Overview
Error handling and exception management in REST APIs is crucial for communicating what went wrong during an API request. Proper error handling improves the API's usability and helps clients to gracefully handle errors. It involves returning meaningful error messages and correct HTTP status codes that reflect the nature of the error.
Key Concepts
- HTTP Status Codes: Utilize standard HTTP status codes to indicate the success or failure of an API request.
- Error Payloads: Sending detailed error information in the response body, including error codes, messages, and sometimes fields that caused the error.
- Exception Handling Patterns: Implementing strategies to catch and handle exceptions globally, reducing code duplication and centralizing error response logic.
Common Interview Questions
Basic Level
- What are the common HTTP status codes used in REST APIs for error handling?
- How do you return a custom error message in a REST API?
Intermediate Level
- How can you implement global exception handling in a REST API?
Advanced Level
- Describe how you would design an error handling framework for a large-scale REST API.
Detailed Answers
1. What are the common HTTP status codes used in REST APIs for error handling?
Answer: HTTP status codes are crucial for indicating the success or failure of an API request. The most common ones used for error handling in REST APIs include:
- 400 Bad Request: The request was invalid or cannot be served. Usually an issue with the request payload.
- 401 Unauthorized: The request lacks valid authentication credentials.
- 403 Forbidden: The request is authenticated but does not have permission to perform the action.
- 404 Not Found: The requested resource was not found.
- 500 Internal Server Error: A generic error indicating an unexpected condition was encountered on the server.
Key Points:
- Use appropriate status codes to reflect the nature of the error accurately.
- Avoid exposing sensitive information through error messages, especially with 4xx and 5xx errors.
- 4xx errors indicate issues on the client side, while 5xx errors indicate server-side problems.
Example:
[HttpGet("{id}")]
public ActionResult<Product> GetProduct(int id)
{
var product = _productService.GetById(id);
if (product == null)
{
return NotFound(new { message = "Product not found" }); // 404 Not Found
}
return Ok(product); // 200 OK
}
2. How do you return a custom error message in a REST API?
Answer: Custom error messages can be returned by creating a specific payload that includes the error message, code, and possibly other details. This payload is then returned with the appropriate HTTP status code.
Key Points:
- Define a consistent error response structure.
- Include clear, developer-friendly error messages.
- Optionally, include error codes for programmatic handling.
Example:
[HttpGet("{id}")]
public ActionResult GetProduct(int id)
{
try
{
var product = _productService.GetById(id);
if (product == null)
{
return NotFound(new { error = "ProductNotFound", message = "Product not found" });
}
return Ok(product);
}
catch (Exception ex)
{
// Log exception details for internal diagnostics
return StatusCode(500, new { error = "InternalServerError", message = "An unexpected error occurred." });
}
}
3. How can you implement global exception handling in a REST API?
Answer: Global exception handling in ASP.NET Core REST APIs can be implemented using middleware or custom exception filters. This approach centralizes error handling logic, making the code cleaner and more maintainable.
Key Points:
- Capture unhandled exceptions globally to prevent the API from crashing.
- Return standardized error responses for unhandled exceptions.
- Log detailed exception information for diagnostics.
Example:
public class ErrorHandlingMiddleware
{
private readonly RequestDelegate _next;
public ErrorHandlingMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task Invoke(HttpContext context)
{
try
{
await _next(context);
}
catch (Exception ex)
{
await HandleExceptionAsync(context, ex);
}
}
private static Task HandleExceptionAsync(HttpContext context, Exception exception)
{
// Log the exception here
var result = JsonConvert.SerializeObject(new { error = "InternalServerError", message = "An unexpected error occurred." });
context.Response.ContentType = "application/json";
context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
return context.Response.WriteAsync(result);
}
}
// In Startup.cs, register the middleware
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
app.UseMiddleware<ErrorHandlingMiddleware>();
}
4. Describe how you would design an error handling framework for a large-scale REST API.
Answer: Designing an error handling framework for a large-scale REST API involves creating a centralized mechanism that can handle different types of exceptions, log them appropriately, and return standardized error responses. This framework should be extendable and easy to maintain.
Key Points:
- Use middleware or filters for global exception handling.
- Define a hierarchical structure for exceptions to handle specific cases more granely.
- Incorporate logging mechanisms that can scale with the application.
- Ensure that the error responses are consistent across the API.
Example:
// Define a base application exception class
public class ApplicationException : Exception
{
public int StatusCode { get; set; }
public string ErrorCode { get; set; }
public ApplicationException(string message, string errorCode, int statusCode = 500) : base(message)
{
StatusCode = statusCode;
ErrorCode = errorCode;
}
}
// Implement a middleware that handles ApplicationException and translates it to HTTP responses
public class ApplicationExceptionMiddleware
{
private readonly RequestDelegate _next;
public ApplicationExceptionMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task Invoke(HttpContext context)
{
try
{
await _next(context);
}
catch (ApplicationException ex)
{
var response = context.Response;
response.ContentType = "application/json";
response.StatusCode = ex.StatusCode;
await response.WriteAsync(JsonConvert.SerializeObject(new { error = ex.ErrorCode, message = ex.Message }));
}
}
}
// Usage in Startup.cs
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
app.UseMiddleware<ApplicationExceptionMiddleware>();
}
This structure allows for fine-grained control over exception handling and response formatting, which is essential for large-scale applications.
