Class: McpToolkit::RateLimiter

Inherits:
Object
  • Object
show all
Defined in:
lib/mcp_toolkit/rate_limiter.rb

Overview

A fixed-window request counter backing the authority transport's built-in rate limiting (McpToolkit::Authority::ControllerMethods#mcp_rate_limit!). It is storage-agnostic: it counts against the injected cache_store (any ActiveSupport::Cache::Store — a shared Rails.cache in production, a MemoryStore in a unit test), so a host enables per-principal throttling by setting config.rate_limit_max_requests alone, without hand-rolling a limiter.

The window is FIXED, not sliding: every request whose time falls in the same window-second bucket shares one counter, keyed by that bucket's start (window_start); the entry expires after window seconds. The counter is incremented once per call, and the request is allowed while the running count is <= max_requests, blocked once it exceeds it (so exactly max_requests requests pass per window).

result = McpToolkit::RateLimiter.new(
key: principal.id, max_requests: 1_000, window: 3_600, cache_store: Rails.cache
).call
result.allowed?     # => false once the count exceeds max_requests
result.limit        # => 1_000
result.remaining    # => max_requests - count, floored at 0
result.reset_at     # => epoch seconds of the next window boundary
result.retry_after  # => seconds until reset_at (0 when already past)

The cache key is namespaced (mcp_toolkit:rate_limit:<key>:<window_start>) so a host's own cache entries never collide with the counter.

Defined Under Namespace

Classes: Result

Instance Method Summary collapse

Constructor Details

#initialize(key:, max_requests:, cache_store:, window: 3_600, now: Time.now) ⇒ RateLimiter

Returns a new instance of RateLimiter.



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# File 'lib/mcp_toolkit/rate_limiter.rb', line 37

def initialize(key:, max_requests:, cache_store:, window: 3_600, now: Time.now)
  @key = key
  @max_requests = max_requests
  @cache_store = cache_store
  @window = window
  @now = now.to_i
end

Instance Method Details

#call ⇒ Object

Increments this window's counter and returns the Result. Called once per request by the transport's rate-limit hook.



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# File 'lib/mcp_toolkit/rate_limiter.rb', line 47

def call
  count = @cache_store.increment(cache_key, 1, expires_in: @window) || 1
  allowed = count <= @max_requests

  Result.new(
    allowed:,
    limit: @max_requests,
    remaining: allowed ? @max_requests - count : 0,
    reset_at:,
    retry_after: [reset_at - @now, 0].max
  )
end