88 lines
2.4 KiB
C#
88 lines
2.4 KiB
C#
// Copyright 2021-2025 The NATS Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// Adapted from server/rate_counter.go in the NATS server Go source.
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namespace ZB.MOM.NatsNet.Server.Internal;
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/// <summary>
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/// A sliding-window rate limiter that allows at most <c>limit</c> events
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/// per <see cref="Interval"/> window.
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/// Mirrors <c>rateCounter</c> in server/rate_counter.go.
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/// </summary>
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public sealed class RateCounter
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{
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private readonly long _limit;
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private long _count;
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private ulong _blocked;
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private DateTime _end;
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// Exposed for tests (mirrors direct field access in rate_counter_test.go).
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public TimeSpan Interval;
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private readonly object _lock = new();
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public RateCounter(long limit)
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{
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_limit = limit;
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Interval = TimeSpan.FromSeconds(1);
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}
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/// <summary>
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/// Factory wrapper for Go parity.
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/// Mirrors <c>newRateCounter</c>.
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/// </summary>
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public static RateCounter NewRateCounter(long limit) => new(limit);
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/// <summary>
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/// Returns true if the event is within the rate limit for the current window.
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/// Mirrors <c>rateCounter.allow</c>.
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/// </summary>
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public bool Allow()
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{
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var now = DateTime.UtcNow;
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lock (_lock)
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{
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if (now > _end)
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{
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_count = 0;
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_end = now + Interval;
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}
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else
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{
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_count++;
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}
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var allow = _count < _limit;
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if (!allow)
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_blocked++;
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return allow;
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}
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}
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/// <summary>
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/// Returns and resets the count of blocked events since the last call.
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/// Mirrors <c>rateCounter.countBlocked</c>.
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/// </summary>
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public ulong CountBlocked()
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{
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lock (_lock)
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{
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var blocked = _blocked;
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_blocked = 0;
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return blocked;
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}
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}
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}
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