Understanding ProblemDetails in Web APIs

10/2/2024

In the modern development of APIs, particularly REST APIs, error handling is critical. When something goes wrong—whether it's a bad request, an unauthorized attempt, or a server error—an API needs to communicate the problem effectively to the client. This is where ProblemDetails comes in. It is a standardized way to represent error information in a structured and easy-to-parse format.

If you’re developing APIs in ASP.NET Core, you’ve probably encountered or heard of ProblemDetails. In this article, we’ll explore what ProblemDetails is, how it works, and how you can use it to improve your error handling.

What is ProblemDetails?

ProblemDetails is a specification defined by RFC 7807 that provides a standardized format for returning machine-readable error details from HTTP APIs. It is designed to provide a consistent response structure for API errors, making it easier for clients to understand the error and handle it accordingly.

{
  "type": "https://example.com/probs/out-of-credit",
  "title": "You do not have enough credit.",
  "status": 403,
  "detail": "Your current balance is 30, but that costs 50.",
  "instance": "/account/12345/transactions/67890"
}

In this format:

  • type: A URI that identifies the problem type.
  • title: A short, human-readable summary of the problem.
  • status: The HTTP status code generated by the server.
  • detail: A human-readable explanation specific to the occurrence.
  • instance: A URI reference that identifies the specific occurrence of the problem.

Why Use ProblemDetails?

ProblemDetails standardizes how errors are communicated between APIs and clients. This provides several benefits:

  • Consistency: A uniform error format across different APIs reduces confusion and makes it easier for clients to integrate with your service.
  • Extensibility: You can add custom properties to extend ProblemDetails and provide additional context about an error.
  • Human-Readable: Both developers and clients get clear, concise error messages that are also machine-readable for programmatic handling.
  • Global Handling: You can set up global error handling in your ASP.NET Core application, meaning you don’t have to handle errors in each controller or method manually.

Implementing ProblemDetails in ASP.NET Core

Now that we understand what ProblemDetails is and why it’s useful, let’s look at how you can implement it in your ASP.NET Core API.

1. Enable Automatic ProblemDetails Responses

ASP.NET Core automatically provides a ProblemDetails response for common HTTP error status codes like 400 and 500. To get started, ensure that your project is using .NET Core 2.2 or higher, as ProblemDetails was introduced in ASP.NET Core 2.2.

2. Global Exception Handling with ProblemDetails

You can configure ASP.NET Core to return ProblemDetails for exceptions that occur in your application. Typically, you would do this in the Startup.cs class by adding an exception-handling middleware:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler(errorApp =>
        {
            errorApp.Run(async context =>
            {
                context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
                context.Response.ContentType = "application/problem+json";

                var problemDetails = new ProblemDetails
                {
                    Status = context.Response.StatusCode,
                    Title = "An error occurred while processing your request.",
                    Type = "https://httpstatuses.com/500"
                };

                var json = JsonSerializer.Serialize(problemDetails);
                await context.Response.WriteAsync(json);
            });
        });
    }

    app.UseRouting();
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });
}
3. Customizing ProblemDetails

While the default ProblemDetails structure is great for general use cases, you might want to add more context or handle specific types of errors differently. You can do this by creating a custom ProblemDetails class and returning it from your controllers.

public class CustomProblemDetails : ProblemDetails
{
    public string AdditionalInfo { get; set; }
}

[ApiController]
[Route("[controller]")]
public class ExampleController : ControllerBase
{
    [HttpGet]
    public IActionResult Get()
    {
        var problemDetails = new CustomProblemDetails
        {
            Status = 404,
            Title = "Resource not found",
            Type = "https://example.com/probs/resource-not-found",
            Detail = "The requested resource could not be found.",
            AdditionalInfo = "Some additional context or info"
        };

        return NotFound(problemDetails);
    }
}

Best Practices for Using ProblemDetails

Here are some best practices when working with ProblemDetails in your API:

  • Use meaningful URIs: The type field should point to a URL that gives additional information about the error. This can be a static page or a documentation page explaining the problem.
  • Keep title and detail concise: The title should be short and high-level, while detail can provide specific information related to the error.
  • Set appropriate status codes: Ensure the status field matches the actual HTTP response code.
  • Extend thoughtfully: Add custom fields like AdditionalInfo only when necessary to provide additional context.

Conclusion

ProblemDetails provides a standardized way to return errors from your APIs, improving consistency and clarity for clients. By leveraging ASP.NET Core’s built-in support for ProblemDetails, you can simplify error handling, improve communication between your API and its consumers, and provide a better developer experience.

Whether you stick to the default implementation or extend it with custom details, ProblemDetails will help you deliver more reliable and understandable API responses.