Exercise 3: Custom Middleware

Objective

Create custom middleware to log requests and measure response times.

Implementation

public class RequestLoggingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<RequestLoggingMiddleware> _logger;

    public RequestLoggingMiddleware(
        RequestDelegate next,
        ILogger<RequestLoggingMiddleware> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var startTime = DateTime.UtcNow;
        var requestId = Guid.NewGuid().ToString();

        _logger.LogInformation(
            "[{RequestId}] {Method} {Path} started",
            requestId,
            context.Request.Method,
            context.Request.Path);

        await _next(context);

        var elapsed = DateTime.UtcNow - startTime;

        _logger.LogInformation(
            "[{RequestId}] {Method} {Path} completed in {ElapsedMs}ms with status {StatusCode}",
            requestId,
            context.Request.Method,
            context.Request.Path,
            elapsed.TotalMilliseconds,
            context.Response.StatusCode);

        context.Response.Headers.Add("X-Response-Time", elapsed.TotalMilliseconds.ToString());
        context.Response.Headers.Add("X-Request-Id", requestId);
    }
}

// Extension method
public static class MiddlewareExtensions
{
    public static IApplicationBuilder UseRequestLogging(
        this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<RequestLoggingMiddleware>();
    }
}

// Usage
app.UseRequestLogging();

Challenge Tasks

1. Add API key validation middleware
2. Create exception handling middleware
3. Implement rate limiting middleware (simple counter)
4. Add request/response body logging

Expected Outcome

• Custom middleware that logs all requests
• Response time header added to responses
• Understanding of middleware execution order