convert k8s.io/kubernetes/pkg/proxy to contextual logging, part 1

Signed-off-by: Ziqi Zhao <zhaoziqi9146@gmail.com>

pkg/proxy/util/linebuffer.go

@@ -19,6 +19,9 @@ package util
 import (
 	"bytes"
 	"fmt"
+	"strings"
+
+	"github.com/go-logr/logr"
 )
 
 // LineBuffer is an interface for writing lines of input to a bytes.Buffer
@@ -46,6 +49,8 @@ type LineBuffer interface {
 	Lines() int
 }
 
+var _ logr.Marshaler = &realLineBuffer{}
+
 type realLineBuffer struct {
 	b     bytes.Buffer
 	lines int
@@ -108,6 +113,11 @@ func (buf *realLineBuffer) Lines() int {
 	return buf.lines
 }
 
+// Implements the logs.Marshaler interface
+func (buf *realLineBuffer) MarshalLog() any {
+	return strings.Split(buf.b.String(), "\n")
+}
+
 type discardLineBuffer struct {
 	lines int
 }