dotnetframework/System.Threading.RateLimitingv9.0.11

About

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Provides a set of types that enable application developers to control the rate of operations. This can be used to ensure that applications do not exceed certain limits when interacting with resources or services.

Key Features

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• Flexible rate-limiting primitives that can be applied to various scenarios.
• Supports token bucket, fixed window, and sliding window strategies.

How to Use

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This is an example of an HttpClient that does client side rate limiting.

Define a rate limiter.

internal sealed class ClientSideRateLimitedHandler : DelegatingHandler, IAsyncDisposable
{
    private readonly RateLimiter _rateLimiter;

    public ClientSideRateLimitedHandler(RateLimiter limiter)
        : base(new HttpClientHandler())
    {
        _rateLimiter = limiter;
    }

    // Override the SendAsync method to apply rate limiting.
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // Try to acquire a token from the rate limiter.
        using RateLimitLease lease = await _rateLimiter.AcquireAsync(permitCount: 1, cancellationToken);

        // If a token is acquired, proceed with sending the request.
        if (lease.IsAcquired)
        {
            return await base.SendAsync(request, cancellationToken);
        }

        // If no token could be acquired, simulate a 429 Too Many Requests response.
        var response = new HttpResponseMessage(HttpStatusCode.TooManyRequests);

        // Add a 'Retry-After' header if the rate limiter provides a retry delay.
        if (lease.TryGetMetadata(MetadataName.RetryAfter, out TimeSpan retryAfter))
        {
            response.Headers.Add("Retry-After", ((int)retryAfter.TotalSeconds).ToString(NumberFormatInfo.InvariantInfo));
        }

        return response;
    }

    // Implement IAsyncDisposable to allow for asynchronous cleanup of resources.
    public async ValueTask DisposeAsync()
    {
        // Dispose of the rate limiter asynchronously.
        await _rateLimiter.DisposeAsync().ConfigureAwait(false);

        // Call the base Dispose method.
        Dispose(disposing: false);

        // Suppress finalization.
        GC.SuppressFinalize(this);
    }

    // Dispose pattern to clean up the rate limiter.
    protected override void Dispose(bool disposing)
    {
        base.Dispose(disposing);

        if (disposing)
        {
            // Synchronously dispose of the rate limiter if disposing is true.
            _rateLimiter.Dispose();
        }
    }
}

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