Ошибка сервера в приложении web api

asked May 24, 2012 at 7:00

For me I usually send back an HttpResponseException and set the status code accordingly depending on the exception thrown and if the exception is fatal or not will determine whether I send back the HttpResponseException immediately.

At the end of the day it’s an API sending back responses and not views, so I think it’s fine to send back a message with the exception and status code to the consumer. I currently haven’t needed to accumulate errors and send them back as most exceptions are usually due to incorrect parameters or calls etc.

An example in my app is that sometimes the client will ask for data, but there isn’t any data available so I throw a custom NoDataAvailableException and let it bubble to the Web API app, where then in my custom filter which captures it sending back a relevant message along with the correct status code.

I am not 100% sure on what’s the best practice for this, but this is working for me currently so that’s what I’m doing.

Update:

Since I answered this question a few blog posts have been written on the topic:

https://weblogs.asp.net/fredriknormen/asp-net-web-api-exception-handling

(this one has some new features in the nightly builds)
https://learn.microsoft.com/archive/blogs/youssefm/error-handling-in-asp-net-webapi

Update 2

Update to our error handling process, we have two cases:

1. For general errors like not found, or invalid parameters being passed to an action we return a HttpResponseException to stop processing immediately. Additionally for model errors in our actions we will hand the model state dictionary to the Request.CreateErrorResponse extension and wrap it in a HttpResponseException. Adding the model state dictionary results in a list of the model errors sent in the response body.

2. For errors that occur in higher layers, server errors, we let the exception bubble to the Web API app, here we have a global exception filter which looks at the exception, logs it with ELMAH and tries to make sense of it setting the correct HTTP status code and a relevant friendly error message as the body again in a HttpResponseException. For exceptions that we aren’t expecting the client will receive the default 500 internal server error, but a generic message due to security reasons.

Update 3

Recently, after picking up Web API 2, for sending back general errors we now use the IHttpActionResult interface, specifically the built in classes for in the System.Web.Http.Results namespace such as NotFound, BadRequest when they fit, if they don’t we extend them, for example a NotFound result with a response message:

public class NotFoundWithMessageResult : IHttpActionResult
{
    private string message;

    public NotFoundWithMessageResult(string message)
    {
        this.message = message;
    }

    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        var response = new HttpResponseMessage(HttpStatusCode.NotFound);
        response.Content = new StringContent(message);
        return Task.FromResult(response);
    }
}

ASP.NET Web API 2 really simplified it. For example, the following code:

public HttpResponseMessage GetProduct(int id)
{
    Product item = repository.Get(id);
    if (item == null)
    {
        var message = string.Format("Product with id = {0} not found", id);
        HttpError err = new HttpError(message);
        return Request.CreateResponse(HttpStatusCode.NotFound, err);
    }
    else
    {
        return Request.CreateResponse(HttpStatusCode.OK, item);
    }
}

returns the following content to the browser when the item is not found:

HTTP/1.1 404 Not Found
Content-Type: application/json; charset=utf-8
Date: Thu, 09 Aug 2012 23:27:18 GMT
Content-Length: 51

{
  "Message": "Product with id = 12 not found"
}

Suggestion: Don’t throw HTTP Error 500 unless there is a catastrophic error (for example, WCF Fault Exception). Pick an appropriate HTTP status code that represents the state of your data. (See the apigee link below.)

Links:

• Exception Handling in ASP.NET Web API (asp.net)
  and
• RESTful API Design: what about errors? (apigee.com)

It looks like you’re having more trouble with Validation than errors/exceptions so I’ll say a bit about both.

Validation

Controller actions should generally take Input Models where the validation is declared directly on the model.

public class Customer
{ 
    [Require]
    public string Name { get; set; }
}

Then you can use an ActionFilter that automatically sends validation messages back to the client.

public class ValidationActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        var modelState = actionContext.ModelState;

        if (!modelState.IsValid) {
            actionContext.Response = actionContext.Request
                 .CreateErrorResponse(HttpStatusCode.BadRequest, modelState);
        }
    }
} 

For more information about this check out http://ben.onfabrik.com/posts/automatic-modelstate-validation-in-aspnet-mvc

Error handling

It’s best to return a message back to the client that represents the exception that happened (with relevant status code).

Out of the box you have to use Request.CreateErrorResponse(HttpStatusCode, message) if you want to specify a message. However, this ties the code to the Request object, which you shouldn’t need to do.

I usually create my own type of «safe» exception that I expect the client would know how to handle and wrap all others with a generic 500 error.

Using an action filter to handle the exceptions would look like this:

public class ApiExceptionFilterAttribute : ExceptionFilterAttribute
{
    public override void OnException(HttpActionExecutedContext context)
    {
        var exception = context.Exception as ApiException;
        if (exception != null) {
            context.Response = context.Request.CreateErrorResponse(exception.StatusCode, exception.Message);
        }
    }
}

Then you can register it globally.

GlobalConfiguration.Configuration.Filters.Add(new ApiExceptionFilterAttribute());

This is my custom exception type.

using System;
using System.Net;

namespace WebApi
{
    public class ApiException : Exception
    {
        private readonly HttpStatusCode statusCode;

        public ApiException (HttpStatusCode statusCode, string message, Exception ex)
            : base(message, ex)
        {
            this.statusCode = statusCode;
        }

        public ApiException (HttpStatusCode statusCode, string message)
            : base(message)
        {
            this.statusCode = statusCode;
        }

        public ApiException (HttpStatusCode statusCode)
        {
            this.statusCode = statusCode;
        }

        public HttpStatusCode StatusCode
        {
            get { return this.statusCode; }
        }
    }
}

An example exception that my API can throw.

public class NotAuthenticatedException : ApiException
{
    public NotAuthenticatedException()
        : base(HttpStatusCode.Forbidden)
    {
    }
}

You can throw a HttpResponseException

HttpResponseMessage response = 
    this.Request.CreateErrorResponse(HttpStatusCode.BadRequest, "your message");
throw new HttpResponseException(response);

answered Mar 4, 2014 at 5:15

If you are using ASP.NET Web API 2, the easiest way is to use the ApiController Short-Method. This will result in a BadRequestResult.

return BadRequest("message");

answered Mar 22, 2018 at 12:22

For Web API 2 my methods consistently return IHttpActionResult so I use…

public IHttpActionResult Save(MyEntity entity)
{
    ....
    if (...errors....)
        return ResponseMessage(
            Request.CreateResponse(
                HttpStatusCode.BadRequest, 
                validationErrors));

    // otherwise success
    return Ok(returnData);
}

answered Jan 20, 2016 at 1:53

answered Mar 18, 2016 at 9:40

RustyRusty

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Tawab WakilTawab Wakil

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Just to update on the current state of ASP.NET WebAPI. The interface is now called IActionResult and implementation hasn’t changed much:

[JsonObject(IsReference = true)]
public class DuplicateEntityException : IActionResult
{        
    public DuplicateEntityException(object duplicateEntity, object entityId)
    {
        this.EntityType = duplicateEntity.GetType().Name;
        this.EntityId = entityId;
    }

    /// <summary>
    ///     Id of the duplicate (new) entity
    /// </summary>
    public object EntityId { get; set; }

    /// <summary>
    ///     Type of the duplicate (new) entity
    /// </summary>
    public string EntityType { get; set; }

    public Task ExecuteResultAsync(ActionContext context)
    {
        var message = new StringContent($"{this.EntityType ?? "Entity"} with id {this.EntityId ?? "(no id)"} already exist in the database");

        var response = new HttpResponseMessage(HttpStatusCode.Ambiguous) { Content = message };

        return Task.FromResult(response);
    }

    #endregion
}

answered May 10, 2016 at 7:51

Try this

[HttpPost]
public async Task<ActionResult<User>> PostUser(int UserTypeId, User user)
{
  if (somethingFails)
  {
    // Return the error message like this.
    return new BadRequestObjectResult(new
    {
      message = "Something is not working here"
    });
  }

  return ok();
}

For those errors where modelstate.isvalid is false, I generally send the error as it is thrown by the code. Its easy to understand for the developer who is consuming my service. I generally send the result using below code.

     if(!ModelState.IsValid) {
                List<string> errorlist=new List<string>();
                foreach (var value in ModelState.Values)
                {
                    foreach(var error in value.Errors)
                    errorlist.Add( error.Exception.ToString());
                    //errorlist.Add(value.Errors);
                }
                HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.BadRequest,errorlist);}

This sends the error to the client in below format which is basically a list of errors:

    [  
    "Newtonsoft.Json.JsonReaderException: **Could not convert string to integer: abc. Path 'Country',** line 6, position 16.rn   
at Newtonsoft.Json.JsonReader.ReadAsInt32Internal()rn   
at Newtonsoft.Json.JsonTextReader.ReadAsInt32()rn   
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ReadForType(JsonReader reader, JsonContract contract, Boolean hasConverter, Boolean inArray)rn   
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)",

       "Newtonsoft.Json.JsonReaderException: **Could not convert string to integer: ab. Path 'State'**, line 7, position 13.rn   
at Newtonsoft.Json.JsonReader.ReadAsInt32Internal()rn   
at Newtonsoft.Json.JsonTextReader.ReadAsInt32()rn   
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ReadForType(JsonReader reader, JsonContract contract, Boolean hasConverter, Boolean inArray)rn   
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)"
    ]