ratelimit

Rate Limit

Warning: this is still a work in progress. Tests succeeding != production ready.

Rate limiting is enabled by default in a default Equinox client. For now the only store available is in-memory, though I want to add Redis support in the future, maybe using a lua script.

Info on rate limiting:

• Hextechdocs
• Riot developer portal

How does it work

Bucket

A limit for the App or Method is a bucket of tokens:

type Bucket struct {
	// Time interval in seconds
	interval time.Duration
	// Maximum number of tokens
	limit int
	// Current number of tokens, starts at limit
	tokens int
	// Next reset
	next  time.Time
	mutex sync.Mutex
}

When creating a bucket, interval is the time in seconds between resets, limit is the maximum number of tokens, and tokens is the current number of tokens.

func NewBucket(interval time.Duration, limit int, tokens int) *Bucket {
	now := time.Now()
	return &Bucket{
		interval: interval * time.Second,
		limit:    limit,
		tokens:   tokens,
		next:     now.Add(interval * time.Second),
		mutex:    sync.Mutex{},
	}
}

When initializing a bucket, the current amount of tokens will be the same as the limit minus the current count provided from the X-App-Rate-Limit-Count or X-Method-Rate-Limit-Count headers.

func parseHeaders(limitHeader string, countHeader string) []*Bucket {
	if limitHeader == "" || countHeader == "" {
		return []*Bucket{}
	}
	limits := strings.Split(limitHeader, ",")
	counts := strings.Split(countHeader, ",")
	rates := make([]*Bucket, len(limits))
	for i := range limits {
		limit, seconds := getNumbersFromPair(limits[i])
		count, _ := getNumbersFromPair(counts[i])
		rates[i] = NewBucket(time.Duration(seconds), limit, limit-count)
	}
	return rates
}

• When a bucket is full, the amount of tokens will be the same as the limit - Not Rate limited, able to Take() a token from the bucket.
• When a bucket is empty, the amount of tokens will be 0 - Rate limited, not able to Take() a token without waiting.

Take

After creating a request and checking if it was cached, the client will use Take(), initializing the App and Method buckets in a route AND the MethodID if not initialized.

If rate limited, Take() will block until the next bucket reset. A context can be passed, allowing for cancellation and checking if the deadline will be exceeded, cancelling the block if it will.

Take() will then decrease tokens for the App and Method in the buckets by one.

Update

After receiving a response, Update() will verify that the current buckets in-memory match the ones received by the Riot API, if they don't, it will force an update in all buckets.

By 'matching', I mean that the current limit and interval in these buckets match the ones received by the Riot API.