@angelru new feature appeared - https://github.com/reactiveui/refit#handling-exceptions in RefitSettings. Now you can write your custom ExceptionFactory.

GitHub

reactiveui/refit

The automatic type-safe REST library for .NET Core, Xamarin and .NET. Heavily inspired by Square's Retrofit library, Refit turns your REST API into a live interface. - reactiveui/refit

[angelru]

@rekosko It is not very clear to me how to use it

[clairernovotny]

Closing due to age. Please try Refit v6 and reopen if still an issue.