C#中間件如何管理API請求速率限制

在C#中，我們可以使用ASP.NET Core的中間件來實現API請求速率限制。以下是一個簡單的示例，展示了如何創建一個自定義中間件來管理API請求速率限制：

1. 首先，安裝Microsoft.AspNetCore.Http和Microsoft.Extensions.Caching.Memory包。

dotnet add package Microsoft.AspNetCore.Http
dotnet add package Microsoft.Extensions.Caching.Memory

2. 創建一個名為RateLimiterMiddleware的新類：

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Caching.Memory;

public class RateLimiterMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IMemoryCache _cache;
    private readonly int _maxRequests;
    private readonly TimeSpan _timeWindow;

    public RateLimiterMiddleware(RequestDelegate next, IMemoryCache cache, int maxRequests, TimeSpan timeWindow)
    {
        _next = next;
        _cache = cache;
        _maxRequests = maxRequests;
        _timeWindow = timeWindow;
    }

    public async Task Invoke(HttpContext context)
    {
        var clientId = context.Connection.RemoteIpAddress.ToString();
        var requestCount = 0;

        if (_cache.TryGetValue(clientId, out int cachedRequestCount))
        {
            requestCount = cachedRequestCount;
        }

        if (requestCount >= _maxRequests)
        {
            context.Response.StatusCode = 429; // Too Many Requests
            await context.Response.WriteAsync("Too many requests.");
            return;
        }

        requestCount++;
        _cache.Set(clientId, requestCount, _timeWindow);

        await _next.Invoke(context);
    }
}

3. 在Startup.cs文件中，將RateLimiterMiddleware添加到請求管道中：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMemoryCache();
        services.AddControllers();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseHttpsRedirection();

        app.UseRouting();

        app.UseAuthorization();

        app.UseMiddleware<RateLimiterMiddleware>(5, TimeSpan.FromMinutes(1)); // 5 requests per minute

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }
}

在這個示例中，我們創建了一個名為RateLimiterMiddleware的中間件，它接收最大請求數和時間窗口作為參數。然后，我們將中間件添加到請求管道中，并設置每分鐘允許的最大請求數。當客戶端超過速率限制時，中間件將返回HTTP 429狀態碼（太多請求）。