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Add jitter to retry-after header. closes PrivateCaptcha/issues#170

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This commit is contained in:
Taras Kushnir
2025-08-11 13:04:23 +03:00
parent a6be38e0be
commit 91edc9c6bf
2 changed files with 9 additions and 4 deletions
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12
pkg/ratelimit/http.go
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@@ -54,6 +54,8 @@ type httpRateLimiter[TKey comparable] struct {
strategy realclientip.Strategy
cleanupCancel context.CancelFunc
keyFunc func(r *http.Request) TKey
// prevent stampeding herds problem with random increase to Retry-After
retryJitterPercent float64
}
var _ HTTPRateLimiter = (*httpRateLimiter[string])(nil)
@@ -83,7 +85,7 @@ func (l *httpRateLimiter[TKey]) RateLimitExFunc(initCapacity leakybucket.TLevel,
addResult := l.buckets.AddEx(key, 1, time.Now(), initCapacity, initLeakInterval)
setRateLimitHeaders(w, addResult)
l.setRateLimitHeaders(w, addResult)
if addResult.Added > 0 {
//slog.Log(r.Context(), common.LevelTrace, "Allowing request", "ratelimiter", l.name,
@@ -110,7 +112,7 @@ func (l *httpRateLimiter[TKey]) RateLimit(next http.Handler) http.Handler {
addResult := l.buckets.Add(key, 1, time.Now())
setRateLimitHeaders(w, addResult)
l.setRateLimitHeaders(w, addResult)
if addResult.Added > 0 {
//slog.Log(r.Context(), common.LevelTrace, "Allowing request", "ratelimiter", l.name,
@@ -138,7 +140,7 @@ func (l *httpRateLimiter[TKey]) UpdateRequestLimits(r *http.Request, capacity le
}
}
func setRateLimitHeaders(w http.ResponseWriter, addResult leakybucket.AddResult) {
func (l *httpRateLimiter[TKey]) setRateLimitHeaders(w http.ResponseWriter, addResult leakybucket.AddResult) {
headers := w.Header()
if v := addResult.Capacity; v > 0 {
@@ -155,7 +157,9 @@ func setRateLimitHeaders(w http.ResponseWriter, addResult leakybucket.AddResult)
}
if v := addResult.RetryAfter; v > 0 {
vi := int(math.Max(1.0, v.Seconds()+0.5))
jitter := randv2.Float64() * l.retryJitterPercent
seconds := v.Seconds() * (1.0 + jitter)
vi := int(math.Max(1.0, seconds+0.5))
headers[retryAfterHeader] = []string{strconv.Itoa(vi)}
}
}

1
pkg/ratelimit/ip.go
View File

@@ -58,6 +58,7 @@ func NewIPAddrRateLimiter(name, header string, buckets *IPAddrBuckets) *httpRate
strategy: strategy,
buckets: buckets,
keyFunc: func(r *http.Request) netip.Addr { return clientIPAddr(strategy, r) },
retryJitter: 0.2, // 20%
}
name = strings.ToLower(name)