limit: clamp bandwidth limiter burst (#5471)

pkg/util/limit/limiter.go

@@ -0,0 +1,37 @@
+// Copyright 2026 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package limit
+
+import (
+	"fmt"
+
+	"golang.org/x/time/rate"
+)
+
+// NewBandwidthLimiter creates a limiter whose rate preserves the configured
+// byte limit while keeping the burst representable as an int on all targets.
+func NewBandwidthLimiter(bytes int64) *rate.Limiter {
+	if bytes <= 0 {
+		return nil
+	}
+
+	maxInt := int64(^uint(0) >> 1)
+	burst := min(bytes, maxInt)
+	return rate.NewLimiter(rate.Limit(float64(bytes)), int(burst))
+}
+
+func invalidBurstError(burst int) error {
+	return fmt.Errorf("invalid limiter burst: %d", burst)
+}