fix: reuse stream scanner buffer in channel handlers (#5225)

relay/helper/stream_scanner.go

@@ -34,6 +34,12 @@ func getScannerBufferSize() int {
 	return DefaultMaxScannerBufferSize
 }
 
+func NewStreamScanner(reader io.Reader) *bufio.Scanner {
+	scanner := bufio.NewScanner(reader)
+	scanner.Buffer(make([]byte, InitialScannerBufferSize), getScannerBufferSize())
+	return scanner
+}
+
 func StreamScannerHandler(c *gin.Context, resp *http.Response, info *relaycommon.RelayInfo, dataHandler func(data string, sr *StreamResult)) {
 
 	if resp == nil || dataHandler == nil {
@@ -54,7 +60,7 @@ func StreamScannerHandler(c *gin.Context, resp *http.Response, info *relaycommon
 
 	var (
 		stopChan   = make(chan bool, 3) // 增加缓冲区避免阻塞
-		scanner    = bufio.NewScanner(resp.Body)
+		scanner    = NewStreamScanner(resp.Body)
 		ticker     = time.NewTicker(streamingTimeout)
 		pingTicker *time.Ticker
 		writeMutex sync.Mutex     // Mutex to protect concurrent writes
@@ -104,7 +110,6 @@ func StreamScannerHandler(c *gin.Context, resp *http.Response, info *relaycommon
 		close(stopChan)
 	}()
 
-	scanner.Buffer(make([]byte, InitialScannerBufferSize), getScannerBufferSize())
 	scanner.Split(bufio.ScanLines)
 	SetEventStreamHeaders(c)
 

relay/helper/stream_scanner_test.go

@@ -1,6 +1,7 @@
 package helper
 
 import (
+	"bufio"
 	"fmt"
 	"io"
 	"net/http"
@@ -81,6 +82,22 @@ func TestStreamScannerHandler_NilInputs(t *testing.T) {
 	StreamScannerHandler(c, &http.Response{Body: io.NopCloser(strings.NewReader(""))}, info, nil)
 }
 
+func TestNewStreamScanner_AllowsLargeStreamLine(t *testing.T) {
+	oldBufferMB := constant.StreamScannerMaxBufferMB
+	constant.StreamScannerMaxBufferMB = 1
+	t.Cleanup(func() {
+		constant.StreamScannerMaxBufferMB = oldBufferMB
+	})
+
+	payload := strings.Repeat("x", 128<<10)
+	scanner := NewStreamScanner(strings.NewReader("data: " + payload + "\n"))
+	scanner.Split(bufio.ScanLines)
+
+	require.True(t, scanner.Scan())
+	assert.Equal(t, "data: "+payload, scanner.Text())
+	require.NoError(t, scanner.Err())
+}
+
 func TestStreamScannerHandler_EmptyBody(t *testing.T) {
 	t.Parallel()