Overview
Handling errors and exceptions in Web APIs is crucial for maintaining a reliable and user-friendly service. Proper error handling involves returning appropriate status codes, meaningful error messages, and implementing logging mechanisms to diagnose issues. This aspect is fundamental in API design and development, ensuring that clients can gracefully handle errors and developers can quickly identify and resolve underlying issues.
Key Concepts
- Status Codes and Error Messages: Utilizing HTTP status codes correctly to convey the nature of the error (client-side or server-side) and providing clear, actionable error messages.
- Exception Handling Mechanisms: Strategies for catching and handling exceptions within the API to prevent the propagation of sensitive information and to maintain the API's stability.
- Logging and Monitoring: Implementing logging to record errors and monitoring tools to track the health and performance of the API.
Common Interview Questions
Basic Level
- What is the purpose of HTTP status codes in Web API error handling?
- How would you implement a basic exception handling middleware in a Web API?
Intermediate Level
- How can you ensure that your API does not expose sensitive information when an error occurs?
Advanced Level
- Describe a strategy for global error handling in a Web API that includes logging and user-friendly error messages.
Detailed Answers
1. What is the purpose of HTTP status codes in Web API error handling?
Answer: HTTP status codes are utilized in Web API error handling to succinctly communicate the nature of an error to the client. They indicate whether an error is client-side (4xx codes) or server-side (5xx codes), allowing clients to take appropriate action. For example, a 404 status code indicates a resource is not found, while a 500 status code indicates an internal server error.
Key Points:
- Status codes provide a standardized method for indicating errors.
- They help in automating error handling on the client side.
- They are essential for RESTful API design principles.
Example:
public IActionResult GetItem(int id)
{
var item = _repository.GetItem(id);
if (item == null)
{
return NotFound(); // Returns a 404 status code
}
return Ok(item); // Returns a 200 status code with the item
}
2. How would you implement a basic exception handling middleware in a Web API?
Answer: A basic exception handling middleware in a Web API can catch unhandled exceptions, log them, and return a standardized error response to the client. This ensures that any unexpected errors are handled gracefully and consistently.
Key Points:
- Middleware can catch exceptions that occur in the request pipeline.
- It can log detailed error information for debugging purposes.
- It returns a user-friendly error message and appropriate HTTP status code.
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)
{
var code = HttpStatusCode.InternalServerError; // 500 if unexpected
var result = JsonConvert.SerializeObject(new { error = "An unexpected error occurred." });
context.Response.ContentType = "application/json";
context.Response.StatusCode = (int)code;
return context.Response.WriteAsync(result);
}
}
3. How can you ensure that your API does not expose sensitive information when an error occurs?
Answer: To ensure that an API does not expose sensitive information during an error, implement custom error handling that returns generic error messages for client-facing responses and logs detailed error information server-side. Use structured exception handling to catch different types of exceptions and mask or replace error messages that could reveal sensitive details about the API's internal workings.
Key Points:
- Use try-catch blocks to manage exceptions explicitly.
- Return generic error messages to the client.
- Log detailed errors internally for debugging.
Example:
try
{
// Code that may throw an exception
}
catch (DatabaseException ex)
{
Log.Error(ex, "Database operation failed."); // Detailed log for the developer
return StatusCode(500, "An error occurred processing your request."); // Generic message for the client
}
4. Describe a strategy for global error handling in a Web API that includes logging and user-friendly error messages.
Answer: A comprehensive strategy for global error handling in a Web API involves implementing a global exception filter or middleware that intercepts all unhandled exceptions. This component should log the details of the exception for debugging purposes and return a standardized, user-friendly error response to the client. Additionally, it can categorize errors to return appropriate HTTP status codes and messages without exposing sensitive details.
Key Points:
- Implement a global exception handler to catch all unhandled exceptions.
- Log exceptions with sufficient details for troubleshooting.
- Return standardized, non-sensitive error messages and appropriate status codes.
Example:
public class GlobalExceptionFilter : IExceptionFilter
{
public void OnException(ExceptionContext context)
{
var code = HttpStatusCode.InternalServerError; // Default to 500
if (context.Exception is NotFoundException) code = HttpStatusCode.NotFound;
// Other specific exceptions and codes...
var result = new JsonResult(new { error = "A server error occurred." });
context.HttpContext.Response.StatusCode = (int)code;
context.Result = result;
// Log the exception details
Log.Error(context.Exception, "Unhandled exception occurred.");
}
}
This filter can be added globally in the Startup.cs to ensure it catches all exceptions thrown by the API controllers.
