Refactoring & extensibility

[cristipufu]

This pull request refactors all the duplicate code and contains multiple fixes and extensibility improvements based on the community issues.

---

Quick summary:

• Update the library to netstandard2.0 and the demo web app to aspnetcore3.0, lang C# 7.3

• No more duplicate code

• Fixes the wildcard match issues [How do you create dynamic URL (parameter) rules? #29 How to ignore query string and/or parameters #41]

• Implement an async named locker for request processing [Every request waiting for the lock and blocking other requests #12] (the lock will no longer block the entire app, but only the requests that match the specific counter id)

The AsyncLock code is also used here and I used Ben.BlockingDetector to detect any blocking calls, so it should be just fine.

using (await AsyncLock.WriterLockAsync(counterId).ConfigureAwait(false))
{
        var entry = await _counterStore.GetAsync(counterId, cancellationToken);

        if (entry.HasValue)
        {
                // entry has not expired
                if (entry.Value.Timestamp + rule.PeriodTimespan.Value >= DateTime.UtcNow)
                {
                    // increment request count
                    var totalRequests = entry.Value.TotalRequests + 1;

                    // deep copy
                    counter = new RateLimitCounter
                    {
                        Timestamp = entry.Value.Timestamp,
                        TotalRequests = totalRequests
                    };
                }
        }

        // stores: id (string) - timestamp (datetime) - total_requests (long)
        await _counterStore.SetAsync(counterId, counter, rule.PeriodTimespan.Value, cancellationToken);
}

• All the stores are now async (performance improvement for Redis-backed stores) - but now you have to manually seed the app settings client / IP policies.

https://andrewlock.net/running-async-tasks-on-app-startup-in-asp-net-core-part-2/

public static async Task Main(string[] args)
{
        IWebHost webHost = CreateWebHostBuilder(args).Build();

        using (var scope = webHost.Services.CreateScope())
        {
            // get the ClientPolicyStore instance
            var clientPolicyStore = scope.ServiceProvider.GetRequiredService<IClientPolicyStore>();

            // seed Client data from appsettings
            await clientPolicyStore.SeedAsync();

            // get the IpPolicyStore instance
            var ipPolicyStore = scope.ServiceProvider.GetRequiredService<IIpPolicyStore>();

            // seed IP data from appsettings
            await ipPolicyStore.SeedAsync();
        }

        await webHost.RunAsync();
}

• Client / IP resolvers - can easily add or replace them (take the client id from headers / query query string parameters / whatever) [[Urgent] Custom Client ID  #47 Abstract away the concept of a clientId in the Client Ratelimiter #54]

public class CustomRateLimitConfiguration : RateLimitConfiguration
{
    protected override void RegisterResolvers()
    {
    	base.RegisterResolvers();

    	ClientResolvers.Add(new ClientQueryStringResolveContributor(HttpContextAccessor, ClientRateLimitOptions.ClientIdHeader));
    }
}

• Adds the notion of counter key builders, so you can easily specify a different endpoint counter key [Implement rule as key #13 How do you create dynamic URL (parameter) rules? #29 How to ignore query string and/or parameters #41]

public class CustomRateLimitConfiguration : RateLimitConfiguration
{
    public override ICounterKeyBuilder EndpointCounterKeyBuilder { get; } = new EndpointCounterKeyBuilder();
}

---

If you want to upgrade and make it all work, you have to configure two new services in your Startup.cs:

// https://github.com/aspnet/Hosting/issues/793
// the IHttpContextAccessor service is not registered by default.
// the ClientId / IP resolvers use it.
services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

// configure the resolvers (default config)
services.AddSingleton<IRateLimitConfiguration, RateLimitConfiguration>();

Summing up the breaking-chages:

• You have to manually seed the appsettings.json policies.
• You have to register two new services.

PS: I will wait a week to discuss/talk about the changes/features before merging this.

Suggestions and feedback are most welcome.

Thanks