ratelimit.c File Reference

Simple IP-based rate limiting middleware implementation. More...

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <uv.h>
#include "csilk/core/internal.h"
#include "csilk/csilk.h"

Include dependency graph for ratelimit.c:

Data Structures
struct	ip_entry_t
	Rate-limit tracking entry for a single IP address. More...

Macros
#define	MAX_IP_ENTRIES   1024
	Maximum number of distinct IP addresses tracked concurrently.
#define	WINDOW_SIZE   60
	Rate limiting sliding window size in seconds.
#define	EVICT_INTERVAL   300
	Interval (in seconds) at which stale entries are garbage-collected.

Functions
static void	init_ratelimit_mutex ()
	Initialize the rate-limiting mutex (called once via uv_once).
static void	evict_stale_entries (time_t now)
	Compact the IP table by removing entries whose last_seen timestamp is older than WINDOW_SIZE seconds.
static void	evict_oldest_entry (void)
	Evict the single oldest entry from the IP table (LRU policy).
void	csilk_rate_limit_middleware (csilk_ctx_t *c, int limit)
	IP-based rate limiting middleware with sliding window.

Variables
static ip_entry_t	ip_table [MAX_IP_ENTRIES]
static int	ip_count = 0
static time_t	last_evict = 0
static uv_mutex_t	ratelimit_mutex
static uv_once_t	ratelimit_once = UV_ONCE_INIT

Detailed Description

Simple IP-based rate limiting middleware implementation.

Copyright

MIT License

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Data Structure Documentation

ip_entry_t

struct ip_entry_t

Rate-limit tracking entry for a single IP address.

Each entry stores the IP string, the request count within the current window, the timestamp when the counting window started, and the timestamp of the most recent request (used for LRU eviction when the table is full).

Data Fields
int	count	Request count in current window.
char	ip[46]	Client IP address string.
time_t	last_reset	Timestamp when the window started.
time_t	last_seen	Timestamp of last request (for LRU eviction).

Macro Definition Documentation

EVICT_INTERVAL

#define EVICT_INTERVAL   300

Interval (in seconds) at which stale entries are garbage-collected.

A periodic eviction pass removes entries whose last_seen timestamp is older than WINDOW_SIZE seconds, preventing the table from filling with dead entries.

MAX_IP_ENTRIES

#define MAX_IP_ENTRIES   1024

Maximum number of distinct IP addresses tracked concurrently.

When the table is full, the least recently seen entry is evicted to make room for new clients.

WINDOW_SIZE

#define WINDOW_SIZE   60

Rate limiting sliding window size in seconds.

The request counter for each IP is reset if the last reset timestamp is older than this many seconds.

Function Documentation

csilk_rate_limit_middleware()

void csilk_rate_limit_middleware	(	csilk_ctx_t *	c,
		int	limit
	)

IP-based rate limiting middleware with sliding window.

Simple per-IP rate-limiting middleware.

Tracks request counts per client IP address within a configurable window. If the number of requests from a given IP exceeds the limit, a 429 Too Many Requests response is sent (with a Retry-After header) and the pipeline is aborted.

The IP table is protected by a libuv mutex for thread safety. Stale entries are periodically evicted to prevent unbounded memory growth.

Parameters

c	The request context.
limit	Maximum number of requests allowed per IP within the WINDOW_SIZE (60-second) sliding window.

Note

The mutex is initialized once via uv_once on the first call.

Warning

Rate limiting is per-worker-process. In multi-process deployments, each process maintains its own independent table unless an external store (Redis, etc.) is used instead.

If csilk_get_client_ip() returns NULL (e.g. in tests or certain proxy setups), the request is passed through without rate limiting.

evict_oldest_entry()

static void evict_oldest_entry ( void  )

static

Evict the single oldest entry from the IP table (LRU policy).

Scans the ip_table for the entry with the smallest last_seen value and replaces it with the last entry in the table, decrementing ip_count. Called when the table is full and a new IP needs to be tracked.

evict_stale_entries()

static void evict_stale_entries ( time_t  now )

static

Compact the IP table by removing entries whose last_seen timestamp is older than WINDOW_SIZE seconds.

Iterates over the table and compacts it in-place, updating ip_count to reflect the number of remaining active entries.

Parameters

now	The current time to compare against last_seen.

init_ratelimit_mutex()

static void init_ratelimit_mutex ( )

static

Initialize the rate-limiting mutex (called once via uv_once).

Creates the libuv mutex that protects the shared ip_table and ip_count from concurrent access across worker threads.

Variable Documentation

ip_count

int ip_count = 0

static

ip_table

ip_entry_t ip_table[MAX_IP_ENTRIES]

static

last_evict

time_t last_evict = 0

static

ratelimit_mutex

uv_mutex_t ratelimit_mutex

static

ratelimit_once

uv_once_t ratelimit_once = UV_ONCE_INIT

static