Cron expression: run task once per-day in ASP.Net Core

Question

My asp.net core program needs to collect all the IP which access the website pre-day.

I need to output the IP list to a txt file when a day is over.

Therefore, the program should run a method to save the IP list once per-day.

How should I design it?

In my opinion, I will add a looping task in the startup.cs and set the Task.Delay to 24 hours(one day).

Should I do it like this? Thank you.

Answer 1

This is how I implement scheduler task in ASP.Net Core. Please note that you have to know how to use cron epxression.

First add this package in your csproj

<PackageReference Include="ncrontab" Version="3.3.1" />

Next I will create SceduledProcessor.cs

public abstract class ScheduledProcessor : ScopedProcessor
    {
        private readonly CrontabSchedule _schedule;
        private DateTime _nextRun;

        protected ScheduledProcessor(IServiceScopeFactory serviceScopeFactory) : base(serviceScopeFactory)
        {
            _schedule = CrontabSchedule.Parse(GetCronExpression(serviceScopeFactory));
            _nextRun = _schedule.GetNextOccurrence(DateTime.Now);
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            do
            {
                var now = DateTime.Now;
                _schedule.GetNextOccurrence(now);

                if (now > _nextRun)
                {
                    await ProcessBackgroundTask();
                    _nextRun = _schedule.GetNextOccurrence(DateTime.Now);
                }

                await Task.Delay(5000, stoppingToken);
            }
            while (!stoppingToken.IsCancellationRequested);
        }

        protected abstract string GetCronExpression(IServiceScopeFactory serviceScopeFactory);
    }

The ExecuteAsync will be run for our scenario

Please note that we have to implement GetCronExpression method

Next I will implement the service class

public class ScheduledEmailService : ScheduledProcessor
    {
        public ScheduledEmailService(
            IServiceScopeFactory serviceScopeFactory) : base(serviceScopeFactory)
        {
        }

        /// <summary>
        /// Get cron setting from db
        /// </summary>
        /// <returns></returns>
        protected override string GetCronExpression(IServiceScopeFactory serviceScopeFactory)
        {
            return ""; // return your cron expression here you can get from db or static string
        }

        public override Task ProcessInScope(IServiceProvider serviceProvider)
        {
            // do something you wish
            return Task.CompletedTask;
        }
    }

Bonus here I small class with predefined value for cron expression you can use it

public static class CronExpression
    {
        public static readonly string EveryMinute = "0 * * * * *";
        public static readonly string EveryDay = "0 0 0 * * *";
        public static readonly string EveryWeek = "0 0 * * 0";
        public static readonly string EveryWeekend = "0 0 0 * * 6,0";
    }

Finally add this to your Startup.cs

services.AddSingleton<IHostedService, ScheduledEmailService>();