limit: clamp bandwidth limiter burst (#5471)

client/proxy/proxy.go

@@ -66,7 +66,7 @@ func NewProxy(
 	var limiter *rate.Limiter
 	limitBytes := pxyConf.GetBaseConfig().Transport.BandwidthLimit.Bytes()
 	if limitBytes > 0 && pxyConf.GetBaseConfig().Transport.BandwidthLimitMode == types.BandwidthLimitModeClient {
-		limiter = rate.NewLimiter(rate.Limit(float64(limitBytes)), int(limitBytes))
+		limiter = limit.NewBandwidthLimiter(limitBytes)
 	}
 
 	baseProxy := BaseProxy{

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)
+}

pkg/util/limit/limiter_test.go

@@ -0,0 +1,65 @@
+// 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 (
+	"bytes"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/time/rate"
+)
+
+func TestNewBandwidthLimiterClampsBurstToTargetInt(t *testing.T) {
+	const bytesPerSecond = int64(1 << 31)
+
+	limiter := NewBandwidthLimiter(bytesPerSecond)
+	require.NotNil(t, limiter)
+
+	wantBurst := bytesPerSecond
+	maxInt := int64(^uint(0) >> 1)
+	if wantBurst > maxInt {
+		wantBurst = maxInt
+	}
+	require.Equal(t, int(wantBurst), limiter.Burst())
+	require.Equal(t, rate.Limit(float64(bytesPerSecond)), limiter.Limit())
+}
+
+func TestNewBandwidthLimiterDisablesNonPositiveLimit(t *testing.T) {
+	require.Nil(t, NewBandwidthLimiter(0))
+	require.Nil(t, NewBandwidthLimiter(-1))
+}
+
+func TestReaderAndWriterRejectInvalidBurst(t *testing.T) {
+	for _, burst := range []int{0, -1} {
+		t.Run("reader/"+strconv.Itoa(burst), func(t *testing.T) {
+			reader := NewReader(strings.NewReader("payload"), rate.NewLimiter(rate.Limit(1), burst))
+			n, err := reader.Read(make([]byte, 1))
+			require.Zero(t, n)
+			require.EqualError(t, err, "invalid limiter burst: "+strconv.Itoa(burst))
+		})
+
+		t.Run("writer/"+strconv.Itoa(burst), func(t *testing.T) {
+			var dst bytes.Buffer
+			writer := NewWriter(&dst, rate.NewLimiter(rate.Limit(1), burst))
+			n, err := writer.Write([]byte("payload"))
+			require.Zero(t, n)
+			require.EqualError(t, err, "invalid limiter burst: "+strconv.Itoa(burst))
+			require.Empty(t, dst.Bytes())
+		})
+	}
+}

pkg/util/limit/reader.go

@@ -35,6 +35,12 @@ func NewReader(r io.Reader, limiter *rate.Limiter) *Reader {
 
 func (r *Reader) Read(p []byte) (n int, err error) {
 	b := r.limiter.Burst()
+	if b <= 0 {
+		if len(p) == 0 {
+			return 0, nil
+		}
+		return 0, invalidBurstError(b)
+	}
 	if b < len(p) {
 		p = p[:b]
 	}

pkg/util/limit/writer.go

@@ -34,8 +34,15 @@ func NewWriter(w io.Writer, limiter *rate.Limiter) *Writer {
 }
 
 func (w *Writer) Write(p []byte) (n int, err error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+
 	var nn int
 	b := w.limiter.Burst()
+	if b <= 0 {
+		return 0, invalidBurstError(b)
+	}
 	for {
 		end := len(p)
 		if end == 0 {

server/proxy/proxy.go

@@ -536,7 +536,7 @@ func NewProxy(ctx context.Context, options *Options) (pxy Proxy, err error) {
 	var limiter *rate.Limiter
 	limitBytes := configurer.GetBaseConfig().Transport.BandwidthLimit.Bytes()
 	if limitBytes > 0 && configurer.GetBaseConfig().Transport.BandwidthLimitMode == types.BandwidthLimitModeServer {
-		limiter = rate.NewLimiter(rate.Limit(float64(limitBytes)), int(limitBytes))
+		limiter = limit.NewBandwidthLimiter(limitBytes)
 	}
 
 	basePxy := BaseProxy{