Philiprehberger.RateLimiter

In-memory rate limiting with fixed window, sliding window, and token bucket algorithms.

Installation

dotnet add package Philiprehberger.RateLimiter

Usage

using Philiprehberger.RateLimiter;

Token Bucket

Tokens refill at a steady rate up to a maximum capacity. Good for smoothing bursts.

var limiter = new TokenBucketLimiter(
    capacity: 10,
    refillRate: 5,
    refillInterval: TimeSpan.FromSeconds(1));

if (limiter.TryAcquire())
{
    // proceed with operation
}

Fixed Window

Permits reset at the start of each time window.

var limiter = new FixedWindowLimiter(
    limit: 100,
    window: TimeSpan.FromMinutes(1));

if (limiter.TryAcquire())
{
    // proceed with operation
}

Sliding Window

Divides the window into segments for smoother rate limiting than fixed windows.

var limiter = new SlidingWindowLimiter(
    limit: 100,
    window: TimeSpan.FromMinutes(1),
    segments: 10);

if (limiter.TryAcquire())
{
    // proceed with operation
}

Async Wait

All limiters support async waiting until a permit is available:

await limiter.WaitAsync(ct: cancellationToken);
// permit acquired

Per-Key Rate Limiting

Use keys to apply independent rate limits per user, IP, or API endpoint:

if (limiter.TryAcquire(key: "user-42"))
{
    // user-42 has permits remaining
}

Fluent Builder

var limiter = RateLimiterBuilder.Create()
    .TokenBucket(capacity: 10, refillRate: 5, per: TimeSpan.FromSeconds(1))
    .PerKey()
    .Build();

API

IRateLimiter

Member	Description
Available	Number of permits currently available
Limit	Maximum number of permits
TryAcquire(key?)	Acquires a permit without blocking. Returns true if successful
WaitAsync(key?, ct)	Waits asynchronously until a permit is available

TokenBucketLimiter

Constructor Parameter	Description
capacity	Maximum number of tokens
refillRate	Tokens added per refill interval
refillInterval	Time between refills

FixedWindowLimiter

Constructor Parameter	Description
limit	Maximum permits per window
window	Window duration

SlidingWindowLimiter

Constructor Parameter	Description
limit	Maximum permits per window
window	Window duration
segments	Number of sub-segments (default 10)

RateLimiterBuilder

Method	Description
Create()	Creates a new builder
TokenBucket(capacity, refillRate, per)	Configures token bucket algorithm
FixedWindow(limit, window)	Configures fixed window algorithm
SlidingWindow(limit, window, segments)	Configures sliding window algorithm
PerKey()	Enables per-key partitioning
Build()	Builds the configured rate limiter

Development

dotnet build src/Philiprehberger.RateLimiter.csproj --configuration Release

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License

MIT