UA-.NETStandard/tests/Opc.Ua.Server.Tests/RateLimiting/ServerRateLimiterTests.cs

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using System;
using System.Collections.Generic;
using System.Net;
using System.Threading.Tasks;
using NUnit.Framework;

namespace Opc.Ua.Server.Tests
{
    /// <summary>
    /// Tests for the server admission-control rate limiters.
    /// </summary>
    [TestFixture]
    [Category("RateLimiting")]
    [SetCulture("en-us")]
    [SetUICulture("en-us")]
    [Parallelizable]
    public class ServerRateLimiterTests
    {
        /// <summary>
        /// Verifies that the token-bucket connection limiter admits up to the burst
        /// capacity and then rejects further connections.
        /// </summary>
        [Test]
        public void ConnectionRateLimiterAdmitsUpToBurstThenRejects()
        {
            using var limiter = new TokenBucketConnectionRateLimiter(
                connectionsPerSecond: 1,
                burst: 5);

            var remote = new IPEndPoint(IPAddress.Loopback, 4840);

            int admitted = 0;
            for (int i = 0; i < 5; i++)
            {
                if (limiter.TryAdmitConnection(remote, out _))
                {
                    admitted++;
                }
            }

            Assert.That(admitted, Is.EqualTo(5), "the full burst should be admitted");

            bool sixth = limiter.TryAdmitConnection(remote, out TimeSpan? retryAfter);
            Assert.That(sixth, Is.False, "the connection beyond the burst must be rejected");
            Assert.That(retryAfter, Is.Not.Null, "a rejected connection should carry a retry-after hint");
        }

        /// <summary>
        /// Verifies that a null remote endpoint is handled without throwing.
        /// </summary>
        [Test]
        public void ConnectionRateLimiterHandlesNullRemoteEndPoint()
        {
            using var limiter = new TokenBucketConnectionRateLimiter(1, 2);

            Assert.That(limiter.TryAdmitConnection(null, out _), Is.True);
        }

        /// <summary>
        /// Verifies that the connection limiter rejects invalid limits.
        /// </summary>
        [Test]
        public void ConnectionRateLimiterRejectsInvalidLimits()
        {
            Assert.That(
                () => new TokenBucketConnectionRateLimiter(0, 1),
                Throws.TypeOf<ArgumentOutOfRangeException>());
            Assert.That(
                () => new TokenBucketConnectionRateLimiter(1, 0),
                Throws.TypeOf<ArgumentOutOfRangeException>());
        }

        /// <summary>
        /// Verifies that when rate limiting is disabled the provider applies no
        /// limits: no connection limiter and session establishment always proceeds.
        /// </summary>
        [Test]
        public void DisabledProviderAppliesNoLimits()
        {
            var options = new ServerRateLimitOptions { Enabled = false };
            using var provider = new DefaultServerRateLimiterProvider(options);

            Assert.That(provider.ConnectionRateLimiter, Is.Null);
            Assert.That(
                provider.TryAcquireSessionEstablishment(out IDisposable? lease, out _),
                Is.True);
            Assert.That(lease, Is.Null);
            // The backlog default is still applied even when limiting is disabled.
            Assert.That(provider.ListenBacklog, Is.EqualTo(ServerRateLimitOptions.DefaultListenBacklog));
        }

        /// <summary>
        /// Verifies that the default (enabled) provider exposes a connection limiter
        /// and the configured listener backlog.
        /// </summary>
        [Test]
        public void EnabledProviderExposesConnectionLimiterAndBacklog()
        {
            var options = new ServerRateLimitOptions { ListenBacklog = 777 };
            using var provider = new DefaultServerRateLimiterProvider(options);

            Assert.That(provider.ConnectionRateLimiter, Is.Not.Null);
            Assert.That(provider.ListenBacklog, Is.EqualTo(777));
        }

        [TestCase(0, 0)]
        [TestCase(-1, -1)]
        [TestCase(0, 1)]
        [TestCase(1, 0)]
        public void ProviderUsesDefaultsForNonPositiveConnectionLimits(
            int connectionsPerSecond,
            int connectionBurst)
        {
            var options = new ServerRateLimitOptions
            {
                ConnectionsPerSecond = connectionsPerSecond,
                ConnectionBurst = connectionBurst
            };

            using var provider = new DefaultServerRateLimiterProvider(options);

            Assert.That(provider.ConnectionRateLimiter, Is.Not.Null);
        }

        /// <summary>
        /// Verifies that the session-establishment concurrency limiter admits up to
        /// the permit limit and rejects the next operation while permits are held,
        /// then admits again after a lease is released.
        /// </summary>
        [Test]
        public void SessionEstablishmentLimiterBoundsConcurrency()
        {
            var options = new ServerRateLimitOptions
            {
                MaxConcurrentSessionEstablishment = 2,
                SessionEstablishmentQueueLimit = 0
            };
            using var provider = new DefaultServerRateLimiterProvider(options);

            var leases = new List<IDisposable?>();

            Assert.That(
                provider.TryAcquireSessionEstablishment(out IDisposable? first, out _),
                Is.True);
            leases.Add(first);

            Assert.That(
                provider.TryAcquireSessionEstablishment(out IDisposable? second, out _),
                Is.True);
            leases.Add(second);

            // Both permits are held: the third establishment must be rejected.
            Assert.That(
                provider.TryAcquireSessionEstablishment(out IDisposable? third, out _),
                Is.False);
            Assert.That(third, Is.Null);

            // Release one permit; a new establishment can now proceed.
            first!.Dispose();
            Assert.That(
                provider.TryAcquireSessionEstablishment(out IDisposable? fourth, out _),
                Is.True);
            leases.Add(fourth);

            foreach (IDisposable? lease in leases)
            {
                lease?.Dispose();
            }
        }

        /// <summary>
        /// Verifies that a session establishment waits in the configured queue for a
        /// permit instead of being rejected, and that a full queue still rejects.
        /// </summary>
        [Test]
        public async Task SessionEstablishmentQueueLimitQueuesUntilPermitIsFreeAsync()
        {
            var options = new ServerRateLimitOptions
            {
                MaxConcurrentSessionEstablishment = 1,
                SessionEstablishmentQueueLimit = 1
            };
            using var provider = new DefaultServerRateLimiterProvider(options);

            (bool acquired, IDisposable? first, _) =
                await provider.AcquireSessionEstablishmentAsync().ConfigureAwait(false);
            Assert.That(acquired, Is.True);

            Task<(bool Acquired, IDisposable? Lease, TimeSpan? RetryAfter)> queued =
                provider.AcquireSessionEstablishmentAsync().AsTask();
            Assert.That(queued.IsCompleted, Is.False);

            (bool overflowAcquired, IDisposable? overflow, _) =
                await provider.AcquireSessionEstablishmentAsync().ConfigureAwait(false);
            Assert.That(overflowAcquired, Is.False);
            Assert.That(overflow, Is.Null);

            first!.Dispose();
            (bool queuedAcquired, IDisposable? second, _) =
                await queued.WaitAsync(TimeSpan.FromSeconds(10)).ConfigureAwait(false);
            Assert.That(queuedAcquired, Is.True);
            second!.Dispose();
        }

        /// <summary>
        /// Verifies that disposing the provider is idempotent.
        /// </summary>
        [Test]
        public void ProviderDisposeIsIdempotent()
        {
            var provider = new DefaultServerRateLimiterProvider(new ServerRateLimitOptions());
            provider.Dispose();
            Assert.That(provider.Dispose, Throws.Nothing);
        }

        /// <summary>
        /// Verifies that a null options argument is rejected.
        /// </summary>
        [Test]
        public void ProviderRejectsNullOptions()
        {
            Assert.That(
                () => new DefaultServerRateLimiterProvider(null!),
                Throws.TypeOf<ArgumentNullException>());
        }
    }
}