Struct RateLimitingMiddleware 

pub struct RateLimitingMiddleware { /* private fields */ }

Rate limiting middleware using token bucket algorithm.

Uses a token bucket algorithm by default, allowing for burst traffic while maintaining a sustainable long-term rate.

Example

use fastmcp_server::rate_limiting::RateLimitingMiddleware;

// Allow 10 requests per second with bursts up to 20
let rate_limiter = RateLimitingMiddleware::new(10.0)
    .burst_capacity(20);

Implementations

impl RateLimitingMiddleware

pub fn new(max_requests_per_second: f64) -> Self

Creates a new rate limiting middleware with the specified rate.

Arguments

• max_requests_per_second - Sustained requests per second allowed

Burst capacity defaults to 2x the sustained rate.

pub fn burst_capacity(self, capacity: usize) -> Self

Sets the burst capacity (maximum tokens in the bucket).

pub fn client_id_extractor<F>(self, extractor: F) -> Self

where F: Fn(&McpContext, &JsonRpcRequest) -> Option<String> + Send + Sync + 'static,

Sets a custom function to extract client ID from the request context.

Identifiers longer than 4096 bytes are rejected. Accepted identifiers are immediately reduced to fixed-width SHA-256 partition keys; their raw values are neither retained nor included in rate-limit errors or debug output. At most 4095 distinct keys receive dedicated partitions. At the cap, a least-recently-used partition idle for at least 60 seconds is reclaimed only after its limiter has naturally reset; otherwise new keys share one overflow partition.

If not set, all clients share the default identity while each method retains an independent rate-limit partition.

pub fn global(self) -> Self

Enables global rate limiting (all clients share one limit).

When enabled, all requests count against a single rate limit regardless of client identity.

Trait Implementations

impl Debug for RateLimitingMiddleware

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Middleware for RateLimitingMiddleware

fn on_request( &self, ctx: &McpContext, request: &JsonRpcRequest, ) -> McpResult<MiddlewareDecision>

Invoked before routing the request.

fn on_response( &self, _ctx: &McpContext, _request: &JsonRpcRequest, response: Value, ) -> McpResult<Value>

Invoked after a successful handler result is produced.

fn on_error( &self, _ctx: &McpContext, _request: &JsonRpcRequest, error: McpError, ) -> McpError

Invoked when a handler or middleware returns an error.