計算線上人數用中介層

OnlineUserCounterMiddleware.cs

using Microsoft.AspNetCore.Http;

using System.Threading.Tasks;

public class OnlineUserCounterMiddleware
{
    private RequestDelegate _next;
    private static int s_onlineUserCount;
    public OnlineUserCounterMiddleware(
       RequestDelegate next)
    {
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        // 僅限單機，多機請用 Redis 處理，但邏輯一樣
        
        var currentOnlineUserCount =  Interlocked.Increment(ref s_onlineUserCount);
        
        context.Items["OnlineUser"] = currentOnlineUserCount;
        
        await _next(context);

        Interlocked.Decrement(ref s_onlineUserCount);
    }
}